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
|
\input texinfo
@setfilename stabs.info
@ifinfo
@format
START-INFO-DIR-ENTRY
* Stabs:: The "stabs" debugging information format.
END-INFO-DIR-ENTRY
@end format
@end ifinfo
@ifinfo
This document describes the stabs debugging symbol tables.
Copyright 1992 Free Software Foundation, Inc.
Contributed by Cygnus Support. Written by Julia Menapace.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
@ignore
Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
@end ignore
Permission is granted to copy or distribute modified versions of this
manual under the terms of the GPL (for which purpose this text may be
regarded as a program in the language TeX).
@end ifinfo
@setchapternewpage odd
@settitle STABS
@titlepage
@title The ``stabs'' debug format
@author Julia Menapace
@author Cygnus Support
@page
@tex
\def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
\xdef\manvers{\$Revision$} % For use in headers, footers too
{\parskip=0pt
\hfill Cygnus Support\par
\hfill \manvers\par
\hfill \TeX{}info \texinfoversion\par
}
@end tex
@vskip 0pt plus 1filll
Copyright @copyright{} 1992 Free Software Foundation, Inc.
Contributed by Cygnus Support.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
@end titlepage
@ifinfo
@node Top
@top The "stabs" representation of debugging information
This document describes the GNU stabs debugging format in a.out files.
@menu
* Overview:: Overview of stabs
* Program structure:: Encoding of the structure of the program
* Constants:: Constants
* Example:: A comprehensive example in C
* Variables::
* Types:: Type definitions
* Symbol Tables:: Symbol information in symbol tables
* Cplusplus::
Appendixes:
* Example2.c:: Source code for extended example
* Example2.s:: Assembly code for extended example
* Stab types:: Table A: Symbol types from stabs
* Assembler types:: Table B: Symbol types from assembler and linker
* Symbol Descriptors:: Table C
* Type Descriptors:: Table D
* Expanded reference:: Reference information by stab type
* Questions:: Questions and anomolies
* xcoff-differences:: Differences between GNU stabs in a.out
and GNU stabs in xcoff
* Sun-differences:: Differences between GNU stabs and Sun
native stabs
@end menu
@end ifinfo
@node Overview
@chapter Overview of stabs
@dfn{Stabs} refers to a format for information that describes a program
to a debugger. This format was apparently invented by
@c FIXME! <<name of inventor>> at
the University of California at Berkeley, for the @code{pdx} Pascal
debugger; the format has spread widely since then.
This document is one of the few published sources of documentation on
stabs. It is believed to be completely comprehensive for stabs used by
C. The lists of symbol descriptors (@pxref{Symbol Descriptors}) and
type descriptors (@pxref{Type Descriptors}) are believed to be completely
comprehensive. There are known to be stabs for C++ and COBOL which are
poorly documented here. Stabs specific to other languages (e.g. Pascal,
Modula-2) are probably not as well documented as they should be.
Other sources of information on stabs are @cite{dbx and dbxtool
interfaces}, 2nd edition, by Sun, circa 1988, and @cite{AIX Version 3.2
Files Reference}, Fourth Edition, September 1992, "dbx Stabstring
Grammar" in the a.out section, page 2-31. This document is believed to
incorporate the information from those two sources except where it
explictly directs you to them for more information.
@menu
* Flow:: Overview of debugging information flow
* Stabs Format:: Overview of stab format
* C example:: A simple example in C source
* Assembly code:: The simple example at the assembly level
@end menu
@node Flow
@section Overview of debugging information flow
The GNU C compiler compiles C source in a @file{.c} file into assembly
language in a @file{.s} file, which is translated by the assembler into
a @file{.o} file, and then linked with other @file{.o} files and
libraries to produce an executable file.
With the @samp{-g} option, GCC puts additional debugging information in
the @file{.s} file, which is slightly transformed by the assembler and
linker, and carried through into the final executable. This debugging
information describes features of the source file like line numbers,
the types and scopes of variables, and functions, their parameters and
their scopes.
For some object file formats, the debugging information is
encapsulated in assembler directives known collectively as `stab' (symbol
table) directives, interspersed with the generated code. Stabs are
the native format for debugging information in the a.out and xcoff
object file formats. The GNU tools can also emit stabs in the coff
and ecoff object file formats.
The assembler adds the information from stabs to the symbol information
it places by default in the symbol table and the string table of the
@file{.o} file it is building. The linker consolidates the @file{.o}
files into one executable file, with one symbol table and one string
table. Debuggers use the symbol and string tables in the executable as
a source of debugging information about the program.
@node Stabs Format
@section Overview of stab format
There are three overall formats for stab assembler directives
differentiated by the first word of the stab. The name of the directive
describes what combination of four possible data fields will follow. It
is either @code{.stabs} (string), @code{.stabn} (number), or
@code{.stabd} (dot). IBM's xcoff uses @code{.stabx} (and some other
directives such as @code{.file} and @code{.bi}) instead of
@code{.stabs}, @code{.stabn} or @code{.stabd}.
The overall format of each class of stab is:
@example
.stabs "@var{string}",@var{type},0,@var{desc},@var{value}
.stabx "@var{string}",@var{value},@var{type},@var{sdb-type}
.stabn @var{type},0,@var{desc},@var{value}
.stabd @var{type},0,@var{desc}
@end example
@c what is the correct term for "current file location"? My AIX
@c assembler manual calls it "the value of the current location counter".
For @code{.stabn} and @code{.stabd}, there is no string (the
@code{n_strx} field is zero, @pxref{Symbol Tables}). For @code{.stabd}
the value field is implicit and has the value of the current file
location. The @var{sdb-type} field to @code{.stabx} is unused for stabs
and can always be set to 0.
The number in the type field gives some basic information about what
type of stab this is (or whether it @emph{is} a stab, as opposed to an
ordinary symbol). Each possible type number defines a different stab
type. The stab type further defines the exact interpretation of, and
possible values for, any remaining @code{"@var{string}"}, @var{desc}, or
@var{value} fields present in the stab. Table A (@pxref{Stab
types,,Table A: Symbol types from stabs}) lists in numeric order the
possible type field values for stab directives. The reference section
that follows Table A describes the meaning of the fields for each stab
type in detail. The examples that follow this overview introduce the
stab types in terms of the source code elements they describe.
For @code{.stabs} the @code{"@var{string}"} field holds the meat of the
debugging information. The generally unstructured nature of this field
is what makes stabs extensible. For some stab types the string field
contains only a name. For other stab types the contents can be a great
deal more complex.
The overall format is of the @code{"@var{string}"} field is:
@example
"@var{name}:@var{symbol-descriptor} @var{type-information}"
@end example
@var{name} is the name of the symbol represented by the stab.
@var{name} can be omitted, which means the stab represents an unnamed
object. For example, @samp{:t10=*2} defines type 10 as a pointer to
type 2, but does not give the type a name. Omitting the @var{name}
field is supported by AIX dbx and GDB after about version 4.8, but not
other debuggers. GCC sometimes uses a single space as the name instead
of omitting the name altogether; apparently that is supported by most
debuggers.
The @var{symbol_descriptor} following the @samp{:} is an alphabetic
character that tells more specifically what kind of symbol the stab
represents. If the @var{symbol_descriptor} is omitted, but type
information follows, then the stab represents a local variable. For a
list of symbol descriptors, see @ref{Symbol Descriptors,,Table C: Symbol
descriptors}.
The @samp{c} symbol descriptor is an exception in that it is not
followed by type information. @xref{Constants}.
Type information is either a @var{type_number}, or a
@samp{@var{type_number}=}. The @var{type_number} alone is a type
reference, referring directly to a type that has already been defined.
The @samp{@var{type_number}=} is a type definition, where the number
represents a new type which is about to be defined. The type definition
may refer to other types by number, and those type numbers may be
followed by @samp{=} and nested definitions.
In a type definition, if the character that follows the equals sign is
non-numeric then it is a @var{type_descriptor}, and tells what kind of
type is about to be defined. Any other values following the
@var{type_descriptor} vary, depending on the @var{type_descriptor}. If
a number follows the @samp{=} then the number is a @var{type_reference}.
This is described more thoroughly in the section on types. @xref{Type
Descriptors,,Table D: Type Descriptors}, for a list of
@var{type_descriptor} values.
There is an AIX extension for type attributes. Following the @samp{=}
is any number of type attributes. Each one starts with @samp{@@} and
ends with @samp{;}. Debuggers, including AIX's dbx, skip any type
attributes they do not recognize. GDB 4.9 does not do this---it will
ignore the entire symbol containing a type attribute. Hopefully this
will be fixed in the next GDB release. Because of a conflict with C++
(@pxref{Cplusplus}), new attributes should not be defined which begin
with a digit, @samp{(}, or @samp{-}; GDB may be unable to distinguish
those from the C++ type descriptor @samp{@@}. The attributes are:
@table @code
@item a@var{boundary}
@var{boundary} is an integer specifying the alignment. I assume it
applies to all variables of this type.
@item s@var{size}
Size in bits of a variable of this type.
@item p@var{integer}
Pointer class (for checking). Not sure what this means, or how
@var{integer} is interpreted.
@item P
Indicate this is a packed type, meaning that structure fields or array
elements are placed more closely in memory, to save memory at the
expense of speed.
@end table
All this can make the @code{"@var{string}"} field quite long. All
versions of GDB, and some versions of DBX, can handle arbitrarily long
strings. But many versions of DBX cretinously limit the strings to
about 80 characters, so compilers which must work with such DBX's need
to split the @code{.stabs} directive into several @code{.stabs}
directives. Each stab duplicates exactly all but the
@code{"@var{string}"} field. The @code{"@var{string}"} field of
every stab except the last is marked as continued with a
double-backslash at the end. Removing the backslashes and concatenating
the @code{"@var{string}"} fields of each stab produces the original,
long string.
@node C example
@section A simple example in C source
To get the flavor of how stabs describe source information for a C
program, let's look at the simple program:
@example
main()
@{
printf("Hello world");
@}
@end example
When compiled with @samp{-g}, the program above yields the following
@file{.s} file. Line numbers have been added to make it easier to refer
to parts of the @file{.s} file in the description of the stabs that
follows.
@node Assembly code
@section The simple example at the assembly level
@example
1 gcc2_compiled.:
2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0
3 .stabs "hello.c",100,0,0,Ltext0
4 .text
5 Ltext0:
6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0
7 .stabs "char:t2=r2;0;127;",128,0,0,0
8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0
9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0
11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0
12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0
13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0
14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0
15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0
16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0
17 .stabs "float:t12=r1;4;0;",128,0,0,0
18 .stabs "double:t13=r1;8;0;",128,0,0,0
19 .stabs "long double:t14=r1;8;0;",128,0,0,0
20 .stabs "void:t15=15",128,0,0,0
21 .align 4
22 LC0:
23 .ascii "Hello, world!\12\0"
24 .align 4
25 .global _main
26 .proc 1
27 _main:
28 .stabn 68,0,4,LM1
29 LM1:
30 !#PROLOGUE# 0
31 save %sp,-136,%sp
32 !#PROLOGUE# 1
33 call ___main,0
34 nop
35 .stabn 68,0,5,LM2
36 LM2:
37 LBB2:
38 sethi %hi(LC0),%o1
39 or %o1,%lo(LC0),%o0
40 call _printf,0
41 nop
42 .stabn 68,0,6,LM3
43 LM3:
44 LBE2:
45 .stabn 68,0,6,LM4
46 LM4:
47 L1:
48 ret
49 restore
50 .stabs "main:F1",36,0,0,_main
51 .stabn 192,0,0,LBB2
52 .stabn 224,0,0,LBE2
@end example
This simple ``hello world'' example demonstrates several of the stab
types used to describe C language source files.
@node Program structure
@chapter Encoding for the structure of the program
@menu
* Source Files:: The path and name of the source file
* Line Numbers::
* Procedures::
* Block Structure::
@end menu
@node Source Files
@section The path and name of the source files
Before any other stabs occur, there must be a stab specifying the source
file. This information is contained in a symbol of stab type
@code{N_SO}; the string contains the name of the file. The value of the
symbol is the start address of portion of the text section corresponding
to that file.
Some compilers (for example, gcc2 and SunOS4 @file{/bin/cc}) also
include the directory in which the source was compiled, in a second
@code{N_SO} symbol preceding the one containing the file name. This
symbol can be distinguished by the fact that it ends in a slash.
According to a comment in GDB's @file{partial-stab.h}, other compilers
(especially unnamed C++ compilers) put out useless N_SO's for
nonexistent source files (after the N_SO for the real source file).
For example:
@example
.stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0 ; 100 is N_SO
.stabs "hello.c",100,0,0,Ltext0
.text
Ltext0:
@end example
Instead of @code{N_SO} symbols, XCOFF uses a @code{.file} assembler
directive which assembles to a standard COFF @code{.file} symbol;
explaining this in detail is outside the scope of this document.
There are several different schemes for dealing with include files: the
traditional @code{N_SOL} approach, Sun's @code{N_BINCL} scheme, and the
XCOFF @code{C_BINCL} (which despite the similar name has little in
common with @code{N_BINCL}).
An @code{N_SOL} symbol specifies which include file subsequent symbols
refer to. The string field is the name of the file and the value is the
text address corresponding to the start of the previous include file and
the start of this one. To specify the main source file again, use an
@code{N_SOL} symbol with the name of the main source file.
A @code{N_BINCL} symbol specifies the start of an include file. In an
object file, only the name is significant. The Sun linker puts data
into some of the other fields. The end of the include file is marked by
a @code{N_EINCL} symbol of the same name. In an ojbect file, there is
no significant data in the @code{N_EINCL} symbol; the Sun linker puts
data into some of the fields. @code{N_BINCL} and @code{N_EINCL} can be
nested. If the linker detects that two source files have identical
stabs with a @code{N_BINCL} and @code{N_EINCL} pair (as will generally
be the case for a header file), then it only puts out the stabs once.
Each additional occurance is replaced by an @code{N_EXCL} symbol. I
believe the Sun (SunOS4, not sure about Solaris) linker is the only one
which supports this feature.
