aboutsummaryrefslogtreecommitdiff
path: root/gdb/go32-nat.c
blob: bcb400a3e1d7881f659ba95fcf17e9212fed177d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
/* Native debugging support for Intel x86 running DJGPP.
   Copyright (C) 1997-2020 Free Software Foundation, Inc.
   Written by Robert Hoehne.

   This file is part of GDB.

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

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

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

/* To whomever it may concern, here's a general description of how
   debugging in DJGPP works, and the special quirks GDB does to
   support that.

   When the DJGPP port of GDB is debugging a DJGPP program natively,
   there aren't 2 separate processes, the debuggee and GDB itself, as
   on other systems.  (This is DOS, where there can only be one active
   process at any given time, remember?)  Instead, GDB and the
   debuggee live in the same process.  So when GDB calls
   go32_create_inferior below, and that function calls edi_init from
   the DJGPP debug support library libdbg.a, we load the debuggee's
   executable file into GDB's address space, set it up for execution
   as the stub loader (a short real-mode program prepended to each
   DJGPP executable) normally would, and do a lot of preparations for
   swapping between GDB's and debuggee's internal state, primarily wrt
   the exception handlers.  This swapping happens every time we resume
   the debuggee or switch back to GDB's code, and it includes:

    . swapping all the segment registers
    . swapping the PSP (the Program Segment Prefix)
    . swapping the signal handlers
    . swapping the exception handlers
    . swapping the FPU status
    . swapping the 3 standard file handles (more about this below)

   Then running the debuggee simply means longjmp into it where its PC
   is and let it run until it stops for some reason.  When it stops,
   GDB catches the exception that stopped it and longjmp's back into
   its own code.  All the possible exit points of the debuggee are
   watched; for example, the normal exit point is recognized because a
   DOS program issues a special system call to exit.  If one of those
   exit points is hit, we mourn the inferior and clean up after it.
   Cleaning up is very important, even if the process exits normally,
   because otherwise we might leave behind traces of previous
   execution, and in several cases GDB itself might be left hosed,
   because all the exception handlers were not restored.

   Swapping of the standard handles (in redir_to_child and
   redir_to_debugger) is needed because, since both GDB and the
   debuggee live in the same process, as far as the OS is concerned,
   the share the same file table.  This means that the standard
   handles 0, 1, and 2 point to the same file table entries, and thus
   are connected to the same devices.  Therefore, if the debugger
   redirects its standard output, the standard output of the debuggee
   is also automagically redirected to the same file/device!
   Similarly, if the debuggee redirects its stdout to a file, you
   won't be able to see debugger's output (it will go to the same file
   where the debuggee has its output); and if the debuggee closes its
   standard input, you will lose the ability to talk to debugger!

   For this reason, every time the debuggee is about to be resumed, we
   call redir_to_child, which redirects the standard handles to where
   the debuggee expects them to be.  When the debuggee stops and GDB
   regains control, we call redir_to_debugger, which redirects those 3
   handles back to where GDB expects.

   Note that only the first 3 handles are swapped, so if the debuggee
   redirects or closes any other handles, GDB will not notice.  In
   particular, the exit code of a DJGPP program forcibly closes all
   file handles beyond the first 3 ones, so when the debuggee exits,
   GDB currently loses its stdaux and stdprn streams.  Fortunately,
   GDB does not use those as of this writing, and will never need
   to.  */

#include "defs.h"

#include <fcntl.h>

#include "x86-nat.h"
#include "inferior.h"
#include "infrun.h"
#include "gdbthread.h"
#include "gdbsupport/gdb_wait.h"
#include "gdbcore.h"
#include "command.h"
#include "gdbcmd.h"
#include "floatformat.h"
#include "buildsym-legacy.h"
#include "i387-tdep.h"
#include "i386-tdep.h"
#include "nat/x86-cpuid.h"
#include "value.h"
#include "regcache.h"
#include "top.h"
#include "cli/cli-utils.h"
#include "inf-child.h"

#include <ctype.h>
#include <unistd.h>
#include <sys/utsname.h>
#include <io.h>
#include <dos.h>
#include <dpmi.h>
#include <go32.h>
#include <sys/farptr.h>
#include <debug/v2load.h>
#include <debug/dbgcom.h>
#if __DJGPP_MINOR__ > 2
#include <debug/redir.h>
#endif

#include <langinfo.h>

#if __DJGPP_MINOR__ < 3
/* This code will be provided from DJGPP 2.03 on.  Until then I code it
   here.  */
typedef struct
  {
    unsigned short sig0;
    unsigned short sig1;
    unsigned short sig2;
    unsigned short sig3;
    unsigned short exponent:15;
    unsigned short sign:1;
  }
NPXREG;

typedef struct
  {
    unsigned int control;
    unsigned int status;
    unsigned int tag;
    unsigned int eip;
    unsigned int cs;
    unsigned int dataptr;
    unsigned int datasel;
    NPXREG reg[8];
  }
NPX;

static NPX npx;

static void save_npx (void);	/* Save the FPU of the debugged program.  */
static void load_npx (void);	/* Restore the FPU of the debugged program.  */

/* ------------------------------------------------------------------------- */
/* Store the contents of the NPX in the global variable `npx'.  */
/* *INDENT-OFF* */

static void
save_npx (void)
{
  asm ("inb    $0xa0, %%al  \n\
       testb $0x20, %%al    \n\
       jz 1f 	    	    \n\
       xorb %%al, %%al	    \n\
       outb %%al, $0xf0     \n\
       movb $0x20, %%al	    \n\
       outb %%al, $0xa0     \n\
       outb %%al, $0x20     \n\
1:     	       	   	    \n\
       fnsave %0	    \n\
       fwait "
:     "=m" (npx)
:				/* No input */
:     "%eax");
}

/* *INDENT-ON* */


/* ------------------------------------------------------------------------- */
/* Reload the contents of the NPX from the global variable `npx'.  */

static void
load_npx (void)
{
  asm ("frstor %0":"=m" (npx));
}
/* ------------------------------------------------------------------------- */
/* Stubs for the missing redirection functions.  */
typedef struct {
  char *command;
  int redirected;
} cmdline_t;

void
redir_cmdline_delete (cmdline_t *ptr)
{
  ptr->redirected = 0;
}

int
redir_cmdline_parse (const char *args, cmdline_t *ptr)
{
  return -1;
}

int
redir_to_child (cmdline_t *ptr)
{
  return 1;
}

int
redir_to_debugger (cmdline_t *ptr)
{
  return 1;
}

int
redir_debug_init (cmdline_t *ptr)
{
  return 0;
}
#endif /* __DJGPP_MINOR < 3 */

typedef enum { wp_insert, wp_remove, wp_count } wp_op;

/* This holds the current reference counts for each debug register.  */
static int dr_ref_count[4];

#define SOME_PID 42

static int prog_has_started = 0;

#define r_ofs(x) (offsetof(TSS,x))

static struct
{
  size_t tss_ofs;
  size_t size;
}
regno_mapping[] =
{
  {r_ofs (tss_eax), 4},	/* normal registers, from a_tss */
  {r_ofs (tss_ecx), 4},
  {r_ofs (tss_edx), 4},
  {r_ofs (tss_ebx), 4},
  {r_ofs (tss_esp), 4},
  {r_ofs (tss_ebp), 4},
  {r_ofs (tss_esi), 4},
  {r_ofs (tss_edi), 4},
  {r_ofs (tss_eip), 4},
  {r_ofs (tss_eflags), 4},
  {r_ofs (tss_cs), 2},
  {r_ofs (tss_ss), 2},
  {r_ofs (tss_ds), 2},
  {r_ofs (tss_es), 2},
  {r_ofs (tss_fs), 2},
  {r_ofs (tss_gs), 2},
  {0, 10},		/* 8 FP registers, from npx.reg[] */
  {1, 10},
  {2, 10},
  {3, 10},
  {4, 10},
  {5, 10},
  {6, 10},
  {7, 10},
	/* The order of the next 7 registers must be consistent
	   with their numbering in config/i386/tm-i386.h, which see.  */
  {0, 2},		/* control word, from npx */
  {4, 2},		/* status word, from npx */
  {8, 2},		/* tag word, from npx */
  {16, 2},		/* last FP exception CS from npx */
  {12, 4},		/* last FP exception EIP from npx */
  {24, 2},		/* last FP exception operand selector from npx */
  {20, 4},		/* last FP exception operand offset from npx */
  {18, 2}		/* last FP opcode from npx */
};

