gdb/i386-linux-nat.c

   1 /* Native-dependent code for GNU/Linux i386.
   2
   3    Copyright (C) 1999-2024 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "inferior.h"
  22 #include "gdbcore.h"
  23 #include "regcache.h"
  24 #include "elf/common.h"
  25 #include "nat/gdb_ptrace.h"
  26 #include <sys/uio.h>
  27 #include "gregset.h"
  28 #include "gdb_proc_service.h"
  29
  30 #include "i386-linux-nat.h"
  31 #include "i387-tdep.h"
  32 #include "i386-tdep.h"
  33 #include "i386-linux-tdep.h"
  34 #include "gdbsupport/x86-xstate.h"
  35
  36 #include "x86-linux-nat.h"
  37 #include "nat/linux-ptrace.h"
  38 #include "inf-ptrace.h"
  39
  40 struct i386_linux_nat_target final : public x86_linux_nat_target
  41 {
  42   /* Add our register access methods.  */
  43   void fetch_registers (struct regcache *, int) override;
  44   void store_registers (struct regcache *, int) override;
  45
  46   /* Override the default ptrace resume method.  */
  47   void low_resume (ptid_t ptid, int step, enum gdb_signal sig) override;
  48 };
  49
  50 static i386_linux_nat_target the_i386_linux_nat_target;
  51
  52 /* The register sets used in GNU/Linux ELF core-dumps are identical to
  53    the register sets in `struct user' that is used for a.out
  54    core-dumps, and is also used by `ptrace'.  The corresponding types
  55    are `elf_gregset_t' for the general-purpose registers (with
  56    `elf_greg_t' the type of a single GP register) and `elf_fpregset_t'
  57    for the floating-point registers.
  58
  59    Those types used to be available under the names `gregset_t' and
  60    `fpregset_t' too, and this file used those names in the past.  But
  61    those names are now used for the register sets used in the
  62    `mcontext_t' type, and have a different size and layout.  */
  63
  64 /* Which ptrace request retrieves which registers?
  65    These apply to the corresponding SET requests as well.  */
  66
  67 #define GETREGS_SUPPLIES(regno) \
  68   ((0 <= (regno) && (regno) <= 15) || (regno) == I386_LINUX_ORIG_EAX_REGNUM)
  69
  70 #define GETFPXREGS_SUPPLIES(regno) \
  71   (I386_ST0_REGNUM <= (regno) && (regno) < I386_SSE_NUM_REGS)
  72
  73 #define GETXSTATEREGS_SUPPLIES(regno) \
  74   (I386_ST0_REGNUM <= (regno) && (regno) < I386_PKEYS_NUM_REGS)
  75
  76 /* Does the current host support the GETREGS request?  */
  77 int have_ptrace_getregs =
  78 #ifdef HAVE_PTRACE_GETREGS
  79   1
  80 #else
  81   0
  82 #endif
  83 ;
  84
  85 /* Does the current host support the GETFPXREGS request?  The header
  86    file may or may not define it, and even if it is defined, the
  87    kernel will return EIO if it's running on a pre-SSE processor.
