aboutsummaryrefslogtreecommitdiff
path: root/gdb/linux-nat.c
blob: 055da9a0cf2ffdf26b47460bef0549cd1459441c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
/* GNU/Linux native-dependent code common to multiple platforms.

   Copyright (C) 2001-2022 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "inferior.h"
#include "infrun.h"
#include "target.h"
#include "nat/linux-nat.h"
#include "nat/linux-waitpid.h"
#include "gdbsupport/gdb_wait.h"
#include <unistd.h>
#include <sys/syscall.h>
#include "nat/gdb_ptrace.h"
#include "linux-nat.h"
#include "nat/linux-ptrace.h"
#include "nat/linux-procfs.h"
#include "nat/linux-personality.h"
#include "linux-fork.h"
#include "gdbthread.h"
#include "gdbcmd.h"
#include "regcache.h"
#include "regset.h"
#include "inf-child.h"
#include "inf-ptrace.h"
#include "auxv.h"
#include <sys/procfs.h>		/* for elf_gregset etc.  */
#include "elf-bfd.h"		/* for elfcore_write_* */
#include "gregset.h"		/* for gregset */
#include "gdbcore.h"		/* for get_exec_file */
#include <ctype.h>		/* for isdigit */
#include <sys/stat.h>		/* for struct stat */
#include <fcntl.h>		/* for O_RDONLY */
#include "inf-loop.h"
#include "gdbsupport/event-loop.h"
#include "gdbsupport/event-pipe.h"
#include "event-top.h"
#include <pwd.h>
#include <sys/types.h>
#include <dirent.h>
#include "xml-support.h"
#include <sys/vfs.h>
#include "solib.h"
#include "nat/linux-osdata.h"
#include "linux-tdep.h"
#include "symfile.h"
#include "gdbsupport/agent.h"
#include "tracepoint.h"
#include "gdbsupport/buffer.h"
#include "target-descriptions.h"
#include "gdbsupport/filestuff.h"
#include "objfiles.h"
#include "nat/linux-namespaces.h"
#include "gdbsupport/fileio.h"
#include "gdbsupport/scope-exit.h"
#include "gdbsupport/gdb-sigmask.h"
#include "gdbsupport/common-debug.h"
#include <unordered_map>

/* This comment documents high-level logic of this file.

Waiting for events in sync mode
===============================

When waiting for an event in a specific thread, we just use waitpid,
passing the specific pid, and not passing WNOHANG.

When waiting for an event in all threads, waitpid is not quite good:

- If the thread group leader exits while other threads in the thread
  group still exist, waitpid(TGID, ...) hangs.  That waitpid won't
  return an exit status until the other threads in the group are
  reaped.

- When a non-leader thread execs, that thread just vanishes without
  reporting an exit (so we'd hang if we waited for it explicitly in
  that case).  The exec event is instead reported to the TGID pid.

The solution is to always use -1 and WNOHANG, together with
sigsuspend.

First, we use non-blocking waitpid to check for events.  If nothing is
found, we use sigsuspend to wait for SIGCHLD.  When SIGCHLD arrives,
it means something happened to a child process.  As soon as we know
there's an event, we get back to calling nonblocking waitpid.

Note that SIGCHLD should be blocked between waitpid and sigsuspend
calls, so that we don't miss a signal.  If SIGCHLD arrives in between,
when it's blocked, the signal becomes pending and sigsuspend
immediately notices it and returns.

Waiting for events in async mode (TARGET_WNOHANG)
=================================================

In async mode, GDB should always be ready to handle both user input
and target events, so neither blocking waitpid nor sigsuspend are
viable options.  Instead, we should asynchronously notify the GDB main
event loop whenever there's an unprocessed event from the target.  We
detect asynchronous target events by handling SIGCHLD signals.  To
notify the event loop about target events, an event pipe is used
--- the pipe is registered as waitable event source in the event loop,
the event loop select/poll's on the read end of this pipe (as well on
other event sources, e.g., stdin), and the SIGCHLD handler marks the
event pipe to raise an event.  This is more portable than relying on
pselect/ppoll, since on kernels that lack those syscalls, libc
emulates them with select/poll+sigprocmask, and that is racy
(a.k.a. plain broken).

Obviously, if we fail to notify the event loop if there's a target
event, it's bad.  OTOH, if we notify the event loop when there's no
event from the target, linux_nat_wait will detect that there's no real
event to report, and return event of type TARGET_WAITKIND_IGNORE.
This is mostly harmless, but it will waste time and is better avoided.

The main design point is that every time GDB is outside linux-nat.c,
we have a SIGCHLD handler installed that is called when something
happens to the target and notifies the GDB event loop.  Whenever GDB
core decides to handle the event, and calls into linux-nat.c, we
process things as in sync mode, except that the we never block in
sigsuspend.

While processing an event, we may end up momentarily blocked in
waitpid calls.  Those waitpid calls, while blocking, are guarantied to
return quickly.  E.g., in all-stop mode, before reporting to the core
that an LWP hit a breakpoint, all LWPs are stopped by sending them
SIGSTOP, and synchronously waiting for the SIGSTOP to be reported.
Note that this is different from blocking indefinitely waiting for the
next event --- here, we're already handling an event.

Use of signals
==============

We stop threads by sending a SIGSTOP.  The use of SIGSTOP instead of another
signal is not entirely significant; we just need for a signal to be delivered,
so that we can intercept it.  SIGSTOP's advantage is that it can not be
blocked.  A disadvantage is that it is not a real-time signal, so it can only
be queued once; we do not keep track of other sources of SIGSTOP.

Two other signals that can't be blocked are SIGCONT and SIGKILL.  But we can't
use them, because they have special behavior when the signal is generated -
not when it is delivered.  SIGCONT resumes the entire thread group and SIGKILL
kills the entire thread group.

A delivered SIGSTOP would stop the entire thread group, not just the thread we
tkill'd.  But we never let the SIGSTOP be delivered; we always intercept and 
cancel it (by PTRACE_CONT without passing SIGSTOP).

We could use a real-time signal instead.  This would solve those problems; we
could use PTRACE_GETSIGINFO to locate the specific stop signals sent by GDB.
But we would still have to have some support for SIGSTOP, since PTRACE_ATTACH
generates it, and there are races with trying to find a signal that is not
blocked.

Exec events
===========

The case of a thread group (process) with 3 or more threads, and a
thread other than the leader execs is worth detailing:

On an exec, the Linux kernel destroys all threads except the execing
one in the thread group, and resets the execing thread's tid to the
tgid.  No exit notification is sent for the execing thread -- from the
ptracer's perspective, it appears as though the execing thread just
vanishes.  Until we reap all other threads except the leader and the
execing thread, the leader will be zombie, and the execing thread will
be in `D (disc sleep)' state.  As soon as all other threads are
reaped, the execing thread changes its tid to the tgid, and the
previous (zombie) leader vanishes, giving place to the "new"
leader.  */

#ifndef O_LARGEFILE
#define O_LARGEFILE 0
#endif

struct linux_nat_target *linux_target;

/* Does the current host support PTRACE_GETREGSET?  */
enum tribool have_ptrace_getregset = TRIBOOL_UNKNOWN;

/* When true, print debug messages relating to the linux native target.  */

static bool debug_linux_nat;

/* Implement 'show debug linux-nat'.  */

static void
show_debug_linux_nat (struct ui_file *file, int from_tty,
		      struct cmd_list_element *c, const char *value)
{
  fprintf_filtered (file, _("Debugging of GNU/Linux native targets is %s.\n"),
		    value);
}

/* Print a linux-nat debug statement.  */

#define linux_nat_debug_printf(fmt, ...) \
  debug_prefixed_printf_cond (debug_linux_nat, "linux-nat", fmt, ##__VA_ARGS__)

/* Print "linux-nat" enter/exit debug statements.  */

#define LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT \
  scoped_debug_enter_exit (debug_linux_nat, "linux-nat")

struct simple_pid_list
{
  int pid;
  int status;
  struct simple_pid_list *next;
};
static struct simple_pid_list *stopped_pids;

/* Whether target_thread_events is in effect.  */
static int report_thread_events;

/* Async mode support.  */

/* The event pipe registered as a waitable file in the event loop.  */
static event_pipe linux_nat_event_pipe;

/* True if we're currently in async mode.  */
#define linux_is_async_p() (linux_nat_event_pipe.is_open ())

/* Flush the event pipe.  */

static void
async_file_flush (void)
{
  linux_nat_event_pipe.flush ();
}

/* Put something (anything, doesn't matter what, or how much) in event
   pipe, so that the select/poll in the event-loop realizes we have
   something to process.  */

static void
async_file_mark (void)
{
  linux_nat_event_pipe.mark ();
}

static int kill_lwp (int lwpid, int signo);

static int stop_callback (struct lwp_info *lp);

static void block_child_signals (sigset_t *prev_mask);
static void restore_child_signals_mask (sigset_t *prev_mask);

struct lwp_info;
static struct lwp_info *add_lwp (ptid_t ptid);
static void purge_lwp_list (int pid);
static void delete_lwp (ptid_t ptid);
static struct lwp_info *find_lwp_pid (ptid_t ptid);

static int lwp_status_pending_p (struct lwp_info *lp);

static void save_stop_reason (struct lwp_info *lp);

static void close_proc_mem_file (pid_t pid);
static void open_proc_mem_file (ptid_t ptid);


/* LWP accessors.  */

/* See nat/linux-nat.h.  */

ptid_t
ptid_of_lwp (struct lwp_info *lwp)
{
  return lwp->ptid;
}

/* See nat/linux-nat.h.  */

void
lwp_set_arch_private_info (struct lwp_info *lwp,
			   struct arch_lwp_info *info)
{
  lwp->arch_private = info;
}

/* See nat/linux-nat.h.  */

struct arch_lwp_info *
lwp_arch_private_info (struct lwp_info *lwp)
{
  return lwp->arch_private;
}

/* See nat/linux-nat.h.  */

int
lwp_is_stopped (struct lwp_info *lwp)
{
  return lwp->stopped;
}

/* See nat/linux-nat.h.  */

enum target_stop_reason
lwp_stop_reason (struct lwp_info *lwp)
{
  return lwp->stop_reason;
}

/* See nat/linux-nat.h.  */

int
lwp_is_stepping (struct lwp_info *lwp)
{
  return lwp->step;
}


/* Trivial list manipulation functions to keep track of a list of
   new stopped processes.  */
static void
add_to_pid_list (struct simple_pid_list **listp, int pid, int status)
{
  struct simple_pid_list *new_pid = XNEW (struct simple_pid_list);

  new_pid->pid = pid;
  new_pid->status = status;
  new_pid->next = *listp;
  *listp = new_pid;
}

static int
pull_pid_from_list (struct simple_pid_list **listp, int pid, int *statusp)
{
  struct simple_pid_list **p;

  for (p = listp; *p != NULL; p = &(*p)->next)
    if ((*p)->pid == pid)
      {
	struct simple_pid_list *next = (*p)->next;

	*statusp = (*p)->status;
	xfree (*p);
	*p = next;
	return 1;
      }
  return 0;
}

/* Return the ptrace options that we want to try to enable.  */

static int
linux_nat_ptrace_options (int attached)
{
  int options = 0;

  if (!attached)
    options |= PTRACE_O_EXITKILL;

  options |= (PTRACE_O_TRACESYSGOOD
	      | PTRACE_O_TRACEVFORKDONE
	      | PTRACE_O_TRACEVFORK
	      | PTRACE_O_TRACEFORK
	      | PTRACE_O_TRACEEXEC);

  return options;
}

/* Initialize ptrace and procfs warnings and check for supported
   ptrace features given PID.

   ATTACHED should be nonzero iff we attached to the inferior.  */

static void
linux_init_ptrace_procfs (pid_t pid, int attached)
{
  int options = linux_nat_ptrace_options (attached);

  linux_enable_event_reporting (pid, options);
  linux_ptrace_init_warnings ();
  linux_proc_init_warnings ();
}

linux_nat_target::~linux_nat_target ()
{}

void
linux_nat_target::post_attach (int pid)
{
  linux_init_ptrace_procfs (pid, 1);
}

/* Implement the virtual inf_ptrace_target::post_startup_inferior method.  */

void
linux_nat_target::post_startup_inferior (ptid_t ptid)
{
  linux_init_ptrace_procfs (ptid.pid (), 0);
}

/* Return the number of known LWPs in the tgid given by PID.  */

static int
num_lwps (int pid)
{
  int count = 0;

  for (const lwp_info *lp ATTRIBUTE_UNUSED : all_lwps ())
    if (lp->ptid.pid () == pid)
      count++;

  return count;
}

/* Deleter for lwp_info unique_ptr specialisation.  */

struct lwp_deleter
{
  void operator() (struct lwp_info *lwp) const
  {
    delete_lwp (lwp->ptid);
  }
};

/* A unique_ptr specialisation for lwp_info.  */

typedef std::unique_ptr<struct lwp_info, lwp_deleter> lwp_info_up;

/* Target hook for follow_fork.  */

void
linux_nat_target::follow_fork (inferior *child_inf, ptid_t child_ptid,
			       target_waitkind fork_kind, bool follow_child,
			       bool detach_fork)
{
  inf_ptrace_target::follow_fork (child_inf, child_ptid, fork_kind,
				  follow_child, detach_fork);

  if (!follow_child)
    {
      bool has_vforked = fork_kind == TARGET_WAITKIND_VFORKED;
      ptid_t parent_ptid = inferior_ptid;
      int parent_pid = parent_ptid.lwp ();
      int child_pid = child_ptid.lwp ();

      /* We're already attached to the parent, by default.  */
      lwp_info *child_lp = add_lwp (child_ptid);
      child_lp->stopped = 1;
      child_lp->last_resume_kind = resume_stop;

      /* Detach new forked process?  */
      if (detach_fork)
	{
	  int child_stop_signal = 0;
	  bool detach_child = true;

	  /* Move CHILD_LP into a unique_ptr and clear the source pointer
	     to prevent us doing anything stupid with it.  */
	  lwp_info_up child_lp_ptr (child_lp);
	  child_lp = nullptr;

	  linux_target->low_prepare_to_resume (child_lp_ptr.get ());

	  /* When debugging an inferior in an architecture that supports
	     hardware single stepping on a kernel without commit
	     6580807da14c423f0d0a708108e6df6ebc8bc83d, the vfork child
	     process starts with the TIF_SINGLESTEP/X86_EFLAGS_TF bits
	     set if the parent process had them set.
	     To work around this, single step the child process
	     once before detaching to clear the flags.  */

	  /* Note that we consult the parent's architecture instead of
	     the child's because there's no inferior for the child at
	     this point.  */
	  if (!gdbarch_software_single_step_p (target_thread_architecture
					       (parent_ptid)))
	    {
	      int status;

	      linux_disable_event_reporting (child_pid);
	      if (ptrace (PTRACE_SINGLESTEP, child_pid, 0, 0) < 0)
		perror_with_name (_("Couldn't do single step"));
	      if (my_waitpid (child_pid, &status, 0) < 0)
		perror_with_name (_("Couldn't wait vfork process"));
	      else
		{
		  detach_child = WIFSTOPPED (status);
		  child_stop_signal = WSTOPSIG (status);
		}
	    }

	  if (detach_child)
	    {
	      int signo = child_stop_signal;

	      if (signo != 0
		  && !signal_pass_state (gdb_signal_from_host (signo)))
		signo = 0;
	      ptrace (PTRACE_DETACH, child_pid, 0, signo);

	      close_proc_mem_file (child_pid);
	    }
	}

      if (has_vforked)
	{
	  lwp_info *parent_lp = find_lwp_pid (parent_ptid);
	  linux_nat_debug_printf ("waiting for VFORK_DONE on %d", parent_pid);
	  parent_lp->stopped = 1;

	  /* We'll handle the VFORK_DONE event like any other
	     event, in target_wait.  */
	}
    }
  else
    {
      struct lwp_info *child_lp;

      child_lp = add_lwp (child_ptid);
      child_lp->stopped = 1;
      child_lp->last_resume_kind = resume_stop;
    }
}


int
linux_nat_target::insert_fork_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::remove_fork_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::insert_vfork_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::remove_vfork_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::insert_exec_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::remove_exec_catchpoint (int pid)
{
  return 0;
}

int
linux_nat_target::set_syscall_catchpoint (int pid, bool needed, int any_count,
					  gdb::array_view<const int> syscall_counts)
{
  /* On GNU/Linux, we ignore the arguments.  It means that we only
     enable the syscall catchpoints, but do not disable them.

