gdb/i386-linux-nat.c

   1 /* Native-dependent code for GNU/Linux i386.
   2
   3    Copyright (C) 1999-2019 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   char xstateregs[X86_XSTATE_MAX_SIZE];
 334   struct iovec iov;
 335
 336   if (have_ptrace_getregset != TRIBOOL_TRUE)
 337     return 0;
 338
 339   iov.iov_base = xstateregs;
 340   iov.iov_len = sizeof(xstateregs);
 341   if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE,
 342               &iov) < 0)
 343     perror_with_name (_("Couldn't read extended state status"));
 344
 345   i387_supply_xsave (regcache, -1, xstateregs);
 346   return 1;
 347 }
 348
 349 /* Store all valid registers in GDB's register array covered by the
 350    PTRACE_SETREGSET request into the process/thread specified by TID.
 351    Return non-zero if successful, zero otherwise.  */
 352
 353 static int
 354 store_xstateregs (const struct regcache *regcache, int tid, int regno)
 355 {
 356   char xstateregs[X86_XSTATE_MAX_SIZE];
 357   struct iovec iov;
 358
 359   if (have_ptrace_getregset != TRIBOOL_TRUE)
 360     return 0;
 361
 362   iov.iov_base = xstateregs;
 363   iov.iov_len = sizeof(xstateregs);
 364   if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE,
 365               &iov) < 0)
 366     perror_with_name (_("Couldn't read extended state status"));
 367
 368   i387_collect_xsave (regcache, regno, xstateregs, 0);
 369
 370   if (ptrace (PTRACE_SETREGSET, tid, (unsigned int) NT_X86_XSTATE,
 371               (int) &iov) < 0)
 372     perror_with_name (_("Couldn't write extended state status"));
 373
 374   return 1;
 375 }
 376
 377 #ifdef HAVE_PTRACE_GETFPXREGS
 378
 379 /* Fetch all registers covered by the PTRACE_GETFPXREGS request from
 380    process/thread TID and store their values in GDB's register array.
 381    Return non-zero if successful, zero otherwise.  */
 382
 383 static int
 384 fetch_fpxregs (struct regcache *regcache, int tid)
 385 {
 386   elf_fpxregset_t fpxregs;
 387
 388   if (! have_ptrace_getfpxregs)
 389     return 0;
 390
 391   if (ptrace (PTRACE_GETFPXREGS, tid, 0, (int) &fpxregs) < 0)
 392     {
 393       if (errno == EIO)
 394         {
 395           have_ptrace_getfpxregs = 0;
 396           return 0;
 397         }
 398
 399       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 400     }
 401
 402   i387_supply_fxsave (regcache, -1, (const elf_fpxregset_t *) &fpxregs);
 403   return 1;
 404 }
 405
 406 /* Store all valid registers in GDB's register array covered by the
 407    PTRACE_SETFPXREGS request into the process/thread specified by TID.
 408    Return non-zero if successful, zero otherwise.  */
 409
 410 static int
 411 store_fpxregs (const struct regcache *regcache, int tid, int regno)
 412 {
 413   elf_fpxregset_t fpxregs;
 414
 415   if (! have_ptrace_getfpxregs)
 416     return 0;
 417
 418   if (ptrace (PTRACE_GETFPXREGS, tid, 0, &fpxregs) == -1)
 419     {
 420       if (errno == EIO)
 421         {
 422           have_ptrace_getfpxregs = 0;
 423           return 0;
 424         }
 425
 426       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 427     }
 428
 429   i387_collect_fxsave (regcache, regno, &fpxregs);
 430
 431   if (ptrace (PTRACE_SETFPXREGS, tid, 0, &fpxregs) == -1)
 432     perror_with_name (_("Couldn't write floating-point and SSE registers"));
 433
 434   return 1;
 435 }
 436
 437 #else
 438
 439 static int
 440 fetch_fpxregs (struct regcache *regcache, int tid)
 441 {
 442   return 0;
 443 }
 444
 445 static int
 446 store_fpxregs (const struct regcache *regcache, int tid, int regno)
 447 {
 448   return 0;
 449 }
 450
 451 #endif /* HAVE_PTRACE_GETFPXREGS */
 452 \f
 453
 454 /* Transferring arbitrary registers between GDB and inferior.  */
 455
 456 /* Fetch register REGNO from the child process.  If REGNO is -1, do
 457    this for all registers (including the floating point and SSE
 458    registers).  */
 459
 460 void
 461 i386_linux_nat_target::fetch_registers (struct regcache *regcache, int regno)
 462 {
 463   pid_t tid;
 464
 465   /* Use the old method of peeking around in `struct user' if the
 466      GETREGS request isn't available.  */
 467   if (!have_ptrace_getregs)