static struct
  {
    int go32_sig;
    enum gdb_signal gdb_sig;
  }
sig_map[] =
{
  {0, GDB_SIGNAL_FPE},
  {1, GDB_SIGNAL_TRAP},
  /* Exception 2 is triggered by the NMI.  DJGPP handles it as SIGILL,
     but I think SIGBUS is better, since the NMI is usually activated
     as a result of a memory parity check failure.  */
  {2, GDB_SIGNAL_BUS},
  {3, GDB_SIGNAL_TRAP},
  {4, GDB_SIGNAL_FPE},
  {5, GDB_SIGNAL_SEGV},
  {6, GDB_SIGNAL_ILL},
  {7, GDB_SIGNAL_EMT},	/* no-coprocessor exception */
  {8, GDB_SIGNAL_SEGV},
  {9, GDB_SIGNAL_SEGV},
  {10, GDB_SIGNAL_BUS},
  {11, GDB_SIGNAL_SEGV},
  {12, GDB_SIGNAL_SEGV},
  {13, GDB_SIGNAL_SEGV},
  {14, GDB_SIGNAL_SEGV},
  {16, GDB_SIGNAL_FPE},
  {17, GDB_SIGNAL_BUS},
  {31, GDB_SIGNAL_ILL},
  {0x1b, GDB_SIGNAL_INT},
  {0x75, GDB_SIGNAL_FPE},
  {0x78, GDB_SIGNAL_ALRM},
  {0x79, GDB_SIGNAL_INT},
  {0x7a, GDB_SIGNAL_QUIT},
  {-1, GDB_SIGNAL_LAST}
};

static struct {
  enum gdb_signal gdb_sig;
  int djgpp_excepno;
} excepn_map[] = {
  {GDB_SIGNAL_0, -1},
  {GDB_SIGNAL_ILL, 6},	/* Invalid Opcode */
  {GDB_SIGNAL_EMT, 7},	/* triggers SIGNOFP */
  {GDB_SIGNAL_SEGV, 13},	/* GPF */
  {GDB_SIGNAL_BUS, 17},	/* Alignment Check */
  /* The rest are fake exceptions, see dpmiexcp.c in djlsr*.zip for
     details.  */
  {GDB_SIGNAL_TERM, 0x1b},	/* triggers Ctrl-Break type of SIGINT */
  {GDB_SIGNAL_FPE, 0x75},
  {GDB_SIGNAL_INT, 0x79},
  {GDB_SIGNAL_QUIT, 0x7a},
  {GDB_SIGNAL_ALRM, 0x78},	/* triggers SIGTIMR */
  {GDB_SIGNAL_PROF, 0x78},
  {GDB_SIGNAL_LAST, -1}
};

/* The go32 target.  */

struct go32_nat_target final : public x86_nat_target<inf_child_target>
{
  void attach (const char *, int) override;

  void resume (ptid_t, int, enum gdb_signal) override;

  ptid_t wait (ptid_t, struct target_waitstatus *, int) override;

  void fetch_registers (struct regcache *, int) override;
  void store_registers (struct regcache *, int) override;

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

  void files_info () override;

  void terminal_init () override;

  void terminal_inferior () override;

  void terminal_ours_for_output () override;

  void terminal_ours () override;

  void terminal_info (const char *, int) override;

  void pass_ctrlc () override;

  void kill () override;

  void create_inferior (const char *, const std::string &,
			char **, int) override;

  void mourn_inferior () override;

  bool thread_alive (ptid_t ptid) override;

  std::string pid_to_str (ptid_t) override;
};

static go32_nat_target the_go32_nat_target;

void
go32_nat_target::attach (const char *args, int from_tty)
{
  error (_("\
You cannot attach to a running program on this platform.\n\
Use the `run' command to run DJGPP programs."));
}

static int resume_is_step;
static int resume_signal = -1;

void
go32_nat_target::resume (ptid_t ptid, int step, enum gdb_signal siggnal)
{
  int i;

  resume_is_step = step;

  if (siggnal != GDB_SIGNAL_0 && siggnal != GDB_SIGNAL_TRAP)
  {
    for (i = 0, resume_signal = -1;
	 excepn_map[i].gdb_sig != GDB_SIGNAL_LAST; i++)
      if (excepn_map[i].gdb_sig == siggnal)
      {
	resume_signal = excepn_map[i].djgpp_excepno;
	break;
      }
    if (resume_signal == -1)
      printf_unfiltered ("Cannot deliver signal %s on this platform.\n",
			 gdb_signal_to_name (siggnal));
  }
}

static char child_cwd[FILENAME_MAX];

ptid_t
go32_nat_target::wait (ptid_t ptid, struct target_waitstatus *status,
		       int options)
{
  int i;
  unsigned char saved_opcode;
  unsigned long INT3_addr = 0;
  int stepping_over_INT = 0;

  a_tss.tss_eflags &= 0xfeff;	/* Reset the single-step flag (TF).  */
  if (resume_is_step)
    {
      /* If the next instruction is INT xx or INTO, we need to handle
	 them specially.  Intel manuals say that these instructions
	 reset the single-step flag (a.k.a. TF).  However, it seems
	 that, at least in the DPMI environment, and at least when
	 stepping over the DPMI interrupt 31h, the problem is having
	 TF set at all when INT 31h is executed: the debuggee either
	 crashes (and takes the system with it) or is killed by a
	 SIGTRAP.

	 So we need to emulate single-step mode: we put an INT3 opcode
	 right after the INT xx instruction, let the debuggee run
	 until it hits INT3 and stops, then restore the original
	 instruction which we overwrote with the INT3 opcode, and back
	 up the debuggee's EIP to that instruction.  */
      read_child (a_tss.tss_eip, &saved_opcode, 1);
      if (saved_opcode == 0xCD || saved_opcode == 0xCE)
	{
	  unsigned char INT3_opcode = 0xCC;

	  INT3_addr
	    = saved_opcode == 0xCD ? a_tss.tss_eip + 2 : a_tss.tss_eip + 1;
	  stepping_over_INT = 1;
	  read_child (INT3_addr, &saved_opcode, 1);
	  write_child (INT3_addr, &INT3_opcode, 1);
	}
      else
	a_tss.tss_eflags |= 0x0100; /* normal instruction: set TF */
    }

  /* The special value FFFFh in tss_trap indicates to run_child that
     tss_irqn holds a signal to be delivered to the debuggee.  */
  if (resume_signal <= -1)
    {
      a_tss.tss_trap = 0;
      a_tss.tss_irqn = 0xff;
    }
  else
    {
      a_tss.tss_trap = 0xffff;	/* run_child looks for this.  */
      a_tss.tss_irqn = resume_signal;
    }

  /* The child might change working directory behind our back.  The
     GDB users won't like the side effects of that when they work with
     relative file names, and GDB might be confused by its current
     directory not being in sync with the truth.  So we always make a
     point of changing back to where GDB thinks is its cwd, when we
     return control to the debugger, but restore child's cwd before we
     run it.  */
  /* Initialize child_cwd, before the first call to run_child and not
     in the initialization, so the child get also the changed directory
     set with the gdb-command "cd ..."  */
  if (!*child_cwd)
    /* Initialize child's cwd with the current one.  */
    getcwd (child_cwd, sizeof (child_cwd));

  chdir (child_cwd);

#if __DJGPP_MINOR__ < 3
  load_npx ();
#endif
  run_child ();
#if __DJGPP_MINOR__ < 3
  save_npx ();
#endif

  /* Did we step over an INT xx instruction?  */
  if (stepping_over_INT && a_tss.tss_eip == INT3_addr + 1)
    {
      /* Restore the original opcode.  */
      a_tss.tss_eip--;	/* EIP points *after* the INT3 instruction.  */
      write_child (a_tss.tss_eip, &saved_opcode, 1);
      /* Simulate a TRAP exception.  */
      a_tss.tss_irqn = 1;
      a_tss.tss_eflags |= 0x0100;
    }

  getcwd (child_cwd, sizeof (child_cwd)); /* in case it has changed */
  if (current_directory != NULL)
    chdir (current_directory);

  if (a_tss.tss_irqn == 0x21)
    {
      status->kind = TARGET_WAITKIND_EXITED;
      status->value.integer = a_tss.tss_eax & 0xff;
    }
  else
    {
      status->value.sig = GDB_SIGNAL_UNKNOWN;
      status->kind = TARGET_WAITKIND_STOPPED;
      for (i = 0; sig_map[i].go32_sig != -1; i++)
	{
	  if (a_tss.tss_irqn == sig_map[i].go32_sig)
	    {
#if __DJGPP_MINOR__ < 3
	      if ((status->value.sig = sig_map[i].gdb_sig) !=
		  GDB_SIGNAL_TRAP)
		status->kind = TARGET_WAITKIND_SIGNALLED;
#else
	      status->value.sig = sig_map[i].gdb_sig;
#endif
	      break;
	    }
	}
    }
  return ptid_t (SOME_PID);
}

static void
fetch_register (struct regcache *regcache, int regno)
{
  struct gdbarch *gdbarch = regcache->arch ();
  if (regno < gdbarch_fp0_regnum (gdbarch))
    regcache->raw_supply (regno,
			  (char *) &a_tss + regno_mapping[regno].tss_ofs);
  else if (i386_fp_regnum_p (gdbarch, regno) || i386_fpc_regnum_p (gdbarch,
								   regno))
    i387_supply_fsave (regcache, regno, &npx);
  else
    internal_error (__FILE__, __LINE__,
		    _("Invalid register no. %d in fetch_register."), regno);
}