  88
  89    My instinct is to attach this to some architecture- or
  90    target-specific data structure, but really, a particular GDB
  91    process can only run on top of one kernel at a time.  So it's okay
  92    for this to be a simple variable.  */
  93 int have_ptrace_getfpxregs =
  94 #ifdef HAVE_PTRACE_GETFPXREGS
  95   -1
  96 #else
  97   0
  98 #endif
  99 ;
 100 \f
 101
 102 /* Accessing registers through the U area, one at a time.  */
 103
 104 /* Fetch one register.  */
 105
 106 static void
 107 fetch_register (struct regcache *regcache, int regno)
 108 {
 109   pid_t tid;
 110   int val;
 111
 112   gdb_assert (!have_ptrace_getregs);
 113   if (i386_linux_gregset_reg_offset[regno] == -1)
 114     {
 115       regcache->raw_supply (regno, NULL);
 116       return;
 117     }
 118
 119   tid = get_ptrace_pid (regcache->ptid ());
 120
 121   errno = 0;
 122   val = ptrace (PTRACE_PEEKUSER, tid,
 123                 i386_linux_gregset_reg_offset[regno], 0);
 124   if (errno != 0)
 125     error (_("Couldn't read register %s (#%d): %s."),
 126            gdbarch_register_name (regcache->arch (), regno),
 127            regno, safe_strerror (errno));
 128
 129   regcache->raw_supply (regno, &val);
 130 }
 131
 132 /* Store one register.  */
 133
 134 static void
 135 store_register (const struct regcache *regcache, int regno)
 136 {
 137   pid_t tid;
 138   int val;
 139
 140   gdb_assert (!have_ptrace_getregs);
 141   if (i386_linux_gregset_reg_offset[regno] == -1)
 142     return;
 143
 144   tid = get_ptrace_pid (regcache->ptid ());
 145
 146   errno = 0;
 147   regcache->raw_collect (regno, &val);
 148   ptrace (PTRACE_POKEUSER, tid,
 149           i386_linux_gregset_reg_offset[regno], val);
 150   if (errno != 0)
 151     error (_("Couldn't write register %s (#%d): %s."),
 152            gdbarch_register_name (regcache->arch (), regno),
 153            regno, safe_strerror (errno));
 154 }
 155 \f
 156
 157 /* Transfering the general-purpose registers between GDB, inferiors
 158    and core files.  */
 159
 160 /* Fill GDB's register array with the general-purpose register values
 161    in *GREGSETP.  */
 162
 163 void
 164 supply_gregset (struct regcache *regcache, const elf_gregset_t *gregsetp)
 165 {
 166   const gdb_byte *regp = (const gdb_byte *) gregsetp;
 167   int i;
 168
 169   for (i = 0; i < I386_NUM_GREGS; i++)
 170     regcache->raw_supply (i, regp + i386_linux_gregset_reg_offset[i]);
 171
 172   if (I386_LINUX_ORIG_EAX_REGNUM
 173         < gdbarch_num_regs (regcache->arch ()))
 174     regcache->raw_supply
 175       (I386_LINUX_ORIG_EAX_REGNUM,
 176        regp + i386_linux_gregset_reg_offset[I386_LINUX_ORIG_EAX_REGNUM]);
 177 }
 178
 179 /* Fill register REGNO (if it is a general-purpose register) in
 180    *GREGSETPS with the value in GDB's register array.  If REGNO is -1,
 181    do this for all registers.  */
 182
 183 void
 184 fill_gregset (const struct regcache *regcache,
 185               elf_gregset_t *gregsetp, int regno)
 186 {
 187   gdb_byte *regp = (gdb_byte *) gregsetp;
 188   int i;
 189
 190   for (i = 0; i < I386_NUM_GREGS; i++)
 191     if (regno == -1 || regno == i)
 192       regcache->raw_collect (i, regp + i386_linux_gregset_reg_offset[i]);
 193
 194   if ((regno == -1 || regno == I386_LINUX_ORIG_EAX_REGNUM)
 195       && I386_LINUX_ORIG_EAX_REGNUM
 196            < gdbarch_num_regs (regcache->arch ()))
 197     regcache->raw_collect
 198       (I386_LINUX_ORIG_EAX_REGNUM,
 199        regp + i386_linux_gregset_reg_offset[I386_LINUX_ORIG_EAX_REGNUM]);
 200 }
 201
 202 #ifdef HAVE_PTRACE_GETREGS
 203
 204 /* Fetch all general-purpose registers from process/thread TID and
 205    store their values in GDB's register array.  */
 206
 207 static void
 208 fetch_regs (struct regcache *regcache, int tid)
 209 {
 210   elf_gregset_t regs;
 211   elf_gregset_t *regs_p = &regs;
 212
 213   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
 214     {
 215       if (errno == EIO)
 216         {
 217           /* The kernel we're running on doesn't support the GETREGS