For the start of an include file in XCOFF, use the @file{.bi} assembler
directive which generates a @code{C_BINCL} symbol. A @file{.ei}
directive, which generates a @code{C_EINCL} symbol, denotes the end of
the include file. Both directives are followed by the name of the
source file in quotes, which becomes the string for the symbol. The
value of each symbol, produced automatically by the assembler and
linker, is an offset into the executable which points to the beginning
(inclusive, as you'd expect) and end (inclusive, as you would not
expect) of the portion of the COFF linetable which corresponds to this
include file. @code{C_BINCL} and @code{C_EINCL} do not nest.
@node Line Numbers
@section Line Numbers
A @code{N_SLINE} symbol represents the start of a source line. The
@var{desc} field contains the line number and the @var{value} field
contains the code address for the start of that source line.
GNU documents @code{N_DSLINE} and @code{N_BSLINE} symbols for line
numbers in the data or bss segments, respectively. They are identical
to @code{N_SLINE} but are relocated differently by the linker. They
were intended to be used to describe the source location of a variable
declaration, but I believe that gcc2 actually puts the line number in
the desc field of the stab for the variable itself. GDB has been
ignoring these symbols (unless they contain a string field) at least
since GDB 3.5.
XCOFF uses COFF line numbers instead, which are outside the scope of
this document, ammeliorated by adequate marking of include files
(@pxref{Source Files}).
For single source lines that generate discontiguous code, such as flow
of control statements, there may be more than one line number entry for
the same source line. In this case there is a line number entry at the
start of each code range, each with the same line number.
@node Procedures
@section Procedures
All of the following stabs use the @samp{N_FUN} symbol type.
A function is represented by a @samp{F} symbol descriptor for a global
(extern) function, and @samp{f} for a static (local) function. The next
@samp{N_SLINE} symbol can be used to find the line number of the start
of the function. The value field is the address of the start of the
function. The type information of the stab represents the return type
of the function; thus @samp{foo:f5} means that foo is a function
returning type 5.
The AIX documentation also defines symbol descriptor @samp{J} as an
internal function. I assume this means a function nested within another
function. It also says Symbol descriptor @samp{m} is a module in
Modula-2 or extended Pascal.
Procedures (functions which do not return values) are represented as
functions returning the void type in C. I don't see why this couldn't
be used for all languages (inventing a void type for this purpose if
necessary), but the AIX documentation defines @samp{I}, @samp{P}, and
@samp{Q} for internal, global, and static procedures, respectively.
These symbol descriptors are unusual in that they are not followed by
type information.
For any of the above symbol descriptors, after the symbol descriptor and
the type information, there is optionally a comma, followed by the name
of the procedure, followed by a comma, followed by a name specifying the
scope. The first name is local to the scope specified. I assume then
that the name of the symbol (before the @samp{:}), if specified, is some
sort of global name. I assume the name specifying the scope is the name
of a function specifying that scope. This feature is an AIX extension,
and this information is based on the manual; I haven't actually tried
it.
The stab representing a procedure is located immediately following the
code of the procedure. This stab is in turn directly followed by a
group of other stabs describing elements of the procedure. These other
stabs describe the procedure's parameters, its block local variables and
its block structure.
@example
48 ret
49 restore
@end example
The @code{.stabs} entry after this code fragment shows the @var{name} of
the procedure (@code{main}); the type descriptor @var{desc} (@code{F},
for a global procedure); a reference to the predefined type @code{int}
for the return type; and the starting @var{address} of the procedure.
Here is an exploded summary (with whitespace introduced for clarity),
followed by line 50 of our sample assembly output, which has this form:
@example
.stabs "@var{name}:
@var{desc} @r{(global proc @samp{F})}
@var{return_type_ref} @r{(int)}
",N_FUN, NIL, NIL,
@var{address}
@end example
@example
50 .stabs "main:F1",36,0,0,_main
@end example
@node Block Structure
@section Block Structure
@table @strong
@item Directive:
@code{.stabn}
@item Types:
@code{N_LBRAC}, @code{N_RBRAC}
@end table
The program's block structure is represented by the @code{N_LBRAC} (left
brace) and the @code{N_RBRAC} (right brace) stab types. The following code
range, which is the body of @code{main}, is labeled with @samp{LBB2:} at the
beginning and @samp{LBE2:} at the end.
@example
37 LBB2:
38 sethi %hi(LC0),%o1
39 or %o1,%lo(LC0),%o0
40 call _printf,0
41 nop
42 .stabn 68,0,6,LM3
43 LM3:
44 LBE2:
@end example
The @code{N_LBRAC} and @code{N_RBRAC} stabs that describe the block
scope of the procedure are located after the @code{N_FUNC} stab that
represents the procedure itself. The @code{N_LBRAC} uses the
@code{LBB2} label as the code address in its value field, and the
@code{N_RBRAC} uses @code{LBE2}.
@example
50 .stabs "main:F1",36,0,0,_main
@end example
@example
.stabn N_LBRAC, NIL, NIL, @var{left-brace-address}
.stabn N_RBRAC, NIL, NIL, @var{right-brace-address}
@end example
@example
51 .stabn 192,0,0,LBB2
52 .stabn 224,0,0,LBE2
@end example
@node Constants
@chapter Constants
The @samp{c} symbol descriptor indicates that this stab represents a
constant. This symbol descriptor is an exception to the general rule
that symbol descriptors are followed by type information. Instead, it
is followed by @samp{=} and one of the following:
@table @code
@item b @var{value}
Boolean constant. @var{value} is a numeric value; I assume it is 0 for
false or 1 for true.
@item c @var{value}
Character constant. @var{value} is the numeric value of the constant.
@item e @var{type-information} , @var{value}
Constant whose value can be represented as integral.
@var{type-information} is the type of the constant, as it would appear
after a symbol descriptor (@pxref{Stabs Format}). @var{value} is the
numeric value of the constant. GDB 4.9 does not actually get the right
value if @var{value} does not fit in a host @code{int}, but it does not
do anything violent, and future debuggers could be extended to accept
integers of any size (whether unsigned or not). This constant type is
usually documented as being only for enumeration constants, but GDB has
never imposed that restriction; I don't know about other debuggers.
@item i @var{value}
Integer constant. @var{value} is the numeric value. The type is some
sort of generic integer type (for GDB, a host @code{int}); to specify
the type explicitly, use @samp{e} instead.
@item r @var{value}
Real constant. @var{value} is the real value, which can be @samp{INF}
(optionally preceded by a sign) for infinity, @samp{QNAN} for a quiet
NaN (not-a-number), or @samp{SNAN} for a signalling NaN. If it is a
normal number the format is that accepted by the C library function
@code{atof}.
@item s @var{string}
String constant. @var{string} is a string enclosed in either @samp{'}
(in which case @samp{'} characters within the string are represented as
@samp{\'} or @samp{"} (in which case @samp{"} characters within the
string are represented as @samp{\"}).
@item S @var{type-information} , @var{elements} , @var{bits} , @var{pattern}
Set constant. @var{type-information} is the type of the constant, as it
would appear after a symbol descriptor (@pxref{Stabs Format}).
@var{elements} is the number of elements in the set (is this just the
number of bits set in @var{pattern}? Or redundant with the type? I
don't get it), @var{bits} is the number of bits in the constant (meaning
it specifies the length of @var{pattern}, I think), and @var{pattern} is
a hexadecimal representation of the set. AIX documentation refers to a
limit of 32 bytes, but I see no reason why this limit should exist.
This form could probably be used for arbitrary constants, not just sets;
the only catch is that @var{pattern} should be understood to be target,
not host, byte order and format.
@end table
The boolean, character, string, and set constants are not supported by
GDB 4.9, but it will ignore them. GDB 4.8 and earlier gave an error
message and refused to read symbols from the file containing the
constants.
This information is followed by @samp{;}.
@node Example
@chapter A Comprehensive Example in C
Now we'll examine a second program, @code{example2}, which builds on the
first example to introduce the rest of the stab types, symbol
descriptors, and type descriptors used in C.
@xref{Example2.c} for the complete @file{.c} source,
and @pxref{Example2.s} for the @file{.s} assembly code.
This description includes parts of those files.
@section Flow of control and nested scopes
@table @strong
@item Directive:
@code{.stabn}
@item Types:
@code{N_SLINE}, @code{N_LBRAC}, @code{N_RBRAC} (cont.)
@end table
Consider the body of @code{main}, from @file{example2.c}. It shows more
about how @code{N_SLINE}, @code{N_RBRAC}, and @code{N_LBRAC} stabs are used.
@example
20 @{
21 static float s_flap;
22 int times;
23 for (times=0; times < s_g_repeat; times++)@{
24 int inner;
25 printf ("Hello world\n");
26 @}
27 @};
@end example
Here we have a single source line, the @samp{for} line, that generates
non-linear flow of control, and non-contiguous code. In this case, an
@code{N_SLINE} stab with the same line number proceeds each block of
non-contiguous code generated from the same source line.
The example also shows nested scopes. The @code{N_LBRAC} and
@code{N_LBRAC} stabs that describe block structure are nested in the
same order as the corresponding code blocks, those of the for loop
inside those for the body of main.
@noindent
This is the label for the @code{N_LBRAC} (left brace) stab marking the
start of @code{main}.
@example
57 LBB2:
@end example
@noindent
In the first code range for C source line 23, the @code{for} loop
initialize and test, @code{N_SLINE} (68) records the line number:
@example
.stabn N_SLINE, NIL,
@var{line},
@var{address}
58 .stabn 68,0,23,LM2
59 LM2:
60 st %g0,[%fp-20]
61 L2:
62 sethi %hi(_s_g_repeat),%o0
63 ld [%fp-20],%o1
64 ld [%o0+%lo(_s_g_repeat)],%o0
65 cmp %o1,%o0
66 bge L3
67 nop
@exdent label for the @code{N_LBRAC} (start block) marking the start of @code{for} loop
68 LBB3:
69 .stabn 68,0,25,LM3
70 LM3:
71 sethi %hi(LC0),%o1
72 or %o1,%lo(LC0),%o0
73 call _printf,0
74 nop
75 .stabn 68,0,26,LM4
76 LM4:
@exdent label for the @code{N_RBRAC} (end block) stab marking the end of the @code{for} loop
77 LBE3:
@end example
@noindent
Now we come to the second code range for source line 23, the @code{for}
loop increment and return. Once again, @code{N_SLINE} (68) records the
source line number:
@example
.stabn, N_SLINE, NIL,
@var{line},
@var{address}
78 .stabn 68,0,23,LM5
79 LM5:
80 L4:
81 ld [%fp-20],%o0
82 add %o0,1,%o1
83 st %o1,[%fp-20]
84 b,a L2
85 L3:
86 .stabn 68,0,27,LM6
87 LM6:
@exdent label for the @code{N_RBRAC} (end block) stab marking the end of the @code{for} loop
88 LBE2:
89 .stabn 68,0,27,LM7
90 LM7:
91 L1:
92 ret
93 restore
94 .stabs "main:F1",36,0,0,_main
95 .stabs "argc:p1",160,0,0,68
96 .stabs "argv:p20=*21=*2",160,0,0,72
97 .stabs "s_flap:V12",40,0,0,_s_flap.0
98 .stabs "times:1",128,0,0,-20
@end example
@noindent
Here is an illustration of stabs describing nested scopes. The scope
nesting is reflected in the nested bracketing stabs (@code{N_LBRAC},
192, appears here).
@example
.stabn N_LBRAC,NIL,NIL,
@var{block-start-address}
99 .stabn 192,0,0,LBB2 ## begin proc label
100 .stabs "inner:1",128,0,0,-24
101 .stabn 192,0,0,LBB3 ## begin for label
@end example
@noindent
@code{N_RBRAC} (224), ``right brace'' ends a lexical block (scope).
@example
.stabn N_RBRAC,NIL,NIL,
@var{block-end-address}
102 .stabn 224,0,0,LBE3 ## end for label
103 .stabn 224,0,0,LBE2 ## end proc label
@end example
@node Variables
@chapter Variables
@menu
* Automatic variables:: locally scoped
* Global Variables::
* Register variables::
* Initialized statics::
* Un-initialized statics::
* Parameters::
@end menu
@node Automatic variables
@section Locally scoped automatic variables
@table @strong
@item Directive:
@code{.stabs}
@item Type:
@code{N_LSYM}
@item Symbol Descriptor:
none
@end table
In addition to describing types, the @code{N_LSYM} stab type also
describes locally scoped automatic variables. Refer again to the body
of @code{main} in @file{example2.c}. It allocates two automatic
variables: @samp{times} is scoped to the body of @code{main}, and
@samp{inner} is scoped to the body of the @code{for} loop.
@samp{s_flap} is locally scoped but not automatic, and will be discussed
later.
@example
20 @{
21 static float s_flap;
22 int times;
23 for (times=0; times < s_g_repeat; times++)@{
24 int inner;
25 printf ("Hello world\n");
26 @}
27 @};
@end example
The @code{N_LSYM} stab for an automatic variable is located just before the
@code{N_LBRAC} stab describing the open brace of the block to which it is
scoped.
@example
@exdent @code{N_LSYM} (128): automatic variable, scoped locally to @code{main}
.stabs "@var{name}:
@var{type information}",
N_LSYM, NIL, NIL,
@var{frame-pointer-offset}
98 .stabs "times:1",128,0,0,-20
99 .stabn 192,0,0,LBB2 ## begin `main' N_LBRAC
@exdent @code{N_LSYM} (128): automatic variable, scoped locally to the @code{for} loop
.stabs "@var{name}:
@var{type information}",
N_LSYM, NIL, NIL,
@var{frame-pointer-offset}
100 .stabs "inner:1",128,0,0,-24
101 .stabn 192,0,0,LBB3 ## begin `for' loop N_LBRAC
@end example
The symbol descriptor is omitted for automatic variables. Since type
information should being with a digit, @samp{-}, or @samp{(}, only
digits, @samp{-}, and @samp{(} are precluded from being used for symbol
descriptors by this fact. However, the Acorn RISC machine (ARM) is said
to get this wrong: it puts out a mere type definition here, without the
preceding @code{@var{typenumber}=}. This is a bad idea; there is no
guarantee that type descriptors are distinct from symbol descriptors.
