gdb/i386-linux-nat.c

   1 /* Native-dependent code for GNU/Linux i386.
   2
   3    Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
   4    Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21 #include "defs.h"
  22 #include "inferior.h"
  23 #include "gdbcore.h"
  24 #include "regcache.h"
  25 #include "target.h"
  26 #include "linux-nat.h"
  27
  28 #include "gdb_assert.h"
  29 #include "gdb_string.h"
  30 #include <sys/ptrace.h>
  31 #include <sys/user.h>
  32 #include <sys/procfs.h>
  33
  34 #ifdef HAVE_SYS_REG_H
  35 #include <sys/reg.h>
  36 #endif
  37
  38 #ifndef ORIG_EAX
  39 #define ORIG_EAX -1
  40 #endif
  41
  42 #ifdef HAVE_SYS_DEBUGREG_H
  43 #include <sys/debugreg.h>
  44 #endif
  45
  46 #ifndef DR_FIRSTADDR
  47 #define DR_FIRSTADDR 0
  48 #endif
  49
  50 #ifndef DR_LASTADDR
  51 #define DR_LASTADDR 3
  52 #endif
  53
  54 #ifndef DR_STATUS
  55 #define DR_STATUS 6
  56 #endif
  57
  58 #ifndef DR_CONTROL
  59 #define DR_CONTROL 7
  60 #endif
  61
  62 /* Prototypes for supply_gregset etc.  */
  63 #include "gregset.h"
  64
  65 #include "i387-tdep.h"
  66 #include "i386-tdep.h"
  67 #include "i386-linux-tdep.h"
  68
  69 /* Defines ps_err_e, struct ps_prochandle.  */
  70 #include "gdb_proc_service.h"
  71 \f
  72
  73 /* The register sets used in GNU/Linux ELF core-dumps are identical to
  74    the register sets in `struct user' that is used for a.out
  75    core-dumps, and is also used by `ptrace'.  The corresponding types
  76    are `elf_gregset_t' for the general-purpose registers (with
  77    `elf_greg_t' the type of a single GP register) and `elf_fpregset_t'
  78    for the floating-point registers.
  79
  80    Those types used to be available under the names `gregset_t' and
  81    `fpregset_t' too, and this file used those names in the past.  But
  82    those names are now used for the register sets used in the
  83    `mcontext_t' type, and have a different size and layout.  */
  84
  85 /* Mapping between the general-purpose registers in `struct user'
  86    format and GDB's register array layout.  */
  87 static int regmap[] =
  88 {
  89   EAX, ECX, EDX, EBX,
  90   UESP, EBP, ESI, EDI,
  91   EIP, EFL, CS, SS,
  92   DS, ES, FS, GS,
  93   -1, -1, -1, -1,               /* st0, st1, st2, st3 */
  94   -1, -1, -1, -1,               /* st4, st5, st6, st7 */
  95   -1, -1, -1, -1,               /* fctrl, fstat, ftag, fiseg */
  96   -1, -1, -1, -1,               /* fioff, foseg, fooff, fop */
  97   -1, -1, -1, -1,               /* xmm0, xmm1, xmm2, xmm3 */
  98   -1, -1, -1, -1,               /* xmm4, xmm5, xmm6, xmm6 */
  99   -1,                           /* mxcsr */
 100   ORIG_EAX
 101 };
 102
 103 /* Which ptrace request retrieves which registers?
 104    These apply to the corresponding SET requests as well.  */
 105
 106 #define GETREGS_SUPPLIES(regno) \
 107   ((0 <= (regno) && (regno) <= 15) || (regno) == I386_LINUX_ORIG_EAX_REGNUM)
 108
 109 #define GETFPXREGS_SUPPLIES(regno) \
 110   (I386_ST0_REGNUM <= (regno) && (regno) < I386_SSE_NUM_REGS)
 111
 112 /* Does the current host support the GETREGS request?  */
 113 int have_ptrace_getregs =
 114 #ifdef HAVE_PTRACE_GETREGS
 115   1
 116 #else
 117   0
 118 #endif
 119 ;
 120
 121 /* Does the current host support the GETFPXREGS request?  The header
 122    file may or may not define it, and even if it is defined, the
 123    kernel will return EIO if it's running on a pre-SSE processor.