 468     {
 469       int i;
 470
 471       for (i = 0; i < gdbarch_num_regs (regcache->arch ()); i++)
 472         if (regno == -1 || regno == i)
 473           fetch_register (regcache, i);
 474
 475       return;
 476     }
 477
 478   tid = get_ptrace_pid (regcache->ptid ());
 479
 480   /* Use the PTRACE_GETFPXREGS request whenever possible, since it
 481      transfers more registers in one system call, and we'll cache the
 482      results.  But remember that fetch_fpxregs can fail, and return
 483      zero.  */
 484   if (regno == -1)
 485     {
 486       fetch_regs (regcache, tid);
 487
 488       /* The call above might reset `have_ptrace_getregs'.  */
 489       if (!have_ptrace_getregs)
 490         {
 491           fetch_registers (regcache, regno);
 492           return;
 493         }
 494
 495       if (fetch_xstateregs (regcache, tid))
 496         return;
 497       if (fetch_fpxregs (regcache, tid))
 498         return;
 499       fetch_fpregs (regcache, tid);
 500       return;
 501     }
 502
 503   if (GETREGS_SUPPLIES (regno))
 504     {
 505       fetch_regs (regcache, tid);
 506       return;
 507     }
 508
 509   if (GETXSTATEREGS_SUPPLIES (regno))
 510     {
 511       if (fetch_xstateregs (regcache, tid))
 512         return;
 513     }
 514
 515   if (GETFPXREGS_SUPPLIES (regno))
 516     {
 517       if (fetch_fpxregs (regcache, tid))
 518         return;
 519
 520       /* Either our processor or our kernel doesn't support the SSE
 521          registers, so read the FP registers in the traditional way,
 522          and fill the SSE registers with dummy values.  It would be
 523          more graceful to handle differences in the register set using
 524          gdbarch.  Until then, this will at least make things work
 525          plausibly.  */
 526       fetch_fpregs (regcache, tid);
 527       return;
 528     }
 529
 530   internal_error (__FILE__, __LINE__,
 531                   _("Got request for bad register number %d."), regno);
 532 }
 533
 534 /* Store register REGNO back into the child process.  If REGNO is -1,
 535    do this for all registers (including the floating point and SSE
 536    registers).  */
 537 void
 538 i386_linux_nat_target::store_registers (struct regcache *regcache, int regno)
 539 {
 540   pid_t tid;
 541
 542   /* Use the old method of poking around in `struct user' if the
 543      SETREGS request isn't available.  */
 544   if (!have_ptrace_getregs)
 545     {
 546       int i;
 547
 548       for (i = 0; i < gdbarch_num_regs (regcache->arch ()); i++)
 549         if (regno == -1 || regno == i)
 550           store_register (regcache, i);
 551
 552       return;
 553     }
 554
 555   tid = get_ptrace_pid (regcache->ptid ());
 556
 557   /* Use the PTRACE_SETFPXREGS requests whenever possible, since it
 558      transfers more registers in one system call.  But remember that
 559      store_fpxregs can fail, and return zero.  */
 560   if (regno == -1)
 561     {
 562       store_regs (regcache, tid, regno);
 563       if (store_xstateregs (regcache, tid, regno))
 564         return;
 565       if (store_fpxregs (regcache, tid, regno))
 566         return;
 567       store_fpregs (regcache, tid, regno);
 568       return;
 569     }
 570
 571   if (GETREGS_SUPPLIES (regno))
 572     {
 573       store_regs (regcache, tid, regno);
 574       return;
 575     }
 576
 577   if (GETXSTATEREGS_SUPPLIES (regno))
 578     {
 579       if (store_xstateregs (regcache, tid, regno))
 580         return;
 581     }
 582
 583   if (GETFPXREGS_SUPPLIES (regno))
 584     {
 585       if (store_fpxregs (regcache, tid, regno))
 586         return;
 587
 588       /* Either our processor or our kernel doesn't support the SSE
 589          registers, so just write the FP registers in the traditional
 590          way.  */
 591       store_fpregs (regcache, tid, regno);
 592       return;
 593     }
 594
 595   internal_error (__FILE__, __LINE__,
 596                   _("Got request to store bad register number %d."), regno);
 597 }
 598 \f
 599
 600 /* Called by libthread_db.  Returns a pointer to the thread local
 601    storage (or its descriptor).  */
 602
 603 ps_err_e