@node Global Variables
@section Global Variables
@table @strong
@item Directive:
@code{.stabs}
@item Type:
@code{N_GSYM}
@item Symbol Descriptor:
@code{G}
@end table
Global variables are represented by the @code{N_GSYM} stab type. The symbol
descriptor, following the colon in the string field, is @samp{G}. Following
the @samp{G} is a type reference or type definition. In this example it is a
type reference to the basic C type, @code{char}. The first source line in
@file{example2.c},
@example
1 char g_foo = 'c';
@end example
@noindent
yields the following stab. The stab immediately precedes the code that
allocates storage for the variable it describes.
@example
@exdent @code{N_GSYM} (32): global symbol
.stabs "@var{name}:
@var{descriptor}
@var{type-ref}",
N_GSYM, NIL, NIL, NIL
21 .stabs "g_foo:G2",32,0,0,0
22 .global _g_foo
23 .data
24 _g_foo:
25 .byte 99
@end example
The address of the variable represented by the @code{N_GSYM} is not contained
in the @code{N_GSYM} stab. The debugger gets this information from the
external symbol for the global variable.
@node Register variables
@section Register variables
@c According to an old version of this manual, AIX uses C_RPSYM instead
@c of C_RSYM. I am skeptical; this should be verified.
Register variables have their own stab type, @code{N_RSYM}, and their
own symbol descriptor, @code{r}. The stab's value field contains the
number of the register where the variable data will be stored.
The value is the register number.
AIX defines a separate symbol descriptor @samp{d} for floating point
registers. This seems incredibly stupid---why not just just give
floating point registers different register numbers? I have not
verified whether the compiler actually uses @samp{d}.
If the register is explicitly allocated to a global variable, but not
initialized, as in
@example
register int g_bar asm ("%g5");
@end example
the stab may be emitted at the end of the object file, with
the other bss symbols.
@node Initialized statics
@section Initialized static variables
@table @strong
@item Directive:
@code{.stabs}
@item Type:
@code{N_STSYM}
@item Symbol Descriptors:
@code{S} (file scope), @code{V} (procedure scope)
@end table
Initialized static variables are represented by the @code{N_STSYM} stab
type. The symbol descriptor part of the string field shows if the
variable is file scope static (@samp{S}) or procedure scope static
(@samp{V}). The source line
@example
3 static int s_g_repeat = 2;
@end example
@noindent
yields the following code. The stab is located immediately preceding
the storage for the variable it represents. Since the variable in
this example is file scope static the symbol descriptor is @samp{S}.
@example
@exdent @code{N_STSYM} (38): initialized static variable (data seg w/internal linkage)
.stabs "@var{name}:
@var{descriptor}
@var{type-ref}",
N_STSYM,NIL,NIL,
@var{address}
26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
27 .align 4
28 _s_g_repeat:
29 .word 2
@end example
@node Un-initialized statics
@section Un-initialized static variables
@table @strong
@item Directive:
@code{.stabs}
@item Type:
@code{N_LCSYM}
@item Symbol Descriptors:
@code{S} (file scope), @code{V} (procedure scope)
@end table
Un-initialized static variables are represented by the @code{N_LCSYM}
stab type. The symbol descriptor part of the string shows if the
variable is file scope static (@samp{S}) or procedure scope static
(@samp{V}). In this example it is procedure scope static. The source
line allocating @code{s_flap} immediately follows the open brace for the
procedure @code{main}.
@example
20 @{
21 static float s_flap;
@end example
The code that reserves storage for the variable @code{s_flap} precedes the
body of body of @code{main}.
@example
39 .reserve _s_flap.0,4,"bss",4
@end example
But since @code{s_flap} is scoped locally to @code{main}, its stab is
located with the other stabs representing symbols local to @code{main}.
The stab for @code{s_flap} is located just before the @code{N_LBRAC} for
@code{main}.
@example
@exdent @code{N_LCSYM} (40): uninitialized static var (BSS seg w/internal linkage)
.stabs "@var{name}:
@var{descriptor}
@var{type-ref}",
N_LCSYM, NIL, NIL,
@var{address}
97 .stabs "s_flap:V12",40,0,0,_s_flap.0
98 .stabs "times:1",128,0,0,-20
99 .stabn 192,0,0,LBB2 # N_LBRAC for main.
@end example
@c ............................................................
@node Parameters
@section Parameters
The symbol descriptor @samp{p} is used to refer to parameters which are
in the arglist. Symbols have symbol type @samp{N_PSYM}. The value of
the symbol is the offset relative to the argument list.
If the parameter is passed in a register, then the traditional way to do
this is to provide two symbols for each argument:
@example
.stabs "arg:p1" . . . ; N_PSYM
.stabs "arg:r1" . . . ; N_RSYM
@end example
Debuggers are expected to use the second one to find the value, and the
first one to know that it is an argument.
Because this is kind of ugly, some compilers use symbol descriptor
@samp{P} or @samp{R} to indicate an argument which is in a register.
The symbol value is the register number. @samp{P} and @samp{R} mean the
same thing, the difference is that @samp{P} is a GNU invention and
@samp{R} is an IBM (xcoff) invention. As of version 4.9, GDB should
handle either one. Symbol type @samp{C_RPSYM} is used with @samp{R} and
@samp{N_RSYM} is used with @samp{P}.
AIX, according to the documentation, uses @samp{D} for a parameter
passed in a floating point register. This strikes me as incredibly
bogus---why doesn't it just use @samp{R} with a register number which
indicates that it's a floating point register? I haven't verified
whether the system actually does what the documentation indicates.
There is at least one case where GCC uses a @samp{p}/@samp{r} pair
rather than @samp{P}; this is where the argument is passed in the
argument list and then loaded into a register.
On the sparc and hppa, for a @samp{P} symbol whose type is a structure
or union, the register contains the address of the structure. On the
sparc, this is also true of a @samp{p}/@samp{r} pair (using Sun cc) or a
@samp{p} symbol. However, if a (small) structure is really in a
register, @samp{r} is used. And, to top it all off, on the hppa it
might be a structure which was passed on the stack and loaded into a
register and for which there is a @samp{p}/@samp{r} pair! I believe
that symbol descriptor @samp{i} is supposed to deal with this case, (it
is said to mean "value parameter by reference, indirect access", I don't
know the source for this information) but I don't know details or what
compilers or debuggers use it, if any (not GDB or GCC). It is not clear
to me whether this case needs to be dealt with differently than
parameters passed by reference (see below).
There is another case similar to an argument in a register, which is an
argument which is actually stored as a local variable. Sometimes this
happens when the argument was passed in a register and then the compiler
stores it as a local variable. If possible, the compiler should claim
that it's in a register, but this isn't always done. Some compilers use
the pair of symbols approach described above ("arg:p" followed by
"arg:"); this includes gcc1 (not gcc2) on the sparc when passing a small
structure and gcc2 (sometimes) when the argument type is float and it is
passed as a double and converted to float by the prologue (in the latter
case the type of the "arg:p" symbol is double and the type of the "arg:"
symbol is float). GCC, at least on the 960, uses a single @samp{p}
symbol descriptor for an argument which is stored as a local variable
but uses @samp{N_LSYM} instead of @samp{N_PSYM}. In this case the value
of the symbol is an offset relative to the local variables for that
function, not relative to the arguments (on some machines those are the
same thing, but not on all).
If the parameter is passed by reference (e.g. Pascal VAR parameters),
then type symbol descriptor is @samp{v} if it is in the argument list,
or @samp{a} if it in a register. Other than the fact that these contain
the address of the parameter other than the parameter itself, they are
identical to @samp{p} and @samp{R}, respectively. I believe @samp{a} is
an AIX invention; @samp{v} is supported by all stabs-using systems as
far as I know.
@c Is this paragraph correct? It is based on piecing together patchy
@c information and some guesswork
Conformant arrays refer to a feature of Modula-2, and perhaps other
languages, in which the size of an array parameter is not known to the
called function until run-time. Such parameters have two stabs, a
@samp{x} for the array itself, and a @samp{C}, which represents the size
of the array. The value of the @samp{x} stab is the offset in the
argument list where the address of the array is stored (it this right?
it is a guess); the value of the @samp{C} stab is the offset in the
argument list where the size of the array (in elements? in bytes?) is
stored.
The following are also said to go with @samp{N_PSYM}:
@example
"name" -> "param_name:#type"
-> pP (<<??>>)
-> pF FORTRAN function parameter
-> X (function result variable)
-> b (based variable)
value -> offset from the argument pointer (positive).
@end example
As a simple example, the code
@example
main (argc, argv)
int argc;
char **argv;
@{
@end example
produces the stabs
@example
.stabs "main:F1",36,0,0,_main ; 36 is N_FUN
.stabs "argc:p1",160,0,0,68 ; 160 is N_PSYM
.stabs "argv:p20=*21=*2",160,0,0,72
@end example
The type definition of argv is interesting because it contains several
type definitions. Type 21 is pointer to type 2 (char) and argv (type 20) is
pointer to type 21.
@node Types
@chapter Type definitions
Now let's look at some variable definitions involving complex types.
This involves understanding better how types are described. In the
examples so far types have been described as references to previously
defined types or defined in terms of subranges of or pointers to
previously defined types. The section that follows will talk about
the various other type descriptors that may follow the = sign in a
type definition.
@menu
* Builtin types:: Integers, floating point, void, etc.
* Miscellaneous Types:: Pointers, sets, files, etc.
* Cross-references:: Referring to a type not yet defined.
* Subranges:: A type with a specific range.
* Arrays:: An aggregate type of same-typed elements.
* Strings:: Like an array but also has a length.
* Enumerations:: Like an integer but the values have names.
* Structures:: An aggregate type of different-typed elements.
* Typedefs:: Giving a type a name
* Unions::
* Function types::
@end menu
@node Builtin types
@section Builtin types
Certain types are built in (@code{int}, @code{short}, @code{void},
@code{float}, etc.); the debugger recognizes these types and knows how
to handle them. Thus don't be surprised if some of the following ways
of specifying builtin types do not specify everything that a debugger
would need to know about the type---in some cases they merely specify
enough information to distinguish the type from other types.
The traditional way to define builtin types is convolunted, so new ways
have been invented to describe them. Sun's ACC uses the @samp{b} and
@samp{R} type descriptors, and IBM uses negative type numbers. GDB can
accept all three, as of version 4.8; dbx just accepts the traditional
builtin types and perhaps one of the other two formats.
@menu
* Traditional Builtin Types:: Put on your seatbelts and prepare for kludgery
* Builtin Type Descriptors:: Builtin types with special type descriptors
* Negative Type Numbers:: Builtin types using negative type numbers
@end menu
@node Traditional Builtin Types
@subsection Traditional Builtin types
Often types are defined as subranges of themselves. If the array bounds
can fit within an @code{int}, then they are given normally. For example:
@example
.stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 ; 128 is N_LSYM
.stabs "char:t2=r2;0;127;",128,0,0,0
@end example
Builtin types can also be described as subranges of @code{int}:
@example
.stabs "unsigned short:t6=r1;0;65535;",128,0,0,0
@end example
If the lower bound of a subrange is 0 and the upper bound is -1, it
means that the type is an unsigned integral type whose bounds are too
big to describe in an int. Traditionally this is only used for
@code{unsigned int} and @code{unsigned long}; GCC also sometimes uses it
for @code{long long} and @code{unsigned long long}, and the only way to
tell those types apart is to look at their names. On other machines GCC
puts out bounds in octal, with a leading 0. In this case a negative
bound consists of a number which is a 1 bit followed by a bunch of 0
bits, and a positive bound is one in which a bunch of bits are 1.
@example
.stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
.stabs "long long int:t7=r1;0;-1;",128,0,0,0
@end example
If the lower bound of a subrange is 0 and the upper bound is negative,
it means that it is an unsigned integral type whose size in bytes is the
absolute value of the upper bound. I believe this is a Convex
convention for @code{unsigned long long}.
If the lower bound of a subrange is negative and the upper bound is 0,
it means that the type is a signed integral type whose size in bytes is
the absolute value of the lower bound. I believe this is a Convex
convention for @code{long long}. To distinguish this from a legitimate
subrange, the type should be a subrange of itself. I'm not sure whether
this is the case for Convex.
If the upper bound of a subrange is 0, it means that this is a floating
point type, and the lower bound of the subrange indicates the number of
bytes in the type:
@example
.stabs "float:t12=r1;4;0;",128,0,0,0
.stabs "double:t13=r1;8;0;",128,0,0,0
@end example
However, GCC writes @code{long double} the same way it writes
@code{double}; the only way to distinguish them is by the name:
@example
.stabs "long double:t14=r1;8;0;",128,0,0,0
@end example
Complex types are defined the same way as floating-point types; the only
way to distinguish a single-precision complex from a double-precision
floating-point type is by the name.
The C @code{void} type is defined as itself:
@example
.stabs "void:t15=15",128,0,0,0
@end example
I'm not sure how a boolean type is represented.
@node Builtin Type Descriptors
@subsection Defining Builtin Types using Builtin Type Descriptors
There are various type descriptors to define builtin types:
@table @code
@c FIXME: clean up description of width and offset, once we figure out
@c what they mean
@item b @var{signed} @var{char-flag} @var{width} ; @var{offset} ; @var{nbits} ;
Define an integral type. @var{signed} is @samp{u} for unsigned or
@samp{s} for signed. @var{char-flag} is @samp{c} which indicates this
is a character type, or is omitted. I assume this is to distinguish an
integral type from a character type of the same size, for example it
might make sense to set it for the C type @code{wchar_t} so the debugger
can print such variables differently (Solaris does not do this). Sun
sets it on the C types @code{signed char} and @code{unsigned char} which
arguably is wrong. @var{width} and @var{offset} appear to be for small
objects stored in larger ones, for example a @code{short} in an
@code{int} register. @var{width} is normally the number of bytes in the
type. @var{offset} seems to always be zero. @var{nbits} is the number
of bits in the type.
Note that type descriptor @samp{b} used for builtin types conflicts with
its use for Pascal space types (@pxref{Miscellaneous Types}); they can
be distinguished because the character following the type descriptor
will be a digit, @samp{(}, or @samp{-} for a Pascal space type, or
@samp{u} or @samp{s} for a builtin type.