     Also, we do not use the `syscall_counts' information because we do not
     filter system calls here.  We let GDB do the logic for us.  */
  return 0;
}

/* List of known LWPs, keyed by LWP PID.  This speeds up the common
   case of mapping a PID returned from the kernel to our corresponding
   lwp_info data structure.  */
static htab_t lwp_lwpid_htab;

/* Calculate a hash from a lwp_info's LWP PID.  */

static hashval_t
lwp_info_hash (const void *ap)
{
  const struct lwp_info *lp = (struct lwp_info *) ap;
  pid_t pid = lp->ptid.lwp ();

  return iterative_hash_object (pid, 0);
}

/* Equality function for the lwp_info hash table.  Compares the LWP's
   PID.  */

static int
lwp_lwpid_htab_eq (const void *a, const void *b)
{
  const struct lwp_info *entry = (const struct lwp_info *) a;
  const struct lwp_info *element = (const struct lwp_info *) b;

  return entry->ptid.lwp () == element->ptid.lwp ();
}

/* Create the lwp_lwpid_htab hash table.  */

static void
lwp_lwpid_htab_create (void)
{
  lwp_lwpid_htab = htab_create (100, lwp_info_hash, lwp_lwpid_htab_eq, NULL);
}

/* Add LP to the hash table.  */

static void
lwp_lwpid_htab_add_lwp (struct lwp_info *lp)
{
  void **slot;

  slot = htab_find_slot (lwp_lwpid_htab, lp, INSERT);
  gdb_assert (slot != NULL && *slot == NULL);
  *slot = lp;
}

/* Head of doubly-linked list of known LWPs.  Sorted by reverse
   creation order.  This order is assumed in some cases.  E.g.,
   reaping status after killing alls lwps of a process: the leader LWP
   must be reaped last.  */

static intrusive_list<lwp_info> lwp_list;

/* See linux-nat.h.  */

lwp_info_range
all_lwps ()
{
  return lwp_info_range (lwp_list.begin ());
}

/* See linux-nat.h.  */

lwp_info_safe_range
all_lwps_safe ()
{
  return lwp_info_safe_range (lwp_list.begin ());
}

/* Add LP to sorted-by-reverse-creation-order doubly-linked list.  */

static void
lwp_list_add (struct lwp_info *lp)
{
  lwp_list.push_front (*lp);
}

/* Remove LP from sorted-by-reverse-creation-order doubly-linked
   list.  */

static void
lwp_list_remove (struct lwp_info *lp)
{
  /* Remove from sorted-by-creation-order list.  */
  lwp_list.erase (lwp_list.iterator_to (*lp));
}



/* Signal mask for use with sigsuspend in linux_nat_wait, initialized in
   _initialize_linux_nat.  */
static sigset_t suspend_mask;

/* Signals to block to make that sigsuspend work.  */
static sigset_t blocked_mask;

/* SIGCHLD action.  */
static struct sigaction sigchld_action;

/* Block child signals (SIGCHLD and linux threads signals), and store
   the previous mask in PREV_MASK.  */

static void
block_child_signals (sigset_t *prev_mask)
{
  /* Make sure SIGCHLD is blocked.  */
  if (!sigismember (&blocked_mask, SIGCHLD))
    sigaddset (&blocked_mask, SIGCHLD);

  gdb_sigmask (SIG_BLOCK, &blocked_mask, prev_mask);
}

/* Restore child signals mask, previously returned by
   block_child_signals.  */

static void
restore_child_signals_mask (sigset_t *prev_mask)
{
  gdb_sigmask (SIG_SETMASK, prev_mask, NULL);
}

/* Mask of signals to pass directly to the inferior.  */
static sigset_t pass_mask;

/* Update signals to pass to the inferior.  */
void
linux_nat_target::pass_signals
  (gdb::array_view<const unsigned char> pass_signals)
{
  int signo;

  sigemptyset (&pass_mask);

  for (signo = 1; signo < NSIG; signo++)
    {
      int target_signo = gdb_signal_from_host (signo);
      if (target_signo < pass_signals.size () && pass_signals[target_signo])
	sigaddset (&pass_mask, signo);
    }
}



/* Prototypes for local functions.  */
static int stop_wait_callback (struct lwp_info *lp);
static int resume_stopped_resumed_lwps (struct lwp_info *lp, const ptid_t wait_ptid);
static int check_ptrace_stopped_lwp_gone (struct lwp_info *lp);



/* Destroy and free LP.  */

lwp_info::~lwp_info ()
{
  /* Let the arch specific bits release arch_lwp_info.  */
  linux_target->low_delete_thread (this->arch_private);
}

/* Traversal function for purge_lwp_list.  */

static int
lwp_lwpid_htab_remove_pid (void **slot, void *info)
{
  struct lwp_info *lp = (struct lwp_info *) *slot;
  int pid = *(int *) info;

  if (lp->ptid.pid () == pid)
    {
      htab_clear_slot (lwp_lwpid_htab, slot);
      lwp_list_remove (lp);
      delete lp;
    }

  return 1;
}

/* Remove all LWPs belong to PID from the lwp list.  */

static void
purge_lwp_list (int pid)
{
  htab_traverse_noresize (lwp_lwpid_htab, lwp_lwpid_htab_remove_pid, &pid);
}

/* Add the LWP specified by PTID to the list.  PTID is the first LWP
   in the process.  Return a pointer to the structure describing the
   new LWP.

   This differs from add_lwp in that we don't let the arch specific
   bits know about this new thread.  Current clients of this callback
   take the opportunity to install watchpoints in the new thread, and
   we shouldn't do that for the first thread.  If we're spawning a
   child ("run"), the thread executes the shell wrapper first, and we
   shouldn't touch it until it execs the program we want to debug.
   For "attach", it'd be okay to call the callback, but it's not
   necessary, because watchpoints can't yet have been inserted into
   the inferior.  */

static struct lwp_info *
add_initial_lwp (ptid_t ptid)
{
  gdb_assert (ptid.lwp_p ());

  lwp_info *lp = new lwp_info (ptid);


  /* Add to sorted-by-reverse-creation-order list.  */
  lwp_list_add (lp);

  /* Add to keyed-by-pid htab.  */
  lwp_lwpid_htab_add_lwp (lp);

  return lp;
}

/* Add the LWP specified by PID to the list.  Return a pointer to the
   structure describing the new LWP.  The LWP should already be
   stopped.  */

static struct lwp_info *
add_lwp (ptid_t ptid)
{
  struct lwp_info *lp;

  lp = add_initial_lwp (ptid);

  /* Let the arch specific bits know about this new thread.  Current
     clients of this callback take the opportunity to install
     watchpoints in the new thread.  We don't do this for the first
     thread though.  See add_initial_lwp.  */
  linux_target->low_new_thread (lp);

  return lp;
}

/* Remove the LWP specified by PID from the list.  */

static void
delete_lwp (ptid_t ptid)
{
  lwp_info dummy (ptid);

  void **slot = htab_find_slot (lwp_lwpid_htab, &dummy, NO_INSERT);
  if (slot == NULL)
    return;

  lwp_info *lp = *(struct lwp_info **) slot;
  gdb_assert (lp != NULL);

  htab_clear_slot (lwp_lwpid_htab, slot);

  /* Remove from sorted-by-creation-order list.  */
  lwp_list_remove (lp);

  /* Release.  */
  delete lp;
}

/* Return a pointer to the structure describing the LWP corresponding
   to PID.  If no corresponding LWP could be found, return NULL.  */

static struct lwp_info *
find_lwp_pid (ptid_t ptid)
{
  int lwp;

  if (ptid.lwp_p ())
    lwp = ptid.lwp ();
  else
    lwp = ptid.pid ();

  lwp_info dummy (ptid_t (0, lwp));
  return (struct lwp_info *) htab_find (lwp_lwpid_htab, &dummy);
}

/* See nat/linux-nat.h.  */

struct lwp_info *
iterate_over_lwps (ptid_t filter,
		   gdb::function_view<iterate_over_lwps_ftype> callback)
{
  for (lwp_info *lp : all_lwps_safe ())
    {
      if (lp->ptid.matches (filter))
	{
	  if (callback (lp) != 0)
	    return lp;
	}
    }

  return NULL;
}

/* Update our internal state when changing from one checkpoint to
   another indicated by NEW_PTID.  We can only switch single-threaded
   applications, so we only create one new LWP, and the previous list
   is discarded.  */

void
linux_nat_switch_fork (ptid_t new_ptid)
{
  struct lwp_info *lp;

  purge_lwp_list (inferior_ptid.pid ());

  lp = add_lwp (new_ptid);
  lp->stopped = 1;

  /* This changes the thread's ptid while preserving the gdb thread
     num.  Also changes the inferior pid, while preserving the
     inferior num.  */
  thread_change_ptid (linux_target, inferior_ptid, new_ptid);

  /* We've just told GDB core that the thread changed target id, but,
     in fact, it really is a different thread, with different register
     contents.  */
  registers_changed ();
}

/* Handle the exit of a single thread LP.  */

static void
exit_lwp (struct lwp_info *lp)
{
  struct thread_info *th = find_thread_ptid (linux_target, lp->ptid);

  if (th)
    {
      if (print_thread_events)
	printf_unfiltered (_("[%s exited]\n"),
			   target_pid_to_str (lp->ptid).c_str ());

      delete_thread (th);
    }

  delete_lwp (lp->ptid);
}

/* Wait for the LWP specified by LP, which we have just attached to.
   Returns a wait status for that LWP, to cache.  */

static int
linux_nat_post_attach_wait (ptid_t ptid, int *signalled)
{
  pid_t new_pid, pid = ptid.lwp ();
  int status;

  if (linux_proc_pid_is_stopped (pid))
    {
      linux_nat_debug_printf ("Attaching to a stopped process");

      /* The process is definitely stopped.  It is in a job control
	 stop, unless the kernel predates the TASK_STOPPED /
	 TASK_TRACED distinction, in which case it might be in a
	 ptrace stop.  Make sure it is in a ptrace stop; from there we
	 can kill it, signal it, et cetera.

	 First make sure there is a pending SIGSTOP.  Since we are
	 already attached, the process can not transition from stopped
	 to running without a PTRACE_CONT; so we know this signal will
	 go into the queue.  The SIGSTOP generated by PTRACE_ATTACH is
	 probably already in the queue (unless this kernel is old
	 enough to use TASK_STOPPED for ptrace stops); but since SIGSTOP
	 is not an RT signal, it can only be queued once.  */
      kill_lwp (pid, SIGSTOP);

      /* Finally, resume the stopped process.  This will deliver the SIGSTOP
	 (or a higher priority signal, just like normal PTRACE_ATTACH).  */
      ptrace (PTRACE_CONT, pid, 0, 0);
    }

  /* Make sure the initial process is stopped.  The user-level threads
     layer might want to poke around in the inferior, and that won't
     work if things haven't stabilized yet.  */
  new_pid = my_waitpid (pid, &status, __WALL);
  gdb_assert (pid == new_pid);

  if (!WIFSTOPPED (status))
    {
      /* The pid we tried to attach has apparently just exited.  */
      linux_nat_debug_printf ("Failed to stop %d: %s", pid,
			      status_to_str (status).c_str ());
      return status;
    }

  if (WSTOPSIG (status) != SIGSTOP)
    {
      *signalled = 1;
      linux_nat_debug_printf ("Received %s after attaching",
			      status_to_str (status).c_str ());
    }

  return status;
}

void
linux_nat_target::create_inferior (const char *exec_file,
				   const std::string &allargs,
				   char **env, int from_tty)
{
  maybe_disable_address_space_randomization restore_personality
    (disable_randomization);

  /* The fork_child mechanism is synchronous and calls target_wait, so
     we have to mask the async mode.  */

  /* Make sure we report all signals during startup.  */
  pass_signals ({});

  inf_ptrace_target::create_inferior (exec_file, allargs, env, from_tty);

  open_proc_mem_file (inferior_ptid);
}

/* Callback for linux_proc_attach_tgid_threads.  Attach to PTID if not
   already attached.  Returns true if a new LWP is found, false
   otherwise.  */

static int
attach_proc_task_lwp_callback (ptid_t ptid)
{
  struct lwp_info *lp;

  /* Ignore LWPs we're already attached to.  */
  lp = find_lwp_pid (ptid);
  if (lp == NULL)
    {
      int lwpid = ptid.lwp ();

      if (ptrace (PTRACE_ATTACH, lwpid, 0, 0) < 0)
	{
	  int err = errno;

	  /* Be quiet if we simply raced with the thread exiting.
	     EPERM is returned if the thread's task still exists, and
	     is marked as exited or zombie, as well as other
	     conditions, so in that case, confirm the status in
	     /proc/PID/status.  */
	  if (err == ESRCH
	      || (err == EPERM && linux_proc_pid_is_gone (lwpid)))
	    {
	      linux_nat_debug_printf
		("Cannot attach to lwp %d: thread is gone (%d: %s)",
		 lwpid, err, safe_strerror (err));

	    }
	  else
	    {
	      std::string reason
		= linux_ptrace_attach_fail_reason_string (ptid, err);

	      warning (_("Cannot attach to lwp %d: %s"),
		       lwpid, reason.c_str ());
	    }
	}
      else
	{
	  linux_nat_debug_printf ("PTRACE_ATTACH %s, 0, 0 (OK)",
				  ptid.to_string ().c_str ());

	  lp = add_lwp (ptid);

	  /* The next time we wait for this LWP we'll see a SIGSTOP as
	     PTRACE_ATTACH brings it to a halt.  */
	  lp->signalled = 1;

	  /* We need to wait for a stop before being able to make the
	     next ptrace call on this LWP.  */
	  lp->must_set_ptrace_flags = 1;

	  /* So that wait collects the SIGSTOP.  */
	  lp->resumed = 1;

	  /* Also add the LWP to gdb's thread list, in case a
	     matching libthread_db is not found (or the process uses
	     raw clone).  */
	  add_thread (linux_target, lp->ptid);
	  set_running (linux_target, lp->ptid, true);
	  set_executing (linux_target, lp->ptid, true);
	}

      return 1;
    }
  return 0;
}

void
linux_nat_target::attach (const char *args, int from_tty)
{
  struct lwp_info *lp;
  int status;
  ptid_t ptid;

  /* Make sure we report all signals during attach.  */
  pass_signals ({});

  try
    {
      inf_ptrace_target::attach (args, from_tty);
    }
  catch (const gdb_exception_error &ex)
    {
      pid_t pid = parse_pid_to_attach (args);
      std::string reason = linux_ptrace_attach_fail_reason (pid);

      if (!reason.empty ())
	throw_error (ex.error, "warning: %s\n%s", reason.c_str (),
		     ex.what ());
      else
	throw_error (ex.error, "%s", ex.what ());
    }

  /* The ptrace base target adds the main thread with (pid,0,0)
     format.  Decorate it with lwp info.  */
  ptid = ptid_t (inferior_ptid.pid (),
		 inferior_ptid.pid ());
  thread_change_ptid (linux_target, inferior_ptid, ptid);

  /* Add the initial process as the first LWP to the list.  */
  lp = add_initial_lwp (ptid);

  status = linux_nat_post_attach_wait (lp->ptid, &lp->signalled);
  if (!WIFSTOPPED (status))
    {
      if (WIFEXITED (status))
	{
	  int exit_code = WEXITSTATUS (status);

	  target_terminal::ours ();
	  target_mourn_inferior (inferior_ptid);
	  if (exit_code == 0)
	    error (_("Unable to attach: program exited normally."));
	  else
	    error (_("Unable to attach: program exited with code %d."),
		   exit_code);
	}
      else if (WIFSIGNALED (status))
	{
	  enum gdb_signal signo;

	  target_terminal::ours ();
	  target_mourn_inferior (inferior_ptid);

	  signo = gdb_signal_from_host (WTERMSIG (status));
	  error (_("Unable to attach: program terminated with signal "
		   "%s, %s."),
		 gdb_signal_to_name (signo),
		 gdb_signal_to_string (signo));
	}

      internal_error (__FILE__, __LINE__,
		      _("unexpected status %d for PID %ld"),
		      status, (long) ptid.lwp ());
    }

  lp->stopped = 1;

  open_proc_mem_file (lp->ptid);

  /* Save the wait status to report later.  */
  lp->resumed = 1;
  linux_nat_debug_printf ("waitpid %ld, saving status %s",
			  (long) lp->ptid.pid (),
			  status_to_str (status).c_str ());

  lp->status = status;

  /* We must attach to every LWP.  If /proc is mounted, use that to
     find them now.  The inferior may be using raw clone instead of
     using pthreads.  But even if it is using pthreads, thread_db
     walks structures in the inferior's address space to find the list
     of threads/LWPs, and those structures may well be corrupted.
     Note that once thread_db is loaded, we'll still use it to list
     threads and associate pthread info with each LWP.  */
  linux_proc_attach_tgid_threads (lp->ptid.pid (),
				  attach_proc_task_lwp_callback);
}

/* Ptrace-detach the thread with pid PID.  */

static void
detach_one_pid (int pid, int signo)
{
  if (ptrace (PTRACE_DETACH, pid, 0, signo) < 0)
    {
      int save_errno = errno;

      /* We know the thread exists, so ESRCH must mean the lwp is
	 zombie.  This can happen if one of the already-detached
	 threads exits the whole thread group.  In that case we're
	 still attached, and must reap the lwp.  */
      if (save_errno == ESRCH)
	{
	  int ret, status;

	  ret = my_waitpid (pid, &status, __WALL);
	  if (ret == -1)
	    {
	      warning (_("Couldn't reap LWP %d while detaching: %s"),
		       pid, safe_strerror (errno));
	    }
	  else if (!WIFEXITED (status) && !WIFSIGNALED (status))
	    {
	      warning (_("Reaping LWP %d while detaching "
			 "returned unexpected status 0x%x"),
		       pid, status);
	    }
	}
      else
	error (_("Can't detach %d: %s"),
	       pid, safe_strerror (save_errno));
    }
  else
    linux_nat_debug_printf ("PTRACE_DETACH (%d, %s, 0) (OK)",
			    pid, strsignal (signo));
}

/* Get pending signal of THREAD as a host signal number, for detaching
   purposes.  This is the signal the thread last stopped for, which we
   need to deliver to the thread when detaching, otherwise, it'd be
   suppressed/lost.  */

static int
get_detach_signal (struct lwp_info *lp)
{
  enum gdb_signal signo = GDB_SIGNAL_0;

  /* If we paused threads momentarily, we may have stored pending
     events in lp->status or lp->waitstatus (see stop_wait_callback),
     and GDB core hasn't seen any signal for those threads.
     Otherwise, the last signal reported to the core is found in the
     thread object's stop_signal.