void
go32_nat_target::fetch_registers (struct regcache *regcache, int regno)
{
  if (regno >= 0)
    fetch_register (regcache, regno);
  else
    {
      for (regno = 0;
	   regno < gdbarch_fp0_regnum (regcache->arch ());
	   regno++)
	fetch_register (regcache, regno);
      i387_supply_fsave (regcache, -1, &npx);
    }
}

static void
store_register (const struct regcache *regcache, int regno)
{
  struct gdbarch *gdbarch = regcache->arch ();
  if (regno < gdbarch_fp0_regnum (gdbarch))
    regcache->raw_collect (regno,
			   (char *) &a_tss + regno_mapping[regno].tss_ofs);
  else if (i386_fp_regnum_p (gdbarch, regno) || i386_fpc_regnum_p (gdbarch,
								   regno))
    i387_collect_fsave (regcache, regno, &npx);
  else
    internal_error (__FILE__, __LINE__,
		    _("Invalid register no. %d in store_register."), regno);
}

void
go32_nat_target::store_registers (struct regcache *regcache, int regno)
{
  unsigned r;

  if (regno >= 0)
    store_register (regcache, regno);
  else
    {
      for (r = 0; r < gdbarch_fp0_regnum (regcache->arch ()); r++)
	store_register (regcache, r);
      i387_collect_fsave (regcache, -1, &npx);
    }
}

/* Const-correct version of DJGPP's write_child, which unfortunately
   takes a non-const buffer pointer.  */

static int
my_write_child (unsigned child_addr, const void *buf, unsigned len)
{
  static void *buffer = NULL;
  static unsigned buffer_len = 0;
  int res;

  if (buffer_len < len)
    {
      buffer = xrealloc (buffer, len);
      buffer_len = len;
    }

  memcpy (buffer, buf, len);
  res = write_child (child_addr, buffer, len);
  return res;
}

/* Helper for go32_xfer_partial that handles memory transfers.
   Arguments are like target_xfer_partial.  */

static enum target_xfer_status
go32_xfer_memory (gdb_byte *readbuf, const gdb_byte *writebuf,
		  ULONGEST memaddr, ULONGEST len, ULONGEST *xfered_len)
{
  int res;

  if (writebuf != NULL)
    res = my_write_child (memaddr, writebuf, len);
  else
    res = read_child (memaddr, readbuf, len);

  /* read_child and write_child return zero on success, non-zero on
     failure.  */
  if (res != 0)
    return TARGET_XFER_E_IO;

  *xfered_len = len;
  return TARGET_XFER_OK;
}

/* Target to_xfer_partial implementation.  */

enum target_xfer_status
go32_nat_target::xfer_partial (enum target_object object,
			       const char *annex, gdb_byte *readbuf,
			       const gdb_byte *writebuf, ULONGEST offset,
			       ULONGEST len,
			       ULONGEST *xfered_len)
{
  switch (object)
    {
    case TARGET_OBJECT_MEMORY:
      return go32_xfer_memory (readbuf, writebuf, offset, len, xfered_len);

    default:
      return this->beneath ()->xfer_partial (object, annex,
					     readbuf, writebuf, offset, len,
					     xfered_len);
    }
}

static cmdline_t child_cmd;	/* Parsed child's command line kept here.  */

void
go32_nat_target::files_info ()
{
  printf_unfiltered ("You are running a DJGPP V2 program.\n");
}

void
go32_nat_target::kill_inferior ()
{
  mourn_inferior ();
}

void
go32_nat_target::create_inferior (const char *exec_file,
				  const std::string &allargs,
				  char **env, int from_tty)
{
  extern char **environ;
  jmp_buf start_state;
  char *cmdline;
  char **env_save = environ;
  size_t cmdlen;
  struct inferior *inf;
  int result;
  const char *args = allargs.c_str ();

  /* If no exec file handed to us, get it from the exec-file command -- with
     a good, common error message if none is specified.  */
  if (exec_file == 0)
    exec_file = get_exec_file (1);

  resume_signal = -1;
  resume_is_step = 0;

  /* Initialize child's cwd as empty to be initialized when starting
     the child.  */
  *child_cwd = 0;

  /* Init command line storage.  */
  if (redir_debug_init (&child_cmd) == -1)
    internal_error (__FILE__, __LINE__,
		    _("Cannot allocate redirection storage: "
		      "not enough memory.\n"));

  /* Parse the command line and create redirections.  */
  if (strpbrk (args, "<>"))
    {
      if (redir_cmdline_parse (args, &child_cmd) == 0)
	args = child_cmd.command;
      else
	error (_("Syntax error in command line."));
    }
  else
    child_cmd.command = xstrdup (args);

  cmdlen = strlen (args);
  /* v2loadimage passes command lines via DOS memory, so it cannot
     possibly handle commands longer than 1MB.  */
  if (cmdlen > 1024*1024)
    error (_("Command line too long."));

  cmdline = (char *) xmalloc (cmdlen + 4);
  strcpy (cmdline + 1, args);
  /* If the command-line length fits into DOS 126-char limits, use the
     DOS command tail format; otherwise, tell v2loadimage to pass it
     through a buffer in conventional memory.  */
  if (cmdlen < 127)
    {
      cmdline[0] = strlen (args);
      cmdline[cmdlen + 1] = 13;
    }
  else
    cmdline[0] = 0xff;	/* Signal v2loadimage it's a long command.  */

  environ = env;

  result = v2loadimage (exec_file, cmdline, start_state);

  environ = env_save;
  xfree (cmdline);

  if (result != 0)
    error (_("Load failed for image %s"), exec_file);

  edi_init (start_state);
#if __DJGPP_MINOR__ < 3
  save_npx ();
#endif

  inferior_ptid = ptid_t (SOME_PID);
  inf = current_inferior ();
  inferior_appeared (inf, SOME_PID);

  if (!target_is_pushed (this))
    push_target (this);

  add_thread_silent (inferior_ptid);

  clear_proceed_status (0);
  insert_breakpoints ();
  prog_has_started = 1;
}

void
go32_nat_target::mourn_inferior ()
{
  ptid_t ptid;

  redir_cmdline_delete (&child_cmd);
  resume_signal = -1;
  resume_is_step = 0;

  cleanup_client ();

  /* We need to make sure all the breakpoint enable bits in the DR7
     register are reset when the inferior exits.  Otherwise, if they
     rerun the inferior, the uncleared bits may cause random SIGTRAPs,
     failure to set more watchpoints, and other calamities.  It would
     be nice if GDB itself would take care to remove all breakpoints
     at all times, but it doesn't, probably under an assumption that
     the OS cleans up when the debuggee exits.  */
  x86_cleanup_dregs ();

  ptid = inferior_ptid;
  inferior_ptid = null_ptid;
  prog_has_started = 0;

  generic_mourn_inferior ();
  maybe_unpush_target ();
}

/* Hardware watchpoint support.  */

#define D_REGS edi.dr
#define CONTROL D_REGS[7]
#define STATUS D_REGS[6]

/* Pass the address ADDR to the inferior in the I'th debug register.
   Here we just store the address in D_REGS, the watchpoint will be
   actually set up when go32_wait runs the debuggee.  */
static void
go32_set_dr (int i, CORE_ADDR addr)
{
  if (i < 0 || i > 3)
    internal_error (__FILE__, __LINE__, 
		    _("Invalid register %d in go32_set_dr.\n"), i);
  D_REGS[i] = addr;
}

/* Pass the value VAL to the inferior in the DR7 debug control
   register.  Here we just store the address in D_REGS, the watchpoint
   will be actually set up when go32_wait runs the debuggee.  */
static void
go32_set_dr7 (unsigned long val)
{
  CONTROL = val;
}

/* Get the value of the DR6 debug status register from the inferior.
   Here we just return the value stored in D_REGS, as we've got it
   from the last go32_wait call.  */
static unsigned long
go32_get_dr6 (void)
{
  return STATUS;
}

/* Get the value of the DR7 debug status register from the inferior.
   Here we just return the value stored in D_REGS, as we've got it
   from the last go32_wait call.  */

static unsigned long
go32_get_dr7 (void)
{
  return CONTROL;
}

/* Get the value of the DR debug register I from the inferior.  Here
   we just return the value stored in D_REGS, as we've got it from the
   last go32_wait call.  */

static CORE_ADDR
go32_get_dr (int i)
{
  if (i < 0 || i > 3)
    internal_error (__FILE__, __LINE__,
		    _("Invalid register %d in go32_get_dr.\n"), i);
  return D_REGS[i];
}