 124
 125    My instinct is to attach this to some architecture- or
 126    target-specific data structure, but really, a particular GDB
 127    process can only run on top of one kernel at a time.  So it's okay
 128    for this to be a simple variable.  */
 129 int have_ptrace_getfpxregs =
 130 #ifdef HAVE_PTRACE_GETFPXREGS
 131   1
 132 #else
 133   0
 134 #endif
 135 ;
 136 \f
 137
 138 /* Accessing registers through the U area, one at a time.  */
 139
 140 /* Fetch one register.  */
 141
 142 static void
 143 fetch_register (struct regcache *regcache, int regno)
 144 {
 145   int tid;
 146   int val;
 147
 148   gdb_assert (!have_ptrace_getregs);
 149   if (regmap[regno] == -1)
 150     {
 151       regcache_raw_supply (regcache, regno, NULL);
 152       return;
 153     }
 154
 155   /* GNU/Linux LWP ID's are process ID's.  */
 156   tid = TIDGET (inferior_ptid);
 157   if (tid == 0)
 158     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 159
 160   errno = 0;
 161   val = ptrace (PTRACE_PEEKUSER, tid, 4 * regmap[regno], 0);
 162   if (errno != 0)
 163     error (_("Couldn't read register %s (#%d): %s."),
 164            gdbarch_register_name (get_regcache_arch (regcache), regno),
 165            regno, safe_strerror (errno));
 166
 167   regcache_raw_supply (regcache, regno, &val);
 168 }
 169
 170 /* Store one register. */
 171
 172 static void
 173 store_register (const struct regcache *regcache, int regno)
 174 {
 175   int tid;
 176   int val;
 177
 178   gdb_assert (!have_ptrace_getregs);
 179   if (regmap[regno] == -1)
 180     return;
 181
 182   /* GNU/Linux LWP ID's are process ID's.  */
 183   tid = TIDGET (inferior_ptid);
 184   if (tid == 0)
 185     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 186
 187   errno = 0;
 188   regcache_raw_collect (regcache, regno, &val);
 189   ptrace (PTRACE_POKEUSER, tid, 4 * regmap[regno], val);
 190   if (errno != 0)
 191     error (_("Couldn't write register %s (#%d): %s."),
 192            gdbarch_register_name (get_regcache_arch (regcache), regno),
 193            regno, safe_strerror (errno));
 194 }
 195 \f
 196
 197 /* Transfering the general-purpose registers between GDB, inferiors
 198    and core files.  */
 199
 200 /* Fill GDB's register array with the general-purpose register values
 201    in *GREGSETP.  */
 202
 203 void
 204 supply_gregset (struct regcache *regcache, const elf_gregset_t *gregsetp)
 205 {
 206   const elf_greg_t *regp = (const elf_greg_t *) gregsetp;
 207   int i;
 208
 209   for (i = 0; i < I386_NUM_GREGS; i++)
 210     regcache_raw_supply (regcache, i, regp + regmap[i]);
 211
 212   if (I386_LINUX_ORIG_EAX_REGNUM
 213         < gdbarch_num_regs (get_regcache_arch (regcache)))
 214     regcache_raw_supply (regcache, I386_LINUX_ORIG_EAX_REGNUM,
 215                          regp + ORIG_EAX);
 216 }
 217
 218 /* Fill register REGNO (if it is a general-purpose register) in
 219    *GREGSETPS with the value in GDB's register array.  If REGNO is -1,
 220    do this for all registers.  */
 221
 222 void
 223 fill_gregset (const struct regcache *regcache,
 224               elf_gregset_t *gregsetp, int regno)
 225 {
 226   elf_greg_t *regp = (elf_greg_t *) gregsetp;
 227   int i;
 228
 229   for (i = 0; i < I386_NUM_GREGS; i++)
 230     if (regno == -1 || regno == i)
 231       regcache_raw_collect (regcache, i, regp + regmap[i]);
 232
 233   if ((regno == -1 || regno == I386_LINUX_ORIG_EAX_REGNUM)
 234       && I386_LINUX_ORIG_EAX_REGNUM
 235            < gdbarch_num_regs (get_regcache_arch (regcache)))
 236     regcache_raw_collect (regcache, I386_LINUX_ORIG_EAX_REGNUM,
 237                           regp + ORIG_EAX);
 238 }
 239
 240 #ifdef HAVE_PTRACE_GETREGS
 241
 242 /* Fetch all general-purpose registers from process/thread TID and
 243    store their values in GDB's register array.  */
 244
 245 static void
 246 fetch_regs (struct regcache *regcache, int tid)
 247 {
 248   elf_gregset_t regs;
 249   elf_gregset_t *regs_p = &regs;
 250
 251   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
 252     {
 253       if (errno == EIO)
 254         {