 218              request.  Reset `have_ptrace_getregs'.  */
 219           have_ptrace_getregs = 0;
 220           return;
 221         }
 222
 223       perror_with_name (_("Couldn't get registers"));
 224     }
 225
 226   supply_gregset (regcache, (const elf_gregset_t *) regs_p);
 227 }
 228
 229 /* Store all valid general-purpose registers in GDB's register array
 230    into the process/thread specified by TID.  */
 231
 232 static void
 233 store_regs (const struct regcache *regcache, int tid, int regno)
 234 {
 235   elf_gregset_t regs;
 236
 237   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
 238     perror_with_name (_("Couldn't get registers"));
 239
 240   fill_gregset (regcache, &regs, regno);
 241
 242   if (ptrace (PTRACE_SETREGS, tid, 0, (int) &regs) < 0)
 243     perror_with_name (_("Couldn't write registers"));
 244 }
 245
 246 #else
 247
 248 static void fetch_regs (struct regcache *regcache, int tid) {}
 249 static void store_regs (const struct regcache *regcache, int tid, int regno) {}
 250
 251 #endif
 252 \f
 253
 254 /* Transfering floating-point registers between GDB, inferiors and cores.  */
 255
 256 /* Fill GDB's register array with the floating-point register values in
 257    *FPREGSETP.  */
 258
 259 void
 260 supply_fpregset (struct regcache *regcache, const elf_fpregset_t *fpregsetp)
 261 {
 262   i387_supply_fsave (regcache, -1, fpregsetp);
 263 }
 264
 265 /* Fill register REGNO (if it is a floating-point register) in
 266    *FPREGSETP with the value in GDB's register array.  If REGNO is -1,
 267    do this for all registers.  */
 268
 269 void
 270 fill_fpregset (const struct regcache *regcache,
 271                elf_fpregset_t *fpregsetp, int regno)
 272 {
 273   i387_collect_fsave (regcache, regno, fpregsetp);
 274 }
 275
 276 #ifdef HAVE_PTRACE_GETREGS
 277
 278 /* Fetch all floating-point registers from process/thread TID and store
 279    thier values in GDB's register array.  */
 280
 281 static void
 282 fetch_fpregs (struct regcache *regcache, int tid)
 283 {
 284   elf_fpregset_t fpregs;
 285
 286   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
 287     perror_with_name (_("Couldn't get floating point status"));
 288
 289   supply_fpregset (regcache, (const elf_fpregset_t *) &fpregs);
 290 }
 291
 292 /* Store all valid floating-point registers in GDB's register array
 293    into the process/thread specified by TID.  */
 294
 295 static void
 296 store_fpregs (const struct regcache *regcache, int tid, int regno)
 297 {
 298   elf_fpregset_t fpregs;
 299
 300   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
 301     perror_with_name (_("Couldn't get floating point status"));
 302
 303   fill_fpregset (regcache, &fpregs, regno);
 304
 305   if (ptrace (PTRACE_SETFPREGS, tid, 0, (int) &fpregs) < 0)
 306     perror_with_name (_("Couldn't write floating point status"));
 307 }
 308
 309 #else
 310
 311 static void
 312 fetch_fpregs (struct regcache *regcache, int tid)
 313 {
 314 }
 315
 316 static void
 317 store_fpregs (const struct regcache *regcache, int tid, int regno)
 318 {
 319 }
 320
 321 #endif
 322 \f
 323
 324 /* Transfering floating-point and SSE registers to and from GDB.  */
 325
 326 /* Fetch all registers covered by the PTRACE_GETREGSET request from
 327    process/thread TID and store their values in GDB's register array.
 328    Return non-zero if successful, zero otherwise.  */
 329
 330 static int
 331 fetch_xstateregs (struct regcache *regcache, int tid)
 332 {
 333   struct gdbarch *gdbarch = regcache->arch ();
 334   const i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
 335   char xstateregs[tdep->xsave_layout.sizeof_xsave];
 336   struct iovec iov;
 337
 338   if (have_ptrace_getregset != TRIBOOL_TRUE)
 339     return 0;
 340
 341   iov.iov_base = xstateregs;
 342   iov.iov_len = sizeof(xstateregs);
 343   if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE,
 344               &iov) < 0)
 345     perror_with_name (_("Couldn't read extended state status"));
 346
 347   i387_supply_xsave (regcache, -1, xstateregs);
 348   return 1;