/* Put the device open on handle FD into either raw or cooked
   mode, return 1 if it was in raw mode, zero otherwise.  */

static int
device_mode (int fd, int raw_p)
{
  int oldmode, newmode;
  __dpmi_regs regs;

  regs.x.ax = 0x4400;
  regs.x.bx = fd;
  __dpmi_int (0x21, &regs);
  if (regs.x.flags & 1)
    return -1;
  newmode = oldmode = regs.x.dx;

  if (raw_p)
    newmode |= 0x20;
  else
    newmode &= ~0x20;

  if (oldmode & 0x80)	/* Only for character dev.  */
  {
    regs.x.ax = 0x4401;
    regs.x.bx = fd;
    regs.x.dx = newmode & 0xff;   /* Force upper byte zero, else it fails.  */
    __dpmi_int (0x21, &regs);
    if (regs.x.flags & 1)
      return -1;
  }
  return (oldmode & 0x20) == 0x20;
}


static int inf_mode_valid = 0;
static int inf_terminal_mode;

/* This semaphore is needed because, amazingly enough, GDB calls
   target.to_terminal_ours more than once after the inferior stops.
   But we need the information from the first call only, since the
   second call will always see GDB's own cooked terminal.  */
static int terminal_is_ours = 1;

void
go32_nat_target::terminal_init ()
{
  inf_mode_valid = 0;	/* Reinitialize, in case they are restarting child.  */
  terminal_is_ours = 1;
}

void
go32_nat_target::terminal_info (const char *args, int from_tty)
{
  printf_unfiltered ("Inferior's terminal is in %s mode.\n",
		     !inf_mode_valid
		     ? "default" : inf_terminal_mode ? "raw" : "cooked");

#if __DJGPP_MINOR__ > 2
  if (child_cmd.redirection)
  {
    int i;

    for (i = 0; i < DBG_HANDLES; i++)
    {
      if (child_cmd.redirection[i]->file_name)
	printf_unfiltered ("\tFile handle %d is redirected to `%s'.\n",
			   i, child_cmd.redirection[i]->file_name);
      else if (_get_dev_info (child_cmd.redirection[i]->inf_handle) == -1)
	printf_unfiltered
	  ("\tFile handle %d appears to be closed by inferior.\n", i);
      /* Mask off the raw/cooked bit when comparing device info words.  */
      else if ((_get_dev_info (child_cmd.redirection[i]->inf_handle) & 0xdf)
	       != (_get_dev_info (i) & 0xdf))
	printf_unfiltered
	  ("\tFile handle %d appears to be redirected by inferior.\n", i);
    }
  }
#endif
}

void
go32_nat_target::terminal_inferior ()
{
  /* Redirect standard handles as child wants them.  */
  errno = 0;
  if (redir_to_child (&child_cmd) == -1)
  {
    redir_to_debugger (&child_cmd);
    error (_("Cannot redirect standard handles for program: %s."),
	   safe_strerror (errno));
  }
  /* Set the console device of the inferior to whatever mode
     (raw or cooked) we found it last time.  */
  if (terminal_is_ours)
  {
    if (inf_mode_valid)
      device_mode (0, inf_terminal_mode);
    terminal_is_ours = 0;
  }
}

void
go32_nat_target::terminal_ours ()
{
  /* Switch to cooked mode on the gdb terminal and save the inferior
     terminal mode to be restored when it is resumed.  */
  if (!terminal_is_ours)
  {
    inf_terminal_mode = device_mode (0, 0);
    if (inf_terminal_mode != -1)
      inf_mode_valid = 1;
    else
      /* If device_mode returned -1, we don't know what happens with
	 handle 0 anymore, so make the info invalid.  */
      inf_mode_valid = 0;
    terminal_is_ours = 1;

    /* Restore debugger's standard handles.  */
    errno = 0;
    if (redir_to_debugger (&child_cmd) == -1)
    {
      redir_to_child (&child_cmd);
      error (_("Cannot redirect standard handles for debugger: %s."),
	     safe_strerror (errno));
    }
  }
}

void
go32_nat_target::pass_ctrlc ()
{
}

bool
go32_nat_target::thread_alive (ptid_t ptid)
{
  return ptid != null_ptid;
}

std::string
go32_nat_target::pid_to_str (ptid_t ptid)
{
  return normal_pid_to_str (ptid);
}

/* Return the current DOS codepage number.  */
static int
dos_codepage (void)
{
  __dpmi_regs regs;

  regs.x.ax = 0x6601;
  __dpmi_int (0x21, &regs);
  if (!(regs.x.flags & 1))
    return regs.x.bx & 0xffff;
  else
    return 437;	/* default */
}

/* Limited emulation of `nl_langinfo', for charset.c.  */
char *
nl_langinfo (nl_item item)
{
  char *retval;

  switch (item)
    {
      case CODESET:
	{
	  /* 8 is enough for SHORT_MAX + "CP" + null.  */
	  char buf[8];
	  int blen = sizeof (buf);
	  int needed = snprintf (buf, blen, "CP%d", dos_codepage ());

	  if (needed > blen)	/* Should never happen.  */
	    buf[0] = 0;
	  retval = xstrdup (buf);
	}
	break;
      default:
	retval = xstrdup ("");
	break;
    }
  return retval;
}

unsigned short windows_major, windows_minor;

/* Compute the version Windows reports via Int 2Fh/AX=1600h.  */
static void
go32_get_windows_version(void)
{
  __dpmi_regs r;

  r.x.ax = 0x1600;
  __dpmi_int(0x2f, &r);
  if (r.h.al > 2 && r.h.al != 0x80 && r.h.al != 0xff
      && (r.h.al > 3 || r.h.ah > 0))
    {
      windows_major = r.h.al;
      windows_minor = r.h.ah;
    }
  else
    windows_major = 0xff;	/* meaning no Windows */
}

/* A subroutine of go32_sysinfo to display memory info.  */
static void
print_mem (unsigned long datum, const char *header, int in_pages_p)
{
  if (datum != 0xffffffffUL)
    {
      if (in_pages_p)
	datum <<= 12;
      puts_filtered (header);
      if (datum > 1024)
	{
	  printf_filtered ("%lu KB", datum >> 10);
	  if (datum > 1024 * 1024)
	    printf_filtered (" (%lu MB)", datum >> 20);
	}
      else
	printf_filtered ("%lu Bytes", datum);
      puts_filtered ("\n");
    }
}

/* Display assorted information about the underlying OS.  */
static void
go32_sysinfo (const char *arg, int from_tty)
{
  static const char test_pattern[] =
    "deadbeafdeadbeafdeadbeafdeadbeafdeadbeaf"
    "deadbeafdeadbeafdeadbeafdeadbeafdeadbeaf"
    "deadbeafdeadbeafdeadbeafdeadbeafdeadbeafdeadbeaf";
  struct utsname u;
  char cpuid_vendor[13];
  unsigned cpuid_max = 0, cpuid_eax, cpuid_ebx, cpuid_ecx, cpuid_edx;
  unsigned true_dos_version = _get_dos_version (1);
  unsigned advertized_dos_version = ((unsigned int)_osmajor << 8) | _osminor;
  int dpmi_flags;
  char dpmi_vendor_info[129];
  int dpmi_vendor_available;
  __dpmi_version_ret dpmi_version_data;
  long eflags;
  __dpmi_free_mem_info mem_info;
  __dpmi_regs regs;

  cpuid_vendor[0] = '\0';
  if (uname (&u))
    strcpy (u.machine, "Unknown x86");
  else if (u.machine[0] == 'i' && u.machine[1] > 4)
    {
      /* CPUID with EAX = 0 returns the Vendor ID.  */
#if 0
      /* Ideally we would use x86_cpuid(), but it needs someone to run
         native tests first to make sure things actually work.  They should.
         http://sourceware.org/ml/gdb-patches/2013-05/msg00164.html  */
      unsigned int eax, ebx, ecx, edx;

      if (x86_cpuid (0, &eax, &ebx, &ecx, &edx))
	{
	  cpuid_max = eax;
	  memcpy (&vendor[0], &ebx, 4);
	  memcpy (&vendor[4], &ecx, 4);
	  memcpy (&vendor[8], &edx, 4);
	  cpuid_vendor[12] = '\0';
	}
#else
      __asm__ __volatile__ ("xorl   %%ebx, %%ebx;"
			    "xorl   %%ecx, %%ecx;"
			    "xorl   %%edx, %%edx;"
			    "movl   $0,    %%eax;"
			    "cpuid;"
			    "movl   %%ebx,  %0;"
			    "movl   %%edx,  %1;"
			    "movl   %%ecx,  %2;"
			    "movl   %%eax,  %3;"
			    : "=m" (cpuid_vendor[0]),
			      "=m" (cpuid_vendor[4]),
			      "=m" (cpuid_vendor[8]),
			      "=m" (cpuid_max)
			    :
			    : "%eax", "%ebx", "%ecx", "%edx");
      cpuid_vendor[12] = '\0';
#endif
    }

  printf_filtered ("CPU Type.......................%s", u.machine);
  if (cpuid_vendor[0])
    printf_filtered (" (%s)", cpuid_vendor);
  puts_filtered ("\n");