 255           /* The kernel we're running on doesn't support the GETREGS
 256              request.  Reset `have_ptrace_getregs'.  */
 257           have_ptrace_getregs = 0;
 258           return;
 259         }
 260
 261       perror_with_name (_("Couldn't get registers"));
 262     }
 263
 264   supply_gregset (regcache, (const elf_gregset_t *) regs_p);
 265 }
 266
 267 /* Store all valid general-purpose registers in GDB's register array
 268    into the process/thread specified by TID.  */
 269
 270 static void
 271 store_regs (const struct regcache *regcache, int tid, int regno)
 272 {
 273   elf_gregset_t regs;
 274
 275   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
 276     perror_with_name (_("Couldn't get registers"));
 277
 278   fill_gregset (regcache, &regs, regno);
 279
 280   if (ptrace (PTRACE_SETREGS, tid, 0, (int) &regs) < 0)
 281     perror_with_name (_("Couldn't write registers"));
 282 }
 283
 284 #else
 285
 286 static void fetch_regs (struct regcache *regcache, int tid) {}
 287 static void store_regs (const struct regcache *regcache, int tid, int regno) {}
 288
 289 #endif
 290 \f
 291
 292 /* Transfering floating-point registers between GDB, inferiors and cores.  */
 293
 294 /* Fill GDB's register array with the floating-point register values in
 295    *FPREGSETP.  */
 296
 297 void
 298 supply_fpregset (struct regcache *regcache, const elf_fpregset_t *fpregsetp)
 299 {
 300   i387_supply_fsave (regcache, -1, fpregsetp);
 301 }
 302
 303 /* Fill register REGNO (if it is a floating-point register) in
 304    *FPREGSETP with the value in GDB's register array.  If REGNO is -1,
 305    do this for all registers.  */
 306
 307 void
 308 fill_fpregset (const struct regcache *regcache,
 309                elf_fpregset_t *fpregsetp, int regno)
 310 {
 311   i387_collect_fsave (regcache, regno, fpregsetp);
 312 }
 313
 314 #ifdef HAVE_PTRACE_GETREGS
 315
 316 /* Fetch all floating-point registers from process/thread TID and store
 317    thier values in GDB's register array.  */
 318
 319 static void
 320 fetch_fpregs (struct regcache *regcache, int tid)
 321 {
 322   elf_fpregset_t fpregs;
 323
 324   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
 325     perror_with_name (_("Couldn't get floating point status"));
 326
 327   supply_fpregset (regcache, (const elf_fpregset_t *) &fpregs);
 328 }
 329
 330 /* Store all valid floating-point registers in GDB's register array
 331    into the process/thread specified by TID.  */
 332
 333 static void
 334 store_fpregs (const struct regcache *regcache, int tid, int regno)
 335 {
 336   elf_fpregset_t fpregs;
 337
 338   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
 339     perror_with_name (_("Couldn't get floating point status"));
 340
 341   fill_fpregset (regcache, &fpregs, regno);
 342
 343   if (ptrace (PTRACE_SETFPREGS, tid, 0, (int) &fpregs) < 0)
 344     perror_with_name (_("Couldn't write floating point status"));
 345 }
 346
 347 #else
 348
 349 static void fetch_fpregs (struct regcache *regcache, int tid) {}
 350 static void store_fpregs (const struct regcache *regcache, int tid, int regno) {}
 351
 352 #endif
 353 \f
 354
 355 /* Transfering floating-point and SSE registers to and from GDB.  */
 356
 357 #ifdef HAVE_PTRACE_GETFPXREGS
 358
 359 /* Fill GDB's register array with the floating-point and SSE register
 360    values in *FPXREGSETP.  */
 361
 362 void
 363 supply_fpxregset (struct regcache *regcache,
 364                   const elf_fpxregset_t *fpxregsetp)
 365 {
 366   i387_supply_fxsave (regcache, -1, fpxregsetp);
 367 }
 368
 369 /* Fill register REGNO (if it is a floating-point or SSE register) in
 370    *FPXREGSETP with the value in GDB's register array.  If REGNO is
 371    -1, do this for all registers.  */
 372
 373 void
 374 fill_fpxregset (const struct regcache *regcache,
 375                 elf_fpxregset_t *fpxregsetp, int regno)
 376 {
 377   i387_collect_fxsave (regcache, regno, fpxregsetp);
 378 }
 379
 380 /* Fetch all registers covered by the PTRACE_GETFPXREGS request from
 381    process/thread TID and store their values in GDB's register array.