@item w
Documented by AIX to define a wide character type, but their compiler
actually uses negative type numbers (@pxref{Negative Type Numbers}).
@item R @var{fp_type} ; @var{bytes} ;
Define a floating point type. @var{fp_type} has one of the following values:
@table @code
@item 1 (NF_SINGLE)
IEEE 32-bit (single precision) floating point format.
@item 2 (NF_DOUBLE)
IEEE 64-bit (double precision) floating point format.
@item 3 (NF_COMPLEX)
@item 4 (NF_COMPLEX16)
@item 5 (NF_COMPLEX32)
These are for complex numbers. A comment in
@file{include/aout/stab_gnu.h} describes them as Fortran complex, double
complex, and complex*16, respectively, but what does that mean? (i.e.
Single precision? Double precison?).
@item 6 (NF_LDOUBLE)
Long double. It would be cleaner to define a different code for every
possible format of long double.
@end table
@var{bytes} is the number of bytes occupied by the type. This allows a
debugger to perform some operations with the type even if it doesn't
understand @var{fp_code}.
@item g @var{type-information} ; @var{nbits}
Documented by AIX to define a floating type, but their compiler actually
uses negative type numbers (@pxref{Negative Type Numbers}).
@item c @var{type-information} ; @var{nbits}
Documented by AIX to define a complex type, but their compiler actually
uses negative type numbers (@pxref{Negative Type Numbers}).
@end table
The C @code{void} type is defined as a signed integral type 0 bits long:
@example
.stabs "void:t19=bs0;0;0",128,0,0,0
@end example
I'm not sure how a boolean type is represented.
@node Negative Type Numbers
@subsection Negative Type numbers
Since the debugger knows about the builtin types anyway, the idea of
negative type numbers is simply to give a special type number which
indicates the built in type. There is no stab defining these types.
I'm not sure whether anyone has tried to define what this means if
@code{int} can be other than 32 bits (or other types can be other than
their customary size). If @code{int} has exactly one size for each
architecture, then it can be handled easily enough, but if the size of
@code{int} can vary according the compiler options, then it gets hairy.
I guess the consistent way to do this would be to define separate
negative type numbers for 16-bit @code{int} and 32-bit @code{int};
therefore I have indicated below the customary size (and other format
information) for each type. The information below is currently correct
because AIX on the RS6000 is the only system which uses these type
numbers. If these type numbers start to get used on other systems, I
suspect the correct thing to do is to define a new number in cases where
a type does not have the size and format indicated below.
Also note that part of the definition of the negative type number is
the name of the type. Types with identical size and format but
different names have different negative type numbers.
@table @code
@item -1
@code{int}, 32 bit signed integral type.
@item -2
@code{char}, 8 bit type holding a character. Both GDB and dbx on AIX
treat this as signed. GCC uses this type whether @code{char} is signed
or not, which seems like a bad idea. The AIX compiler (xlc) seems to
avoid this type; it uses -5 instead for @code{char}.
@item -3
@code{short}, 16 bit signed integral type.
@item -4
@code{long}, 32 bit signed integral type.
@item -5
@code{unsigned char}, 8 bit unsigned integral type.
@item -6
@code{signed char}, 8 bit signed integral type.
@item -7
@code{unsigned short}, 16 bit unsigned integral type.
@item -8
@code{unsigned int}, 32 bit unsigned integral type.
@item -9
@code{unsigned}, 32 bit unsigned integral type.
@item -10
@code{unsigned long}, 32 bit unsigned integral type.
@item -11
@code{void}, type indicating the lack of a value.
@item -12
@code{float}, IEEE single precision.
@item -13
@code{double}, IEEE double precision.
@item -14
@code{long double}, IEEE double precision. The compiler claims the size
will increase in a future release, and for binary compatibility you have
to avoid using @code{long double}. I hope when they increase it they
use a new negative type number.
@item -15
@code{integer}. 32 bit signed integral type.
@item -16
@code{boolean}. Only one bit is used, not sure about the actual size of the
type.
@item -17
@code{short real}. IEEE single precision.
@item -18
@code{real}. IEEE double precision.
@item -19
@code{stringptr}. @xref{Strings}.
@item -20
@code{character}, 8 bit unsigned type.
@item -21
@code{logical*1}, 8 bit unsigned integral type.
@item -22
@code{logical*2}, 16 bit unsigned integral type.
@item -23
@code{logical*4}, 32 bit unsigned integral type.
@item -24
@code{logical}, 32 bit unsigned integral type.
@item -25
@code{complex}. A complex type consisting of two IEEE single-precision
floating point values.
@item -26
@code{complex}. A complex type consisting of two IEEE double-precision
floating point values.
@item -27
@code{integer*1}, 8 bit signed integral type.
@item -28
@code{integer*2}, 16 bit signed integral type.
@item -29
@code{integer*4}, 32 bit signed integral type.
@item -30
@code{wchar}. Wide character, 16 bits wide (Unicode format?). This is
not used for the C type @code{wchar_t}.
@end table
@node Miscellaneous Types
@section Miscellaneous Types
@table @code
@item b @var{type-information} ; @var{bytes}
Pascal space type. This is documented by IBM; what does it mean?
Note that this use of the @samp{b} type descriptor can be distinguished
from its use for builtin integral types (@pxref{Builtin Type
Descriptors}) because the character following the type descriptor is
always a digit, @samp{(}, or @samp{-}.
@item B @var{type-information}
A volatile-qualified version of @var{type-information}. This is a Sun
extension. A volatile-qualified type means that references and stores
to a variable of that type must not be optimized or cached; they must
occur as the user specifies them.
@item d @var{type-information}
File of type @var{type-information}. As far as I know this is only used
by Pascal.
@item k @var{type-information}
A const-qualified version of @var{type-information}. This is a Sun
extension. A const-qualified type means that a variable of this type
cannot be modified.
@item M @var{type-information} ; @var{length}
Multiple instance type. The type seems to composed of @var{length}
repetitions of @var{type-information}, for example @code{character*3} is
represented by @samp{M-2;3}, where @samp{-2} is a reference to a
character type (@pxref{Negative Type Numbers}). I'm not sure how this
differs from an array. This appears to be a FORTRAN feature.
@var{length} is a bound, like those in range types, @xref{Subranges}.
@item S @var{type-information}
Pascal set type. @var{type-information} must be a small type such as an
enumeration or a subrange, and the type is a bitmask whose length is
specified by the number of elements in @var{type-information}.
@item * @var{type-information}
Pointer to @var{type-information}.
@end table
@node Cross-references
@section Cross-references to other types
If a type is used before it is defined, one common way to deal with this
is just to use a type reference to a type which has not yet been
defined. The debugger is expected to be able to deal with this.
Another way is with the @samp{x} type descriptor, which is followed by
@samp{s} for a structure tag, @samp{u} for a union tag, or @samp{e} for
a enumerator tag, followed by the name of the tag, followed by @samp{:}.
for example the following C declarations:
@example
struct foo;
struct foo *bar;
@end example
produce
@example
.stabs "bar:G16=*17=xsfoo:",32,0,0,0
@end example
Not all debuggers support the @samp{x} type descriptor, so on some
machines GCC does not use it. I believe that for the above example it
would just emit a reference to type 17 and never define it, but I
haven't verified that.
Modula-2 imported types, at least on AIX, use the @samp{i} type
descriptor, which is followed by the name of the module from which the
type is imported, followed by @samp{:}, followed by the name of the
type. There is then optionally a comma followed by type information for
the type (This differs from merely naming the type (@pxref{Typedefs}) in
that it identifies the module; I don't understand whether the name of
the type given here is always just the same as the name we are giving
it, or whether this type descriptor is used with a nameless stab
(@pxref{Stabs Format}), or what). The symbol ends with @samp{;}.
@node Subranges
@section Subrange types
The @samp{r} type descriptor defines a type as a subrange of another
type. It is followed by type information for the type which it is a
subrange of, a semicolon, an integral lower bound, a semicolon, an
integral upper bound, and a semicolon. The AIX documentation does not
specify the trailing semicolon, in an effort to specify array indexes
more cleanly, but a subrange which is not an array index has always
included a trailing semicolong (@pxref{Arrays}).
Instead of an integer, either bound can be one of the following:
@table @code
@item A @var{offset}
The bound is passed by reference on the stack at offset @var{offset}
from the argument list. @xref{Parameters}, for more information on such
offsets.
@item T @var{offset}
The bound is passed by value on the stack at offset @var{offset} from
the argument list.
@item a @var{register-number}
The bound is pased by reference in register number
@var{register-number}.
@item t @var{register-number}
The bound is passed by value in register number @var{register-number}.
@item J
There is no bound.
@end table
Subranges are also used for builtin types, @xref{Traditional Builtin Types}.
@node Arrays
@section Array types
Arrays use the @samp{a} type descriptor. Following the type descriptor
is the type of the index and the type of the array elements. If the
index type is a range type, it will end in a semicolon; if it is not a
range type (for example, if it is a type reference), there does not
appear to be any way to tell where the types are separated. In an
effort to clean up this mess, IBM documents the two types as being
separated by a semicolon, and a range type as not ending in a semicolon
(but this is not right for range types which are not array indexes,
@pxref{Subranges}). I think probably the best solution is to specify
that a semicolon ends a range type, and that the index type and element
type of an array are separated by a semicolon, but that if the index
type is a range type, the extra semicolon can be omitted. GDB (at least
through version 4.9) doesn't support any kind of index type other than a
range anyway; I'm not sure about dbx.
The type of the index is often a range type, expressed as the letter r
and some parameters. It defines the size of the array. In the example
below, the range @code{r1;0;2;} defines an index type which is a
subrange of type 1 (integer), with a lower bound of 0 and an upper bound
of 2. This defines the valid range of subscripts of a three-element C
array.
For example, the definition
@example
char char_vec[3] = @{'a','b','c'@};
@end example
@noindent
produces the output
@example
.stabs "char_vec:G19=ar1;0;2;2",32,0,0,0
.global _char_vec
.align 4
_char_vec:
.byte 97
.byte 98
.byte 99
@end example
If an array is @dfn{packed}, it means that the elements are spaced more
closely than normal, saving memory at the expense of speed. For
example, an array of 3-byte objects might, if unpacked, have each
element aligned on a 4-byte boundary, but if packed, have no padding.
One way to specify that something is packed is with type attributes
(@pxref{Stabs Format}), in the case of arrays another is to use the
@samp{P} type descriptor instead of @samp{a}. Other than specifying a
packed array, @samp{P} is identical to @samp{a}.
@c FIXME-what is it? A pointer?
An open array is represented by the @samp{A} type descriptor followed by
type information specifying the type of the array elements.
@c FIXME: what is the format of this type? A pointer to a vector of pointers?
An N-dimensional dynamic array is represented by
@example
D @var{dimensions} ; @var{type-information}
@end example
@c Does dimensions really have this meaning? The AIX documentation
@c doesn't say.
@var{dimensions} is the number of dimensions; @var{type-information}
specifies the type of the array elements.
@c FIXME: what is the format of this type? A pointer to some offsets in
@c another array?
A subarray of an N-dimensional array is represented by
@example
E @var{dimensions} ; @var{type-information}
@end example
@c Does dimensions really have this meaning? The AIX documentation
@c doesn't say.
@var{dimensions} is the number of dimensions; @var{type-information}
specifies the type of the array elements.
@node Strings
@section Strings
Some languages, like C or the original Pascal, do not have string types,
they just have related things like arrays of characters. But most
Pascals and various other languages have string types, which are
indicated as follows:
@table @code
@item n @var{type-information} ; @var{bytes}
@var{bytes} is the maximum length. I'm not sure what
@var{type-information} is; I suspect that it means that this is a string
of @var{type-information} (thus allowing a string of integers, a string
of wide characters, etc., as well as a string of characters). Not sure
what the format of this type is. This is an AIX feature.
@item z @var{type-information} ; @var{bytes}
Just like @samp{n} except that this is a gstring, not an ordinary
string. I don't know the difference.
@item N
Pascal Stringptr. What is this? This is an AIX feature.
@end table
@node Enumerations
@section Enumerations
Enumerations are defined with the @samp{e} type descriptor.
@c FIXME: Where does this information properly go? Perhaps it is
@c redundant with something we already explain.
The source line below declares an enumeration type. It is defined at
file scope between the bodies of main and s_proc in example2.c.
The type definition is located after the N_RBRAC that marks the end of
the previous procedure's block scope, and before the N_FUN that marks
the beginning of the next procedure's block scope. Therefore it does not
describe a block local symbol, but a file local one.
The source line:
@example
enum e_places @{first,second=3,last@};
@end example
@noindent
generates the following stab
@example
.stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0
@end example
The symbol descriptor (T) says that the stab describes a structure,
enumeration, or type tag. The type descriptor e, following the 22= of
the type definition narrows it down to an enumeration type. Following
the e is a list of the elements of the enumeration. The format is
name:value,. The list of elements ends with a ;.
There is no standard way to specify the size of an enumeration type; it
is determined by the architecture (normally all enumerations types are
32 bits). There should be a way to specify an enumeration type of
another size; type attributes would be one way to do this @xref{Stabs
Format}.
@node Structures
@section Structures
@table @strong
@item Directive:
@code{.stabs}
@item Type:
@code{N_LSYM} or @code{C_DECL}
@item Symbol Descriptor:
@code{T}
@item Type Descriptor:
@code{s}
@end table
The following source code declares a structure tag and defines an
instance of the structure in global scope. Then a typedef equates the
structure tag with a new type. A seperate stab is generated for the
structure tag, the structure typedef, and the structure instance. The
stabs for the tag and the typedef are emited when the definitions are
encountered. Since the structure elements are not initialized, the
stab and code for the structure variable itself is located at the end
of the program in .common.
@example
6 struct s_tag @{
7 int s_int;
8 float s_float;
9 char s_char_vec[8];
10 struct s_tag* s_next;
11 @} g_an_s;
12
13 typedef struct s_tag s_typedef;
@end example
The structure tag is an N_LSYM stab type because, like the enum, the
symbol is file scope. Like the enum, the symbol descriptor is T, for
enumeration, struct or tag type. The symbol descriptor s following
the 16= of the type definition narrows the symbol type to struct.