  /* CPUID with EAX = 1 returns processor signature and features.  */
  if (cpuid_max >= 1)
    {
      static const char *brand_name[] = {
	"",
	" Celeron",
	" III",
	" III Xeon",
	"", "", "", "",
	" 4"
      };
      char cpu_string[80];
      char cpu_brand[20];
      unsigned brand_idx;
      int intel_p = strcmp (cpuid_vendor, "GenuineIntel") == 0;
      int amd_p = strcmp (cpuid_vendor, "AuthenticAMD") == 0;
      int hygon_p = strcmp (cpuid_vendor, "HygonGenuine") == 0;
      unsigned cpu_family, cpu_model;

#if 0
      /* See comment above about cpuid usage.  */
      x86_cpuid (1, &cpuid_eax, &cpuid_ebx, NULL, &cpuid_edx);
#else
      __asm__ __volatile__ ("movl   $1, %%eax;"
			    "cpuid;"
			    : "=a" (cpuid_eax),
			      "=b" (cpuid_ebx),
			      "=d" (cpuid_edx)
			    :
			    : "%ecx");
#endif
      brand_idx = cpuid_ebx & 0xff;
      cpu_family = (cpuid_eax >> 8) & 0xf;
      cpu_model  = (cpuid_eax >> 4) & 0xf;
      cpu_brand[0] = '\0';
      if (intel_p)
	{
	  if (brand_idx > 0
	      && brand_idx < sizeof(brand_name)/sizeof(brand_name[0])
	      && *brand_name[brand_idx])
	    strcpy (cpu_brand, brand_name[brand_idx]);
	  else if (cpu_family == 5)
	    {
	      if (((cpuid_eax >> 12) & 3) == 0 && cpu_model == 4)
		strcpy (cpu_brand, " MMX");
	      else if (cpu_model > 1 && ((cpuid_eax >> 12) & 3) == 1)
		strcpy (cpu_brand, " OverDrive");
	      else if (cpu_model > 1 && ((cpuid_eax >> 12) & 3) == 2)
		strcpy (cpu_brand, " Dual");
	    }
	  else if (cpu_family == 6 && cpu_model < 8)
	    {
	      switch (cpu_model)
		{
		  case 1:
		    strcpy (cpu_brand, " Pro");
		    break;
		  case 3:
		    strcpy (cpu_brand, " II");
		    break;
		  case 5:
		    strcpy (cpu_brand, " II Xeon");
		    break;
		  case 6:
		    strcpy (cpu_brand, " Celeron");
		    break;
		  case 7:
		    strcpy (cpu_brand, " III");
		    break;
		}
	    }
	}
      else if (amd_p)
	{
	  switch (cpu_family)
	    {
	      case 4:
		strcpy (cpu_brand, "486/5x86");
		break;
	      case 5:
		switch (cpu_model)
		  {
		    case 0:
		    case 1:
		    case 2:
		    case 3:
		      strcpy (cpu_brand, "-K5");
		      break;
		    case 6:
		    case 7:
		      strcpy (cpu_brand, "-K6");
		      break;
		    case 8:
		      strcpy (cpu_brand, "-K6-2");
		      break;
		    case 9:
		      strcpy (cpu_brand, "-K6-III");
		      break;
		  }
		break;
	      case 6:
		switch (cpu_model)
		  {
		    case 1:
		    case 2:
		    case 4:
		      strcpy (cpu_brand, " Athlon");
		      break;
		    case 3:
		      strcpy (cpu_brand, " Duron");
		      break;
		  }
		break;
	    }
	}
      xsnprintf (cpu_string, sizeof (cpu_string), "%s%s Model %d Stepping %d",
	         intel_p ? "Pentium" : (amd_p ? "AMD" : (hygon_p ? "Hygon" : "ix86")),
	         cpu_brand, cpu_model, cpuid_eax & 0xf);
      printfi_filtered (31, "%s\n", cpu_string);
      if (((cpuid_edx & (6 | (0x0d << 23))) != 0)
	  || ((cpuid_edx & 1) == 0)
	  || ((amd_p || hygon_p) && (cpuid_edx & (3 << 30)) != 0))
	{
	  puts_filtered ("CPU Features...................");
	  /* We only list features which might be useful in the DPMI
	     environment.  */
	  if ((cpuid_edx & 1) == 0)
	    puts_filtered ("No FPU "); /* It's unusual to not have an FPU.  */
	  if ((cpuid_edx & (1 << 1)) != 0)
	    puts_filtered ("VME ");
	  if ((cpuid_edx & (1 << 2)) != 0)
	    puts_filtered ("DE ");
	  if ((cpuid_edx & (1 << 4)) != 0)
	    puts_filtered ("TSC ");
	  if ((cpuid_edx & (1 << 23)) != 0)
	    puts_filtered ("MMX ");
	  if ((cpuid_edx & (1 << 25)) != 0)
	    puts_filtered ("SSE ");
	  if ((cpuid_edx & (1 << 26)) != 0)
	    puts_filtered ("SSE2 ");
	  if (amd_p || hygon_p)
	    {
	      if ((cpuid_edx & (1 << 31)) != 0)
		puts_filtered ("3DNow! ");
	      if ((cpuid_edx & (1 << 30)) != 0)
		puts_filtered ("3DNow!Ext");
	    }
	  puts_filtered ("\n");
	}
    }
  puts_filtered ("\n");
  printf_filtered ("DOS Version....................%s %s.%s",
		   _os_flavor, u.release, u.version);
  if (true_dos_version != advertized_dos_version)
    printf_filtered (" (disguised as v%d.%d)", _osmajor, _osminor);
  puts_filtered ("\n");
  if (!windows_major)
    go32_get_windows_version ();
  if (windows_major != 0xff)
    {
      const char *windows_flavor;

      printf_filtered ("Windows Version................%d.%02d (Windows ",
		       windows_major, windows_minor);
      switch (windows_major)
	{
	  case 3:
	    windows_flavor = "3.X";
	    break;
	  case 4:
	    switch (windows_minor)
	      {
		case 0:
		  windows_flavor = "95, 95A, or 95B";
		  break;
		case 3:
		  windows_flavor = "95B OSR2.1 or 95C OSR2.5";
		  break;
		case 10:
		  windows_flavor = "98 or 98 SE";
		  break;
		case 90:
		  windows_flavor = "ME";
		  break;
		default:
		  windows_flavor = "9X";
		  break;
	      }
	    break;
	  default:
	    windows_flavor = "??";
	    break;
	}
      printf_filtered ("%s)\n", windows_flavor);
    }
  else if (true_dos_version == 0x532 && advertized_dos_version == 0x500)
    printf_filtered ("Windows Version................"
		     "Windows NT family (W2K/XP/W2K3/Vista/W2K8)\n");
  puts_filtered ("\n");
  /* On some versions of Windows, __dpmi_get_capabilities returns
     zero, but the buffer is not filled with info, so we fill the
     buffer with a known pattern and test for it afterwards.  */
  memcpy (dpmi_vendor_info, test_pattern, sizeof(dpmi_vendor_info));
  dpmi_vendor_available =
    __dpmi_get_capabilities (&dpmi_flags, dpmi_vendor_info);
  if (dpmi_vendor_available == 0
      && memcmp (dpmi_vendor_info, test_pattern,
		 sizeof(dpmi_vendor_info)) != 0)
    {
      /* The DPMI spec says the vendor string should be ASCIIZ, but
	 I don't trust the vendors to follow that...  */
      if (!memchr (&dpmi_vendor_info[2], 0, 126))
	dpmi_vendor_info[128] = '\0';
      printf_filtered ("DPMI Host......................"
		       "%s v%d.%d (capabilities: %#x)\n",
		       &dpmi_vendor_info[2],
		       (unsigned)dpmi_vendor_info[0],
		       (unsigned)dpmi_vendor_info[1],
		       ((unsigned)dpmi_flags & 0x7f));
    }
  else
    printf_filtered ("DPMI Host......................(Info not available)\n");
  __dpmi_get_version (&dpmi_version_data);
  printf_filtered ("DPMI Version...................%d.%02d\n",
		   dpmi_version_data.major, dpmi_version_data.minor);
  printf_filtered ("DPMI Info......................"
		   "%s-bit DPMI, with%s Virtual Memory support\n",
		   (dpmi_version_data.flags & 1) ? "32" : "16",
		   (dpmi_version_data.flags & 4) ? "" : "out");
  printfi_filtered (31, "Interrupts reflected to %s mode\n",
		   (dpmi_version_data.flags & 2) ? "V86" : "Real");
  printfi_filtered (31, "Processor type: i%d86\n",
		   dpmi_version_data.cpu);
  printfi_filtered (31, "PIC base interrupt: Master: %#x  Slave: %#x\n",
		   dpmi_version_data.master_pic, dpmi_version_data.slave_pic);