 382    Return non-zero if successful, zero otherwise.  */
 383
 384 static int
 385 fetch_fpxregs (struct regcache *regcache, int tid)
 386 {
 387   elf_fpxregset_t fpxregs;
 388
 389   if (! have_ptrace_getfpxregs)
 390     return 0;
 391
 392   if (ptrace (PTRACE_GETFPXREGS, tid, 0, (int) &fpxregs) < 0)
 393     {
 394       if (errno == EIO)
 395         {
 396           have_ptrace_getfpxregs = 0;
 397           return 0;
 398         }
 399
 400       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 401     }
 402
 403   supply_fpxregset (regcache, (const elf_fpxregset_t *) &fpxregs);
 404   return 1;
 405 }
 406
 407 /* Store all valid registers in GDB's register array covered by the
 408    PTRACE_SETFPXREGS request into the process/thread specified by TID.
 409    Return non-zero if successful, zero otherwise.  */
 410
 411 static int
 412 store_fpxregs (const struct regcache *regcache, int tid, int regno)
 413 {
 414   elf_fpxregset_t fpxregs;
 415
 416   if (! have_ptrace_getfpxregs)
 417     return 0;
 418
 419   if (ptrace (PTRACE_GETFPXREGS, tid, 0, &fpxregs) == -1)
 420     {
 421       if (errno == EIO)
 422         {
 423           have_ptrace_getfpxregs = 0;
 424           return 0;
 425         }
 426
 427       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 428     }
 429
 430   fill_fpxregset (regcache, &fpxregs, regno);
 431
 432   if (ptrace (PTRACE_SETFPXREGS, tid, 0, &fpxregs) == -1)
 433     perror_with_name (_("Couldn't write floating-point and SSE registers"));
 434
 435   return 1;
 436 }
 437
 438 #else
 439
 440 static int fetch_fpxregs (struct regcache *regcache, int tid) { return 0; }
 441 static int store_fpxregs (const struct regcache *regcache, int tid, int regno) { return 0; }
 442
 443 #endif /* HAVE_PTRACE_GETFPXREGS */
 444 \f
 445
 446 /* Transferring arbitrary registers between GDB and inferior.  */
 447
 448 /* Fetch register REGNO from the child process.  If REGNO is -1, do
 449    this for all registers (including the floating point and SSE
 450    registers).  */
 451
 452 static void
 453 i386_linux_fetch_inferior_registers (struct regcache *regcache, int regno)
 454 {
 455   int tid;
 456
 457   /* Use the old method of peeking around in `struct user' if the
 458      GETREGS request isn't available.  */
 459   if (!have_ptrace_getregs)
 460     {
 461       int i;
 462
 463       for (i = 0; i < gdbarch_num_regs (get_regcache_arch (regcache)); i++)
 464         if (regno == -1 || regno == i)
 465           fetch_register (regcache, i);
 466
 467       return;
 468     }
 469
 470   /* GNU/Linux LWP ID's are process ID's.  */
 471   tid = TIDGET (inferior_ptid);
 472   if (tid == 0)
 473     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 474
 475   /* Use the PTRACE_GETFPXREGS request whenever possible, since it
 476      transfers more registers in one system call, and we'll cache the
 477      results.  But remember that fetch_fpxregs can fail, and return
 478      zero.  */
 479   if (regno == -1)
 480     {
 481       fetch_regs (regcache, tid);
 482
 483       /* The call above might reset `have_ptrace_getregs'.  */
 484       if (!have_ptrace_getregs)
 485         {
 486           i386_linux_fetch_inferior_registers (regcache, regno);
 487           return;
 488         }
 489
 490       if (fetch_fpxregs (regcache, tid))
 491         return;
 492       fetch_fpregs (regcache, tid);
 493       return;
 494     }
 495
 496   if (GETREGS_SUPPLIES (regno))
 497     {
 498       fetch_regs (regcache, tid);
 499       return;
 500     }
 501
 502   if (GETFPXREGS_SUPPLIES (regno))
 503     {
 504       if (fetch_fpxregs (regcache, tid))
 505         return;
 506
 507       /* Either our processor or our kernel doesn't support the SSE