 349 }
 350
 351 /* Store all valid registers in GDB's register array covered by the
 352    PTRACE_SETREGSET request into the process/thread specified by TID.
 353    Return non-zero if successful, zero otherwise.  */
 354
 355 static int
 356 store_xstateregs (const struct regcache *regcache, int tid, int regno)
 357 {
 358   struct gdbarch *gdbarch = regcache->arch ();
 359   const i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
 360   char xstateregs[tdep->xsave_layout.sizeof_xsave];
 361   struct iovec iov;
 362
 363   if (have_ptrace_getregset != TRIBOOL_TRUE)
 364     return 0;
 365
 366   iov.iov_base = xstateregs;
 367   iov.iov_len = sizeof(xstateregs);
 368   if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE,
 369               &iov) < 0)
 370     perror_with_name (_("Couldn't read extended state status"));
 371
 372   i387_collect_xsave (regcache, regno, xstateregs, 0);
 373
 374   if (ptrace (PTRACE_SETREGSET, tid, (unsigned int) NT_X86_XSTATE,
 375               (int) &iov) < 0)
 376     perror_with_name (_("Couldn't write extended state status"));
 377
 378   return 1;
 379 }
 380
 381 #ifdef HAVE_PTRACE_GETFPXREGS
 382
 383 /* Fetch all registers covered by the PTRACE_GETFPXREGS request from
 384    process/thread TID and store their values in GDB's register array.
 385    Return non-zero if successful, zero otherwise.  */
 386
 387 static int
 388 fetch_fpxregs (struct regcache *regcache, int tid)
 389 {
 390   elf_fpxregset_t fpxregs;
 391
 392   if (! have_ptrace_getfpxregs)
 393     return 0;
 394
 395   if (ptrace (PTRACE_GETFPXREGS, tid, 0, (int) &fpxregs) < 0)
 396     {
 397       if (errno == EIO)
 398         {
 399           have_ptrace_getfpxregs = 0;
 400           return 0;
 401         }
 402
 403       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 404     }
 405
 406   i387_supply_fxsave (regcache, -1, (const elf_fpxregset_t *) &fpxregs);
 407   return 1;
 408 }
 409
 410 /* Store all valid registers in GDB's register array covered by the
 411    PTRACE_SETFPXREGS request into the process/thread specified by TID.
 412    Return non-zero if successful, zero otherwise.  */
 413
 414 static int
 415 store_fpxregs (const struct regcache *regcache, int tid, int regno)
 416 {
 417   elf_fpxregset_t fpxregs;
 418
 419   if (! have_ptrace_getfpxregs)
 420     return 0;
 421
 422   if (ptrace (PTRACE_GETFPXREGS, tid, 0, &fpxregs) == -1)
 423     {
 424       if (errno == EIO)
 425         {
 426           have_ptrace_getfpxregs = 0;
 427           return 0;
 428         }
 429
 430       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 431     }
 432
 433   i387_collect_fxsave (regcache, regno, &fpxregs);
 434
 435   if (ptrace (PTRACE_SETFPXREGS, tid, 0, &fpxregs) == -1)
 436     perror_with_name (_("Couldn't write floating-point and SSE registers"));
 437
 438   return 1;
 439 }
 440
 441 #else
 442
 443 static int
 444 fetch_fpxregs (struct regcache *regcache, int tid)
 445 {
 446   return 0;
 447 }
 448
 449 static int
 450 store_fpxregs (const struct regcache *regcache, int tid, int regno)
 451 {
 452   return 0;
 453 }
 454
 455 #endif /* HAVE_PTRACE_GETFPXREGS */
 456 \f
 457
 458 /* Transferring arbitrary registers between GDB and inferior.  */
 459
 460 /* Fetch register REGNO from the child process.  If REGNO is -1, do
 461    this for all registers (including the floating point and SSE
 462    registers).  */
 463
 464 void
 465 i386_linux_nat_target::fetch_registers (struct regcache *regcache, int regno)
 466 {
 467   pid_t tid;
 468
 469   /* Use the old method of peeking around in `struct user' if the
 470      GETREGS request isn't available.  */
 471   if (!have_ptrace_getregs)
 472     {
 473       int i;
 474
 475       for (i = 0; i < gdbarch_num_regs (regcache->arch ()); i++)
 476         if (regno == -1 || regno == i)
 477           fetch_register (regcache, i);
 478
 479       return;
 480     }
 481
 482   tid = get_ptrace_pid (regcache->ptid ());
 483
 484   /* Use the PTRACE_GETFPXREGS request whenever possible, since it
 485      transfers more registers in one system call, and we'll cache the
 486      results.  But remember that fetch_fpxregs can fail, and return
 487      zero.  */
 488   if (regno == -1)
 489     {
 490       fetch_regs (regcache, tid);
 491
 492       /* The call above might reset `have_ptrace_getregs'.  */
 493       if (!have_ptrace_getregs)
 494         {
 495           fetch_registers (regcache, regno);
 496           return;