  /* a_tss is only initialized when the debuggee is first run.  */
  if (prog_has_started)
    {
      __asm__ __volatile__ ("pushfl ; popl %0" : "=g" (eflags));
      printf_filtered ("Protection....................."
		       "Ring %d (in %s), with%s I/O protection\n",
		       a_tss.tss_cs & 3, (a_tss.tss_cs & 4) ? "LDT" : "GDT",
		       (a_tss.tss_cs & 3) > ((eflags >> 12) & 3) ? "" : "out");
    }
  puts_filtered ("\n");
  __dpmi_get_free_memory_information (&mem_info);
  print_mem (mem_info.total_number_of_physical_pages,
	     "DPMI Total Physical Memory.....", 1);
  print_mem (mem_info.total_number_of_free_pages,
	     "DPMI Free Physical Memory......", 1);
  print_mem (mem_info.size_of_paging_file_partition_in_pages,
	     "DPMI Swap Space................", 1);
  print_mem (mem_info.linear_address_space_size_in_pages,
	     "DPMI Total Linear Address Size.", 1);
  print_mem (mem_info.free_linear_address_space_in_pages,
	     "DPMI Free Linear Address Size..", 1);
  print_mem (mem_info.largest_available_free_block_in_bytes,
	     "DPMI Largest Free Memory Block.", 0);

  regs.h.ah = 0x48;
  regs.x.bx = 0xffff;
  __dpmi_int (0x21, &regs);
  print_mem (regs.x.bx << 4, "Free DOS Memory................", 0);
  regs.x.ax = 0x5800;
  __dpmi_int (0x21, &regs);
  if ((regs.x.flags & 1) == 0)
    {
      static const char *dos_hilo[] = {
	"Low", "", "", "", "High", "", "", "", "High, then Low"
      };
      static const char *dos_fit[] = {
	"First", "Best", "Last"
      };
      int hilo_idx = (regs.x.ax >> 4) & 0x0f;
      int fit_idx  = regs.x.ax & 0x0f;

      if (hilo_idx > 8)
	hilo_idx = 0;
      if (fit_idx > 2)
	fit_idx = 0;
      printf_filtered ("DOS Memory Allocation..........%s memory, %s fit\n",
		       dos_hilo[hilo_idx], dos_fit[fit_idx]);
      regs.x.ax = 0x5802;
      __dpmi_int (0x21, &regs);
      if ((regs.x.flags & 1) != 0)
	regs.h.al = 0;
      printfi_filtered (31, "UMBs %sin DOS memory chain\n",
			regs.h.al == 0 ? "not " : "");
    }
}

struct seg_descr {
  unsigned short limit0;
  unsigned short base0;
  unsigned char  base1;
  unsigned       stype:5;
  unsigned       dpl:2;
  unsigned       present:1;
  unsigned       limit1:4;
  unsigned       available:1;
  unsigned       dummy:1;
  unsigned       bit32:1;
  unsigned       page_granular:1;
  unsigned char  base2;
} __attribute__ ((packed));

struct gate_descr {
  unsigned short offset0;
  unsigned short selector;
  unsigned       param_count:5;
  unsigned       dummy:3;
  unsigned       stype:5;
  unsigned       dpl:2;
  unsigned       present:1;
  unsigned short offset1;
} __attribute__ ((packed));

/* Read LEN bytes starting at logical address ADDR, and put the result
   into DEST.  Return 1 if success, zero if not.  */
static int
read_memory_region (unsigned long addr, void *dest, size_t len)
{
  unsigned long dos_ds_limit = __dpmi_get_segment_limit (_dos_ds);
  int retval = 1;

  /* For the low memory, we can simply use _dos_ds.  */
  if (addr <= dos_ds_limit - len)
    dosmemget (addr, len, dest);
  else
    {
      /* For memory above 1MB we need to set up a special segment to
	 be able to access that memory.  */
      int sel = __dpmi_allocate_ldt_descriptors (1);

      if (sel <= 0)
	retval = 0;
      else
	{
	  int access_rights = __dpmi_get_descriptor_access_rights (sel);
	  size_t segment_limit = len - 1;

	  /* Make sure the crucial bits in the descriptor access
	     rights are set correctly.  Some DPMI providers might barf
	     if we set the segment limit to something that is not an
	     integral multiple of 4KB pages if the granularity bit is
	     not set to byte-granular, even though the DPMI spec says
	     it's the host's responsibility to set that bit correctly.  */
	  if (len > 1024 * 1024)
	    {
	      access_rights |= 0x8000;
	      /* Page-granular segments should have the low 12 bits of
		 the limit set.  */
	      segment_limit |= 0xfff;
	    }
	  else
	    access_rights &= ~0x8000;

	  if (__dpmi_set_segment_base_address (sel, addr) != -1
	      && __dpmi_set_descriptor_access_rights (sel, access_rights) != -1
	      && __dpmi_set_segment_limit (sel, segment_limit) != -1
	      /* W2K silently fails to set the segment limit, leaving
		 it at zero; this test avoids the resulting crash.  */
	      && __dpmi_get_segment_limit (sel) >= segment_limit)
	    movedata (sel, 0, _my_ds (), (unsigned)dest, len);
	  else
	    retval = 0;

	  __dpmi_free_ldt_descriptor (sel);
	}
    }
  return retval;
}

/* Get a segment descriptor stored at index IDX in the descriptor
   table whose base address is TABLE_BASE.  Return the descriptor
   type, or -1 if failure.  */
static int
get_descriptor (unsigned long table_base, int idx, void *descr)
{
  unsigned long addr = table_base + idx * 8; /* 8 bytes per entry */

  if (read_memory_region (addr, descr, 8))
    return (int)((struct seg_descr *)descr)->stype;
  return -1;
}

struct dtr_reg {
  unsigned short limit __attribute__((packed));
  unsigned long  base  __attribute__((packed));
};

/* Display a segment descriptor stored at index IDX in a descriptor
   table whose type is TYPE and whose base address is BASE_ADDR.  If
   FORCE is non-zero, display even invalid descriptors.  */
static void
display_descriptor (unsigned type, unsigned long base_addr, int idx, int force)
{
  struct seg_descr descr;
  struct gate_descr gate;

  /* Get the descriptor from the table.  */
  if (idx == 0 && type == 0)
    puts_filtered ("0x000: null descriptor\n");
  else if (get_descriptor (base_addr, idx, &descr) != -1)
    {
      /* For each type of descriptor table, this has a bit set if the
	 corresponding type of selectors is valid in that table.  */
      static unsigned allowed_descriptors[] = {
	  0xffffdafeL,   /* GDT */
	  0x0000c0e0L,   /* IDT */
	  0xffffdafaL    /* LDT */
      };

      /* If the program hasn't started yet, assume the debuggee will
	 have the same CPL as the debugger.  */
      int cpl = prog_has_started ? (a_tss.tss_cs & 3) : _my_cs () & 3;
      unsigned long limit = (descr.limit1 << 16) | descr.limit0;

      if (descr.present
	  && (allowed_descriptors[type] & (1 << descr.stype)) != 0)
	{
	  printf_filtered ("0x%03x: ",
			   type == 1
			   ? idx : (idx * 8) | (type ? (cpl | 4) : 0));
	  if (descr.page_granular)
	    limit = (limit << 12) | 0xfff; /* big segment: low 12 bit set */
	  if (descr.stype == 1 || descr.stype == 2 || descr.stype == 3
	      || descr.stype == 9 || descr.stype == 11
	      || (descr.stype >= 16 && descr.stype < 32))
	    printf_filtered ("base=0x%02x%02x%04x limit=0x%08lx",
			     descr.base2, descr.base1, descr.base0, limit);

	  switch (descr.stype)
	    {
	      case 1:
	      case 3:
		printf_filtered (" 16-bit TSS  (task %sactive)",
				 descr.stype == 3 ? "" : "in");
		break;
	      case 2:
		puts_filtered (" LDT");
		break;
	      case 4:
		memcpy (&gate, &descr, sizeof gate);
		printf_filtered ("selector=0x%04x  offs=0x%04x%04x",
				 gate.selector, gate.offset1, gate.offset0);
		printf_filtered (" 16-bit Call Gate (params=%d)",
				 gate.param_count);
		break;
	      case 5:
		printf_filtered ("TSS selector=0x%04x", descr.base0);
		printfi_filtered (16, "Task Gate");
		break;
	      case 6:
	      case 7:
		memcpy (&gate, &descr, sizeof gate);
		printf_filtered ("selector=0x%04x  offs=0x%04x%04x",
				 gate.selector, gate.offset1, gate.offset0);
		printf_filtered (" 16-bit %s Gate",
				 descr.stype == 6 ? "Interrupt" : "Trap");
		break;
	      case 9:
	      case 11:
		printf_filtered (" 32-bit TSS (task %sactive)",
				 descr.stype == 3 ? "" : "in");
		break;
	      case 12:
		memcpy (&gate, &descr, sizeof gate);
		printf_filtered ("selector=0x%04x  offs=0x%04x%04x",
				 gate.selector, gate.offset1, gate.offset0);
		printf_filtered (" 32-bit Call Gate (params=%d)",
				 gate.param_count);
		break;
	      case 14:
	      case 15:
		memcpy (&gate, &descr, sizeof gate);
		printf_filtered ("selector=0x%04x  offs=0x%04x%04x",
				 gate.selector, gate.offset1, gate.offset0);
		printf_filtered (" 32-bit %s Gate",
				 descr.stype == 14 ? "Interrupt" : "Trap");
		break;
	      case 16:		/* data segments */
	      case 17:
	      case 18:
	      case 19:
	      case 20:
	      case 21:
	      case 22:
	      case 23:
		printf_filtered (" %s-bit Data (%s Exp-%s%s)",
				 descr.bit32 ? "32" : "16",
				 descr.stype & 2
				 ? "Read/Write," : "Read-Only, ",
				 descr.stype & 4 ? "down" : "up",
				 descr.stype & 1 ? "" : ", N.Acc");
		break;
	      case 24:		/* code segments */
	      case 25:
	      case 26:
	      case 27:
	      case 28:
	      case 29:
	      case 30:
	      case 31:
		printf_filtered (" %s-bit Code (%s,  %sConf%s)",
				 descr.bit32 ? "32" : "16",
				 descr.stype & 2 ? "Exec/Read" : "Exec-Only",
				 descr.stype & 4 ? "" : "N.",
				 descr.stype & 1 ? "" : ", N.Acc");
		break;
	      default:
		printf_filtered ("Unknown type 0x%02x", descr.stype);
		break;
	    }
	  puts_filtered ("\n");
	}
      else if (force)
	{
	  printf_filtered ("0x%03x: ",
			   type == 1
			   ? idx : (idx * 8) | (type ? (cpl | 4) : 0));
	  if (!descr.present)
	    puts_filtered ("Segment not present\n");
	  else
	    printf_filtered ("Segment type 0x%02x is invalid in this table\n",
			     descr.stype);
	}
    }
  else if (force)
    printf_filtered ("0x%03x: Cannot read this descriptor\n", idx);
}