 604 ps_get_thread_area (struct ps_prochandle *ph,
 605                     lwpid_t lwpid, int idx, void **base)
 606 {
 607   unsigned int base_addr;
 608   ps_err_e result;
 609
 610   result = x86_linux_get_thread_area (lwpid, (void *) idx, &base_addr);
 611
 612   if (result == PS_OK)
 613     *(int *) base = base_addr;
 614
 615   return result;
 616 }
 617 \f
 618
 619 /* The instruction for a GNU/Linux system call is:
 620        int $0x80
 621    or 0xcd 0x80.  */
 622
 623 static const unsigned char linux_syscall[] = { 0xcd, 0x80 };
 624
 625 #define LINUX_SYSCALL_LEN (sizeof linux_syscall)
 626
 627 /* The system call number is stored in the %eax register.  */
 628 #define LINUX_SYSCALL_REGNUM I386_EAX_REGNUM
 629
 630 /* We are specifically interested in the sigreturn and rt_sigreturn
 631    system calls.  */
 632
 633 #ifndef SYS_sigreturn
 634 #define SYS_sigreturn           0x77
 635 #endif
 636 #ifndef SYS_rt_sigreturn
 637 #define SYS_rt_sigreturn        0xad
 638 #endif
 639
 640 /* Offset to saved processor flags, from <asm/sigcontext.h>.  */
 641 #define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64)
 642
 643 /* Resume execution of the inferior process.
 644    If STEP is nonzero, single-step it.
 645    If SIGNAL is nonzero, give it that signal.  */
 646
 647 void
 648 i386_linux_nat_target::low_resume (ptid_t ptid, int step, enum gdb_signal signal)
 649 {
 650   int pid = ptid.lwp ();
 651   int request;
 652
 653   if (catch_syscall_enabled () > 0)
 654    request = PTRACE_SYSCALL;
 655   else
 656     request = PTRACE_CONT;
 657
 658   if (step)
 659     {
 660       struct regcache *regcache = get_thread_regcache (ptid);
 661       struct gdbarch *gdbarch = regcache->arch ();
 662       enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 663       ULONGEST pc;
 664       gdb_byte buf[LINUX_SYSCALL_LEN];
 665
 666       request = PTRACE_SINGLESTEP;
 667
 668       regcache_cooked_read_unsigned (regcache,
 669                                      gdbarch_pc_regnum (gdbarch), &pc);
 670
 671       /* Returning from a signal trampoline is done by calling a
 672          special system call (sigreturn or rt_sigreturn, see
 673          i386-linux-tdep.c for more information).  This system call
 674          restores the registers that were saved when the signal was
 675          raised, including %eflags.  That means that single-stepping
 676          won't work.  Instead, we'll have to modify the signal context
 677          that's about to be restored, and set the trace flag there.  */
 678
 679       /* First check if PC is at a system call.  */
 680       if (target_read_memory (pc, buf, LINUX_SYSCALL_LEN) == 0
 681           && memcmp (buf, linux_syscall, LINUX_SYSCALL_LEN) == 0)
 682         {
 683           ULONGEST syscall;
 684           regcache_cooked_read_unsigned (regcache,
 685                                          LINUX_SYSCALL_REGNUM, &syscall);
 686
 687           /* Then check the system call number.  */
 688           if (syscall == SYS_sigreturn || syscall == SYS_rt_sigreturn)
 689             {
 690               ULONGEST sp, addr;
 691               unsigned long int eflags;
 692
 693               regcache_cooked_read_unsigned (regcache, I386_ESP_REGNUM, &sp);
 694               if (syscall == SYS_rt_sigreturn)
 695                 addr = read_memory_unsigned_integer (sp + 8, 4, byte_order)
 696                   + 20;
 697               else
 698                 addr = sp;
 699
 700               /* Set the trace flag in the context that's about to be
 701                  restored.  */
 702               addr += LINUX_SIGCONTEXT_EFLAGS_OFFSET;
 703               read_memory (addr, (gdb_byte *) &eflags, 4);
 704               eflags |= 0x0100;
 705               write_memory (addr, (gdb_byte *) &eflags, 4);
 706             }
 707         }
 708     }
 709
 710   if (ptrace (request, pid, 0, gdb_signal_to_host (signal)) == -1)
 711     perror_with_name (("ptrace"));
 712 }
 713
 714 void
 715 _initialize_i386_linux_nat (void)
 716 {
 717   linux_target = &the_i386_linux_nat_target;
 718
 719   /* Add the target.  */
 720   add_inf_child_target (linux_target);
 721 }