 508          registers, so read the FP registers in the traditional way,
 509          and fill the SSE registers with dummy values.  It would be
 510          more graceful to handle differences in the register set using
 511          gdbarch.  Until then, this will at least make things work
 512          plausibly.  */
 513       fetch_fpregs (regcache, tid);
 514       return;
 515     }
 516
 517   internal_error (__FILE__, __LINE__,
 518                   _("Got request for bad register number %d."), regno);
 519 }
 520
 521 /* Store register REGNO back into the child process.  If REGNO is -1,
 522    do this for all registers (including the floating point and SSE
 523    registers).  */
 524 static void
 525 i386_linux_store_inferior_registers (struct regcache *regcache, int regno)
 526 {
 527   int tid;
 528
 529   /* Use the old method of poking around in `struct user' if the
 530      SETREGS request isn't available.  */
 531   if (!have_ptrace_getregs)
 532     {
 533       int i;
 534
 535       for (i = 0; i < gdbarch_num_regs (get_regcache_arch (regcache)); i++)
 536         if (regno == -1 || regno == i)
 537           store_register (regcache, i);
 538
 539       return;
 540     }
 541
 542   /* GNU/Linux LWP ID's are process ID's.  */
 543   tid = TIDGET (inferior_ptid);
 544   if (tid == 0)
 545     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 546
 547   /* Use the PTRACE_SETFPXREGS requests whenever possible, since it
 548      transfers more registers in one system call.  But remember that
 549      store_fpxregs can fail, and return zero.  */
 550   if (regno == -1)
 551     {
 552       store_regs (regcache, tid, regno);
 553       if (store_fpxregs (regcache, tid, regno))
 554         return;
 555       store_fpregs (regcache, tid, regno);
 556       return;
 557     }
 558
 559   if (GETREGS_SUPPLIES (regno))
 560     {
 561       store_regs (regcache, tid, regno);
 562       return;
 563     }
 564
 565   if (GETFPXREGS_SUPPLIES (regno))
 566     {
 567       if (store_fpxregs (regcache, tid, regno))
 568         return;
 569
 570       /* Either our processor or our kernel doesn't support the SSE
 571          registers, so just write the FP registers in the traditional
 572          way.  */
 573       store_fpregs (regcache, tid, regno);
 574       return;
 575     }
 576
 577   internal_error (__FILE__, __LINE__,
 578                   _("Got request to store bad register number %d."), regno);
 579 }
 580 \f
 581
 582 /* Support for debug registers.  */
 583
 584 static unsigned long i386_linux_dr[DR_CONTROL + 1];
 585
 586 static unsigned long
 587 i386_linux_dr_get (ptid_t ptid, int regnum)
 588 {
 589   int tid;
 590   unsigned long value;
 591
 592   tid = TIDGET (ptid);
 593   if (tid == 0)
 594     tid = PIDGET (ptid);
 595
 596   /* FIXME: kettenis/2001-03-27: Calling perror_with_name if the
 597      ptrace call fails breaks debugging remote targets.  The correct
 598      way to fix this is to add the hardware breakpoint and watchpoint
 599      stuff to the target vector.  For now, just return zero if the
 600      ptrace call fails.  */
 601   errno = 0;
 602   value = ptrace (PTRACE_PEEKUSER, tid,
 603                   offsetof (struct user, u_debugreg[regnum]), 0);
 604   if (errno != 0)
 605 #if 0
 606     perror_with_name (_("Couldn't read debug register"));
 607 #else
 608     return 0;
 609 #endif
 610
 611   return value;
 612 }
 613
 614 static void
 615 i386_linux_dr_set (ptid_t ptid, int regnum, unsigned long value)
 616 {
 617   int tid;
 618
 619   tid = TIDGET (ptid);
 620   if (tid == 0)
 621     tid = PIDGET (ptid);
 622
 623   errno = 0;
 624   ptrace (PTRACE_POKEUSER, tid,