Following the struct symbol descriptor is the number of bytes the
struct occupies, followed by a description of each structure element.
The structure element descriptions are of the form name:type, bit
offset from the start of the struct, and number of bits in the
element.
@example
<128> N_LSYM - type definition
.stabs "name:sym_desc(struct tag) Type_def(16)=type_desc(struct type)
struct_bytes
elem_name:type_ref(int),bit_offset,field_bits;
elem_name:type_ref(float),bit_offset,field_bits;
elem_name:type_def(17)=type_desc(array)
index_type(range of int from 0 to 7);
element_type(char),bit_offset,field_bits;;",
N_LSYM,NIL,NIL,NIL
30 .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;
s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
@end example
In this example, two of the structure elements are previously defined
types. For these, the type following the name: part of the element
description is a simple type reference. The other two structure
elements are new types. In this case there is a type definition
embedded after the name:. The type definition for the array element
looks just like a type definition for a standalone array. The s_next
field is a pointer to the same kind of structure that the field is an
element of. So the definition of structure type 16 contains an type
definition for an element which is a pointer to type 16.
@node Typedefs
@section Giving a type a name
To give a type a name, use the @samp{t} symbol descriptor. For example,
@example
.stabs "s_typedef:t16",128,0,0,0
@end example
specifies that @code{s_typedef} refers to type number 16. Such stabs
have symbol type @code{N_LSYM} or @code{C_DECL}.
If instead, you are giving a name to a tag for a structure, union, or
enumeration, use the @samp{T} symbol descriptor instead. I believe C is
the only language with this feature.
If the type is an opaque type (I believe this is a Modula-2 feature),
AIX provides a type descriptor to specify it. The type descriptor is
@samp{o} and is followed by a name. I don't know what the name
means---is it always the same as the name of the type, or is this type
descriptor used with a nameless stab (@pxref{Stabs Format})? There
optionally follows a comma followed by type information which defines
the type of this type. If omitted, a semicolon is used in place of the
comma and the type information, and, the type is much like a generic
pointer type---it has a known size but little else about it is
specified.
@node Unions
@section Unions
Next let's look at unions. In example2 this union type is declared
locally to a procedure and an instance of the union is defined.
@example
36 union u_tag @{
37 int u_int;
38 float u_float;
39 char* u_char;
40 @} an_u;
@end example
This code generates a stab for the union tag and a stab for the union
variable. Both use the N_LSYM stab type. Since the union variable is
scoped locally to the procedure in which it is defined, its stab is
located immediately preceding the N_LBRAC for the procedure's block
start.
The stab for the union tag, however is located preceding the code for
the procedure in which it is defined. The stab type is N_LSYM. This
would seem to imply that the union type is file scope, like the struct
type s_tag. This is not true. The contents and position of the stab
for u_type do not convey any infomation about its procedure local
scope.
@display
<128> N_LSYM - type
.stabs "name:sym_desc(union tag)type_def(22)=type_desc(union)
byte_size(4)
elem_name:type_ref(int),bit_offset(0),bit_size(32);
elem_name:type_ref(float),bit_offset(0),bit_size(32);
elem_name:type_ref(ptr to char),bit_offset(0),bit_size(32);;"
N_LSYM, NIL, NIL, NIL
@end display
@smallexample
105 .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
128,0,0,0
@end smallexample
The symbol descriptor, T, following the name: means that the stab
describes an enumeration, struct or type tag. The type descriptor u,
following the 23= of the type definition, narrows it down to a union
type definition. Following the u is the number of bytes in the union.
After that is a list of union element descriptions. Their format is
name:type, bit offset into the union, and number of bytes for the
element;.
The stab for the union variable follows. Notice that the frame
pointer offset for local variables is negative.
@display
<128> N_LSYM - local variable (with no symbol descriptor)
.stabs "name:type_ref(u_tag)", N_LSYM, NIL, NIL, frame_ptr_offset
@end display
@example
130 .stabs "an_u:23",128,0,0,-20
@end example
@node Function types
@section Function types
There are various types for function variables. These types are not
used in defining functions; see symbol descriptor @samp{f}; they are
used for things like pointers to functions.
The simple, traditional, type is type descriptor @samp{f} is followed by
type information for the return type of the function, followed by a
semicolon.
This does not deal with functions the number and type of whose
parameters are part of their type, as found in Modula-2 or ANSI C. AIX
provides extensions to specify these, using the @samp{f}, @samp{F},
@samp{p}, and @samp{R} type descriptors.
First comes the type descriptor. Then, if it is @samp{f} or @samp{F},
this is a function, and the type information for the return type of the
function follows, followed by a comma. Then comes the number of
parameters to the function and a semicolon. Then, for each parameter,
there is the name of the parameter followed by a colon (this is only
present for type descriptors @samp{R} and @samp{F} which represent
Pascal function or procedure parameters), type information for the
parameter, a comma, @samp{0} if passed by reference or @samp{1} if
passed by value, and a semicolon. The type definition ends with a
semicolon.
For example,
@example
int (*g_pf)();
@end example
@noindent
generates the following code:
@example
.stabs "g_pf:G24=*25=f1",32,0,0,0
.common _g_pf,4,"bss"
@end example
The variable defines a new type, 24, which is a pointer to another new
type, 25, which is defined as a function returning int.
@node Symbol Tables
@chapter Symbol information in symbol tables
This section examines more closely the format of symbol table entries
and how stab assembler directives map to them. It also describes what
transformations the assembler and linker make on data from stabs.
Each time the assembler encounters a stab in its input file it puts
each field of the stab into corresponding fields in a symbol table
entry of its output file. If the stab contains a string field, the
symbol table entry for that stab points to a string table entry
containing the string data from the stab. Assembler labels become
relocatable addresses. Symbol table entries in a.out have the format:
@example
struct internal_nlist @{
unsigned long n_strx; /* index into string table of name */
unsigned char n_type; /* type of symbol */
unsigned char n_other; /* misc info (usually empty) */
unsigned short n_desc; /* description field */
bfd_vma n_value; /* value of symbol */
@};
@end example
For .stabs directives, the n_strx field holds the character offset
from the start of the string table to the string table entry
containing the "string" field. For other classes of stabs (.stabn and
.stabd) this field is null.
Symbol table entries with n_type fields containing a value greater or
equal to 0x20 originated as stabs generated by the compiler (with one
random exception). Those with n_type values less than 0x20 were
placed in the symbol table of the executable by the assembler or the
linker.
The linker concatenates object files and does fixups of externally
defined symbols. You can see the transformations made on stab data by
the assembler and linker by examining the symbol table after each pass
of the build, first the assemble and then the link.
To do this use nm with the -ap options. This dumps the symbol table,
including debugging information, unsorted. For stab entries the
columns are: value, other, desc, type, string. For assembler and
linker symbols, the columns are: value, type, string.
There are a few important things to notice about symbol tables. Where
the value field of a stab contains a frame pointer offset, or a
register number, that value is unchanged by the rest of the build.
Where the value field of a stab contains an assembly language label,
it is transformed by each build step. The assembler turns it into a
relocatable address and the linker turns it into an absolute address.
This source line defines a static variable at file scope:
@example
3 static int s_g_repeat
@end example
@noindent
The following stab describes the symbol.
@example
26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
@end example
@noindent
The assembler transforms the stab into this symbol table entry in the
@file{.o} file. The location is expressed as a data segment offset.
@example
21 00000084 - 00 0000 STSYM s_g_repeat:S1
@end example
@noindent
in the symbol table entry from the executable, the linker has made the
relocatable address absolute.
@example
22 0000e00c - 00 0000 STSYM s_g_repeat:S1
@end example
Stabs for global variables do not contain location information. In
this case the debugger finds location information in the assembler or
linker symbol table entry describing the variable. The source line:
@example
1 char g_foo = 'c';
@end example
@noindent
generates the stab:
@example
21 .stabs "g_foo:G2",32,0,0,0
@end example
The variable is represented by the following two symbol table entries
in the object file. The first one originated as a stab. The second
one is an external symbol. The upper case D signifies that the n_type
field of the symbol table contains 7, N_DATA with local linkage (see
Table B). The value field following the file's line number is empty
for the stab entry. For the linker symbol it contains the
rellocatable address corresponding to the variable.
@example
19 00000000 - 00 0000 GSYM g_foo:G2
20 00000080 D _g_foo
@end example
@noindent
These entries as transformed by the linker. The linker symbol table
entry now holds an absolute address.
@example
21 00000000 - 00 0000 GSYM g_foo:G2
@dots{}
215 0000e008 D _g_foo
@end example
@node Cplusplus
@chapter GNU C++ stabs
@menu
* Basic Cplusplus types::
* Simple classes::
* Class instance::
* Methods:: Method definition
* Protections::
* Method Modifiers:: (const, volatile, const volatile)
* Virtual Methods::
* Inheritence::
* Virtual Base Classes::
* Static Members::
@end menu
@subsection type descriptors added for C++ descriptions
@table @code
@item #
method type (two ## if minimal debug)
@item @@
Member (class and variable) type. It is followed by type information
for the offset basetype, a comma, and type information for the type of
the field being pointed to. (FIXME: this is acknowledged to be
gibberish. Can anyone say what really goes here?).
Note that there is a conflict between this and type attributes
(@pxref{Stabs Format}); both use type descriptor @samp{@@}.
Fortunately, the @samp{@@} type descriptor used in this C++ sense always
will be followed by a digit, @samp{(}, or @samp{-}, and type attributes
never start with those things.
@end table
@node Basic Cplusplus types
@section Basic types for C++
<< the examples that follow are based on a01.C >>
C++ adds two more builtin types to the set defined for C. These are
the unknown type and the vtable record type. The unknown type, type
16, is defined in terms of itself like the void type.
The vtable record type, type 17, is defined as a structure type and
then as a structure tag. The structure has four fields, delta, index,
pfn, and delta2. pfn is the function pointer.
<< In boilerplate $vtbl_ptr_type, what are the fields delta,
index, and delta2 used for? >>
This basic type is present in all C++ programs even if there are no
virtual methods defined.
@display
.stabs "struct_name:sym_desc(type)type_def(17)=type_desc(struct)struct_bytes(8)
elem_name(delta):type_ref(short int),bit_offset(0),field_bits(16);
elem_name(index):type_ref(short int),bit_offset(16),field_bits(16);
elem_name(pfn):type_def(18)=type_desc(ptr to)type_ref(void),
bit_offset(32),field_bits(32);
elem_name(delta2):type_def(short int);bit_offset(32),field_bits(16);;"
N_LSYM, NIL, NIL
@end display
@smallexample
.stabs "$vtbl_ptr_type:t17=s8
delta:6,0,16;index:6,16,16;pfn:18=*15,32,32;delta2:6,32,16;;"
,128,0,0,0
@end smallexample
@display
.stabs "name:sym_dec(struct tag)type_ref($vtbl_ptr_type)",N_LSYM,NIL,NIL,NIL
@end display
@example
.stabs "$vtbl_ptr_type:T17",128,0,0,0
@end example
@node Simple classes
@section Simple class definition
The stabs describing C++ language features are an extension of the
stabs describing C. Stabs representing C++ class types elaborate
extensively on the stab format used to describe structure types in C.
Stabs representing class type variables look just like stabs
representing C language variables.
Consider the following very simple class definition.
@example
class baseA @{
public:
int Adat;
int Ameth(int in, char other);
@};
@end example
The class baseA is represented by two stabs. The first stab describes
the class as a structure type. The second stab describes a structure
tag of the class type. Both stabs are of stab type N_LSYM. Since the
stab is not located between an N_FUN and a N_LBRAC stab this indicates
that the class is defined at file scope. If it were, then the N_LSYM
would signify a local variable.
A stab describing a C++ class type is similar in format to a stab
describing a C struct, with each class member shown as a field in the
structure. The part of the struct format describing fields is
expanded to include extra information relevent to C++ class members.
In addition, if the class has multiple base classes or virtual
functions the struct format outside of the field parts is also
augmented.
In this simple example the field part of the C++ class stab
representing member data looks just like the field part of a C struct
stab. The section on protections describes how its format is
sometimes extended for member data.
The field part of a C++ class stab representing a member function
differs substantially from the field part of a C struct stab. It
still begins with `name:' but then goes on to define a new type number
for the member function, describe its return type, its argument types,
its protection level, any qualifiers applied to the method definition,
and whether the method is virtual or not. If the method is virtual
then the method description goes on to give the vtable index of the
method, and the type number of the first base class defining the
method.
When the field name is a method name it is followed by two colons
rather than one. This is followed by a new type definition for the
method. This is a number followed by an equal sign and then the
symbol descriptor `##', indicating a method type. This is followed by
a type reference showing the return type of the method and a
semi-colon.
The format of an overloaded operator method name differs from that
of other methods. It is "op$::XXXX." where XXXX is the operator name
such as + or +=. The name ends with a period, and any characters except
the period can occur in the XXXX string.
The next part of the method description represents the arguments to
the method, preceeded by a colon and ending with a semi-colon. The
types of the arguments are expressed in the same way argument types
are expressed in C++ name mangling. In this example an int and a char
map to `ic'.
This is followed by a number, a letter, and an asterisk or period,
followed by another semicolon. The number indicates the protections
that apply to the member function. Here the 2 means public. The
letter encodes any qualifier applied to the method definition. In
this case A means that it is a normal function definition. The dot
shows that the method is not virtual. The sections that follow
elaborate further on these fields and describe the additional
information present for virtual methods.
@display
.stabs "class_name:sym_desc(type)type_def(20)=type_desc(struct)struct_bytes(4)
field_name(Adat):type(int),bit_offset(0),field_bits(32);
method_name(Ameth)::type_def(21)=type_desc(method)return_type(int);
:arg_types(int char);
protection(public)qualifier(normal)virtual(no);;"
N_LSYM,NIL,NIL,NIL
@end display
@smallexample
.stabs "baseA:t20=s4Adat:1,0,32;Ameth::21=##1;:ic;2A.;;",128,0,0,0
.stabs "class_name:sym_desc(struct tag)",N_LSYM,NIL,NIL,NIL
.stabs "baseA:T20",128,0,0,0
@end smallexample
@node Class instance
@section Class instance
As shown above, describing even a simple C++ class definition is
accomplished by massively extending the stab format used in C to
describe structure types. However, once the class is defined, C stabs
with no modifications can be used to describe class instances. The
following source:
@example
main () @{
baseA AbaseA;
@}
@end example
@noindent
yields the following stab describing the class instance. It looks no
different from a standard C stab describing a local variable.