 497         }
 498
 499       if (fetch_xstateregs (regcache, tid))
 500         return;
 501       if (fetch_fpxregs (regcache, tid))
 502         return;
 503       fetch_fpregs (regcache, tid);
 504       return;
 505     }
 506
 507   if (GETREGS_SUPPLIES (regno))
 508     {
 509       fetch_regs (regcache, tid);
 510       return;
 511     }
 512
 513   if (GETXSTATEREGS_SUPPLIES (regno))
 514     {
 515       if (fetch_xstateregs (regcache, tid))
 516         return;
 517     }
 518
 519   if (GETFPXREGS_SUPPLIES (regno))
 520     {
 521       if (fetch_fpxregs (regcache, tid))
 522         return;
 523
 524       /* Either our processor or our kernel doesn't support the SSE
 525          registers, so read the FP registers in the traditional way,
 526          and fill the SSE registers with dummy values.  It would be
 527          more graceful to handle differences in the register set using
 528          gdbarch.  Until then, this will at least make things work
 529          plausibly.  */
 530       fetch_fpregs (regcache, tid);
 531       return;
 532     }
 533
 534   internal_error (_("Got request for bad register number %d."), regno);
 535 }
 536
 537 /* Store register REGNO back into the child process.  If REGNO is -1,
 538    do this for all registers (including the floating point and SSE
 539    registers).  */
 540 void
 541 i386_linux_nat_target::store_registers (struct regcache *regcache, int regno)
 542 {
 543   pid_t tid;
 544
 545   /* Use the old method of poking around in `struct user' if the
 546      SETREGS request isn't available.  */
 547   if (!have_ptrace_getregs)
 548     {
 549       int i;
 550
 551       for (i = 0; i < gdbarch_num_regs (regcache->arch ()); i++)
 552         if (regno == -1 || regno == i)
 553           store_register (regcache, i);
 554
 555       return;
 556     }
 557
 558   tid = get_ptrace_pid (regcache->ptid ());
 559
 560   /* Use the PTRACE_SETFPXREGS requests whenever possible, since it
 561      transfers more registers in one system call.  But remember that
 562      store_fpxregs can fail, and return zero.  */
 563   if (regno == -1)
 564     {
 565       store_regs (regcache, tid, regno);
 566       if (store_xstateregs (regcache, tid, regno))
 567         return;
 568       if (store_fpxregs (regcache, tid, regno))
 569         return;
 570       store_fpregs (regcache, tid, regno);
 571       return;
 572     }
 573
 574   if (GETREGS_SUPPLIES (regno))
 575     {
 576       store_regs (regcache, tid, regno);
 577       return;
 578     }
 579
 580   if (GETXSTATEREGS_SUPPLIES (regno))
 581     {
 582       if (store_xstateregs (regcache, tid, regno))
 583         return;
 584     }
 585
 586   if (GETFPXREGS_SUPPLIES (regno))
 587     {
 588       if (store_fpxregs (regcache, tid, regno))
 589         return;
 590
 591       /* Either our processor or our kernel doesn't support the SSE
 592          registers, so just write the FP registers in the traditional
 593          way.  */
 594       store_fpregs (regcache, tid, regno);
 595       return;
 596     }
 597
 598   internal_error (_("Got request to store bad register number %d."), regno);
 599 }
 600 \f
 601
 602 /* Called by libthread_db.  Returns a pointer to the thread local
 603    storage (or its descriptor).  */
 604
 605 ps_err_e
 606 ps_get_thread_area (struct ps_prochandle *ph,
 607                     lwpid_t lwpid, int idx, void **base)
 608 {
 609   unsigned int base_addr;
 610   ps_err_e result;
 611
 612   result = x86_linux_get_thread_area (lwpid, (void *) idx, &base_addr);
 613
 614   if (result == PS_OK)
 615     *(int *) base = base_addr;
 616
 617   return result;
 618 }
 619 \f
 620
 621 /* The instruction for a GNU/Linux system call is:
 622        int $0x80
 623    or 0xcd 0x80.  */
 624
 625 static const unsigned char linux_syscall[] = { 0xcd, 0x80 };
 626
 627 #define LINUX_SYSCALL_LEN (sizeof linux_syscall)
 628
 629 /* The system call number is stored in the %eax register.  */
 630 #define LINUX_SYSCALL_REGNUM I386_EAX_REGNUM
 631
 632 /* We are specifically interested in the sigreturn and rt_sigreturn
 633    system calls.  */
 634
 635 #ifndef SYS_sigreturn
 636 #define SYS_sigreturn           0x77
 637 #endif
 638 #ifndef SYS_rt_sigreturn
 639 #define SYS_rt_sigreturn        0xad
 640 #endif
 641
 642 /* Offset to saved processor flags, from <asm/sigcontext.h>.  */
 643 #define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64)
 644
 645 /* Resume execution of the inferior process.