 625           offsetof (struct user, u_debugreg[regnum]), value);
 626   if (errno != 0)
 627     perror_with_name (_("Couldn't write debug register"));
 628 }
 629
 630 void
 631 i386_linux_dr_set_control (unsigned long control)
 632 {
 633   struct lwp_info *lp;
 634   ptid_t ptid;
 635
 636   i386_linux_dr[DR_CONTROL] = control;
 637   ALL_LWPS (lp, ptid)
 638     i386_linux_dr_set (ptid, DR_CONTROL, control);
 639 }
 640
 641 void
 642 i386_linux_dr_set_addr (int regnum, CORE_ADDR addr)
 643 {
 644   struct lwp_info *lp;
 645   ptid_t ptid;
 646
 647   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 648
 649   i386_linux_dr[DR_FIRSTADDR + regnum] = addr;
 650   ALL_LWPS (lp, ptid)
 651     i386_linux_dr_set (ptid, DR_FIRSTADDR + regnum, addr);
 652 }
 653
 654 void
 655 i386_linux_dr_reset_addr (int regnum)
 656 {
 657   i386_linux_dr_set_addr (regnum, 0);
 658 }
 659
 660 unsigned long
 661 i386_linux_dr_get_status (void)
 662 {
 663   return i386_linux_dr_get (inferior_ptid, DR_STATUS);
 664 }
 665
 666 static void
 667 i386_linux_new_thread (ptid_t ptid)
 668 {
 669   int i;
 670
 671   for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
 672     i386_linux_dr_set (ptid, i, i386_linux_dr[i]);
 673
 674   i386_linux_dr_set (ptid, DR_CONTROL, i386_linux_dr[DR_CONTROL]);
 675 }
 676 \f
 677
 678 /* Called by libthread_db.  Returns a pointer to the thread local
 679    storage (or its descriptor).  */
 680
 681 ps_err_e
 682 ps_get_thread_area (const struct ps_prochandle *ph,
 683                     lwpid_t lwpid, int idx, void **base)
 684 {
 685   /* NOTE: cagney/2003-08-26: The definition of this buffer is found
 686      in the kernel header <asm-i386/ldt.h>.  It, after padding, is 4 x
 687      4 byte integers in size: `entry_number', `base_addr', `limit',
 688      and a bunch of status bits.
 689
 690      The values returned by this ptrace call should be part of the
 691      regcache buffer, and ps_get_thread_area should channel its
 692      request through the regcache.  That way remote targets could
 693      provide the value using the remote protocol and not this direct
 694      call.
 695
 696      Is this function needed?  I'm guessing that the `base' is the
 697      address of a a descriptor that libthread_db uses to find the
 698      thread local address base that GDB needs.  Perhaps that
 699      descriptor is defined by the ABI.  Anyway, given that
 700      libthread_db calls this function without prompting (gdb
 701      requesting tls base) I guess it needs info in there anyway.  */
 702   unsigned int desc[4];
 703   gdb_assert (sizeof (int) == 4);
 704
 705 #ifndef PTRACE_GET_THREAD_AREA
 706 #define PTRACE_GET_THREAD_AREA 25
 707 #endif
 708
 709   if (ptrace (PTRACE_GET_THREAD_AREA, lwpid,
 710               (void *) idx, (unsigned long) &desc) < 0)
 711     return PS_ERR;
 712
 713   *(int *)base = desc[1];
 714   return PS_OK;
 715 }
 716 \f
 717
 718 /* The instruction for a GNU/Linux system call is:
 719        int $0x80
 720    or 0xcd 0x80.  */
 721
 722 static const unsigned char linux_syscall[] = { 0xcd, 0x80 };
 723
 724 #define LINUX_SYSCALL_LEN (sizeof linux_syscall)
 725
 726 /* The system call number is stored in the %eax register.  */
 727 #define LINUX_SYSCALL_REGNUM I386_EAX_REGNUM
 728
 729 /* We are specifically interested in the sigreturn and rt_sigreturn
 730    system calls.  */
 731
 732 #ifndef SYS_sigreturn
 733 #define SYS_sigreturn           0x77
 734 #endif
 735 #ifndef SYS_rt_sigreturn
 736 #define SYS_rt_sigreturn        0xad
 737 #endif
 738
 739 /* Offset to saved processor flags, from <asm/sigcontext.h>.  */
 740 #define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64)
 741
 742 /* Resume execution of the inferior process.