@display
.stabs "name:type_ref(baseA)", N_LSYM, NIL, NIL, frame_ptr_offset
@end display
@example
.stabs "AbaseA:20",128,0,0,-20
@end example
@node Methods
@section Method defintion
The class definition shown above declares Ameth. The C++ source below
defines Ameth:
@example
int
baseA::Ameth(int in, char other)
@{
return in;
@};
@end example
This method definition yields three stabs following the code of the
method. One stab describes the method itself and following two
describe its parameters. Although there is only one formal argument
all methods have an implicit argument which is the `this' pointer.
The `this' pointer is a pointer to the object on which the method was
called. Note that the method name is mangled to encode the class name
and argument types. << Name mangling is not described by this
document - Is there already such a doc? >>
@example
.stabs "name:symbol_desriptor(global function)return_type(int)",
N_FUN, NIL, NIL, code_addr_of_method_start
.stabs "Ameth__5baseAic:F1",36,0,0,_Ameth__5baseAic
@end example
Here is the stab for the `this' pointer implicit argument. The name
of the `this' pointer is always `this.' Type 19, the `this' pointer is
defined as a pointer to type 20, baseA, but a stab defining baseA has
not yet been emited. Since the compiler knows it will be emited
shortly, here it just outputs a cross reference to the undefined
symbol, by prefixing the symbol name with xs.
@example
.stabs "name:sym_desc(register param)type_def(19)=
type_desc(ptr to)type_ref(baseA)=
type_desc(cross-reference to)baseA:",N_RSYM,NIL,NIL,register_number
.stabs "this:P19=*20=xsbaseA:",64,0,0,8
@end example
The stab for the explicit integer argument looks just like a parameter
to a C function. The last field of the stab is the offset from the
argument pointer, which in most systems is the same as the frame
pointer.
@example
.stabs "name:sym_desc(value parameter)type_ref(int)",
N_PSYM,NIL,NIL,offset_from_arg_ptr
.stabs "in:p1",160,0,0,72
@end example
<< The examples that follow are based on A1.C >>
@node Protections
@section Protections
In the simple class definition shown above all member data and
functions were publicly accessable. The example that follows
contrasts public, protected and privately accessable fields and shows
how these protections are encoded in C++ stabs.
Protections for class member data are signified by two characters
embeded in the stab defining the class type. These characters are
located after the name: part of the string. /0 means private, /1
means protected, and /2 means public. If these characters are omited
this means that the member is public. The following C++ source:
@example
class all_data @{
private:
int priv_dat;
protected:
char prot_dat;
public:
float pub_dat;
@};
@end example
@noindent
generates the following stab to describe the class type all_data.
@display
.stabs "class_name:sym_desc(type)type_def(19)=type_desc(struct)struct_bytes
data_name:/protection(private)type_ref(int),bit_offset,num_bits;
data_name:/protection(protected)type_ref(char),bit_offset,num_bits;
data_name:(/num omited, private)type_ref(float),bit_offset,num_bits;;"
N_LSYM,NIL,NIL,NIL
@end display
@smallexample
.stabs "all_data:t19=s12
priv_dat:/01,0,32;prot_dat:/12,32,8;pub_dat:12,64,32;;",128,0,0,0
@end smallexample
Protections for member functions are signified by one digit embeded in
the field part of the stab describing the method. The digit is 0 if
private, 1 if protected and 2 if public. Consider the C++ class
definition below:
@example
class all_methods @{
private:
int priv_meth(int in)@{return in;@};
protected:
char protMeth(char in)@{return in;@};
public:
float pubMeth(float in)@{return in;@};
@};
@end example
It generates the following stab. The digit in question is to the left
of an `A' in each case. Notice also that in this case two symbol
descriptors apply to the class name struct tag and struct type.
@display
.stabs "class_name:sym_desc(struct tag&type)type_def(21)=
sym_desc(struct)struct_bytes(1)
meth_name::type_def(22)=sym_desc(method)returning(int);
:args(int);protection(private)modifier(normal)virtual(no);
meth_name::type_def(23)=sym_desc(method)returning(char);
:args(char);protection(protected)modifier(normal)virual(no);
meth_name::type_def(24)=sym_desc(method)returning(float);
:args(float);protection(public)modifier(normal)virtual(no);;",
N_LSYM,NIL,NIL,NIL
@end display
@smallexample
.stabs "all_methods:Tt21=s1priv_meth::22=##1;:i;0A.;protMeth::23=##2;:c;1A.;
pubMeth::24=##12;:f;2A.;;",128,0,0,0
@end smallexample
@node Method Modifiers
@section Method Modifiers (const, volatile, const volatile)
<< based on a6.C >>
In the class example described above all the methods have the normal
modifier. This method modifier information is located just after the
protection information for the method. This field has four possible
character values. Normal methods use A, const methods use B, volatile
methods use C, and const volatile methods use D. Consider the class
definition below:
@example
class A @{
public:
int ConstMeth (int arg) const @{ return arg; @};
char VolatileMeth (char arg) volatile @{ return arg; @};
float ConstVolMeth (float arg) const volatile @{return arg; @};
@};
@end example
This class is described by the following stab:
@display
.stabs "class(A):sym_desc(struct)type_def(20)=type_desc(struct)struct_bytes(1)
meth_name(ConstMeth)::type_def(21)sym_desc(method)
returning(int);:arg(int);protection(public)modifier(const)virtual(no);
meth_name(VolatileMeth)::type_def(22)=sym_desc(method)
returning(char);:arg(char);protection(public)modifier(volatile)virt(no)
meth_name(ConstVolMeth)::type_def(23)=sym_desc(method)
returning(float);:arg(float);protection(public)modifer(const volatile)
virtual(no);;", @dots{}
@end display
@example
.stabs "A:T20=s1ConstMeth::21=##1;:i;2B.;VolatileMeth::22=##2;:c;2C.;
ConstVolMeth::23=##12;:f;2D.;;",128,0,0,0
@end example
@node Virtual Methods
@section Virtual Methods
<< The following examples are based on a4.C >>
The presence of virtual methods in a class definition adds additional
data to the class description. The extra data is appended to the
description of the virtual method and to the end of the class
description. Consider the class definition below:
@example
class A @{
public:
int Adat;
virtual int A_virt (int arg) @{ return arg; @};
@};
@end example
This results in the stab below describing class A. It defines a new
type (20) which is an 8 byte structure. The first field of the class
struct is Adat, an integer, starting at structure offset 0 and
occupying 32 bits.
The second field in the class struct is not explicitly defined by the
C++ class definition but is implied by the fact that the class
contains a virtual method. This field is the vtable pointer. The
name of the vtable pointer field starts with $vf and continues with a
type reference to the class it is part of. In this example the type
reference for class A is 20 so the name of its vtable pointer field is
$vf20, followed by the usual colon.
Next there is a type definition for the vtable pointer type (21).
This is in turn defined as a pointer to another new type (22).
Type 22 is the vtable itself, which is defined as an array, indexed by
a range of integers between 0 and 1, and whose elements are of type
17. Type 17 was the vtable record type defined by the boilerplate C++
type definitions, as shown earlier.
The bit offset of the vtable pointer field is 32. The number of bits
in the field are not specified when the field is a vtable pointer.
Next is the method definition for the virtual member function A_virt.
Its description starts out using the same format as the non-virtual
member functions described above, except instead of a dot after the
`A' there is an asterisk, indicating that the function is virtual.
Since is is virtual some addition information is appended to the end
of the method description.
The first number represents the vtable index of the method. This is a
32 bit unsigned number with the high bit set, followed by a
semi-colon.
The second number is a type reference to the first base class in the
inheritence hierarchy defining the virtual member function. In this
case the class stab describes a base class so the virtual function is
not overriding any other definition of the method. Therefore the
reference is to the type number of the class that the stab is
describing (20).
This is followed by three semi-colons. One marks the end of the
current sub-section, one marks the end of the method field, and the
third marks the end of the struct definition.
For classes containing virtual functions the very last section of the
string part of the stab holds a type reference to the first base
class. This is preceeded by `~%' and followed by a final semi-colon.
@display
.stabs "class_name(A):type_def(20)=sym_desc(struct)struct_bytes(8)
field_name(Adat):type_ref(int),bit_offset(0),field_bits(32);
field_name(A virt func ptr):type_def(21)=type_desc(ptr to)type_def(22)=
sym_desc(array)index_type_ref(range of int from 0 to 1);
elem_type_ref(vtbl elem type),
bit_offset(32);
meth_name(A_virt)::typedef(23)=sym_desc(method)returning(int);
:arg_type(int),protection(public)normal(yes)virtual(yes)
vtable_index(1);class_first_defining(A);;;~%first_base(A);",
N_LSYM,NIL,NIL,NIL
@end display
@example
.stabs "A:t20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32;A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0
@end example
@node Inheritence
@section Inheritence
Stabs describing C++ derived classes include additional sections that
describe the inheritence hierarchy of the class. A derived class stab
also encodes the number of base classes. For each base class it tells
if the base class is virtual or not, and if the inheritence is private
or public. It also gives the offset into the object of the portion of
the object corresponding to each base class.
This additional information is embeded in the class stab following the
number of bytes in the struct. First the number of base classes
appears bracketed by an exclamation point and a comma.
Then for each base type there repeats a series: two digits, a number,
a comma, another number, and a semi-colon.
The first of the two digits is 1 if the base class is virtual and 0 if
not. The second digit is 2 if the derivation is public and 0 if not.
The number following the first two digits is the offset from the start
of the object to the part of the object pertaining to the base class.
After the comma, the second number is a type_descriptor for the base
type. Finally a semi-colon ends the series, which repeats for each
base class.
The source below defines three base classes A, B, and C and the
derived class D.
@example
class A @{
public:
int Adat;
virtual int A_virt (int arg) @{ return arg; @};
@};
class B @{
public:
int B_dat;
virtual int B_virt (int arg) @{return arg; @};
@};
class C @{
public:
int Cdat;
virtual int C_virt (int arg) @{return arg; @};
@};
class D : A, virtual B, public C @{
public:
int Ddat;
virtual int A_virt (int arg ) @{ return arg+1; @};
virtual int B_virt (int arg) @{ return arg+2; @};
virtual int C_virt (int arg) @{ return arg+3; @};
virtual int D_virt (int arg) @{ return arg; @};
@};
@end example
Class stabs similar to the ones described earlier are generated for
each base class.
@c FIXME!!! the linebreaks in the following example probably make the
@c examples literally unusable, but I don't know any other way to get
@c them on the page.
@c One solution would be to put some of the type definitions into
@c separate stabs, even if that's not exactly what the compiler actually
@c emits.
@smallexample
.stabs "A:T20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32;
A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0
.stabs "B:Tt25=s8Bdat:1,0,32;$vf25:21,32;B_virt::26=##1;
:i;2A*-2147483647;25;;;~%25;",128,0,0,0
.stabs "C:Tt28=s8Cdat:1,0,32;$vf28:21,32;C_virt::29=##1;
:i;2A*-2147483647;28;;;~%28;",128,0,0,0
@end smallexample
In the stab describing derived class D below, the information about
the derivation of this class is encoded as follows.
@display
.stabs "derived_class_name:symbol_descriptors(struct tag&type)=
type_descriptor(struct)struct_bytes(32)!num_bases(3),
base_virtual(no)inheritence_public(no)base_offset(0),
base_class_type_ref(A);
base_virtual(yes)inheritence_public(no)base_offset(NIL),
base_class_type_ref(B);
base_virtual(no)inheritence_public(yes)base_offset(64),
base_class_type_ref(C); @dots{}
@end display
@c FIXME! fake linebreaks.
@smallexample
.stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:
1,160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt:
:32:i;2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;
28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0
@end smallexample
@node Virtual Base Classes
@section Virtual Base Classes
A derived class object consists of a concatination in memory of the
data areas defined by each base class, starting with the leftmost and
ending with the rightmost in the list of base classes. The exception
to this rule is for virtual inheritence. In the example above, class
D inherits virtually from base class B. This means that an instance
of a D object will not contain it's own B part but merely a pointer to
a B part, known as a virtual base pointer.
In a derived class stab, the base offset part of the derivation
information, described above, shows how the base class parts are
ordered. The base offset for a virtual base class is always given as
0. Notice that the base offset for B is given as 0 even though B is
not the first base class. The first base class A starts at offset 0.
The field information part of the stab for class D describes the field
which is the pointer to the virtual base class B. The vbase pointer
name is $vb followed by a type reference to the virtual base class.
Since the type id for B in this example is 25, the vbase pointer name
is $vb25.
@c FIXME!! fake linebreaks below
@smallexample
.stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:1,
160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i;
2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;28;;D_virt:
:32:i;2A*-2147483646;31;;;~%20;",128,0,0,0
@end smallexample
Following the name and a semicolon is a type reference describing the
type of the virtual base class pointer, in this case 24. Type 24 was
defined earlier as the type of the B class `this` pointer. The
`this' pointer for a class is a pointer to the class type.
@example
.stabs "this:P24=*25=xsB:",64,0,0,8
@end example
Finally the field offset part of the vbase pointer field description
shows that the vbase pointer is the first field in the D object,
before any data fields defined by the class. The layout of a D class
object is a follows, Adat at 0, the vtable pointer for A at 32, Cdat
at 64, the vtable pointer for C at 96, the virtual ase pointer for B
at 128, and Ddat at 160.
@node Static Members
@section Static Members
The data area for a class is a concatenation of the space used by the
data members of the class. If the class has virtual methods, a vtable
pointer follows the class data. The field offset part of each field
description in the class stab shows this ordering.