 646    If STEP is nonzero, single-step it.
 647    If SIGNAL is nonzero, give it that signal.  */
 648
 649 void
 650 i386_linux_nat_target::low_resume (ptid_t ptid, int step, enum gdb_signal signal)
 651 {
 652   int pid = ptid.lwp ();
 653   int request;
 654
 655   if (catch_syscall_enabled ())
 656    request = PTRACE_SYSCALL;
 657   else
 658     request = PTRACE_CONT;
 659
 660   if (step)
 661     {
 662       struct regcache *regcache = get_thread_regcache (this, ptid);
 663       struct gdbarch *gdbarch = regcache->arch ();
 664       enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 665       ULONGEST pc;
 666       gdb_byte buf[LINUX_SYSCALL_LEN];
 667
 668       request = PTRACE_SINGLESTEP;
 669
 670       regcache_cooked_read_unsigned (regcache,
 671                                      gdbarch_pc_regnum (gdbarch), &pc);
 672
 673       /* Returning from a signal trampoline is done by calling a
 674          special system call (sigreturn or rt_sigreturn, see
 675          i386-linux-tdep.c for more information).  This system call
 676          restores the registers that were saved when the signal was
 677          raised, including %eflags.  That means that single-stepping
 678          won't work.  Instead, we'll have to modify the signal context
 679          that's about to be restored, and set the trace flag there.  */
 680
 681       /* First check if PC is at a system call.  */
 682       if (target_read_memory (pc, buf, LINUX_SYSCALL_LEN) == 0
 683           && memcmp (buf, linux_syscall, LINUX_SYSCALL_LEN) == 0)
 684         {
 685           ULONGEST syscall;
 686           regcache_cooked_read_unsigned (regcache,
 687                                          LINUX_SYSCALL_REGNUM, &syscall);
 688
 689           /* Then check the system call number.  */
 690           if (syscall == SYS_sigreturn || syscall == SYS_rt_sigreturn)
 691             {
 692               ULONGEST sp, addr;
 693               unsigned long int eflags;
 694
 695               regcache_cooked_read_unsigned (regcache, I386_ESP_REGNUM, &sp);
 696               if (syscall == SYS_rt_sigreturn)
 697                 addr = read_memory_unsigned_integer (sp + 8, 4, byte_order)
 698                   + 20;
 699               else
 700                 addr = sp;
 701
 702               /* Set the trace flag in the context that's about to be
 703                  restored.  */
 704               addr += LINUX_SIGCONTEXT_EFLAGS_OFFSET;
 705               read_memory (addr, (gdb_byte *) &eflags, 4);
 706               eflags |= 0x0100;
 707               write_memory (addr, (gdb_byte *) &eflags, 4);
 708             }
 709         }
 710     }
 711
 712   if (ptrace (request, pid, 0, gdb_signal_to_host (signal)) == -1)
 713     perror_with_name (("ptrace"));
 714 }
 715
 716 void _initialize_i386_linux_nat ();
 717 void
 718 _initialize_i386_linux_nat ()
 719 {
 720   linux_target = &the_i386_linux_nat_target;
 721
 722   /* Add the target.  */
 723   add_inf_child_target (linux_target);
 724 }