static void
go32_sldt (const char *arg, int from_tty)
{
  struct dtr_reg gdtr;
  unsigned short ldtr = 0;
  int ldt_idx;
  struct seg_descr ldt_descr;
  long ldt_entry = -1L;
  int cpl = (prog_has_started ? a_tss.tss_cs : _my_cs ()) & 3;

  if (arg && *arg)
    {
      arg = skip_spaces (arg);

      if (*arg)
	{
	  ldt_entry = parse_and_eval_long (arg);
	  if (ldt_entry < 0
	      || (ldt_entry & 4) == 0
	      || (ldt_entry & 3) != (cpl & 3))
	    error (_("Invalid LDT entry 0x%03lx."), (unsigned long)ldt_entry);
	}
    }

  __asm__ __volatile__ ("sgdt   %0" : "=m" (gdtr) : /* no inputs */ );
  __asm__ __volatile__ ("sldt   %0" : "=m" (ldtr) : /* no inputs */ );
  ldt_idx = ldtr / 8;
  if (ldt_idx == 0)
    puts_filtered ("There is no LDT.\n");
  /* LDT's entry in the GDT must have the type LDT, which is 2.  */
  else if (get_descriptor (gdtr.base, ldt_idx, &ldt_descr) != 2)
    printf_filtered ("LDT is present (at %#x), but unreadable by GDB.\n",
		     ldt_descr.base0
		     | (ldt_descr.base1 << 16)
		     | (ldt_descr.base2 << 24));
  else
    {
      unsigned base =
	ldt_descr.base0
	| (ldt_descr.base1 << 16)
	| (ldt_descr.base2 << 24);
      unsigned limit = ldt_descr.limit0 | (ldt_descr.limit1 << 16);
      int max_entry;

      if (ldt_descr.page_granular)
	/* Page-granular segments must have the low 12 bits of their
	   limit set.  */
	limit = (limit << 12) | 0xfff;
      /* LDT cannot have more than 8K 8-byte entries, i.e. more than
	 64KB.  */
      if (limit > 0xffff)
	limit = 0xffff;

      max_entry = (limit + 1) / 8;

      if (ldt_entry >= 0)
	{
	  if (ldt_entry > limit)
	    error (_("Invalid LDT entry %#lx: outside valid limits [0..%#x]"),
		   (unsigned long)ldt_entry, limit);

	  display_descriptor (ldt_descr.stype, base, ldt_entry / 8, 1);
	}
      else
	{
	  int i;

	  for (i = 0; i < max_entry; i++)
	    display_descriptor (ldt_descr.stype, base, i, 0);
	}
    }
}

static void
go32_sgdt (const char *arg, int from_tty)
{
  struct dtr_reg gdtr;
  long gdt_entry = -1L;
  int max_entry;

  if (arg && *arg)
    {
      arg = skip_spaces (arg);

      if (*arg)
	{
	  gdt_entry = parse_and_eval_long (arg);
	  if (gdt_entry < 0 || (gdt_entry & 7) != 0)
	    error (_("Invalid GDT entry 0x%03lx: "
		     "not an integral multiple of 8."),
		   (unsigned long)gdt_entry);
	}
    }

  __asm__ __volatile__ ("sgdt   %0" : "=m" (gdtr) : /* no inputs */ );
  max_entry = (gdtr.limit + 1) / 8;

  if (gdt_entry >= 0)
    {
      if (gdt_entry > gdtr.limit)
	error (_("Invalid GDT entry %#lx: outside valid limits [0..%#x]"),
	       (unsigned long)gdt_entry, gdtr.limit);

      display_descriptor (0, gdtr.base, gdt_entry / 8, 1);
    }
  else
    {
      int i;

      for (i = 0; i < max_entry; i++)
	display_descriptor (0, gdtr.base, i, 0);
    }
}

static void
go32_sidt (const char *arg, int from_tty)
{
  struct dtr_reg idtr;
  long idt_entry = -1L;
  int max_entry;

  if (arg && *arg)
    {
      arg = skip_spaces (arg);

      if (*arg)
	{
	  idt_entry = parse_and_eval_long (arg);
	  if (idt_entry < 0)
	    error (_("Invalid (negative) IDT entry %ld."), idt_entry);
	}
    }

  __asm__ __volatile__ ("sidt   %0" : "=m" (idtr) : /* no inputs */ );
  max_entry = (idtr.limit + 1) / 8;
  if (max_entry > 0x100)	/* No more than 256 entries.  */
    max_entry = 0x100;

  if (idt_entry >= 0)
    {
      if (idt_entry > idtr.limit)
	error (_("Invalid IDT entry %#lx: outside valid limits [0..%#x]"),
	       (unsigned long)idt_entry, idtr.limit);

      display_descriptor (1, idtr.base, idt_entry, 1);
    }
  else
    {
      int i;

      for (i = 0; i < max_entry; i++)
	display_descriptor (1, idtr.base, i, 0);
    }
}

/* Cached linear address of the base of the page directory.  For
   now, available only under CWSDPMI.  Code based on ideas and
   suggestions from Charles Sandmann <sandmann@clio.rice.edu>.  */
static unsigned long pdbr;

static unsigned long
get_cr3 (void)
{
  unsigned offset;
  unsigned taskreg;
  unsigned long taskbase, cr3;
  struct dtr_reg gdtr;

  if (pdbr > 0 && pdbr <= 0xfffff)
    return pdbr;

  /* Get the linear address of GDT and the Task Register.  */
  __asm__ __volatile__ ("sgdt   %0" : "=m" (gdtr) : /* no inputs */ );
  __asm__ __volatile__ ("str    %0" : "=m" (taskreg) : /* no inputs */ );

  /* Task Register is a segment selector for the TSS of the current
     task.  Therefore, it can be used as an index into the GDT to get
     at the segment descriptor for the TSS.  To get the index, reset
     the low 3 bits of the selector (which give the CPL).  Add 2 to the
     offset to point to the 3 low bytes of the base address.  */
  offset = gdtr.base + (taskreg & 0xfff8) + 2;


  /* CWSDPMI's task base is always under the 1MB mark.  */
  if (offset > 0xfffff)
    return 0;

  _farsetsel (_dos_ds);
  taskbase  = _farnspeekl (offset) & 0xffffffU;
  taskbase += _farnspeekl (offset + 2) & 0xff000000U;
  if (taskbase > 0xfffff)
    return 0;

  /* CR3 (a.k.a. PDBR, the Page Directory Base Register) is stored at
     offset 1Ch in the TSS.  */
  cr3 = _farnspeekl (taskbase + 0x1c) & ~0xfff;
  if (cr3 > 0xfffff)
    {
#if 0  /* Not fully supported yet.  */
      /* The Page Directory is in UMBs.  In that case, CWSDPMI puts
	 the first Page Table right below the Page Directory.  Thus,
	 the first Page Table's entry for its own address and the Page
	 Directory entry for that Page Table will hold the same
	 physical address.  The loop below searches the entire UMB
	 range of addresses for such an occurrence.  */
      unsigned long addr, pte_idx;

      for (addr = 0xb0000, pte_idx = 0xb0;
	   pte_idx < 0xff;
	   addr += 0x1000, pte_idx++)
	{
	  if (((_farnspeekl (addr + 4 * pte_idx) & 0xfffff027) ==
	       (_farnspeekl (addr + 0x1000) & 0xfffff027))
	      && ((_farnspeekl (addr + 4 * pte_idx + 4) & 0xfffff000) == cr3))
	    {
	      cr3 = addr + 0x1000;
	      break;
	    }
	}
#endif

      if (cr3 > 0xfffff)
	cr3 = 0;
    }

  return cr3;
}

/* Return the N'th Page Directory entry.  */
static unsigned long
get_pde (int n)
{
  unsigned long pde = 0;

  if (pdbr && n >= 0 && n < 1024)
    {
      pde = _farpeekl (_dos_ds, pdbr + 4*n);
    }
  return pde;
}