     There's a corner case that isn't handled here at present.  Only
     if the thread stopped with a TARGET_WAITKIND_STOPPED does
     stop_signal make sense as a real signal to pass to the inferior.
     Some catchpoint related events, like
     TARGET_WAITKIND_(V)FORK|EXEC|SYSCALL, have their stop_signal set
     to GDB_SIGNAL_SIGTRAP when the catchpoint triggers.  But,
     those traps are debug API (ptrace in our case) related and
     induced; the inferior wouldn't see them if it wasn't being
     traced.  Hence, we should never pass them to the inferior, even
     when set to pass state.  Since this corner case isn't handled by
     infrun.c when proceeding with a signal, for consistency, neither
     do we handle it here (or elsewhere in the file we check for
     signal pass state).  Normally SIGTRAP isn't set to pass state, so
     this is really a corner case.  */

  if (lp->waitstatus.kind () != TARGET_WAITKIND_IGNORE)
    signo = GDB_SIGNAL_0; /* a pending ptrace event, not a real signal.  */
  else if (lp->status)
    signo = gdb_signal_from_host (WSTOPSIG (lp->status));
  else
    {
      struct thread_info *tp = find_thread_ptid (linux_target, lp->ptid);

      if (target_is_non_stop_p () && !tp->executing ())
	{
	  if (tp->has_pending_waitstatus ())
	    {
	      /* If the thread has a pending event, and it was stopped with a
	         signal, use that signal to resume it.  If it has a pending
		 event of another kind, it was not stopped with a signal, so
		 resume it without a signal.  */
	      if (tp->pending_waitstatus ().kind () == TARGET_WAITKIND_STOPPED)
		signo = tp->pending_waitstatus ().sig ();
	      else
		signo = GDB_SIGNAL_0;
	    }
	  else
	    signo = tp->stop_signal ();
	}
      else if (!target_is_non_stop_p ())
	{
	  ptid_t last_ptid;
	  process_stratum_target *last_target;

	  get_last_target_status (&last_target, &last_ptid, nullptr);

	  if (last_target == linux_target
	      && lp->ptid.lwp () == last_ptid.lwp ())
	    signo = tp->stop_signal ();
	}
    }

  if (signo == GDB_SIGNAL_0)
    {
      linux_nat_debug_printf ("lwp %s has no pending signal",
			      lp->ptid.to_string ().c_str ());
    }
  else if (!signal_pass_state (signo))
    {
      linux_nat_debug_printf
	("lwp %s had signal %s but it is in no pass state",
	 lp->ptid.to_string ().c_str (), gdb_signal_to_string (signo));
    }
  else
    {
      linux_nat_debug_printf ("lwp %s has pending signal %s",
			      lp->ptid.to_string ().c_str (),
			      gdb_signal_to_string (signo));

      return gdb_signal_to_host (signo);
    }

  return 0;
}

/* Detach from LP.  If SIGNO_P is non-NULL, then it points to the
   signal number that should be passed to the LWP when detaching.
   Otherwise pass any pending signal the LWP may have, if any.  */

static void
detach_one_lwp (struct lwp_info *lp, int *signo_p)
{
  int lwpid = lp->ptid.lwp ();
  int signo;

  gdb_assert (lp->status == 0 || WIFSTOPPED (lp->status));

  /* If the lwp/thread we are about to detach has a pending fork event,
     there is a process GDB is attached to that the core of GDB doesn't know
     about.  Detach from it.  */

  /* Check in lwp_info::status.  */
  if (WIFSTOPPED (lp->status) && linux_is_extended_waitstatus (lp->status))
    {
      int event = linux_ptrace_get_extended_event (lp->status);

      if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK)
	{
	  unsigned long child_pid;
	  int ret = ptrace (PTRACE_GETEVENTMSG, lp->ptid.lwp (), 0, &child_pid);
	  if (ret == 0)
	    detach_one_pid (child_pid, 0);
	  else
	    perror_warning_with_name (_("Failed to detach fork child"));
	}
    }

  /* Check in lwp_info::waitstatus.  */
  if (lp->waitstatus.kind () == TARGET_WAITKIND_VFORKED
      || lp->waitstatus.kind () == TARGET_WAITKIND_FORKED)
    detach_one_pid (lp->waitstatus.child_ptid ().pid (), 0);


  /* Check in thread_info::pending_waitstatus.  */
  thread_info *tp = find_thread_ptid (linux_target, lp->ptid);
  if (tp->has_pending_waitstatus ())
    {
      const target_waitstatus &ws = tp->pending_waitstatus ();

      if (ws.kind () == TARGET_WAITKIND_VFORKED
	  || ws.kind () == TARGET_WAITKIND_FORKED)
	detach_one_pid (ws.child_ptid ().pid (), 0);
    }

  /* Check in thread_info::pending_follow.  */
  if (tp->pending_follow.kind () == TARGET_WAITKIND_VFORKED
      || tp->pending_follow.kind () == TARGET_WAITKIND_FORKED)
    detach_one_pid (tp->pending_follow.child_ptid ().pid (), 0);

  if (lp->status != 0)
    linux_nat_debug_printf ("Pending %s for %s on detach.",
			    strsignal (WSTOPSIG (lp->status)),
			    lp->ptid.to_string ().c_str ());

  /* If there is a pending SIGSTOP, get rid of it.  */
  if (lp->signalled)
    {
      linux_nat_debug_printf ("Sending SIGCONT to %s",
			      lp->ptid.to_string ().c_str ());

      kill_lwp (lwpid, SIGCONT);
      lp->signalled = 0;
    }

  if (signo_p == NULL)
    {
      /* Pass on any pending signal for this LWP.  */
      signo = get_detach_signal (lp);
    }
  else
    signo = *signo_p;

  /* Preparing to resume may try to write registers, and fail if the
     lwp is zombie.  If that happens, ignore the error.  We'll handle
     it below, when detach fails with ESRCH.  */
  try
    {
      linux_target->low_prepare_to_resume (lp);
    }
  catch (const gdb_exception_error &ex)
    {
      if (!check_ptrace_stopped_lwp_gone (lp))
	throw;
    }

  detach_one_pid (lwpid, signo);

  delete_lwp (lp->ptid);
}

static int
detach_callback (struct lwp_info *lp)
{
  /* We don't actually detach from the thread group leader just yet.
     If the thread group exits, we must reap the zombie clone lwps
     before we're able to reap the leader.  */
  if (lp->ptid.lwp () != lp->ptid.pid ())
    detach_one_lwp (lp, NULL);
  return 0;
}

void
linux_nat_target::detach (inferior *inf, int from_tty)
{
  struct lwp_info *main_lwp;
  int pid = inf->pid;

  /* Don't unregister from the event loop, as there may be other
     inferiors running. */

  /* Stop all threads before detaching.  ptrace requires that the
     thread is stopped to successfully detach.  */
  iterate_over_lwps (ptid_t (pid), stop_callback);
  /* ... and wait until all of them have reported back that
     they're no longer running.  */
  iterate_over_lwps (ptid_t (pid), stop_wait_callback);

  /* We can now safely remove breakpoints.  We don't this in earlier
     in common code because this target doesn't currently support
     writing memory while the inferior is running.  */
  remove_breakpoints_inf (current_inferior ());

  iterate_over_lwps (ptid_t (pid), detach_callback);

  /* Only the initial process should be left right now.  */
  gdb_assert (num_lwps (pid) == 1);

  main_lwp = find_lwp_pid (ptid_t (pid));

  if (forks_exist_p ())
    {
      /* Multi-fork case.  The current inferior_ptid is being detached
	 from, but there are other viable forks to debug.  Detach from
	 the current fork, and context-switch to the first
	 available.  */
      linux_fork_detach (from_tty);
    }
  else
    {
      target_announce_detach (from_tty);

      /* Pass on any pending signal for the last LWP.  */
      int signo = get_detach_signal (main_lwp);

      detach_one_lwp (main_lwp, &signo);

      detach_success (inf);
    }

  close_proc_mem_file (pid);
}

/* Resume execution of the inferior process.  If STEP is nonzero,
   single-step it.  If SIGNAL is nonzero, give it that signal.  */

static void
linux_resume_one_lwp_throw (struct lwp_info *lp, int step,
			    enum gdb_signal signo)
{
  lp->step = step;

  /* stop_pc doubles as the PC the LWP had when it was last resumed.
     We only presently need that if the LWP is stepped though (to
     handle the case of stepping a breakpoint instruction).  */
  if (step)
    {
      struct regcache *regcache = get_thread_regcache (linux_target, lp->ptid);

      lp->stop_pc = regcache_read_pc (regcache);
    }
  else
    lp->stop_pc = 0;

  linux_target->low_prepare_to_resume (lp);
  linux_target->low_resume (lp->ptid, step, signo);

  /* Successfully resumed.  Clear state that no longer makes sense,
     and mark the LWP as running.  Must not do this before resuming
     otherwise if that fails other code will be confused.  E.g., we'd
     later try to stop the LWP and hang forever waiting for a stop
     status.  Note that we must not throw after this is cleared,
     otherwise handle_zombie_lwp_error would get confused.  */
  lp->stopped = 0;
  lp->core = -1;
  lp->stop_reason = TARGET_STOPPED_BY_NO_REASON;
  registers_changed_ptid (linux_target, lp->ptid);
}

/* Called when we try to resume a stopped LWP and that errors out.  If
   the LWP is no longer in ptrace-stopped state (meaning it's zombie,
   or about to become), discard the error, clear any pending status
   the LWP may have, and return true (we'll collect the exit status
   soon enough).  Otherwise, return false.  */

static int
check_ptrace_stopped_lwp_gone (struct lwp_info *lp)
{
  /* If we get an error after resuming the LWP successfully, we'd
     confuse !T state for the LWP being gone.  */
  gdb_assert (lp->stopped);

  /* We can't just check whether the LWP is in 'Z (Zombie)' state,
     because even if ptrace failed with ESRCH, the tracee may be "not
     yet fully dead", but already refusing ptrace requests.  In that
     case the tracee has 'R (Running)' state for a little bit
     (observed in Linux 3.18).  See also the note on ESRCH in the
     ptrace(2) man page.  Instead, check whether the LWP has any state
     other than ptrace-stopped.  */

  /* Don't assume anything if /proc/PID/status can't be read.  */
  if (linux_proc_pid_is_trace_stopped_nowarn (lp->ptid.lwp ()) == 0)
    {
      lp->stop_reason = TARGET_STOPPED_BY_NO_REASON;
      lp->status = 0;
      lp->waitstatus.set_ignore ();
      return 1;
    }
  return 0;
}

/* Like linux_resume_one_lwp_throw, but no error is thrown if the LWP
   disappears while we try to resume it.  */

static void
linux_resume_one_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
{
  try
    {
      linux_resume_one_lwp_throw (lp, step, signo);
    }
  catch (const gdb_exception_error &ex)
    {
      if (!check_ptrace_stopped_lwp_gone (lp))
	throw;
    }
}

/* Resume LP.  */

static void
resume_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
{
  if (lp->stopped)
    {
      struct inferior *inf = find_inferior_ptid (linux_target, lp->ptid);

      if (inf->vfork_child != NULL)
	{
	  linux_nat_debug_printf ("Not resuming %s (vfork parent)",
				  lp->ptid.to_string ().c_str ());
	}
      else if (!lwp_status_pending_p (lp))
	{
	  linux_nat_debug_printf ("Resuming sibling %s, %s, %s",
				  lp->ptid.to_string ().c_str (),
				  (signo != GDB_SIGNAL_0
				   ? strsignal (gdb_signal_to_host (signo))
				   : "0"),
				  step ? "step" : "resume");

	  linux_resume_one_lwp (lp, step, signo);
	}
      else
	{
	  linux_nat_debug_printf ("Not resuming sibling %s (has pending)",
				  lp->ptid.to_string ().c_str ());
	}
    }
  else
    linux_nat_debug_printf ("Not resuming sibling %s (not stopped)",
			    lp->ptid.to_string ().c_str ());
}

/* Callback for iterate_over_lwps.  If LWP is EXCEPT, do nothing.
   Resume LWP with the last stop signal, if it is in pass state.  */

static int
linux_nat_resume_callback (struct lwp_info *lp, struct lwp_info *except)
{
  enum gdb_signal signo = GDB_SIGNAL_0;

  if (lp == except)
    return 0;

  if (lp->stopped)
    {
      struct thread_info *thread;

      thread = find_thread_ptid (linux_target, lp->ptid);
      if (thread != NULL)
	{
	  signo = thread->stop_signal ();
	  thread->set_stop_signal (GDB_SIGNAL_0);
	}
    }

  resume_lwp (lp, 0, signo);
  return 0;
}

static int
resume_clear_callback (struct lwp_info *lp)
{
  lp->resumed = 0;
  lp->last_resume_kind = resume_stop;
  return 0;
}

static int
resume_set_callback (struct lwp_info *lp)
{
  lp->resumed = 1;
  lp->last_resume_kind = resume_continue;
  return 0;
}

void
linux_nat_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
{
  struct lwp_info *lp;
  int resume_many;

  linux_nat_debug_printf ("Preparing to %s %s, %s, inferior_ptid %s",
			  step ? "step" : "resume",
			  ptid.to_string ().c_str (),
			  (signo != GDB_SIGNAL_0
			   ? strsignal (gdb_signal_to_host (signo)) : "0"),
			  inferior_ptid.to_string ().c_str ());

  /* A specific PTID means `step only this process id'.  */
  resume_many = (minus_one_ptid == ptid
		 || ptid.is_pid ());

  /* Mark the lwps we're resuming as resumed and update their
     last_resume_kind to resume_continue.  */
  iterate_over_lwps (ptid, resume_set_callback);

  /* See if it's the current inferior that should be handled
     specially.  */
  if (resume_many)
    lp = find_lwp_pid (inferior_ptid);
  else
    lp = find_lwp_pid (ptid);
  gdb_assert (lp != NULL);

  /* Remember if we're stepping.  */
  lp->last_resume_kind = step ? resume_step : resume_continue;

  /* If we have a pending wait status for this thread, there is no
     point in resuming the process.  But first make sure that
     linux_nat_wait won't preemptively handle the event - we
     should never take this short-circuit if we are going to
     leave LP running, since we have skipped resuming all the
     other threads.  This bit of code needs to be synchronized
     with linux_nat_wait.  */

  if (lp->status && WIFSTOPPED (lp->status))
    {
      if (!lp->step
	  && WSTOPSIG (lp->status)
	  && sigismember (&pass_mask, WSTOPSIG (lp->status)))
	{
	  linux_nat_debug_printf
	    ("Not short circuiting for ignored status 0x%x", lp->status);

	  /* FIXME: What should we do if we are supposed to continue
	     this thread with a signal?  */
	  gdb_assert (signo == GDB_SIGNAL_0);
	  signo = gdb_signal_from_host (WSTOPSIG (lp->status));
	  lp->status = 0;
	}
    }

  if (lwp_status_pending_p (lp))
    {
      /* FIXME: What should we do if we are supposed to continue
	 this thread with a signal?  */
      gdb_assert (signo == GDB_SIGNAL_0);

      linux_nat_debug_printf ("Short circuiting for status 0x%x",
			      lp->status);

      if (target_can_async_p ())
	{
	  target_async (1);
	  /* Tell the event loop we have something to process.  */
	  async_file_mark ();
	}
      return;
    }

  if (resume_many)
    iterate_over_lwps (ptid, [=] (struct lwp_info *info)
			     {
			       return linux_nat_resume_callback (info, lp);
			     });

  linux_nat_debug_printf ("%s %s, %s (resume event thread)",
			  step ? "PTRACE_SINGLESTEP" : "PTRACE_CONT",
			  lp->ptid.to_string ().c_str (),
			  (signo != GDB_SIGNAL_0
			   ? strsignal (gdb_signal_to_host (signo)) : "0"));

  linux_resume_one_lwp (lp, step, signo);
}

/* Send a signal to an LWP.  */

static int
kill_lwp (int lwpid, int signo)
{
  int ret;

  errno = 0;
  ret = syscall (__NR_tkill, lwpid, signo);
  if (errno == ENOSYS)
    {
      /* If tkill fails, then we are not using nptl threads, a
	 configuration we no longer support.  */
      perror_with_name (("tkill"));
    }
  return ret;
}

/* Handle a GNU/Linux syscall trap wait response.  If we see a syscall
   event, check if the core is interested in it: if not, ignore the
   event, and keep waiting; otherwise, we need to toggle the LWP's
   syscall entry/exit status, since the ptrace event itself doesn't
   indicate it, and report the trap to higher layers.  */

static int
linux_handle_syscall_trap (struct lwp_info *lp, int stopping)
{
  struct target_waitstatus *ourstatus = &lp->waitstatus;
  struct gdbarch *gdbarch = target_thread_architecture (lp->ptid);
  thread_info *thread = find_thread_ptid (linux_target, lp->ptid);
  int syscall_number = (int) gdbarch_get_syscall_number (gdbarch, thread);

  if (stopping)
    {
      /* If we're stopping threads, there's a SIGSTOP pending, which
	 makes it so that the LWP reports an immediate syscall return,
	 followed by the SIGSTOP.  Skip seeing that "return" using
	 PTRACE_CONT directly, and let stop_wait_callback collect the
	 SIGSTOP.  Later when the thread is resumed, a new syscall
	 entry event.  If we didn't do this (and returned 0), we'd
	 leave a syscall entry pending, and our caller, by using
	 PTRACE_CONT to collect the SIGSTOP, skips the syscall return
	 itself.  Later, when the user re-resumes this LWP, we'd see
	 another syscall entry event and we'd mistake it for a return.