 743    If STEP is nonzero, single-step it.
 744    If SIGNAL is nonzero, give it that signal.  */
 745
 746 static void
 747 i386_linux_resume (ptid_t ptid, int step, enum target_signal signal)
 748 {
 749   int pid = PIDGET (ptid);
 750
 751   int request = PTRACE_CONT;
 752
 753   if (step)
 754     {
 755       struct regcache *regcache = get_thread_regcache (pid_to_ptid (pid));
 756       ULONGEST pc;
 757       gdb_byte buf[LINUX_SYSCALL_LEN];
 758
 759       request = PTRACE_SINGLESTEP;
 760
 761       regcache_cooked_read_unsigned
 762         (regcache, gdbarch_pc_regnum (get_regcache_arch (regcache)), &pc);
 763
 764       /* Returning from a signal trampoline is done by calling a
 765          special system call (sigreturn or rt_sigreturn, see
 766          i386-linux-tdep.c for more information).  This system call
 767          restores the registers that were saved when the signal was
 768          raised, including %eflags.  That means that single-stepping
 769          won't work.  Instead, we'll have to modify the signal context
 770          that's about to be restored, and set the trace flag there.  */
 771
 772       /* First check if PC is at a system call.  */
 773       if (read_memory_nobpt (pc, buf, LINUX_SYSCALL_LEN) == 0
 774           && memcmp (buf, linux_syscall, LINUX_SYSCALL_LEN) == 0)
 775         {
 776           ULONGEST syscall;
 777           regcache_cooked_read_unsigned (regcache,
 778                                          LINUX_SYSCALL_REGNUM, &syscall);
 779
 780           /* Then check the system call number.  */
 781           if (syscall == SYS_sigreturn || syscall == SYS_rt_sigreturn)
 782             {
 783               ULONGEST sp, addr;
 784               unsigned long int eflags;
 785
 786               regcache_cooked_read_unsigned (regcache, I386_ESP_REGNUM, &sp);
 787               if (syscall == SYS_rt_sigreturn)
 788                 addr = read_memory_integer (sp + 8, 4) + 20;
 789               else
 790                 addr = sp;
 791
 792               /* Set the trace flag in the context that's about to be
 793                  restored.  */
 794               addr += LINUX_SIGCONTEXT_EFLAGS_OFFSET;
 795               read_memory (addr, (gdb_byte *) &eflags, 4);
 796               eflags |= 0x0100;
 797               write_memory (addr, (gdb_byte *) &eflags, 4);
 798             }
 799         }
 800     }
 801
 802   if (ptrace (request, pid, 0, target_signal_to_host (signal)) == -1)
 803     perror_with_name (("ptrace"));
 804 }
 805
 806 static void (*super_post_startup_inferior) (ptid_t ptid);
 807
 808 static void
 809 i386_linux_child_post_startup_inferior (ptid_t ptid)
 810 {
 811   i386_cleanup_dregs ();
 812   super_post_startup_inferior (ptid);
 813 }
 814
 815 void
 816 _initialize_i386_linux_nat (void)
 817 {
 818   struct target_ops *t;
 819
 820   /* Fill in the generic GNU/Linux methods.  */
 821   t = linux_target ();
 822
 823   /* Override the default ptrace resume method.  */
 824   t->to_resume = i386_linux_resume;
 825
 826   /* Override the GNU/Linux inferior startup hook.  */
 827   super_post_startup_inferior = t->to_post_startup_inferior;
 828   t->to_post_startup_inferior = i386_linux_child_post_startup_inferior;
 829
 830   /* Add our register access methods.  */
 831   t->to_fetch_registers = i386_linux_fetch_inferior_registers;
 832   t->to_store_registers = i386_linux_store_inferior_registers;
 833
 834   /* Register the target.  */
 835   linux_nat_add_target (t);
 836   linux_nat_set_new_thread (t, i386_linux_new_thread);
 837 }