/* Return the N'th entry of the Page Table whose Page Directory entry
   is PDE.  */
static unsigned long
get_pte (unsigned long pde, int n)
{
  unsigned long pte = 0;

  /* pde & 0x80 tests the 4MB page bit.  We don't support 4MB
     page tables, for now.  */
  if ((pde & 1) && !(pde & 0x80) && n >= 0 && n < 1024)
    {
      pde &= ~0xfff;	/* Clear non-address bits.  */
      pte = _farpeekl (_dos_ds, pde + 4*n);
    }
  return pte;
}

/* Display a Page Directory or Page Table entry.  IS_DIR, if non-zero,
   says this is a Page Directory entry.  If FORCE is non-zero, display
   the entry even if its Present flag is off.  OFF is the offset of the
   address from the page's base address.  */
static void
display_ptable_entry (unsigned long entry, int is_dir, int force, unsigned off)
{
  if ((entry & 1) != 0)
    {
      printf_filtered ("Base=0x%05lx000", entry >> 12);
      if ((entry & 0x100) && !is_dir)
	puts_filtered (" Global");
      if ((entry & 0x40) && !is_dir)
	puts_filtered (" Dirty");
      printf_filtered (" %sAcc.", (entry & 0x20) ? "" : "Not-");
      printf_filtered (" %sCached", (entry & 0x10) ? "" : "Not-");
      printf_filtered (" Write-%s", (entry & 8) ? "Thru" : "Back");
      printf_filtered (" %s", (entry & 4) ? "Usr" : "Sup");
      printf_filtered (" Read-%s", (entry & 2) ? "Write" : "Only");
      if (off)
	printf_filtered (" +0x%x", off);
      puts_filtered ("\n");
    }
  else if (force)
    printf_filtered ("Page%s not present or not supported; value=0x%lx.\n",
		     is_dir ? " Table" : "", entry >> 1);
}

static void
go32_pde (const char *arg, int from_tty)
{
  long pde_idx = -1, i;

  if (arg && *arg)
    {
      arg = skip_spaces (arg);

      if (*arg)
	{
	  pde_idx = parse_and_eval_long (arg);
	  if (pde_idx < 0 || pde_idx >= 1024)
	    error (_("Entry %ld is outside valid limits [0..1023]."), pde_idx);
	}
    }

  pdbr = get_cr3 ();
  if (!pdbr)
    puts_filtered ("Access to Page Directories is "
		   "not supported on this system.\n");
  else if (pde_idx >= 0)
    display_ptable_entry (get_pde (pde_idx), 1, 1, 0);
  else
    for (i = 0; i < 1024; i++)
      display_ptable_entry (get_pde (i), 1, 0, 0);
}

/* A helper function to display entries in a Page Table pointed to by
   the N'th entry in the Page Directory.  If FORCE is non-zero, say
   something even if the Page Table is not accessible.  */
static void
display_page_table (long n, int force)
{
  unsigned long pde = get_pde (n);

  if ((pde & 1) != 0)
    {
      int i;

      printf_filtered ("Page Table pointed to by "
		       "Page Directory entry 0x%lx:\n", n);
      for (i = 0; i < 1024; i++)
	display_ptable_entry (get_pte (pde, i), 0, 0, 0);
      puts_filtered ("\n");
    }
  else if (force)
    printf_filtered ("Page Table not present; value=0x%lx.\n", pde >> 1);
}

static void
go32_pte (const char *arg, int from_tty)
{
  long pde_idx = -1L, i;

  if (arg && *arg)
    {
      arg = skip_spaces (arg);

      if (*arg)
	{
	  pde_idx = parse_and_eval_long (arg);
	  if (pde_idx < 0 || pde_idx >= 1024)
	    error (_("Entry %ld is outside valid limits [0..1023]."), pde_idx);
	}
    }

  pdbr = get_cr3 ();
  if (!pdbr)
    puts_filtered ("Access to Page Tables is not supported on this system.\n");
  else if (pde_idx >= 0)
    display_page_table (pde_idx, 1);
  else
    for (i = 0; i < 1024; i++)
      display_page_table (i, 0);
}

static void
go32_pte_for_address (const char *arg, int from_tty)
{
  CORE_ADDR addr = 0, i;

  if (arg && *arg)
    {
      arg = skip_spaces (arg);

      if (*arg)
	addr = parse_and_eval_address (arg);
    }
  if (!addr)
    error_no_arg (_("linear address"));

  pdbr = get_cr3 ();
  if (!pdbr)
    puts_filtered ("Access to Page Tables is not supported on this system.\n");
  else
    {
      int pde_idx = (addr >> 22) & 0x3ff;
      int pte_idx = (addr >> 12) & 0x3ff;
      unsigned offs = addr & 0xfff;

      printf_filtered ("Page Table entry for address %s:\n",
		       hex_string(addr));
      display_ptable_entry (get_pte (get_pde (pde_idx), pte_idx), 0, 1, offs);
    }
}

static struct cmd_list_element *info_dos_cmdlist = NULL;

static void
go32_info_dos_command (const char *args, int from_tty)
{
  help_list (info_dos_cmdlist, "info dos ", class_info, gdb_stdout);
}

void
_initialize_go32_nat (void)
{
  x86_dr_low.set_control = go32_set_dr7;
  x86_dr_low.set_addr = go32_set_dr;
  x86_dr_low.get_status = go32_get_dr6;
  x86_dr_low.get_control = go32_get_dr7;
  x86_dr_low.get_addr = go32_get_dr;
  x86_set_debug_register_length (4);

  add_inf_child_target (&the_go32_nat_target);

  /* Initialize child's cwd as empty to be initialized when starting
     the child.  */
  *child_cwd = 0;

  /* Initialize child's command line storage.  */
  if (redir_debug_init (&child_cmd) == -1)
    internal_error (__FILE__, __LINE__,
		    _("Cannot allocate redirection storage: "
		      "not enough memory.\n"));

  /* We are always processing GCC-compiled programs.  */
  processing_gcc_compilation = 2;

  add_prefix_cmd ("dos", class_info, go32_info_dos_command, _("\
Print information specific to DJGPP (aka MS-DOS) debugging."),
		  &info_dos_cmdlist, "info dos ", 0, &infolist);

  add_cmd ("sysinfo", class_info, go32_sysinfo, _("\
Display information about the target system, including CPU, OS, DPMI, etc."),
	   &info_dos_cmdlist);
  add_cmd ("ldt", class_info, go32_sldt, _("\
Display entries in the LDT (Local Descriptor Table).\n\
Entry number (an expression) as an argument means display only that entry."),
	   &info_dos_cmdlist);
  add_cmd ("gdt", class_info, go32_sgdt, _("\
Display entries in the GDT (Global Descriptor Table).\n\
Entry number (an expression) as an argument means display only that entry."),
	   &info_dos_cmdlist);
  add_cmd ("idt", class_info, go32_sidt, _("\
Display entries in the IDT (Interrupt Descriptor Table).\n\
Entry number (an expression) as an argument means display only that entry."),
	   &info_dos_cmdlist);
  add_cmd ("pde", class_info, go32_pde, _("\
Display entries in the Page Directory.\n\
Entry number (an expression) as an argument means display only that entry."),
	   &info_dos_cmdlist);
  add_cmd ("pte", class_info, go32_pte, _("\
Display entries in Page Tables.\n\
Entry number (an expression) as an argument means display only entries\n\
from the Page Table pointed to by the specified Page Directory entry."),
	   &info_dos_cmdlist);
  add_cmd ("address-pte", class_info, go32_pte_for_address, _("\
Display a Page Table entry for a linear address.\n\
The address argument must be a linear address, after adding to\n\
it the base address of the appropriate segment.\n\
The base address of variables and functions in the debuggee's data\n\
or code segment is stored in the variable __djgpp_base_address,\n\
so use `__djgpp_base_address + (char *)&var' as the argument.\n\
For other segments, look up their base address in the output of\n\
the `info dos ldt' command."),
	   &info_dos_cmdlist);
}

pid_t
tcgetpgrp (int fd)
{
  if (isatty (fd))
    return SOME_PID;
  errno = ENOTTY;
  return -1;
}

int
tcsetpgrp (int fd, pid_t pgid)
{
  if (isatty (fd) && pgid == SOME_PID)
    return 0;
  errno = pgid == SOME_PID ? ENOTTY : ENOSYS;
  return -1;
}