	 If stop_wait_callback didn't force the SIGSTOP out of the LWP
	 (leaving immediately with LWP->signalled set, without issuing
	 a PTRACE_CONT), it would still be problematic to leave this
	 syscall enter pending, as later when the thread is resumed,
	 it would then see the same syscall exit mentioned above,
	 followed by the delayed SIGSTOP, while the syscall didn't
	 actually get to execute.  It seems it would be even more
	 confusing to the user.  */

      linux_nat_debug_printf
	("ignoring syscall %d for LWP %ld (stopping threads), resuming with "
	 "PTRACE_CONT for SIGSTOP", syscall_number, lp->ptid.lwp ());

      lp->syscall_state = TARGET_WAITKIND_IGNORE;
      ptrace (PTRACE_CONT, lp->ptid.lwp (), 0, 0);
      lp->stopped = 0;
      return 1;
    }

  /* Always update the entry/return state, even if this particular
     syscall isn't interesting to the core now.  In async mode,
     the user could install a new catchpoint for this syscall
     between syscall enter/return, and we'll need to know to
     report a syscall return if that happens.  */
  lp->syscall_state = (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
		       ? TARGET_WAITKIND_SYSCALL_RETURN
		       : TARGET_WAITKIND_SYSCALL_ENTRY);

  if (catch_syscall_enabled ())
    {
      if (catching_syscall_number (syscall_number))
	{
	  /* Alright, an event to report.  */
	  if (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY)
	    ourstatus->set_syscall_entry (syscall_number);
	  else if (lp->syscall_state == TARGET_WAITKIND_SYSCALL_RETURN)
	    ourstatus->set_syscall_return (syscall_number);
	  else
	    gdb_assert_not_reached ("unexpected syscall state");

	  linux_nat_debug_printf
	    ("stopping for %s of syscall %d for LWP %ld",
	     (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
	      ? "entry" : "return"), syscall_number, lp->ptid.lwp ());

	  return 0;
	}

      linux_nat_debug_printf
	("ignoring %s of syscall %d for LWP %ld",
	 (lp->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY
	  ? "entry" : "return"), syscall_number, lp->ptid.lwp ());
    }
  else
    {
      /* If we had been syscall tracing, and hence used PT_SYSCALL
	 before on this LWP, it could happen that the user removes all
	 syscall catchpoints before we get to process this event.
	 There are two noteworthy issues here:

	 - When stopped at a syscall entry event, resuming with
	   PT_STEP still resumes executing the syscall and reports a
	   syscall return.

	 - Only PT_SYSCALL catches syscall enters.  If we last
	   single-stepped this thread, then this event can't be a
	   syscall enter.  If we last single-stepped this thread, this
	   has to be a syscall exit.

	 The points above mean that the next resume, be it PT_STEP or
	 PT_CONTINUE, can not trigger a syscall trace event.  */
      linux_nat_debug_printf
	("caught syscall event with no syscall catchpoints. %d for LWP %ld, "
	 "ignoring", syscall_number, lp->ptid.lwp ());
      lp->syscall_state = TARGET_WAITKIND_IGNORE;
    }

  /* The core isn't interested in this event.  For efficiency, avoid
     stopping all threads only to have the core resume them all again.
     Since we're not stopping threads, if we're still syscall tracing
     and not stepping, we can't use PTRACE_CONT here, as we'd miss any
     subsequent syscall.  Simply resume using the inf-ptrace layer,
     which knows when to use PT_SYSCALL or PT_CONTINUE.  */

  linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
  return 1;
}

/* Handle a GNU/Linux extended wait response.  If we see a clone
   event, we need to add the new LWP to our list (and not report the
   trap to higher layers).  This function returns non-zero if the
   event should be ignored and we should wait again.  If STOPPING is
   true, the new LWP remains stopped, otherwise it is continued.  */

static int
linux_handle_extended_wait (struct lwp_info *lp, int status)
{
  int pid = lp->ptid.lwp ();
  struct target_waitstatus *ourstatus = &lp->waitstatus;
  int event = linux_ptrace_get_extended_event (status);

  /* All extended events we currently use are mid-syscall.  Only
     PTRACE_EVENT_STOP is delivered more like a signal-stop, but
     you have to be using PTRACE_SEIZE to get that.  */
  lp->syscall_state = TARGET_WAITKIND_SYSCALL_ENTRY;

  if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK
      || event == PTRACE_EVENT_CLONE)
    {
      unsigned long new_pid;
      int ret;

      ptrace (PTRACE_GETEVENTMSG, pid, 0, &new_pid);

      /* If we haven't already seen the new PID stop, wait for it now.  */
      if (! pull_pid_from_list (&stopped_pids, new_pid, &status))
	{
	  /* The new child has a pending SIGSTOP.  We can't affect it until it
	     hits the SIGSTOP, but we're already attached.  */
	  ret = my_waitpid (new_pid, &status, __WALL);
	  if (ret == -1)
	    perror_with_name (_("waiting for new child"));
	  else if (ret != new_pid)
	    internal_error (__FILE__, __LINE__,
			    _("wait returned unexpected PID %d"), ret);
	  else if (!WIFSTOPPED (status))
	    internal_error (__FILE__, __LINE__,
			    _("wait returned unexpected status 0x%x"), status);
	}

      ptid_t child_ptid (new_pid, new_pid);

      if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK)
	{
	  open_proc_mem_file (child_ptid);

	  /* The arch-specific native code may need to know about new
	     forks even if those end up never mapped to an
	     inferior.  */
	  linux_target->low_new_fork (lp, new_pid);
	}
      else if (event == PTRACE_EVENT_CLONE)
	{
	  linux_target->low_new_clone (lp, new_pid);
	}

      if (event == PTRACE_EVENT_FORK
	  && linux_fork_checkpointing_p (lp->ptid.pid ()))
	{
	  /* Handle checkpointing by linux-fork.c here as a special
	     case.  We don't want the follow-fork-mode or 'catch fork'
	     to interfere with this.  */

	  /* This won't actually modify the breakpoint list, but will
	     physically remove the breakpoints from the child.  */
	  detach_breakpoints (ptid_t (new_pid, new_pid));

	  /* Retain child fork in ptrace (stopped) state.  */
	  if (!find_fork_pid (new_pid))
	    add_fork (new_pid);

	  /* Report as spurious, so that infrun doesn't want to follow
	     this fork.  We're actually doing an infcall in
	     linux-fork.c.  */
	  ourstatus->set_spurious ();

	  /* Report the stop to the core.  */
	  return 0;
	}

      if (event == PTRACE_EVENT_FORK)
	ourstatus->set_forked (child_ptid);
      else if (event == PTRACE_EVENT_VFORK)
	ourstatus->set_vforked (child_ptid);
      else if (event == PTRACE_EVENT_CLONE)
	{
	  struct lwp_info *new_lp;

	  ourstatus->set_ignore ();

	  linux_nat_debug_printf
	    ("Got clone event from LWP %d, new child is LWP %ld", pid, new_pid);

	  new_lp = add_lwp (ptid_t (lp->ptid.pid (), new_pid));
	  new_lp->stopped = 1;
	  new_lp->resumed = 1;

	  /* If the thread_db layer is active, let it record the user
	     level thread id and status, and add the thread to GDB's
	     list.  */
	  if (!thread_db_notice_clone (lp->ptid, new_lp->ptid))
	    {
	      /* The process is not using thread_db.  Add the LWP to
		 GDB's list.  */
	      target_post_attach (new_lp->ptid.lwp ());
	      add_thread (linux_target, new_lp->ptid);
	    }

	  /* Even if we're stopping the thread for some reason
	     internal to this module, from the perspective of infrun
	     and the user/frontend, this new thread is running until
	     it next reports a stop.  */
	  set_running (linux_target, new_lp->ptid, true);
	  set_executing (linux_target, new_lp->ptid, true);

	  if (WSTOPSIG (status) != SIGSTOP)
	    {
	      /* This can happen if someone starts sending signals to
		 the new thread before it gets a chance to run, which
		 have a lower number than SIGSTOP (e.g. SIGUSR1).
		 This is an unlikely case, and harder to handle for
		 fork / vfork than for clone, so we do not try - but
		 we handle it for clone events here.  */

	      new_lp->signalled = 1;

	      /* We created NEW_LP so it cannot yet contain STATUS.  */
	      gdb_assert (new_lp->status == 0);

	      /* Save the wait status to report later.  */
	      linux_nat_debug_printf
		("waitpid of new LWP %ld, saving status %s",
		 (long) new_lp->ptid.lwp (), status_to_str (status).c_str ());
	      new_lp->status = status;
	    }
	  else if (report_thread_events)
	    {
	      new_lp->waitstatus.set_thread_created ();
	      new_lp->status = status;
	    }

	  return 1;
	}

      return 0;
    }

  if (event == PTRACE_EVENT_EXEC)
    {
      linux_nat_debug_printf ("Got exec event from LWP %ld", lp->ptid.lwp ());

      /* Close the previous /proc/PID/mem file for this inferior,
	 which was using the address space which is now gone.
	 Reading/writing from this file would return 0/EOF.  */
      close_proc_mem_file (lp->ptid.pid ());

      /* Open a new file for the new address space.  */
      open_proc_mem_file (lp->ptid);

      ourstatus->set_execd
	(make_unique_xstrdup (linux_proc_pid_to_exec_file (pid)));

      /* The thread that execed must have been resumed, but, when a
	 thread execs, it changes its tid to the tgid, and the old
	 tgid thread might have not been resumed.  */
      lp->resumed = 1;
      return 0;
    }

  if (event == PTRACE_EVENT_VFORK_DONE)
    {
      if (current_inferior ()->waiting_for_vfork_done)
	{
	  linux_nat_debug_printf
	    ("Got expected PTRACE_EVENT_VFORK_DONE from LWP %ld: stopping",
	     lp->ptid.lwp ());

	  ourstatus->set_vfork_done ();
	  return 0;
	}

      linux_nat_debug_printf
	("Got PTRACE_EVENT_VFORK_DONE from LWP %ld: ignoring", lp->ptid.lwp ());

      return 1;
    }

  internal_error (__FILE__, __LINE__,
		  _("unknown ptrace event %d"), event);
}

/* Suspend waiting for a signal.  We're mostly interested in
   SIGCHLD/SIGINT.  */

static void
wait_for_signal ()
{
  linux_nat_debug_printf ("about to sigsuspend");
  sigsuspend (&suspend_mask);

  /* If the quit flag is set, it means that the user pressed Ctrl-C
     and we're debugging a process that is running on a separate
     terminal, so we must forward the Ctrl-C to the inferior.  (If the
     inferior is sharing GDB's terminal, then the Ctrl-C reaches the
     inferior directly.)  We must do this here because functions that
     need to block waiting for a signal loop forever until there's an
     event to report before returning back to the event loop.  */
  if (!target_terminal::is_ours ())
    {
      if (check_quit_flag ())
	target_pass_ctrlc ();
    }
}

/* Wait for LP to stop.  Returns the wait status, or 0 if the LWP has
   exited.  */

static int
wait_lwp (struct lwp_info *lp)
{
  pid_t pid;
  int status = 0;
  int thread_dead = 0;
  sigset_t prev_mask;

  gdb_assert (!lp->stopped);
  gdb_assert (lp->status == 0);

  /* Make sure SIGCHLD is blocked for sigsuspend avoiding a race below.  */
  block_child_signals (&prev_mask);

  for (;;)
    {
      pid = my_waitpid (lp->ptid.lwp (), &status, __WALL | WNOHANG);
      if (pid == -1 && errno == ECHILD)
	{
	  /* The thread has previously exited.  We need to delete it
	     now because if this was a non-leader thread execing, we
	     won't get an exit event.  See comments on exec events at
	     the top of the file.  */
	  thread_dead = 1;
	  linux_nat_debug_printf ("%s vanished.",
				  lp->ptid.to_string ().c_str ());
	}
      if (pid != 0)
	break;

      /* Bugs 10970, 12702.
	 Thread group leader may have exited in which case we'll lock up in
	 waitpid if there are other threads, even if they are all zombies too.
	 Basically, we're not supposed to use waitpid this way.
	  tkill(pid,0) cannot be used here as it gets ESRCH for both
	 for zombie and running processes.

	 As a workaround, check if we're waiting for the thread group leader and
	 if it's a zombie, and avoid calling waitpid if it is.

	 This is racy, what if the tgl becomes a zombie right after we check?
	 Therefore always use WNOHANG with sigsuspend - it is equivalent to
	 waiting waitpid but linux_proc_pid_is_zombie is safe this way.  */

      if (lp->ptid.pid () == lp->ptid.lwp ()
	  && linux_proc_pid_is_zombie (lp->ptid.lwp ()))
	{
	  thread_dead = 1;
	  linux_nat_debug_printf ("Thread group leader %s vanished.",
				  lp->ptid.to_string ().c_str ());
	  break;
	}

      /* Wait for next SIGCHLD and try again.  This may let SIGCHLD handlers
	 get invoked despite our caller had them intentionally blocked by
	 block_child_signals.  This is sensitive only to the loop of
	 linux_nat_wait_1 and there if we get called my_waitpid gets called
	 again before it gets to sigsuspend so we can safely let the handlers
	 get executed here.  */
      wait_for_signal ();
    }

  restore_child_signals_mask (&prev_mask);

  if (!thread_dead)
    {
      gdb_assert (pid == lp->ptid.lwp ());

      linux_nat_debug_printf ("waitpid %s received %s",
			      lp->ptid.to_string ().c_str (),
			      status_to_str (status).c_str ());

      /* Check if the thread has exited.  */
      if (WIFEXITED (status) || WIFSIGNALED (status))
	{
	  if (report_thread_events
	      || lp->ptid.pid () == lp->ptid.lwp ())
	    {
	      linux_nat_debug_printf ("LWP %d exited.", lp->ptid.pid ());

	      /* If this is the leader exiting, it means the whole
		 process is gone.  Store the status to report to the
		 core.  Store it in lp->waitstatus, because lp->status
		 would be ambiguous (W_EXITCODE(0,0) == 0).  */
	      lp->waitstatus = host_status_to_waitstatus (status);
	      return 0;
	    }

	  thread_dead = 1;
	  linux_nat_debug_printf ("%s exited.",
				  lp->ptid.to_string ().c_str ());
	}
    }

  if (thread_dead)
    {
      exit_lwp (lp);
      return 0;
    }

  gdb_assert (WIFSTOPPED (status));
  lp->stopped = 1;

  if (lp->must_set_ptrace_flags)
    {
      inferior *inf = find_inferior_pid (linux_target, lp->ptid.pid ());
      int options = linux_nat_ptrace_options (inf->attach_flag);

      linux_enable_event_reporting (lp->ptid.lwp (), options);
      lp->must_set_ptrace_flags = 0;
    }

  /* Handle GNU/Linux's syscall SIGTRAPs.  */
  if (WIFSTOPPED (status) && WSTOPSIG (status) == SYSCALL_SIGTRAP)
    {
      /* No longer need the sysgood bit.  The ptrace event ends up
	 recorded in lp->waitstatus if we care for it.  We can carry
	 on handling the event like a regular SIGTRAP from here
	 on.  */
      status = W_STOPCODE (SIGTRAP);
      if (linux_handle_syscall_trap (lp, 1))
	return wait_lwp (lp);
    }
  else
    {
      /* Almost all other ptrace-stops are known to be outside of system
	 calls, with further exceptions in linux_handle_extended_wait.  */
      lp->syscall_state = TARGET_WAITKIND_IGNORE;
    }

  /* Handle GNU/Linux's extended waitstatus for trace events.  */
  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP
      && linux_is_extended_waitstatus (status))
    {
      linux_nat_debug_printf ("Handling extended status 0x%06x", status);
      linux_handle_extended_wait (lp, status);
      return 0;
    }

  return status;
}

/* Send a SIGSTOP to LP.  */

static int
stop_callback (struct lwp_info *lp)
{
  if (!lp->stopped && !lp->signalled)
    {
      int ret;

      linux_nat_debug_printf ("kill %s **<SIGSTOP>**",
			      lp->ptid.to_string ().c_str ());

      errno = 0;
      ret = kill_lwp (lp->ptid.lwp (), SIGSTOP);
      linux_nat_debug_printf ("lwp kill %d %s", ret,
			      errno ? safe_strerror (errno) : "ERRNO-OK");

      lp->signalled = 1;
      gdb_assert (lp->status == 0);
    }

  return 0;
}

/* Request a stop on LWP.  */

void
linux_stop_lwp (struct lwp_info *lwp)
{
  stop_callback (lwp);
}

/* See linux-nat.h  */

void
linux_stop_and_wait_all_lwps (void)
{
  /* Stop all LWP's ...  */
  iterate_over_lwps (minus_one_ptid, stop_callback);

  /* ... and wait until all of them have reported back that
     they're no longer running.  */
  iterate_over_lwps (minus_one_ptid, stop_wait_callback);
}

/* See linux-nat.h  */

void
linux_unstop_all_lwps (void)
{
  iterate_over_lwps (minus_one_ptid,
		     [] (struct lwp_info *info)
		     {
		       return resume_stopped_resumed_lwps (info, minus_one_ptid);
		     });
}

/* Return non-zero if LWP PID has a pending SIGINT.  */

static int
linux_nat_has_pending_sigint (int pid)
{
  sigset_t pending, blocked, ignored;

  linux_proc_pending_signals (pid, &pending, &blocked, &ignored);

  if (sigismember (&pending, SIGINT)
      && !sigismember (&ignored, SIGINT))
    return 1;

  return 0;
}

/* Set a flag in LP indicating that we should ignore its next SIGINT.  */

static int
set_ignore_sigint (struct lwp_info *lp)
{
  /* If a thread has a pending SIGINT, consume it; otherwise, set a
     flag to consume the next one.  */
  if (lp->stopped && lp->status != 0 && WIFSTOPPED (lp->status)
      && WSTOPSIG (lp->status) == SIGINT)
    lp->status = 0;
  else
    lp->ignore_sigint = 1;

  return 0;
}

/* If LP does not have a SIGINT pending, then clear the ignore_sigint flag.
   This function is called after we know the LWP has stopped; if the LWP
   stopped before the expected SIGINT was delivered, then it will never have
   arrived.  Also, if the signal was delivered to a shared queue and consumed
   by a different thread, it will never be delivered to this LWP.  */

static void
maybe_clear_ignore_sigint (struct lwp_info *lp)
{
  if (!lp->ignore_sigint)
    return;

  if (!linux_nat_has_pending_sigint (lp->ptid.lwp ()))
    {
      linux_nat_debug_printf ("Clearing bogus flag for %s",
			      lp->ptid.to_string ().c_str ());
      lp->ignore_sigint = 0;
    }
}

/* Fetch the possible triggered data watchpoint info and store it in
   LP.