<< How is this reflected in stabs? See Cygnus bug #677 for some info. >>
@node Example2.c
@appendix Example2.c - source code for extended example
@example
1 char g_foo = 'c';
2 register int g_bar asm ("%g5");
3 static int s_g_repeat = 2;
4 int (*g_pf)();
5
6 struct s_tag @{
7 int s_int;
8 float s_float;
9 char s_char_vec[8];
10 struct s_tag* s_next;
11 @} g_an_s;
12
13 typedef struct s_tag s_typedef;
14
15 char char_vec[3] = @{'a','b','c'@};
16
17 main (argc, argv)
18 int argc;
19 char* argv[];
20 @{
21 static float s_flap;
22 int times;
23 for (times=0; times < s_g_repeat; times++)@{
24 int inner;
25 printf ("Hello world\n");
26 @}
27 @};
28
29 enum e_places @{first,second=3,last@};
30
31 static s_proc (s_arg, s_ptr_arg, char_vec)
32 s_typedef s_arg;
33 s_typedef* s_ptr_arg;
34 char* char_vec;
35 @{
36 union u_tag @{
37 int u_int;
38 float u_float;
39 char* u_char;
40 @} an_u;
41 @}
42
43
@end example
@node Example2.s
@appendix Example2.s - assembly code for extended example
@example
1 gcc2_compiled.:
2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0
3 .stabs "example2.c",100,0,0,Ltext0
4 .text
5 Ltext0:
6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0
7 .stabs "char:t2=r2;0;127;",128,0,0,0
8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0
9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0
11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0
12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0
13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0
14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0
15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0
16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0
17 .stabs "float:t12=r1;4;0;",128,0,0,0
18 .stabs "double:t13=r1;8;0;",128,0,0,0
19 .stabs "long double:t14=r1;8;0;",128,0,0,0
20 .stabs "void:t15=15",128,0,0,0
21 .stabs "g_foo:G2",32,0,0,0
22 .global _g_foo
23 .data
24 _g_foo:
25 .byte 99
26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
27 .align 4
28 _s_g_repeat:
29 .word 2
@c FIXME! fake linebreak in line 30
30 .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;s_char_vec:
17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
31 .stabs "s_typedef:t16",128,0,0,0
32 .stabs "char_vec:G19=ar1;0;2;2",32,0,0,0
33 .global _char_vec
34 .align 4
35 _char_vec:
36 .byte 97
37 .byte 98
38 .byte 99
39 .reserve _s_flap.0,4,"bss",4
40 .text
41 .align 4
42 LC0:
43 .ascii "Hello world\12\0"
44 .align 4
45 .global _main
46 .proc 1
47 _main:
48 .stabn 68,0,20,LM1
49 LM1:
50 !#PROLOGUE# 0
51 save %sp,-144,%sp
52 !#PROLOGUE# 1
53 st %i0,[%fp+68]
54 st %i1,[%fp+72]
55 call ___main,0
56 nop
57 LBB2:
58 .stabn 68,0,23,LM2
59 LM2:
60 st %g0,[%fp-20]
61 L2:
62 sethi %hi(_s_g_repeat),%o0
63 ld [%fp-20],%o1
64 ld [%o0+%lo(_s_g_repeat)],%o0
65 cmp %o1,%o0
66 bge L3
67 nop
68 LBB3:
69 .stabn 68,0,25,LM3
70 LM3:
71 sethi %hi(LC0),%o1
72 or %o1,%lo(LC0),%o0
73 call _printf,0
74 nop
75 .stabn 68,0,26,LM4
76 LM4:
77 LBE3:
78 .stabn 68,0,23,LM5
79 LM5:
80 L4:
81 ld [%fp-20],%o0
82 add %o0,1,%o1
83 st %o1,[%fp-20]
84 b,a L2
85 L3:
86 .stabn 68,0,27,LM6
87 LM6:
88 LBE2:
89 .stabn 68,0,27,LM7
90 LM7:
91 L1:
92 ret
93 restore
94 .stabs "main:F1",36,0,0,_main
95 .stabs "argc:p1",160,0,0,68
96 .stabs "argv:p20=*21=*2",160,0,0,72
97 .stabs "s_flap:V12",40,0,0,_s_flap.0
98 .stabs "times:1",128,0,0,-20
99 .stabn 192,0,0,LBB2
100 .stabs "inner:1",128,0,0,-24
101 .stabn 192,0,0,LBB3
102 .stabn 224,0,0,LBE3
103 .stabn 224,0,0,LBE2
104 .stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0
@c FIXME: fake linebreak in line 105
105 .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
128,0,0,0
106 .align 4
107 .proc 1
108 _s_proc:
109 .stabn 68,0,35,LM8
110 LM8:
111 !#PROLOGUE# 0
112 save %sp,-120,%sp
113 !#PROLOGUE# 1
114 mov %i0,%o0
115 st %i1,[%fp+72]
116 st %i2,[%fp+76]
117 LBB4:
118 .stabn 68,0,41,LM9
119 LM9:
120 LBE4:
121 .stabn 68,0,41,LM10
122 LM10:
123 L5:
124 ret
125 restore
126 .stabs "s_proc:f1",36,0,0,_s_proc
127 .stabs "s_arg:p16",160,0,0,0
128 .stabs "s_ptr_arg:p18",160,0,0,72
129 .stabs "char_vec:p21",160,0,0,76
130 .stabs "an_u:23",128,0,0,-20
131 .stabn 192,0,0,LBB4
132 .stabn 224,0,0,LBE4
133 .stabs "g_bar:r1",64,0,0,5
134 .stabs "g_pf:G24=*25=f1",32,0,0,0
135 .common _g_pf,4,"bss"
136 .stabs "g_an_s:G16",32,0,0,0
137 .common _g_an_s,20,"bss"
@end example
@node Stab types
@appendix Table A: Symbol types from stabs
Table A lists stab types sorted by type number. Stab type numbers are
32 and greater. This is the full list of stab numbers, including stab
types that are used in languages other than C.
The #define names for these stab types are defined in:
devo/include/aout/stab.def
@smallexample
type type #define used to describe
dec hex name source program feature
------------------------------------------------
32 0x20 N_GYSM global symbol
34 0X22 N_FNAME function name (for BSD Fortran)
36 0x24 N_FUN function name or text segment variable for C
38 0x26 N_STSYM static symbol (data segment w/internal linkage)
40 0x28 N_LCSYM .lcomm symbol(BSS-seg variable w/internal linkage)
42 0x2a N_MAIN Name of main routine (not used in C)
48 0x30 N_PC global symbol (for Pascal)
50 0x32 N_NSYMS number of symbols (according to Ultrix V4.0)
52 0x34 N_NOMAP no DST map for sym (according to Ultrix V4.0)
64 0x40 N_RSYM register variable
66 0x42 N_M2C Modula-2 compilation unit
68 0x44 N_SLINE line number in text segment
70 0x46 N_DSLINE line number in data segment
72 0x48 N_BSLINE line number in bss segment
72 0x48 N_BROWS Sun source code browser, path to .cb file
74 0x4a N_DEFD GNU Modula2 definition module dependency
80 0x50 N_EHDECL GNU C++ exception variable
80 0x50 N_MOD2 Modula2 info "for imc" (according to Ultrix V4.0)
84 0x54 N_CATCH GNU C++ "catch" clause
96 0x60 N_SSYM structure of union element
100 0x64 N_SO path and name of source file
128 0x80 N_LSYM automatic var in the stack
(also used for type desc.)
130 0x82 N_BINCL beginning of an include file (Sun only)
132 0x84 N_SOL Name of sub-source (#include) file.
160 0xa0 N_PSYM parameter variable
162 0xa2 N_EINCL end of an include file
164 0xa4 N_ENTRY alternate entry point
192 0xc0 N_LBRAC beginning of a lexical block
194 0xc2 N_EXCL place holder for a deleted include file
196 0xc4 N_SCOPE modula2 scope information (Sun linker)
224 0xe0 N_RBRAC end of a lexical block
226 0xe2 N_BCOMM begin named common block
228 0xe4 N_ECOMM end named common block
232 0xe8 N_ECOML end common (local name)
<< used on Gould systems for non-base registers syms >>
240 0xf0 N_NBTEXT ??
242 0xf2 N_NBDATA ??
244 0xf4 N_NBBSS ??
246 0xf6 N_NBSTS ??
248 0xf8 N_NBLCS ??
@end smallexample
@node Assembler types
@appendix Table B: Symbol types from assembler and linker
Table B shows the types of symbol table entries that hold assembler
and linker symbols.
The #define names for these n_types values are defined in
/include/aout/aout64.h
@smallexample
dec hex #define
n_type n_type name used to describe
------------------------------------------
1 0x0 N_UNDF undefined symbol
2 0x2 N_ABS absolute symbol -- defined at a particular address
3 0x3 extern " (vs. file scope)
4 0x4 N_TEXT text symbol -- defined at offset in text segment
5 0x5 extern " (vs. file scope)
6 0x6 N_DATA data symbol -- defined at offset in data segment
7 0x7 extern " (vs. file scope)
8 0x8 N_BSS BSS symbol -- defined at offset in zero'd segment
9 extern " (vs. file scope)
12 0x0C N_FN_SEQ func name for Sequent compilers (stab exception)
49 0x12 N_COMM common sym -- visable after shared lib dynamic link
31 0x1f N_FN file name of a .o file
@end smallexample
@node Symbol Descriptors
@appendix Table C: Symbol descriptors
@c Please keep this alphabetical
@table @code
@item @var{(digit)}
@itemx (
@itemx -
Local variable, @xref{Automatic variables}.
@item a
Parameter passed by reference in register, @xref{Parameters}.
@item c
Constant, @xref{Constants}.
@item C
Conformant array bound (Pascal, maybe other languages),
@xref{Parameters}. Name of a caught exception (GNU C++). These can be
distinguished because the latter uses N_CATCH and the former uses
another symbol type.
@item d
Floating point register variable, @xref{Register variables}.
@item D
Parameter in floating point register, @xref{Parameters}.
@item f
Static function, @xref{Procedures}.
@item F
Global function, @xref{Procedures}.
@item G
Global variable, @xref{Global Variables}.
@item i
@xref{Parameters}.
@item I
Internal (nested) procedure, @xref{Procedures}.
@item J
Internal (nested) function, @xref{Procedures}.
@item L
Label name (documented by AIX, no further information known).
@item m
Module, @xref{Procedures}.
@item p
Argument list parameter, @xref{Parameters}.
@item pP
@xref{Parameters}.
@item pF
FORTRAN Function parameter, @xref{Parameters}.
@item P
Unfortunately, three separate meanings have been independently invented
for this symbol descriptor. At least the GNU and Sun uses can be
distinguished by the symbol type. Global Procedure (AIX) (symbol type
used unknown), @xref{Procedures}. Register parameter (GNU) (symbol type
N_PSYM), @xref{Parameters}. Prototype of function referenced by this
file (Sun acc) (symbol type N_FUN).
@item Q
Static Procedure, @xref{Procedures}.
@item R
Register parameter @xref{Parameters}.
@item r
Register variable, @xref{Register variables}.
@item S
Static file scope variable @xref{Initialized statics},
@xref{Un-initialized statics}.
@item t
Type name, @xref{Typedefs}.
@item T
enumeration, struct or union tag, @xref{Typedefs}.
@item v
Parameter passed by reference, @xref{Parameters}.
@item V
Static procedure scope variable @xref{Initialized statics},
@xref{Un-initialized statics}.
@item x
Conformant array, @xref{Parameters}.
@item X
Function return variable, @xref{Parameters}.
@end table
@node Type Descriptors
@appendix Table D: Type Descriptors
@table @code
@item @var{digit}
@itemx (
Type reference, @xref{Stabs Format}.
@item -
Reference to builtin type, @xref{Negative Type Numbers}.
@item #
Method (C++), @xref{Cplusplus}.
@item *
Pointer, @xref{Miscellaneous Types}.
@item &
Reference (C++).
@item @@
Type Attributes (AIX), @xref{Stabs Format}. Member (class and variable)
type (GNU C++), @xref{Cplusplus}.
@item a
Array, @xref{Arrays}.
@item A
Open array, @xref{Arrays}.
@item b
Pascal space type (AIX), @xref{Miscellaneous Types}. Builtin integer
type (Sun), @xref{Builtin Type Descriptors}.
@item B
Volatile-qualified type, @xref{Miscellaneous Types}.
@item c
Complex builtin type, @xref{Builtin Type Descriptors}.
@item C
COBOL Picture type. See AIX documentation for details.
@item d
File type, @xref{Miscellaneous Types}.
@item D
N-dimensional dynamic array, @xref{Arrays}.
@item e
Enumeration type, @xref{Enumerations}.
@item E
N-dimensional subarray, @xref{Arrays}.
@item f
Function type, @xref{Function types}.
@item g
Builtin floating point type, @xref{Builtin Type Descriptors}.
@item G
COBOL Group. See AIX documentation for details.
@item i
Imported type, @xref{Cross-references}.
@item k
Const-qualified type, @xref{Miscellaneous Types}.
@item K
COBOL File Descriptor. See AIX documentation for details.
@item n
String type, @xref{Strings}.
@item N
Stringptr, @xref{Strings}.
@item M
Multiple instance type, @xref{Miscellaneous Types}.
@item o
Opaque type, @xref{Typedefs}.
@item P
Packed array, @xref{Arrays}.
@item r
Range type, @xref{Subranges}.
@item R
Builtin floating type, @xref{Builtin Type Descriptors}.
@item s
Structure type, @xref{Structures}.
@item S
Set type, @xref{Miscellaneous Types}.
@item u
Union, @xref{Unions}.
@item v
Variant record. This is a Pascal and Modula-2 feature which is like a
union within a struct in C. See AIX documentation for details.
@item w
Wide character, @xref{Builtin Type Descriptors}.
@item x
Cross-reference, @xref{Cross-references}.
@item z
gstring, @xref{Strings}.
@end table
@node Expanded reference
@appendix Expanded reference by stab type.
@c FIXME: For most types this should be much shorter and much sweeter,
@c see N_PSYM or N_SO for an example.
@c FIXME: It probably should be merged with Tables A and B.
Format of an entry:
The first line is the symbol type expressed in decimal, hexadecimal,
and as a #define (see devo/include/aout/stab.def).
The second line describes the language constructs the symbol type
represents.
The third line is the stab format with the significant stab fields
named and the rest NIL.