   On some archs, like x86, that use debug registers to set
   watchpoints, it's possible that the way to know which watched
   address trapped, is to check the register that is used to select
   which address to watch.  Problem is, between setting the watchpoint
   and reading back which data address trapped, the user may change
   the set of watchpoints, and, as a consequence, GDB changes the
   debug registers in the inferior.  To avoid reading back a stale
   stopped-data-address when that happens, we cache in LP the fact
   that a watchpoint trapped, and the corresponding data address, as
   soon as we see LP stop with a SIGTRAP.  If GDB changes the debug
   registers meanwhile, we have the cached data we can rely on.  */

static int
check_stopped_by_watchpoint (struct lwp_info *lp)
{
  scoped_restore save_inferior_ptid = make_scoped_restore (&inferior_ptid);
  inferior_ptid = lp->ptid;

  if (linux_target->low_stopped_by_watchpoint ())
    {
      lp->stop_reason = TARGET_STOPPED_BY_WATCHPOINT;
      lp->stopped_data_address_p
	= linux_target->low_stopped_data_address (&lp->stopped_data_address);
    }

  return lp->stop_reason == TARGET_STOPPED_BY_WATCHPOINT;
}

/* Returns true if the LWP had stopped for a watchpoint.  */

bool
linux_nat_target::stopped_by_watchpoint ()
{
  struct lwp_info *lp = find_lwp_pid (inferior_ptid);

  gdb_assert (lp != NULL);

  return lp->stop_reason == TARGET_STOPPED_BY_WATCHPOINT;
}

bool
linux_nat_target::stopped_data_address (CORE_ADDR *addr_p)
{
  struct lwp_info *lp = find_lwp_pid (inferior_ptid);

  gdb_assert (lp != NULL);

  *addr_p = lp->stopped_data_address;

  return lp->stopped_data_address_p;
}

/* Commonly any breakpoint / watchpoint generate only SIGTRAP.  */

bool
linux_nat_target::low_status_is_event (int status)
{
  return WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP;
}

/* Wait until LP is stopped.  */

static int
stop_wait_callback (struct lwp_info *lp)
{
  inferior *inf = find_inferior_ptid (linux_target, lp->ptid);

  /* If this is a vfork parent, bail out, it is not going to report
     any SIGSTOP until the vfork is done with.  */
  if (inf->vfork_child != NULL)
    return 0;

  if (!lp->stopped)
    {
      int status;

      status = wait_lwp (lp);
      if (status == 0)
	return 0;

      if (lp->ignore_sigint && WIFSTOPPED (status)
	  && WSTOPSIG (status) == SIGINT)
	{
	  lp->ignore_sigint = 0;

	  errno = 0;
	  ptrace (PTRACE_CONT, lp->ptid.lwp (), 0, 0);
	  lp->stopped = 0;
	  linux_nat_debug_printf
	    ("PTRACE_CONT %s, 0, 0 (%s) (discarding SIGINT)",
	     lp->ptid.to_string ().c_str (),
	     errno ? safe_strerror (errno) : "OK");

	  return stop_wait_callback (lp);
	}

      maybe_clear_ignore_sigint (lp);

      if (WSTOPSIG (status) != SIGSTOP)
	{
	  /* The thread was stopped with a signal other than SIGSTOP.  */

	  linux_nat_debug_printf ("Pending event %s in %s",
				  status_to_str ((int) status).c_str (),
				  lp->ptid.to_string ().c_str ());

	  /* Save the sigtrap event.  */
	  lp->status = status;
	  gdb_assert (lp->signalled);
	  save_stop_reason (lp);
	}
      else
	{
	  /* We caught the SIGSTOP that we intended to catch.  */

	  linux_nat_debug_printf ("Expected SIGSTOP caught for %s.",
				  lp->ptid.to_string ().c_str ());

	  lp->signalled = 0;

	  /* If we are waiting for this stop so we can report the thread
	     stopped then we need to record this status.  Otherwise, we can
	     now discard this stop event.  */
	  if (lp->last_resume_kind == resume_stop)
	    {
	      lp->status = status;
	      save_stop_reason (lp);
	    }
	}
    }

  return 0;
}

/* Return non-zero if LP has a wait status pending.  Discard the
   pending event and resume the LWP if the event that originally
   caused the stop became uninteresting.  */

static int
status_callback (struct lwp_info *lp)
{
  /* Only report a pending wait status if we pretend that this has
     indeed been resumed.  */
  if (!lp->resumed)
    return 0;

  if (!lwp_status_pending_p (lp))
    return 0;

  if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT
      || lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT)
    {
      struct regcache *regcache = get_thread_regcache (linux_target, lp->ptid);
      CORE_ADDR pc;
      int discard = 0;

      pc = regcache_read_pc (regcache);

      if (pc != lp->stop_pc)
	{
	  linux_nat_debug_printf ("PC of %s changed.  was=%s, now=%s",
				  lp->ptid.to_string ().c_str (),
				  paddress (target_gdbarch (), lp->stop_pc),
				  paddress (target_gdbarch (), pc));
	  discard = 1;
	}

#if !USE_SIGTRAP_SIGINFO
      else if (!breakpoint_inserted_here_p (regcache->aspace (), pc))
	{
	  linux_nat_debug_printf ("previous breakpoint of %s, at %s gone",
				  lp->ptid.to_string ().c_str (),
				  paddress (target_gdbarch (), lp->stop_pc));

	  discard = 1;
	}
#endif

      if (discard)
	{
	  linux_nat_debug_printf ("pending event of %s cancelled.",
				  lp->ptid.to_string ().c_str ());

	  lp->status = 0;
	  linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
	  return 0;
	}
    }

  return 1;
}

/* Count the LWP's that have had events.  */

static int
count_events_callback (struct lwp_info *lp, int *count)
{
  gdb_assert (count != NULL);

  /* Select only resumed LWPs that have an event pending.  */
  if (lp->resumed && lwp_status_pending_p (lp))
    (*count)++;

  return 0;
}

/* Select the LWP (if any) that is currently being single-stepped.  */

static int
select_singlestep_lwp_callback (struct lwp_info *lp)
{
  if (lp->last_resume_kind == resume_step
      && lp->status != 0)
    return 1;
  else
    return 0;
}

/* Returns true if LP has a status pending.  */

static int
lwp_status_pending_p (struct lwp_info *lp)
{
  /* We check for lp->waitstatus in addition to lp->status, because we
     can have pending process exits recorded in lp->status and
     W_EXITCODE(0,0) happens to be 0.  */
  return lp->status != 0 || lp->waitstatus.kind () != TARGET_WAITKIND_IGNORE;
}

/* Select the Nth LWP that has had an event.  */

static int
select_event_lwp_callback (struct lwp_info *lp, int *selector)
{
  gdb_assert (selector != NULL);

  /* Select only resumed LWPs that have an event pending.  */
  if (lp->resumed && lwp_status_pending_p (lp))
    if ((*selector)-- == 0)
      return 1;

  return 0;
}

/* Called when the LWP stopped for a signal/trap.  If it stopped for a
   trap check what caused it (breakpoint, watchpoint, trace, etc.),
   and save the result in the LWP's stop_reason field.  If it stopped
   for a breakpoint, decrement the PC if necessary on the lwp's
   architecture.  */

static void
save_stop_reason (struct lwp_info *lp)
{
  struct regcache *regcache;
  struct gdbarch *gdbarch;
  CORE_ADDR pc;
  CORE_ADDR sw_bp_pc;
#if USE_SIGTRAP_SIGINFO
  siginfo_t siginfo;
#endif

  gdb_assert (lp->stop_reason == TARGET_STOPPED_BY_NO_REASON);
  gdb_assert (lp->status != 0);

  if (!linux_target->low_status_is_event (lp->status))
    return;

  regcache = get_thread_regcache (linux_target, lp->ptid);
  gdbarch = regcache->arch ();

  pc = regcache_read_pc (regcache);
  sw_bp_pc = pc - gdbarch_decr_pc_after_break (gdbarch);

#if USE_SIGTRAP_SIGINFO
  if (linux_nat_get_siginfo (lp->ptid, &siginfo))
    {
      if (siginfo.si_signo == SIGTRAP)
	{
	  if (GDB_ARCH_IS_TRAP_BRKPT (siginfo.si_code)
	      && GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code))
	    {
	      /* The si_code is ambiguous on this arch -- check debug
		 registers.  */
	      if (!check_stopped_by_watchpoint (lp))
		lp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
	    }
	  else if (GDB_ARCH_IS_TRAP_BRKPT (siginfo.si_code))
	    {
	      /* If we determine the LWP stopped for a SW breakpoint,
		 trust it.  Particularly don't check watchpoint
		 registers, because, at least on s390, we'd find
		 stopped-by-watchpoint as long as there's a watchpoint
		 set.  */
	      lp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
	    }
	  else if (GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code))
	    {
	      /* This can indicate either a hardware breakpoint or
		 hardware watchpoint.  Check debug registers.  */
	      if (!check_stopped_by_watchpoint (lp))
		lp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;
	    }
	  else if (siginfo.si_code == TRAP_TRACE)
	    {
	      linux_nat_debug_printf ("%s stopped by trace",
				      lp->ptid.to_string ().c_str ());

	      /* We may have single stepped an instruction that
		 triggered a watchpoint.  In that case, on some
		 architectures (such as x86), instead of TRAP_HWBKPT,
		 si_code indicates TRAP_TRACE, and we need to check
		 the debug registers separately.  */
	      check_stopped_by_watchpoint (lp);
	    }
	}
    }
#else
  if ((!lp->step || lp->stop_pc == sw_bp_pc)
      && software_breakpoint_inserted_here_p (regcache->aspace (),
					      sw_bp_pc))
    {
      /* The LWP was either continued, or stepped a software
	 breakpoint instruction.  */
      lp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
    }

  if (hardware_breakpoint_inserted_here_p (regcache->aspace (), pc))
    lp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;

  if (lp->stop_reason == TARGET_STOPPED_BY_NO_REASON)
    check_stopped_by_watchpoint (lp);
#endif

  if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT)
    {
      linux_nat_debug_printf ("%s stopped by software breakpoint",
			      lp->ptid.to_string ().c_str ());

      /* Back up the PC if necessary.  */
      if (pc != sw_bp_pc)
	regcache_write_pc (regcache, sw_bp_pc);

      /* Update this so we record the correct stop PC below.  */
      pc = sw_bp_pc;
    }
  else if (lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT)
    {
      linux_nat_debug_printf ("%s stopped by hardware breakpoint",
			      lp->ptid.to_string ().c_str ());
    }
  else if (lp->stop_reason == TARGET_STOPPED_BY_WATCHPOINT)
    {
      linux_nat_debug_printf ("%s stopped by hardware watchpoint",
			      lp->ptid.to_string ().c_str ());
    }

  lp->stop_pc = pc;
}


/* Returns true if the LWP had stopped for a software breakpoint.  */

bool
linux_nat_target::stopped_by_sw_breakpoint ()
{
  struct lwp_info *lp = find_lwp_pid (inferior_ptid);

  gdb_assert (lp != NULL);

  return lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT;
}

/* Implement the supports_stopped_by_sw_breakpoint method.  */

bool
linux_nat_target::supports_stopped_by_sw_breakpoint ()
{
  return USE_SIGTRAP_SIGINFO;
}

/* Returns true if the LWP had stopped for a hardware
   breakpoint/watchpoint.  */

bool
linux_nat_target::stopped_by_hw_breakpoint ()
{
  struct lwp_info *lp = find_lwp_pid (inferior_ptid);

  gdb_assert (lp != NULL);

  return lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT;
}

/* Implement the supports_stopped_by_hw_breakpoint method.  */

bool
linux_nat_target::supports_stopped_by_hw_breakpoint ()
{
  return USE_SIGTRAP_SIGINFO;
}

/* Select one LWP out of those that have events pending.  */

static void
select_event_lwp (ptid_t filter, struct lwp_info **orig_lp, int *status)
{
  int num_events = 0;
  int random_selector;
  struct lwp_info *event_lp = NULL;

  /* Record the wait status for the original LWP.  */
  (*orig_lp)->status = *status;

  /* In all-stop, give preference to the LWP that is being
     single-stepped.  There will be at most one, and it will be the
     LWP that the core is most interested in.  If we didn't do this,
     then we'd have to handle pending step SIGTRAPs somehow in case
     the core later continues the previously-stepped thread, as
     otherwise we'd report the pending SIGTRAP then, and the core, not
     having stepped the thread, wouldn't understand what the trap was
     for, and therefore would report it to the user as a random
     signal.  */
  if (!target_is_non_stop_p ())
    {
      event_lp = iterate_over_lwps (filter, select_singlestep_lwp_callback);
      if (event_lp != NULL)
	{
	  linux_nat_debug_printf ("Select single-step %s",
				  event_lp->ptid.to_string ().c_str ());
	}
    }

  if (event_lp == NULL)
    {
      /* Pick one at random, out of those which have had events.  */

      /* First see how many events we have.  */
      iterate_over_lwps (filter,
			 [&] (struct lwp_info *info)
			 {
			   return count_events_callback (info, &num_events);
			 });
      gdb_assert (num_events > 0);

      /* Now randomly pick a LWP out of those that have had
	 events.  */
      random_selector = (int)
	((num_events * (double) rand ()) / (RAND_MAX + 1.0));

      if (num_events > 1)
	linux_nat_debug_printf ("Found %d events, selecting #%d",
				num_events, random_selector);

      event_lp
	= (iterate_over_lwps
	   (filter,
	    [&] (struct lwp_info *info)
	    {
	      return select_event_lwp_callback (info,
						&random_selector);
	    }));
    }

  if (event_lp != NULL)
    {
      /* Switch the event LWP.  */
      *orig_lp = event_lp;
      *status = event_lp->status;
    }

  /* Flush the wait status for the event LWP.  */
  (*orig_lp)->status = 0;
}

/* Return non-zero if LP has been resumed.  */

static int
resumed_callback (struct lwp_info *lp)
{
  return lp->resumed;
}

/* Check if we should go on and pass this event to common code.

   If so, save the status to the lwp_info structure associated to LWPID.  */

static void
linux_nat_filter_event (int lwpid, int status)
{
  struct lwp_info *lp;
  int event = linux_ptrace_get_extended_event (status);

  lp = find_lwp_pid (ptid_t (lwpid));

  /* Check for stop events reported by a process we didn't already
     know about - anything not already in our LWP list.

     If we're expecting to receive stopped processes after
     fork, vfork, and clone events, then we'll just add the
     new one to our list and go back to waiting for the event
     to be reported - the stopped process might be returned
     from waitpid before or after the event is.

     But note the case of a non-leader thread exec'ing after the
     leader having exited, and gone from our lists.  The non-leader
     thread changes its tid to the tgid.  */

  if (WIFSTOPPED (status) && lp == NULL
      && (WSTOPSIG (status) == SIGTRAP && event == PTRACE_EVENT_EXEC))
    {
      /* A multi-thread exec after we had seen the leader exiting.  */
      linux_nat_debug_printf ("Re-adding thread group leader LWP %d.", lwpid);

      lp = add_lwp (ptid_t (lwpid, lwpid));
      lp->stopped = 1;
      lp->resumed = 1;
      add_thread (linux_target, lp->ptid);
    }

  if (WIFSTOPPED (status) && !lp)
    {
      linux_nat_debug_printf ("saving LWP %ld status %s in stopped_pids list",
			      (long) lwpid, status_to_str (status).c_str ());
      add_to_pid_list (&stopped_pids, lwpid, status);
      return;
    }

  /* Make sure we don't report an event for the exit of an LWP not in
     our list, i.e. not part of the current process.  This can happen
     if we detach from a program we originally forked and then it
     exits.  */
  if (!WIFSTOPPED (status) && !lp)
    return;

  /* This LWP is stopped now.  (And if dead, this prevents it from
     ever being continued.)  */
  lp->stopped = 1;

  if (WIFSTOPPED (status) && lp->must_set_ptrace_flags)
    {
      inferior *inf = find_inferior_pid (linux_target, lp->ptid.pid ());
      int options = linux_nat_ptrace_options (inf->attach_flag);

      linux_enable_event_reporting (lp->ptid.lwp (), options);
      lp->must_set_ptrace_flags = 0;
    }

  /* Handle GNU/Linux's syscall SIGTRAPs.  */
  if (WIFSTOPPED (status) && WSTOPSIG (status) == SYSCALL_SIGTRAP)
    {
      /* No longer need the sysgood bit.  The ptrace event ends up
	 recorded in lp->waitstatus if we care for it.  We can carry
	 on handling the event like a regular SIGTRAP from here
	 on.  */
      status = W_STOPCODE (SIGTRAP);
      if (linux_handle_syscall_trap (lp, 0))
	return;
    }
  else
    {
      /* Almost all other ptrace-stops are known to be outside of system
	 calls, with further exceptions in linux_handle_extended_wait.  */
      lp->syscall_state = TARGET_WAITKIND_IGNORE;
    }

  /* Handle GNU/Linux's extended waitstatus for trace events.  */
  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP
      && linux_is_extended_waitstatus (status))
    {
      linux_nat_debug_printf ("Handling extended status 0x%06x", status);

      if (linux_handle_extended_wait (lp, status))
	return;
    }

  /* Check if the thread has exited.  */
  if (WIFEXITED (status) || WIFSIGNALED (status))
    {
      if (!report_thread_events
	  && num_lwps (lp->ptid.pid ()) > 1)
	{
	  linux_nat_debug_printf ("%s exited.",
				  lp->ptid.to_string ().c_str ());

	  /* If there is at least one more LWP, then the exit signal
	     was not the end of the debugged application and should be
	     ignored.  */
	  exit_lwp (lp);
	  return;
	}

      /* Note that even if the leader was ptrace-stopped, it can still
	 exit, if e.g., some other thread brings down the whole
	 process (calls `exit').  So don't assert that the lwp is
	 resumed.  */
      linux_nat_debug_printf ("LWP %ld exited (resumed=%d)",
			      lp->ptid.lwp (), lp->resumed);

      /* Dead LWP's aren't expected to reported a pending sigstop.  */
      lp->signalled = 0;

      /* Store the pending event in the waitstatus, because
	 W_EXITCODE(0,0) == 0.  */
      lp->waitstatus = host_status_to_waitstatus (status);
      return;
    }

  /* Make sure we don't report a SIGSTOP that we sent ourselves in
     an attempt to stop an LWP.  */
  if (lp->signalled
      && WIFSTOPPED (status) && WSTOPSIG (status) == SIGSTOP)
    {
      lp->signalled = 0;

      if (lp->last_resume_kind == resume_stop)
	{
	  linux_nat_debug_printf ("resume_stop SIGSTOP caught for %s.",
				  lp->ptid.to_string ().c_str ());
	}
      else
	{
	  /* This is a delayed SIGSTOP.  Filter out the event.  */

	  linux_nat_debug_printf
	    ("%s %s, 0, 0 (discard delayed SIGSTOP)",
	     lp->step ? "PTRACE_SINGLESTEP" : "PTRACE_CONT",
	     lp->ptid.to_string ().c_str ());

	  linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
	  gdb_assert (lp->resumed);
	  return;
	}
    }

  /* Make sure we don't report a SIGINT that we have already displayed
     for another thread.  */
  if (lp->ignore_sigint
      && WIFSTOPPED (status) && WSTOPSIG (status) == SIGINT)
    {
      linux_nat_debug_printf ("Delayed SIGINT caught for %s.",
			      lp->ptid.to_string ().c_str ());

      /* This is a delayed SIGINT.  */
      lp->ignore_sigint = 0;

      linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
      linux_nat_debug_printf ("%s %s, 0, 0 (discard SIGINT)",
			      lp->step ? "PTRACE_SINGLESTEP" : "PTRACE_CONT",
			      lp->ptid.to_string ().c_str ());
      gdb_assert (lp->resumed);

      /* Discard the event.  */
      return;
    }

  /* Don't report signals that GDB isn't interested in, such as
     signals that are neither printed nor stopped upon.  Stopping all
     threads can be a bit time-consuming, so if we want decent
     performance with heavily multi-threaded programs, especially when
     they're using a high frequency timer, we'd better avoid it if we
     can.  */
  if (WIFSTOPPED (status))
    {
      enum gdb_signal signo = gdb_signal_from_host (WSTOPSIG (status));

      if (!target_is_non_stop_p ())
	{
	  /* Only do the below in all-stop, as we currently use SIGSTOP
	     to implement target_stop (see linux_nat_stop) in
	     non-stop.  */
	  if (signo == GDB_SIGNAL_INT && signal_pass_state (signo) == 0)
	    {
	      /* If ^C/BREAK is typed at the tty/console, SIGINT gets
		 forwarded to the entire process group, that is, all LWPs
		 will receive it - unless they're using CLONE_THREAD to
		 share signals.  Since we only want to report it once, we
		 mark it as ignored for all LWPs except this one.  */
	      iterate_over_lwps (ptid_t (lp->ptid.pid ()), set_ignore_sigint);
	      lp->ignore_sigint = 0;
	    }
	  else
	    maybe_clear_ignore_sigint (lp);
	}

      /* When using hardware single-step, we need to report every signal.
	 Otherwise, signals in pass_mask may be short-circuited
	 except signals that might be caused by a breakpoint, or SIGSTOP
	 if we sent the SIGSTOP and are waiting for it to arrive.  */
      if (!lp->step
	  && WSTOPSIG (status) && sigismember (&pass_mask, WSTOPSIG (status))
	  && (WSTOPSIG (status) != SIGSTOP
	      || !find_thread_ptid (linux_target, lp->ptid)->stop_requested)
	  && !linux_wstatus_maybe_breakpoint (status))
	{
	  linux_resume_one_lwp (lp, lp->step, signo);
	  linux_nat_debug_printf
	    ("%s %s, %s (preempt 'handle')",
	     lp->step ? "PTRACE_SINGLESTEP" : "PTRACE_CONT",
	     lp->ptid.to_string ().c_str (),
	     (signo != GDB_SIGNAL_0
	      ? strsignal (gdb_signal_to_host (signo)) : "0"));
	  return;
	}
    }

  /* An interesting event.  */
  gdb_assert (lp);
  lp->status = status;
  save_stop_reason (lp);
}

/* Detect zombie thread group leaders, and "exit" them.  We can't reap
   their exits until all other threads in the group have exited.  */

static void
check_zombie_leaders (void)
{
  for (inferior *inf : all_inferiors ())
    {
      struct lwp_info *leader_lp;

      if (inf->pid == 0)
	continue;

      leader_lp = find_lwp_pid (ptid_t (inf->pid));
      if (leader_lp != NULL
	  /* Check if there are other threads in the group, as we may
	     have raced with the inferior simply exiting.  */
	  && num_lwps (inf->pid) > 1
	  && linux_proc_pid_is_zombie (inf->pid))
	{
	  linux_nat_debug_printf ("Thread group leader %d zombie "
				  "(it exited, or another thread execd).",
				  inf->pid);

	  /* A leader zombie can mean one of two things:

	     - It exited, and there's an exit status pending
	     available, or only the leader exited (not the whole
	     program).  In the latter case, we can't waitpid the
	     leader's exit status until all other threads are gone.

	     - There are 3 or more threads in the group, and a thread
	     other than the leader exec'd.  See comments on exec
	     events at the top of the file.  We could try
	     distinguishing the exit and exec cases, by waiting once
	     more, and seeing if something comes out, but it doesn't
	     sound useful.  The previous leader _does_ go away, and
	     we'll re-add the new one once we see the exec event
	     (which is just the same as what would happen if the
	     previous leader did exit voluntarily before some other
	     thread execs).  */

	  linux_nat_debug_printf ("Thread group leader %d vanished.", inf->pid);
	  exit_lwp (leader_lp);
	}
    }
}

/* Convenience function that is called when the kernel reports an exit
   event.  This decides whether to report the event to GDB as a
   process exit event, a thread exit event, or to suppress the
   event.  */

static ptid_t
filter_exit_event (struct lwp_info *event_child,
		   struct target_waitstatus *ourstatus)
{
  ptid_t ptid = event_child->ptid;

  if (num_lwps (ptid.pid ()) > 1)
    {
      if (report_thread_events)
	ourstatus->set_thread_exited (0);
      else
	ourstatus->set_ignore ();

      exit_lwp (event_child);
    }

  return ptid;
}

static ptid_t
linux_nat_wait_1 (ptid_t ptid, struct target_waitstatus *ourstatus,
		  target_wait_flags target_options)
{
  sigset_t prev_mask;
  enum resume_kind last_resume_kind;
  struct lwp_info *lp;
  int status;

  linux_nat_debug_printf ("enter");

  /* The first time we get here after starting a new inferior, we may
     not have added it to the LWP list yet - this is the earliest
     moment at which we know its PID.  */
  if (ptid.is_pid () && find_lwp_pid (ptid) == nullptr)
    {
      ptid_t lwp_ptid (ptid.pid (), ptid.pid ());

      /* Upgrade the main thread's ptid.  */
      thread_change_ptid (linux_target, ptid, lwp_ptid);
      lp = add_initial_lwp (lwp_ptid);
      lp->resumed = 1;
    }

  /* Make sure SIGCHLD is blocked until the sigsuspend below.  */
  block_child_signals (&prev_mask);

  /* First check if there is a LWP with a wait status pending.  */
  lp = iterate_over_lwps (ptid, status_callback);
  if (lp != NULL)
    {
      linux_nat_debug_printf ("Using pending wait status %s for %s.",
			      status_to_str (lp->status).c_str (),
			      lp->ptid.to_string ().c_str ());
    }

  /* But if we don't find a pending event, we'll have to wait.  Always
     pull all events out of the kernel.  We'll randomly select an
     event LWP out of all that have events, to prevent starvation.  */

  while (lp == NULL)
    {
      pid_t lwpid;

      /* Always use -1 and WNOHANG, due to couple of a kernel/ptrace
	 quirks:

	 - If the thread group leader exits while other threads in the
	   thread group still exist, waitpid(TGID, ...) hangs.  That
	   waitpid won't return an exit status until the other threads
	   in the group are reaped.

	 - When a non-leader thread execs, that thread just vanishes
	   without reporting an exit (so we'd hang if we waited for it
	   explicitly in that case).  The exec event is reported to
	   the TGID pid.  */

      errno = 0;
      lwpid = my_waitpid (-1, &status,  __WALL | WNOHANG);

      linux_nat_debug_printf ("waitpid(-1, ...) returned %d, %s",
			      lwpid,
			      errno ? safe_strerror (errno) : "ERRNO-OK");

      if (lwpid > 0)
	{
	  linux_nat_debug_printf ("waitpid %ld received %s",
				  (long) lwpid,
				  status_to_str (status).c_str ());

	  linux_nat_filter_event (lwpid, status);
	  /* Retry until nothing comes out of waitpid.  A single
	     SIGCHLD can indicate more than one child stopped.  */
	  continue;
	}

      /* Now that we've pulled all events out of the kernel, resume
	 LWPs that don't have an interesting event to report.  */
      iterate_over_lwps (minus_one_ptid,
			 [] (struct lwp_info *info)
			 {
			   return resume_stopped_resumed_lwps (info, minus_one_ptid);
			 });

      /* ... and find an LWP with a status to report to the core, if
	 any.  */
      lp = iterate_over_lwps (ptid, status_callback);
      if (lp != NULL)
	break;

      /* Check for zombie thread group leaders.  Those can't be reaped
	 until all other threads in the thread group are.  */
      check_zombie_leaders ();

      /* If there are no resumed children left, bail.  We'd be stuck
	 forever in the sigsuspend call below otherwise.  */
      if (iterate_over_lwps (ptid, resumed_callback) == NULL)
	{
	  linux_nat_debug_printf ("exit (no resumed LWP)");

	  ourstatus->set_no_resumed ();

	  restore_child_signals_mask (&prev_mask);
	  return minus_one_ptid;
	}

      /* No interesting event to report to the core.  */

      if (target_options & TARGET_WNOHANG)
	{
	  linux_nat_debug_printf ("exit (ignore)");

	  ourstatus->set_ignore ();
	  restore_child_signals_mask (&prev_mask);
	  return minus_one_ptid;
	}

      /* We shouldn't end up here unless we want to try again.  */
      gdb_assert (lp == NULL);

      /* Block until we get an event reported with SIGCHLD.  */
      wait_for_signal ();
    }

  gdb_assert (lp);

  status = lp->status;
  lp->status = 0;

  if (!target_is_non_stop_p ())
    {
      /* Now stop all other LWP's ...  */
      iterate_over_lwps (minus_one_ptid, stop_callback);

      /* ... and wait until all of them have reported back that
	 they're no longer running.  */
      iterate_over_lwps (minus_one_ptid, stop_wait_callback);
    }

  /* If we're not waiting for a specific LWP, choose an event LWP from
     among those that have had events.  Giving equal priority to all
     LWPs that have had events helps prevent starvation.  */
  if (ptid == minus_one_ptid || ptid.is_pid ())
    select_event_lwp (ptid, &lp, &status);

  gdb_assert (lp != NULL);

  /* Now that we've selected our final event LWP, un-adjust its PC if
     it was a software breakpoint, and we can't reliably support the
     "stopped by software breakpoint" stop reason.  */
  if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT
      && !USE_SIGTRAP_SIGINFO)
    {
      struct regcache *regcache = get_thread_regcache (linux_target, lp->ptid);
      struct gdbarch *gdbarch = regcache->arch ();
      int decr_pc = gdbarch_decr_pc_after_break (gdbarch);

      if (decr_pc != 0)
	{
	  CORE_ADDR pc;

	  pc = regcache_read_pc (regcache);
	  regcache_write_pc (regcache, pc + decr_pc);
	}
    }

  /* We'll need this to determine whether to report a SIGSTOP as
     GDB_SIGNAL_0.  Need to take a copy because resume_clear_callback
     clears it.  */
  last_resume_kind = lp->last_resume_kind;

  if (!target_is_non_stop_p ())
    {
      /* In all-stop, from the core's perspective, all LWPs are now
	 stopped until a new resume action is sent over.  */
      iterate_over_lwps (minus_one_ptid, resume_clear_callback);
    }
  else
    {
      resume_clear_callback (lp);
    }

  if (linux_target->low_status_is_event (status))
    {
      linux_nat_debug_printf ("trap ptid is %s.",
			      lp->ptid.to_string ().c_str ());
    }

  if (lp->waitstatus.kind () != TARGET_WAITKIND_IGNORE)
    {
      *ourstatus = lp->waitstatus;
      lp->waitstatus.set_ignore ();
    }
  else
    *ourstatus = host_status_to_waitstatus (status);

  linux_nat_debug_printf ("exit");

  restore_child_signals_mask (&prev_mask);

  if (last_resume_kind == resume_stop
      && ourstatus->kind () == TARGET_WAITKIND_STOPPED
      && WSTOPSIG (status) == SIGSTOP)
    {
      /* A thread that has been requested to stop by GDB with
	 target_stop, and it stopped cleanly, so report as SIG0.  The
	 use of SIGSTOP is an implementation detail.  */
      ourstatus->set_stopped (GDB_SIGNAL_0);
    }

  if (ourstatus->kind () == TARGET_WAITKIND_EXITED
      || ourstatus->kind () == TARGET_WAITKIND_SIGNALLED)
    lp->core = -1;
  else
    lp->core = linux_common_core_of_thread (lp->ptid);

  if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
    return filter_exit_event (lp, ourstatus);

  return lp->ptid;
}

/* Resume LWPs that are currently stopped without any pending status
   to report, but are resumed from the core's perspective.  */

static int
resume_stopped_resumed_lwps (struct lwp_info *lp, const ptid_t wait_ptid)
{
  if (!lp->stopped)
    {
      linux_nat_debug_printf ("NOT resuming LWP %s, not stopped",
			      lp->ptid.to_string ().c_str ());
    }
  else if (!lp->resumed)
    {
      linux_nat_debug_printf ("NOT resuming LWP %s, not resumed",
			      lp->ptid.to_string ().c_str ());
    }
  else if (lwp_status_pending_p (lp))
    {
      linux_nat_debug_printf ("NOT resuming LWP %s, has pending status",
			      lp->ptid.to_string ().c_str ());
    }
  else
    {
      struct regcache *regcache = get_thread_regcache (linux_target, lp->ptid);
      struct gdbarch *gdbarch = regcache->arch ();

      try
	{
	  CORE_ADDR pc = regcache_read_pc (regcache);
	  int leave_stopped = 0;