Subsequent lines expand upon the meaning and possible values for each
significant stab field. # stands in for the type descriptor.
Finally, any further information.
@menu
* N_GSYM:: Global variable
* N_FNAME:: Function name (BSD Fortran)
* N_FUN:: C Function name or text segment variable
* N_STSYM:: Initialized static symbol
* N_LCSYM:: Uninitialized static symbol
* N_MAIN:: Name of main routine (not for C)
* N_PC:: Pascal global symbol
* N_NSYMS:: Number of symbols
* N_NOMAP:: No DST map
* N_RSYM:: Register variable
* N_M2C:: Modula-2 compilation unit
* N_SLINE: Line Numbers. Line number in text segment
* N_DSLINE: Line Numbers. Line number in data segment
* N_BSLINE: Line Numbers. Line number in bss segment
* N_BROWS:: Path to .cb file for Sun source code browser
* N_DEFD:: GNU Modula2 definition module dependency
* N_EHDECL:: GNU C++ exception variable
* N_MOD2:: Modula2 information "for imc"
* N_CATCH:: GNU C++ "catch" clause
* N_SSYM:: Structure or union element
* N_SO: Source Files. Source file
* N_LSYM:: Automatic variable
* N_BINCL: Source Files. Beginning of include file
* N_SOL: Source Files. Name of include file
* N_PSYM: Parameters. Parameter variable
* N_EINCL: Source Files. End of include file
* N_ENTRY:: Alternate entry point
* N_LBRAC:: Beginning of lexical block
* N_EXCL: Source Files. Deleted include file
* N_SCOPE:: Modula2 scope information (Sun only)
* N_RBRAC:: End of lexical block
* N_BCOMM:: Begin named common block
* N_ECOMM:: End named common block
* N_ECOML:: End common
* Gould:: non-base register symbols used on Gould systems
* N_LENG:: Length of preceding entry
@end menu
@node N_GSYM
@section 32 - 0x20 - N_GYSM
@display
Global variable.
.stabs "name", N_GSYM, NIL, NIL, NIL
@end display
@example
"name" -> "symbol_name:#type"
# -> G
@end example
Only the "name" field is significant. The location of the variable is
obtained from the corresponding external symbol.
@node N_FNAME
@section 34 - 0x22 - N_FNAME
Function name (for BSD Fortran)
@display
.stabs "name", N_FNAME, NIL, NIL, NIL
@end display
@example
"name" -> "function_name"
@end example
Only the "name" field is significant. The location of the symbol is
obtained from the corresponding extern symbol.
@node N_FUN
@section 36 - 0x24 - N_FUN
Function name (@pxref{Procedures}) or text segment variable
(@pxref{Variables}).
@example
@exdent @emph{For functions:}
"name" -> "proc_name:#return_type"
# -> F (global function)
f (local function)
desc -> line num for proc start. (GCC doesn't set and DBX doesn't miss it.)
value -> Code address of proc start.
@exdent @emph{For text segment variables:}
<<How to create one?>>
@end example
@node N_STSYM
@section 38 - 0x26 - N_STSYM
Initialized static symbol (data segment w/internal linkage).
@display
.stabs "name", N_STSYM, NIL, NIL, value
@end display
@example
"name" -> "symbol_name#type"
# -> S (scope global to compilation unit)
-> V (scope local to a procedure)
value -> Data Address
@end example
@node N_LCSYM
@section 40 - 0x28 - N_LCSYM
Unitialized static (.lcomm) symbol(BSS segment w/internal linkage).
@display
.stabs "name", N_LCLSYM, NIL, NIL, value
@end display
@example
"name" -> "symbol_name#type"
# -> S (scope global to compilation unit)
-> V (scope local to procedure)
value -> BSS Address
@end example
@node N_MAIN
@section 42 - 0x2a - N_MAIN
Name of main routine (not used in C)
@display
.stabs "name", N_MAIN, NIL, NIL, NIL
@end display
@example
"name" -> "name_of_main_routine"
@end example
@node N_PC
@section 48 - 0x30 - N_PC
Global symbol (for Pascal)
@display
.stabs "name", N_PC, NIL, NIL, value
@end display
@example
"name" -> "symbol_name" <<?>>
value -> supposedly the line number (stab.def is skeptical)
@end example
@display
stabdump.c says:
global pascal symbol: name,,0,subtype,line
<< subtype? >>
@end display
@node N_NSYMS
@section 50 - 0x32 - N_NSYMS
Number of symbols (according to Ultrix V4.0)
@display
0, files,,funcs,lines (stab.def)
@end display
@node N_NOMAP
@section 52 - 0x34 - N_NOMAP
no DST map for sym (according to Ultrix V4.0)
@display
name, ,0,type,ignored (stab.def)
@end display
@node N_RSYM
@section 64 - 0x40 - N_RSYM
register variable
@display
.stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc)
@end display
@node N_M2C
@section 66 - 0x42 - N_M2C
Modula-2 compilation unit
@display
.stabs "name", N_M2C, 0, desc, value
@end display
@example
"name" -> "unit_name,unit_time_stamp[,code_time_stamp]
desc -> unit_number
value -> 0 (main unit)
1 (any other unit)
@end example
@node N_BROWS
@section 72 - 0x48 - N_BROWS
Sun source code browser, path to .cb file
<<?>>
"path to associated .cb file"
Note: type field value overlaps with N_BSLINE
@node N_DEFD
@section 74 - 0x4a - N_DEFD
GNU Modula2 definition module dependency
GNU Modula-2 definition module dependency. Value is the modification
time of the definition file. Other is non-zero if it is imported with
the GNU M2 keyword %INITIALIZE. Perhaps N_M2C can be used if there
are enough empty fields?
@node N_EHDECL
@section 80 - 0x50 - N_EHDECL
GNU C++ exception variable <<?>>
"name is variable name"
Note: conflicts with N_MOD2.
@node N_MOD2
@section 80 - 0x50 - N_MOD2
Modula2 info "for imc" (according to Ultrix V4.0)
Note: conflicts with N_EHDECL <<?>>
@node N_CATCH
@section 84 - 0x54 - N_CATCH
GNU C++ "catch" clause
GNU C++ `catch' clause. Value is its address. Desc is nonzero if
this entry is immediately followed by a CAUGHT stab saying what
exception was caught. Multiple CAUGHT stabs means that multiple
exceptions can be caught here. If Desc is 0, it means all exceptions
are caught here.
@node N_SSYM
@section 96 - 0x60 - N_SSYM
Structure or union element
Value is offset in the structure.
<<?looking at structs and unions in C I didn't see these>>
@node N_LSYM
@section 128 - 0x80 - N_LSYM
Automatic var in the stack (also used for type descriptors.)
@display
.stabs "name" N_LSYM, NIL, NIL, value
@end display
@example
@exdent @emph{For stack based local variables:}
"name" -> name of the variable
value -> offset from frame pointer (negative)
@exdent @emph{For type descriptors:}
"name" -> "name_of_the_type:#type"
# -> t
type -> type_ref (or) type_def
type_ref -> type_number
type_def -> type_number=type_desc etc.
@end example
Type may be either a type reference or a type definition. A type
reference is a number that refers to a previously defined type. A
type definition is the number that will refer to this type, followed
by an equals sign, a type descriptor and the additional data that
defines the type. See the Table D for type descriptors and the
section on types for what data follows each type descriptor.
@node N_ENTRY
@section 164 - 0xa4 - N_ENTRY
Alternate entry point.
Value is its address.
<<?>>
@node N_LBRAC
@section 192 - 0xc0 - N_LBRAC
Beginning of a lexical block (left brace). The variable defined
inside the block precede the N_LBRAC symbol. Or can they follow as
well as long as a new N_FUNC was not encountered. <<?>>
@display
.stabn N_LBRAC, NIL, NIL, value
@end display
@example
value -> code address of block start.
@end example
@node N_SCOPE
@section 196 - 0xc4 - N_SCOPE
Modula2 scope information (Sun linker)
<<?>>
@node N_RBRAC
@section 224 - 0xe0 - N_RBRAC
End of a lexical block (right brace)
@display
.stabn N_RBRAC, NIL, NIL, value
@end display
@example
value -> code address of the end of the block.
@end example
@node N_BCOMM
@section 226 - 0xe2 - N_BCOMM
Begin named common block.
Only the name is significant.
<<?>>
@node N_ECOMM
@section 228 - 0xe4 - N_ECOMM
End named common block.
Only the name is significant and it should match the N_BCOMM
<<?>>
@node N_ECOML
@section 232 - 0xe8 - N_ECOML
End common (local name)
value is address.
<<?>>
@node Gould
@section Non-base registers on Gould systems
<< used on Gould systems for non-base registers syms, values assigned
at random, need real info from Gould. >>
<<?>>
@example
240 0xf0 N_NBTEXT ??
242 0xf2 N_NBDATA ??
244 0xf4 N_NBBSS ??
246 0xf6 N_NBSTS ??
248 0xf8 N_NBLCS ??
@end example
@node N_LENG
@section - 0xfe - N_LENG
Second symbol entry containing a length-value for the preceding entry.
The value is the length.
@node Questions
@appendix Questions and anomalies
@itemize @bullet
@item
For GNU C stabs defining local and global variables (N_LSYM and
N_GSYM), the desc field is supposed to contain the source line number
on which the variable is defined. In reality the desc field is always
0. (This behavour is defined in dbxout.c and putting a line number in
desc is controlled by #ifdef WINNING_GDB which defaults to false). Gdb
supposedly uses this information if you say 'list var'. In reality
var can be a variable defined in the program and gdb says `function
var not defined'
@item
In GNU C stabs there seems to be no way to differentiate tag types:
structures, unions, and enums (symbol descriptor T) and typedefs
(symbol descriptor t) defined at file scope from types defined locally
to a procedure or other more local scope. They all use the N_LSYM
stab type. Types defined at procedure scope are emited after the
N_RBRAC of the preceding function and before the code of the
procedure in which they are defined. This is exactly the same as
types defined in the source file between the two procedure bodies.
GDB overcompensates by placing all types in block #1, the block for
symbols of file scope. This is true for default, -ansi and
-traditional compiler options. (Bugs gcc/1063, gdb/1066.)
@item
What ends the procedure scope? Is it the proc block's N_RBRAC or the
next N_FUN? (I believe its the first.)
@item
The comment in xcoff.h says DBX_STATIC_CONST_VAR_CODE is used for
static const variables. DBX_STATIC_CONST_VAR_CODE is set to N_FUN by
default, in dbxout.c. If included, xcoff.h redefines it to N_STSYM.
But testing the default behaviour, my Sun4 native example shows
N_STSYM not N_FUN is used to describe file static initialized
variables. (the code tests for TREE_READONLY(decl) &&
!TREE_THIS_VOLATILE(decl) and if true uses DBX_STATIC_CONST_VAR_CODE).
@item
Global variable stabs don't have location information. This comes
from the external symbol for the same variable. The external symbol
has a leading underbar on the _name of the variable and the stab does
not. How do we know these two symbol table entries are talking about
the same symbol when their names are different?
@item
Can gcc be configured to output stabs the way the Sun compiler
does, so that their native debugging tools work? <NO?> It doesn't by
default. GDB reads either format of stab. (gcc or SunC). How about
dbx?
@end itemize
@node xcoff-differences
@appendix Differences between GNU stabs in a.out and GNU stabs in xcoff
@c FIXME: Merge *all* these into the main body of the document.
(The AIX/RS6000 native object file format is xcoff with stabs). This
appendix only covers those differences which are not covered in the main
body of this document.
@itemize @bullet
@item
BSD a.out stab types correspond to AIX xcoff storage classes. In general the
mapping is N_STABTYPE becomes C_STABTYPE. Some stab types in a.out
are not supported in xcoff. See Table E. for full mappings.
exception:
initialised static N_STSYM and un-initialized static N_LCSYM both map
to the C_STSYM storage class. But the destinction is preserved
because in xcoff N_STSYM and N_LCSYM must be emited in a named static
block. Begin the block with .bs s[RW] data_section_name for N_STSYM
or .bs s bss_section_name for N_LCSYM. End the block with .es
@item
If the xcoff stab is a N_FUN (C_FUN) then follow the string field with
,. instead of just ,
@end itemize
(I think that's it for .s file differences. They could stand to be
better presented. This is just a list of what I have noticed so far.
There are a *lot* of differences in the information in the symbol
tables of the executable and object files.)
Table E: mapping a.out stab types to xcoff storage classes
@example
stab type storage class
-------------------------------
N_GSYM C_GSYM
N_FNAME unknown
N_FUN C_FUN
N_STSYM C_STSYM
N_LCSYM C_STSYM
N_MAIN unkown
N_PC unknown
N_RSYM C_RSYM
N_RPSYM (0x8e) C_RPSYM
N_M2C unknown
N_SLINE unknown
N_DSLINE unknown
N_BSLINE unknown
N_BROWSE unchanged
N_CATCH unknown
N_SSYM unknown
N_SO unknown
N_LSYM C_LSYM
N_DECL (0x8c) C_DECL
N_BINCL unknown
N_SOL unknown
N_PSYM C_PSYM
N_EINCL unknown
N_ENTRY C_ENTRY
N_LBRAC unknown
N_EXCL unknown
N_SCOPE unknown
N_RBRAC unknown
N_BCOMM C_BCOMM
N_ECOMM C_ECOMM
N_ECOML C_ECOML
N_LENG unknown
@end example
@node Sun-differences
@appendix Differences between GNU stabs and Sun native stabs.
@c FIXME: Merge all this stuff into the main body of the document.
@itemize @bullet
@item
GNU C stabs define *all* types, file or procedure scope, as
N_LSYM. Sun doc talks about using N_GSYM too.
@item
Stabs describing block scopes, N_LBRAC and N_RBRAC are supposed to
contain the nesting level of the block in the desc field, re Sun doc.
GNU stabs always have 0 in that field. dbx seems not to care.
@item
Sun C stabs use type number pairs in the format (a,b) where a is a
number starting with 1 and incremented for each sub-source file in the
compilation. b is a number starting with 1 and incremented for each
new type defined in the compilation. GNU C stabs use the type number
alone, with no source file number.
@end itemize
@contents
@bye
|