	  /* Don't bother if there's a breakpoint at PC that we'd hit
	     immediately, and we're not waiting for this LWP.  */
	  if (!lp->ptid.matches (wait_ptid))
	    {
	      if (breakpoint_inserted_here_p (regcache->aspace (), pc))
		leave_stopped = 1;
	    }

	  if (!leave_stopped)
	    {
	      linux_nat_debug_printf
		("resuming stopped-resumed LWP %s at %s: step=%d",
		 lp->ptid.to_string ().c_str (), paddress (gdbarch, pc),
		 lp->step);

	      linux_resume_one_lwp_throw (lp, lp->step, GDB_SIGNAL_0);
	    }
	}
      catch (const gdb_exception_error &ex)
	{
	  if (!check_ptrace_stopped_lwp_gone (lp))
	    throw;
	}
    }

  return 0;
}

ptid_t
linux_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
			target_wait_flags target_options)
{
  ptid_t event_ptid;

  linux_nat_debug_printf ("[%s], [%s]", ptid.to_string ().c_str (),
			  target_options_to_string (target_options).c_str ());

  /* Flush the async file first.  */
  if (target_is_async_p ())
    async_file_flush ();

  /* Resume LWPs that are currently stopped without any pending status
     to report, but are resumed from the core's perspective.  LWPs get
     in this state if we find them stopping at a time we're not
     interested in reporting the event (target_wait on a
     specific_process, for example, see linux_nat_wait_1), and
     meanwhile the event became uninteresting.  Don't bother resuming
     LWPs we're not going to wait for if they'd stop immediately.  */
  if (target_is_non_stop_p ())
    iterate_over_lwps (minus_one_ptid,
		       [=] (struct lwp_info *info)
		       {
			 return resume_stopped_resumed_lwps (info, ptid);
		       });

  event_ptid = linux_nat_wait_1 (ptid, ourstatus, target_options);

  /* If we requested any event, and something came out, assume there
     may be more.  If we requested a specific lwp or process, also
     assume there may be more.  */
  if (target_is_async_p ()
      && ((ourstatus->kind () != TARGET_WAITKIND_IGNORE
	   && ourstatus->kind () != TARGET_WAITKIND_NO_RESUMED)
	  || ptid != minus_one_ptid))
    async_file_mark ();

  return event_ptid;
}

/* Kill one LWP.  */

static void
kill_one_lwp (pid_t pid)
{
  /* PTRACE_KILL may resume the inferior.  Send SIGKILL first.  */

  errno = 0;
  kill_lwp (pid, SIGKILL);

  if (debug_linux_nat)
    {
      int save_errno = errno;

      linux_nat_debug_printf
	("kill (SIGKILL) %ld, 0, 0 (%s)", (long) pid,
	 save_errno != 0 ? safe_strerror (save_errno) : "OK");
    }

  /* Some kernels ignore even SIGKILL for processes under ptrace.  */

  errno = 0;
  ptrace (PTRACE_KILL, pid, 0, 0);
  if (debug_linux_nat)
    {
      int save_errno = errno;

      linux_nat_debug_printf
	("PTRACE_KILL %ld, 0, 0 (%s)", (long) pid,
	 save_errno ? safe_strerror (save_errno) : "OK");
    }
}

/* Wait for an LWP to die.  */

static void
kill_wait_one_lwp (pid_t pid)
{
  pid_t res;

  /* We must make sure that there are no pending events (delayed
     SIGSTOPs, pending SIGTRAPs, etc.) to make sure the current
     program doesn't interfere with any following debugging session.  */

  do
    {
      res = my_waitpid (pid, NULL, __WALL);
      if (res != (pid_t) -1)
	{
	  linux_nat_debug_printf ("wait %ld received unknown.", (long) pid);

	  /* The Linux kernel sometimes fails to kill a thread
	     completely after PTRACE_KILL; that goes from the stop
	     point in do_fork out to the one in get_signal_to_deliver
	     and waits again.  So kill it again.  */
	  kill_one_lwp (pid);
	}
    }
  while (res == pid);

  gdb_assert (res == -1 && errno == ECHILD);
}

/* Callback for iterate_over_lwps.  */

static int
kill_callback (struct lwp_info *lp)
{
  kill_one_lwp (lp->ptid.lwp ());
  return 0;
}

/* Callback for iterate_over_lwps.  */

static int
kill_wait_callback (struct lwp_info *lp)
{
  kill_wait_one_lwp (lp->ptid.lwp ());
  return 0;
}

/* Kill the fork children of any threads of inferior INF that are
   stopped at a fork event.  */

static void
kill_unfollowed_fork_children (struct inferior *inf)
{
  for (thread_info *thread : inf->non_exited_threads ())
    {
      struct target_waitstatus *ws = &thread->pending_follow;

      if (ws->kind () == TARGET_WAITKIND_FORKED
	  || ws->kind () == TARGET_WAITKIND_VFORKED)
	{
	  ptid_t child_ptid = ws->child_ptid ();
	  int child_pid = child_ptid.pid ();
	  int child_lwp = child_ptid.lwp ();

	  kill_one_lwp (child_lwp);
	  kill_wait_one_lwp (child_lwp);

	  /* Let the arch-specific native code know this process is
	     gone.  */
	  linux_target->low_forget_process (child_pid);
	}
    }
}

void
linux_nat_target::kill ()
{
  /* If we're stopped while forking and we haven't followed yet,
     kill the other task.  We need to do this first because the
     parent will be sleeping if this is a vfork.  */
  kill_unfollowed_fork_children (current_inferior ());

  if (forks_exist_p ())
    linux_fork_killall ();
  else
    {
      ptid_t ptid = ptid_t (inferior_ptid.pid ());

      /* Stop all threads before killing them, since ptrace requires
	 that the thread is stopped to successfully PTRACE_KILL.  */
      iterate_over_lwps (ptid, stop_callback);
      /* ... and wait until all of them have reported back that
	 they're no longer running.  */
      iterate_over_lwps (ptid, stop_wait_callback);

      /* Kill all LWP's ...  */
      iterate_over_lwps (ptid, kill_callback);

      /* ... and wait until we've flushed all events.  */
      iterate_over_lwps (ptid, kill_wait_callback);
    }

  target_mourn_inferior (inferior_ptid);
}

void
linux_nat_target::mourn_inferior ()
{
  int pid = inferior_ptid.pid ();

  purge_lwp_list (pid);

  close_proc_mem_file (pid);

  if (! forks_exist_p ())
    /* Normal case, no other forks available.  */
    inf_ptrace_target::mourn_inferior ();
  else
    /* Multi-fork case.  The current inferior_ptid has exited, but
       there are other viable forks to debug.  Delete the exiting
       one and context-switch to the first available.  */
    linux_fork_mourn_inferior ();

  /* Let the arch-specific native code know this process is gone.  */
  linux_target->low_forget_process (pid);
}

/* Convert a native/host siginfo object, into/from the siginfo in the
   layout of the inferiors' architecture.  */

static void
siginfo_fixup (siginfo_t *siginfo, gdb_byte *inf_siginfo, int direction)
{
  /* If the low target didn't do anything, then just do a straight
     memcpy.  */
  if (!linux_target->low_siginfo_fixup (siginfo, inf_siginfo, direction))
    {
      if (direction == 1)
	memcpy (siginfo, inf_siginfo, sizeof (siginfo_t));
      else
	memcpy (inf_siginfo, siginfo, sizeof (siginfo_t));
    }
}

static enum target_xfer_status
linux_xfer_siginfo (enum target_object object,
		    const char *annex, gdb_byte *readbuf,
		    const gdb_byte *writebuf, ULONGEST offset, ULONGEST len,
		    ULONGEST *xfered_len)
{
  int pid;
  siginfo_t siginfo;
  gdb_byte inf_siginfo[sizeof (siginfo_t)];

  gdb_assert (object == TARGET_OBJECT_SIGNAL_INFO);
  gdb_assert (readbuf || writebuf);

  pid = inferior_ptid.lwp ();
  if (pid == 0)
    pid = inferior_ptid.pid ();

  if (offset > sizeof (siginfo))
    return TARGET_XFER_E_IO;

  errno = 0;
  ptrace (PTRACE_GETSIGINFO, pid, (PTRACE_TYPE_ARG3) 0, &siginfo);
  if (errno != 0)
    return TARGET_XFER_E_IO;

  /* When GDB is built as a 64-bit application, ptrace writes into
     SIGINFO an object with 64-bit layout.  Since debugging a 32-bit
     inferior with a 64-bit GDB should look the same as debugging it
     with a 32-bit GDB, we need to convert it.  GDB core always sees
     the converted layout, so any read/write will have to be done
     post-conversion.  */
  siginfo_fixup (&siginfo, inf_siginfo, 0);

  if (offset + len > sizeof (siginfo))
    len = sizeof (siginfo) - offset;

  if (readbuf != NULL)
    memcpy (readbuf, inf_siginfo + offset, len);
  else
    {
      memcpy (inf_siginfo + offset, writebuf, len);

      /* Convert back to ptrace layout before flushing it out.  */
      siginfo_fixup (&siginfo, inf_siginfo, 1);

      errno = 0;
      ptrace (PTRACE_SETSIGINFO, pid, (PTRACE_TYPE_ARG3) 0, &siginfo);
      if (errno != 0)
	return TARGET_XFER_E_IO;
    }

  *xfered_len = len;
  return TARGET_XFER_OK;
}

static enum target_xfer_status
linux_nat_xfer_osdata (enum target_object object,
		       const char *annex, gdb_byte *readbuf,
		       const gdb_byte *writebuf, ULONGEST offset, ULONGEST len,
		       ULONGEST *xfered_len);

static enum target_xfer_status
linux_proc_xfer_memory_partial (gdb_byte *readbuf, const gdb_byte *writebuf,
				ULONGEST offset, LONGEST len, ULONGEST *xfered_len);

enum target_xfer_status
linux_nat_target::xfer_partial (enum target_object object,
				const char *annex, gdb_byte *readbuf,
				const gdb_byte *writebuf,
				ULONGEST offset, ULONGEST len, ULONGEST *xfered_len)
{
  if (object == TARGET_OBJECT_SIGNAL_INFO)
    return linux_xfer_siginfo (object, annex, readbuf, writebuf,
			       offset, len, xfered_len);

  /* The target is connected but no live inferior is selected.  Pass
     this request down to a lower stratum (e.g., the executable
     file).  */
  if (object == TARGET_OBJECT_MEMORY && inferior_ptid == null_ptid)
    return TARGET_XFER_EOF;

  if (object == TARGET_OBJECT_AUXV)
    return memory_xfer_auxv (this, object, annex, readbuf, writebuf,
			     offset, len, xfered_len);

  if (object == TARGET_OBJECT_OSDATA)
    return linux_nat_xfer_osdata (object, annex, readbuf, writebuf,
				  offset, len, xfered_len);

  if (object == TARGET_OBJECT_MEMORY)
    {
      /* GDB calculates all addresses in the largest possible address
	 width.  The address width must be masked before its final use
	 by linux_proc_xfer_partial.

	 Compare ADDR_BIT first to avoid a compiler warning on shift overflow.  */
      int addr_bit = gdbarch_addr_bit (target_gdbarch ());

      if (addr_bit < (sizeof (ULONGEST) * HOST_CHAR_BIT))
	offset &= ((ULONGEST) 1 << addr_bit) - 1;

      return linux_proc_xfer_memory_partial (readbuf, writebuf,
					     offset, len, xfered_len);
    }

  return inf_ptrace_target::xfer_partial (object, annex, readbuf, writebuf,
					  offset, len, xfered_len);
}

bool
linux_nat_target::thread_alive (ptid_t ptid)
{
  /* As long as a PTID is in lwp list, consider it alive.  */
  return find_lwp_pid (ptid) != NULL;
}

/* Implement the to_update_thread_list target method for this
   target.  */

void
linux_nat_target::update_thread_list ()
{
  /* We add/delete threads from the list as clone/exit events are
     processed, so just try deleting exited threads still in the
     thread list.  */
  delete_exited_threads ();

  /* Update the processor core that each lwp/thread was last seen
     running on.  */
  for (lwp_info *lwp : all_lwps ())
    {
      /* Avoid accessing /proc if the thread hasn't run since we last
	 time we fetched the thread's core.  Accessing /proc becomes
	 noticeably expensive when we have thousands of LWPs.  */
      if (lwp->core == -1)
	lwp->core = linux_common_core_of_thread (lwp->ptid);
    }
}

std::string
linux_nat_target::pid_to_str (ptid_t ptid)
{
  if (ptid.lwp_p ()
      && (ptid.pid () != ptid.lwp ()
	  || num_lwps (ptid.pid ()) > 1))
    return string_printf ("LWP %ld", ptid.lwp ());

  return normal_pid_to_str (ptid);
}

const char *
linux_nat_target::thread_name (struct thread_info *thr)
{
  return linux_proc_tid_get_name (thr->ptid);
}

/* Accepts an integer PID; Returns a string representing a file that
   can be opened to get the symbols for the child process.  */

char *
linux_nat_target::pid_to_exec_file (int pid)
{
  return linux_proc_pid_to_exec_file (pid);
}

/* Object representing an /proc/PID/mem open file.  We keep one such
   file open per inferior.

   It might be tempting to think about only ever opening one file at
   most for all inferiors, closing/reopening the file as we access
   memory of different inferiors, to minimize number of file
   descriptors open, which can otherwise run into resource limits.
   However, that does not work correctly -- if the inferior execs and
   we haven't processed the exec event yet, and, we opened a
   /proc/PID/mem file, we will get a mem file accessing the post-exec
   address space, thinking we're opening it for the pre-exec address
   space.  That is dangerous as we can poke memory (e.g. clearing
   breakpoints) in the post-exec memory by mistake, corrupting the
   inferior.  For that reason, we open the mem file as early as
   possible, right after spawning, forking or attaching to the
   inferior, when the inferior is stopped and thus before it has a
   chance of execing.

   Note that after opening the file, even if the thread we opened it
   for subsequently exits, the open file is still usable for accessing
   memory.  It's only when the whole process exits or execs that the
   file becomes invalid, at which point reads/writes return EOF.  */

class proc_mem_file
{
public:
  proc_mem_file (ptid_t ptid, int fd)
    : m_ptid (ptid), m_fd (fd)
  {
    gdb_assert (m_fd != -1);
  }

  ~proc_mem_file ()
  {
    linux_nat_debug_printf ("closing fd %d for /proc/%d/task/%ld/mem",
			    m_fd, m_ptid.pid (), m_ptid.lwp ());
    close (m_fd);
  }

  DISABLE_COPY_AND_ASSIGN (proc_mem_file);

  int fd ()
  {
    return m_fd;
  }

private:
  /* The LWP this file was opened for.  Just for debugging
     purposes.  */
  ptid_t m_ptid;

  /* The file descriptor.  */
  int m_fd = -1;
};

/* The map between an inferior process id, and the open /proc/PID/mem
   file.  This is stored in a map instead of in a per-inferior
   structure because we need to be able to access memory of processes
   which don't have a corresponding struct inferior object.  E.g.,
   with "detach-on-fork on" (the default), and "follow-fork parent"
   (also default), we don't create an inferior for the fork child, but
   we still need to remove breakpoints from the fork child's
   memory.  */
static std::unordered_map<int, proc_mem_file> proc_mem_file_map;

/* Close the /proc/PID/mem file for PID.  */

static void
close_proc_mem_file (pid_t pid)
{
  proc_mem_file_map.erase (pid);
}

/* Open the /proc/PID/mem file for the process (thread group) of PTID.
   We actually open /proc/PID/task/LWP/mem, as that's the LWP we know
   exists and is stopped right now.  We prefer the
   /proc/PID/task/LWP/mem form over /proc/LWP/mem to avoid tid-reuse
   races, just in case this is ever called on an already-waited
   LWP.  */

static void
open_proc_mem_file (ptid_t ptid)
{
  auto iter = proc_mem_file_map.find (ptid.pid ());
  gdb_assert (iter == proc_mem_file_map.end ());

  char filename[64];
  xsnprintf (filename, sizeof filename,
	     "/proc/%d/task/%ld/mem", ptid.pid (), ptid.lwp ());

  int fd = gdb_open_cloexec (filename, O_RDWR | O_LARGEFILE, 0).release ();

  if (fd == -1)
    {
      warning (_("opening /proc/PID/mem file for lwp %d.%ld failed: %s (%d)"),
	       ptid.pid (), ptid.lwp (),
	       safe_strerror (errno), errno);
      return;
    }

  proc_mem_file_map.emplace (std::piecewise_construct,
			     std::forward_as_tuple (ptid.pid ()),
			     std::forward_as_tuple (ptid, fd));

  linux_nat_debug_printf ("opened fd %d for lwp %d.%ld",
			  fd, ptid.pid (), ptid.lwp ());
}

/* Implement the to_xfer_partial target method using /proc/PID/mem.
   Because we can use a single read/write call, this can be much more
   efficient than banging away at PTRACE_PEEKTEXT.  Also, unlike
   PTRACE_PEEKTEXT/PTRACE_POKETEXT, this works with running
   threads.  */

static enum target_xfer_status
linux_proc_xfer_memory_partial (gdb_byte *readbuf, const gdb_byte *writebuf,
				ULONGEST offset, LONGEST len,
				ULONGEST *xfered_len)
{
  ssize_t ret;

  auto iter = proc_mem_file_map.find (inferior_ptid.pid ());
  if (iter == proc_mem_file_map.end ())
    return TARGET_XFER_EOF;

  int fd = iter->second.fd ();

  gdb_assert (fd != -1);

  /* Use pread64/pwrite64 if available, since they save a syscall and can
     handle 64-bit offsets even on 32-bit platforms (for instance, SPARC
     debugging a SPARC64 application).  */
#ifdef HAVE_PREAD64
  ret = (readbuf ? pread64 (fd, readbuf, len, offset)
	 : pwrite64 (fd, writebuf, len, offset));
#else
  ret = lseek (fd, offset, SEEK_SET);
  if (ret != -1)
    ret = (readbuf ? read (fd, readbuf, len)
	   : write (fd, writebuf, len));
#endif

  if (ret == -1)
    {
      linux_nat_debug_printf ("accessing fd %d for pid %d failed: %s (%d)",
			      fd, inferior_ptid.pid (),
			      safe_strerror (errno), errno);
      return TARGET_XFER_EOF;
    }
  else if (ret == 0)
    {
      /* EOF means the address space is gone, the whole process exited
	 or execed.  */
      linux_nat_debug_printf ("accessing fd %d for pid %d got EOF",
			      fd, inferior_ptid.pid ());
      return TARGET_XFER_EOF;
    }
  else
    {
      *xfered_len = ret;
      return TARGET_XFER_OK;
    }
}

/* Parse LINE as a signal set and add its set bits to SIGS.  */

static void
add_line_to_sigset (const char *line, sigset_t *sigs)
{
  int len = strlen (line) - 1;
  const char *p;
  int signum;

  if (line[len] != '\n')
    error (_("Could not parse signal set: %s"), line);

  p = line;
  signum = len * 4;
  while (len-- > 0)
    {
      int digit;

      if (*p >= '0' && *p <= '9')
	digit = *p - '0';
      else if (*p >= 'a' && *p <= 'f')
	digit = *p - 'a' + 10;
      else
	error (_("Could not parse signal set: %s"), line);

      signum -= 4;

      if (digit & 1)
	sigaddset (sigs, signum + 1);
      if (digit & 2)
	sigaddset (sigs, signum + 2);
      if (digit & 4)
	sigaddset (sigs, signum + 3);
      if (digit & 8)
	sigaddset (sigs, signum + 4);

      p++;
    }
}

/* Find process PID's pending signals from /proc/pid/status and set
   SIGS to match.  */

void
linux_proc_pending_signals (int pid, sigset_t *pending,
			    sigset_t *blocked, sigset_t *ignored)
{
  char buffer[PATH_MAX], fname[PATH_MAX];

  sigemptyset (pending);
  sigemptyset (blocked);
  sigemptyset (ignored);
  xsnprintf (fname, sizeof fname, "/proc/%d/status", pid);
  gdb_file_up procfile = gdb_fopen_cloexec (fname, "r");
  if (procfile == NULL)
    error (_("Could not open %s"), fname);

  while (fgets (buffer, PATH_MAX, procfile.get ()) != NULL)
    {
      /* Normal queued signals are on the SigPnd line in the status
	 file.  However, 2.6 kernels also have a "shared" pending
	 queue for delivering signals to a thread group, so check for
	 a ShdPnd line also.

	 Unfortunately some Red Hat kernels include the shared pending
	 queue but not the ShdPnd status field.  */

      if (startswith (buffer, "SigPnd:\t"))
	add_line_to_sigset (buffer + 8, pending);
      else if (startswith (buffer, "ShdPnd:\t"))
	add_line_to_sigset (buffer + 8, pending);
      else if (startswith (buffer, "SigBlk:\t"))
	add_line_to_sigset (buffer + 8, blocked);
      else if (startswith (buffer, "SigIgn:\t"))
	add_line_to_sigset (buffer + 8, ignored);
    }
}

static enum target_xfer_status
linux_nat_xfer_osdata (enum target_object object,
		       const char *annex, gdb_byte *readbuf,
		       const gdb_byte *writebuf, ULONGEST offset, ULONGEST len,
		       ULONGEST *xfered_len)
{
  gdb_assert (object == TARGET_OBJECT_OSDATA);

  *xfered_len = linux_common_xfer_osdata (annex, readbuf, offset, len);
  if (*xfered_len == 0)
    return TARGET_XFER_EOF;
  else
    return TARGET_XFER_OK;
}

std::vector<static_tracepoint_marker>
linux_nat_target::static_tracepoint_markers_by_strid (const char *strid)
{
  char s[IPA_CMD_BUF_SIZE];
  int pid = inferior_ptid.pid ();
  std::vector<static_tracepoint_marker> markers;
  const char *p = s;
  ptid_t ptid = ptid_t (pid, 0);
  static_tracepoint_marker marker;

  /* Pause all */
  target_stop (ptid);

  memcpy (s, "qTfSTM", sizeof ("qTfSTM"));
  s[sizeof ("qTfSTM")] = 0;

  agent_run_command (pid, s, strlen (s) + 1);

  /* Unpause all.  */
  SCOPE_EXIT { target_continue_no_signal (ptid); };

  while (*p++ == 'm')
    {
      do
	{
	  parse_static_tracepoint_marker_definition (p, &p, &marker);

	  if (strid == NULL || marker.str_id == strid)
	    markers.push_back (std::move (marker));
	}
      while (*p++ == ',');	/* comma-separated list */

      memcpy (s, "qTsSTM", sizeof ("qTsSTM"));
      s[sizeof ("qTsSTM")] = 0;
      agent_run_command (pid, s, strlen (s) + 1);
      p = s;
    }

  return markers;
}

/* target_is_async_p implementation.  */

bool
linux_nat_target::is_async_p ()
{
  return linux_is_async_p ();
}

/* target_can_async_p implementation.  */

bool
linux_nat_target::can_async_p ()
{
  /* This flag should be checked in the common target.c code.  */
  gdb_assert (target_async_permitted);
  
  /* Otherwise, this targets is always able to support async mode.  */
  return true;
}

bool
linux_nat_target::supports_non_stop ()
{
  return true;
}

/* to_always_non_stop_p implementation.  */

bool
linux_nat_target::always_non_stop_p ()
{
  return true;
}

bool
linux_nat_target::supports_multi_process ()
{
  return true;
}

bool
linux_nat_target::supports_disable_randomization ()
{
  return true;
}

/* SIGCHLD handler that serves two purposes: In non-stop/async mode,
   so we notice when any child changes state, and notify the
   event-loop; it allows us to use sigsuspend in linux_nat_wait_1
   above to wait for the arrival of a SIGCHLD.  */

static void
sigchld_handler (int signo)
{
  int old_errno = errno;

  if (debug_linux_nat)
    gdb_stdlog->write_async_safe ("sigchld\n", sizeof ("sigchld\n") - 1);

  if (signo == SIGCHLD
      && linux_nat_event_pipe.is_open ())
    async_file_mark (); /* Let the event loop know that there are
			   events to handle.  */

  errno = old_errno;
}

/* Callback registered with the target events file descriptor.  */

static void
handle_target_event (int error, gdb_client_data client_data)
{
  inferior_event_handler (INF_REG_EVENT);
}

/* Create/destroy the target events pipe.  Returns previous state.  */

static int
linux_async_pipe (int enable)
{
  int previous = linux_is_async_p ();

  if (previous != enable)
    {
      sigset_t prev_mask;

      /* Block child signals while we create/destroy the pipe, as
	 their handler writes to it.  */
      block_child_signals (&prev_mask);

      if (enable)
	{
	  if (!linux_nat_event_pipe.open ())
	    internal_error (__FILE__, __LINE__,
			    "creating event pipe failed.");
	}
      else
	{
	  linux_nat_event_pipe.close ();
	}

      restore_child_signals_mask (&prev_mask);
    }

  return previous;
}

int
linux_nat_target::async_wait_fd ()
{
  return linux_nat_event_pipe.event_fd ();
}

/* target_async implementation.  */

void
linux_nat_target::async (int enable)
{
  if (enable)
    {
      if (!linux_async_pipe (1))
	{
	  add_file_handler (linux_nat_event_pipe.event_fd (),
			    handle_target_event, NULL,
			    "linux-nat");
	  /* There may be pending events to handle.  Tell the event loop
	     to poll them.  */
	  async_file_mark ();
	}
    }
  else
    {
      delete_file_handler (linux_nat_event_pipe.event_fd ());
      linux_async_pipe (0);
    }
  return;
}

/* Stop an LWP, and push a GDB_SIGNAL_0 stop status if no other
   event came out.  */

static int
linux_nat_stop_lwp (struct lwp_info *lwp)
{
  if (!lwp->stopped)
    {
      linux_nat_debug_printf ("running -> suspending %s",
			      lwp->ptid.to_string ().c_str ());


      if (lwp->last_resume_kind == resume_stop)
	{
	  linux_nat_debug_printf ("already stopping LWP %ld at GDB's request",
				  lwp->ptid.lwp ());
	  return 0;
	}

      stop_callback (lwp);
      lwp->last_resume_kind = resume_stop;
    }
  else
    {
      /* Already known to be stopped; do nothing.  */

      if (debug_linux_nat)
	{
	  if (find_thread_ptid (linux_target, lwp->ptid)->stop_requested)
	    linux_nat_debug_printf ("already stopped/stop_requested %s",
				    lwp->ptid.to_string ().c_str ());
	  else
	    linux_nat_debug_printf ("already stopped/no stop_requested yet %s",
				    lwp->ptid.to_string ().c_str ());
	}
    }
  return 0;
}

void
linux_nat_target::stop (ptid_t ptid)
{
  LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT;
  iterate_over_lwps (ptid, linux_nat_stop_lwp);
}

void
linux_nat_target::close ()
{
  /* Unregister from the event loop.  */
  if (is_async_p ())
    async (0);

  inf_ptrace_target::close ();
}

/* When requests are passed down from the linux-nat layer to the
   single threaded inf-ptrace layer, ptids of (lwpid,0,0) form are
   used.  The address space pointer is stored in the inferior object,
   but the common code that is passed such ptid can't tell whether
   lwpid is a "main" process id or not (it assumes so).  We reverse
   look up the "main" process id from the lwp here.  */

struct address_space *
linux_nat_target::thread_address_space (ptid_t ptid)
{
  struct lwp_info *lwp;
  struct inferior *inf;
  int pid;

  if (ptid.lwp () == 0)
    {
      /* An (lwpid,0,0) ptid.  Look up the lwp object to get at the
	 tgid.  */
      lwp = find_lwp_pid (ptid);
      pid = lwp->ptid.pid ();
    }
  else
    {
      /* A (pid,lwpid,0) ptid.  */
      pid = ptid.pid ();
    }

  inf = find_inferior_pid (this, pid);
  gdb_assert (inf != NULL);
  return inf->aspace;
}

/* Return the cached value of the processor core for thread PTID.  */

int
linux_nat_target::core_of_thread (ptid_t ptid)
{
  struct lwp_info *info = find_lwp_pid (ptid);

  if (info)
    return info->core;
  return -1;
}

/* Implementation of to_filesystem_is_local.  */

bool
linux_nat_target::filesystem_is_local ()
{
  struct inferior *inf = current_inferior ();

  if (inf->fake_pid_p || inf->pid == 0)
    return true;

  return linux_ns_same (inf->pid, LINUX_NS_MNT);
}

/* Convert the INF argument passed to a to_fileio_* method
   to a process ID suitable for passing to its corresponding
   linux_mntns_* function.  If INF is non-NULL then the
   caller is requesting the filesystem seen by INF.  If INF
   is NULL then the caller is requesting the filesystem seen
   by the GDB.  We fall back to GDB's filesystem in the case
   that INF is non-NULL but its PID is unknown.  */

static pid_t
linux_nat_fileio_pid_of (struct inferior *inf)
{
  if (inf == NULL || inf->fake_pid_p || inf->pid == 0)
    return getpid ();
  else
    return inf->pid;
}

/* Implementation of to_fileio_open.  */

int
linux_nat_target::fileio_open (struct inferior *inf, const char *filename,
			       int flags, int mode, int warn_if_slow,
			       int *target_errno)
{
  int nat_flags;
  mode_t nat_mode;
  int fd;

  if (fileio_to_host_openflags (flags, &nat_flags) == -1
      || fileio_to_host_mode (mode, &nat_mode) == -1)
    {
      *target_errno = FILEIO_EINVAL;
      return -1;
    }

  fd = linux_mntns_open_cloexec (linux_nat_fileio_pid_of (inf),
				 filename, nat_flags, nat_mode);
  if (fd == -1)
    *target_errno = host_to_fileio_error (errno);

  return fd;
}

/* Implementation of to_fileio_readlink.  */

gdb::optional<std::string>
linux_nat_target::fileio_readlink (struct inferior *inf, const char *filename,
				   int *target_errno)
{
  char buf[PATH_MAX];
  int len;

  len = linux_mntns_readlink (linux_nat_fileio_pid_of (inf),
			      filename, buf, sizeof (buf));
  if (len < 0)
    {
      *target_errno = host_to_fileio_error (errno);
      return {};
    }

  return std::string (buf, len);
}

/* Implementation of to_fileio_unlink.  */

int
linux_nat_target::fileio_unlink (struct inferior *inf, const char *filename,
				 int *target_errno)
{
  int ret;

  ret = linux_mntns_unlink (linux_nat_fileio_pid_of (inf),
			    filename);
  if (ret == -1)
    *target_errno = host_to_fileio_error (errno);

  return ret;
}

/* Implementation of the to_thread_events method.  */

void
linux_nat_target::thread_events (int enable)
{
  report_thread_events = enable;
}

linux_nat_target::linux_nat_target ()
{
  /* We don't change the stratum; this target will sit at
     process_stratum and thread_db will set at thread_stratum.  This
     is a little strange, since this is a multi-threaded-capable
     target, but we want to be on the stack below thread_db, and we
     also want to be used for single-threaded processes.  */
}

/* See linux-nat.h.  */

int
linux_nat_get_siginfo (ptid_t ptid, siginfo_t *siginfo)
{
  int pid;

  pid = ptid.lwp ();
  if (pid == 0)
    pid = ptid.pid ();

  errno = 0;
  ptrace (PTRACE_GETSIGINFO, pid, (PTRACE_TYPE_ARG3) 0, siginfo);
  if (errno != 0)
    {
      memset (siginfo, 0, sizeof (*siginfo));
      return 0;
    }
  return 1;
}

/* See nat/linux-nat.h.  */

ptid_t
current_lwp_ptid (void)
{
  gdb_assert (inferior_ptid.lwp_p ());
  return inferior_ptid;
}

void _initialize_linux_nat ();
void
_initialize_linux_nat ()
{
  add_setshow_boolean_cmd ("linux-nat", class_maintenance,
			   &debug_linux_nat, _("\
Set debugging of GNU/Linux native target."), _("	\
Show debugging of GNU/Linux native target."), _("	\
When on, print debug messages relating to the GNU/Linux native target."),
			   nullptr,
			   show_debug_linux_nat,
			   &setdebuglist, &showdebuglist);

  add_setshow_boolean_cmd ("linux-namespaces", class_maintenance,
			   &debug_linux_namespaces, _("\
Set debugging of GNU/Linux namespaces module."), _("\
Show debugging of GNU/Linux namespaces module."), _("\
Enables printf debugging output."),
			   NULL,
			   NULL,
			   &setdebuglist, &showdebuglist);

  /* Install a SIGCHLD handler.  */
  sigchld_action.sa_handler = sigchld_handler;
  sigemptyset (&sigchld_action.sa_mask);
  sigchld_action.sa_flags = SA_RESTART;

  /* Make it the default.  */
  sigaction (SIGCHLD, &sigchld_action, NULL);

  /* Make sure we don't block SIGCHLD during a sigsuspend.  */
  gdb_sigmask (SIG_SETMASK, NULL, &suspend_mask);
  sigdelset (&suspend_mask, SIGCHLD);

  sigemptyset (&blocked_mask);

  lwp_lwpid_htab_create ();
}


/* FIXME: kettenis/2000-08-26: The stuff on this page is specific to
   the GNU/Linux Threads library and therefore doesn't really belong
   here.  */

/* NPTL reserves the first two RT signals, but does not provide any
   way for the debugger to query the signal numbers - fortunately
   they don't change.  */
static int lin_thread_signals[] = { __SIGRTMIN, __SIGRTMIN + 1 };

/* See linux-nat.h.  */

unsigned int
lin_thread_get_thread_signal_num (void)
{
  return sizeof (lin_thread_signals) / sizeof (lin_thread_signals[0]);
}

/* See linux-nat.h.  */

int
lin_thread_get_thread_signal (unsigned int i)
{
  gdb_assert (i < lin_thread_get_thread_signal_num ());
  return lin_thread_signals[i];
}