gdb/i386-linux-nat.c - gdb

Global variables defined

Functions defined

Macros defined

Source code

  1. /* Native-dependent code for GNU/Linux i386.

  3.    Copyright (C) 1999-2015 Free Software Foundation, Inc.

  5.    This file is part of GDB.

  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.

  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.

  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/>.  */

  20. #include "defs.h"
  21. #include "inferior.h"
  22. #include "gdbcore.h"
  23. #include "regcache.h"
  24. #include "elf/common.h"
  25. #include <sys/ptrace.h>
  26. #include <sys/uio.h>
  27. #include "gregset.h"
  28. #include "gdb_proc_service.h"

  30. #include "i386-linux-nat.h"
  31. #include "i387-tdep.h"
  32. #include "i386-tdep.h"
  33. #include "i386-linux-tdep.h"
  34. #include "x86-xstate.h"

  36. #include "x86-linux-nat.h"

  38. /* The register sets used in GNU/Linux ELF core-dumps are identical to
  39.    the register sets in `struct user' that is used for a.out
  40.    core-dumps, and is also used by `ptrace'.  The corresponding types
  41.    are `elf_gregset_t' for the general-purpose registers (with
  42.    `elf_greg_t' the type of a single GP register) and `elf_fpregset_t'
  43.    for the floating-point registers.

  45.    Those types used to be available under the names `gregset_t' and
  46.    `fpregset_t' too, and this file used those names in the past.  But
  47.    those names are now used for the register sets used in the
  48.    `mcontext_t' type, and have a different size and layout.  */

  50. /* Which ptrace request retrieves which registers?
  51.    These apply to the corresponding SET requests as well.  */

  53. ‌#define GETREGS_SUPPLIES(regno) \
  54.   ((0 <= (regno) && (regno) <= 15) || (regno) == I386_LINUX_ORIG_EAX_REGNUM)

  56. ‌#define GETFPXREGS_SUPPLIES(regno) \
  57.   (I386_ST0_REGNUM <= (regno) && (regno) < I386_SSE_NUM_REGS)

  59. ‌#define GETXSTATEREGS_SUPPLIES(regno) \
  60.   (I386_ST0_REGNUM <= (regno) && (regno) < I386_AVX512_NUM_REGS)

  62. /* Does the current host support the GETREGS request?  */
  63. ‌int have_ptrace_getregs =
  64. #ifdef HAVE_PTRACE_GETREGS
  65.   1
  66. #else
  67.   0
  68. #endif
  69. ;

  71. /* Does the current host support the GETFPXREGS request?  The header
  72.    file may or may not define it, and even if it is defined, the
  73.    kernel will return EIO if it's running on a pre-SSE processor.

  75.    My instinct is to attach this to some architecture- or
  76.    target-specific data structure, but really, a particular GDB
  77.    process can only run on top of one kernel at a time.  So it's okay
  78.    for this to be a simple variable.  */
  79. ‌int have_ptrace_getfpxregs =
  80. #ifdef HAVE_PTRACE_GETFPXREGS
  81.   -1
  82. #else
  83.   0
  84. #endif
  85. ;


  88. /* Accessing registers through the U area, one at a time.  */

  90. /* Fetch one register.  */

  92. static void
  93. ‌fetch_register (struct regcache *regcache, int regno)
  94. {
  95.   int tid;
  96.   int val;

  98.   gdb_assert (!have_ptrace_getregs);
  99.   if (i386_linux_gregset_reg_offset[regno] == -1)
  100.     {
  101.       regcache_raw_supply (regcache, regno, NULL);
  102.       return;
  103.     }

  105.   /* GNU/Linux LWP ID's are process ID's.  */
  106.   tid = ptid_get_lwp (inferior_ptid);
  107.   if (tid == 0)
  108.     tid = ptid_get_pid (inferior_ptid); /* Not a threaded program.  */

  110.   errno = 0;
  111.   val = ptrace (PTRACE_PEEKUSER, tid,
  112.                 i386_linux_gregset_reg_offset[regno], 0);
  113.   if (errno != 0)
  114.     error (_("Couldn't read register %s (#%d): %s."),
  115.            gdbarch_register_name (get_regcache_arch (regcache), regno),
  116.            regno, safe_strerror (errno));

  118.   regcache_raw_supply (regcache, regno, &val);
  119. }

  121. /* Store one register.  */

  123. static void
  124. ‌store_register (const struct regcache *regcache, int regno)
  125. {
  126.   int tid;
  127.   int val;

  129.   gdb_assert (!have_ptrace_getregs);
  130.   if (i386_linux_gregset_reg_offset[regno] == -1)
  131.     return;

  133.   /* GNU/Linux LWP ID's are process ID's.  */
  134.   tid = ptid_get_lwp (inferior_ptid);
  135.   if (tid == 0)
  136.     tid = ptid_get_pid (inferior_ptid); /* Not a threaded program.  */

  138.   errno = 0;
  139.   regcache_raw_collect (regcache, regno, &val);
  140.   ptrace (PTRACE_POKEUSER, tid,
  141.           i386_linux_gregset_reg_offset[regno], val);
  142.   if (errno != 0)
  143.     error (_("Couldn't write register %s (#%d): %s."),
  144.            gdbarch_register_name (get_regcache_arch (regcache), regno),
  145.            regno, safe_strerror (errno));
  146. }


  149. /* Transfering the general-purpose registers between GDB, inferiors
  150.    and core files.  */

  152. /* Fill GDB's register array with the general-purpose register values
  153.    in *GREGSETP.  */

  155. void
  156. ‌supply_gregset (struct regcache *regcache, const elf_gregset_t *gregsetp)
  157. {
  158.   const gdb_byte *regp = (const gdb_byte *) gregsetp;
  159.   int i;

  161.   for (i = 0; i < I386_NUM_GREGS; i++)
  162.     regcache_raw_supply (regcache, i,
  163.                          regp + i386_linux_gregset_reg_offset[i]);

  165.   if (I386_LINUX_ORIG_EAX_REGNUM
  166.         < gdbarch_num_regs (get_regcache_arch (regcache)))
  167.     regcache_raw_supply (regcache, I386_LINUX_ORIG_EAX_REGNUM, regp
  168.                          + i386_linux_gregset_reg_offset[I386_LINUX_ORIG_EAX_REGNUM]);
  169. }

  171. /* Fill register REGNO (if it is a general-purpose register) in
  172.    *GREGSETPS with the value in GDB's register array.  If REGNO is -1,
  173.    do this for all registers.  */

  175. void
  176. ‌fill_gregset (const struct regcache *regcache,
  177.               elf_gregset_t *gregsetp, int regno)
  178. {
  179.   gdb_byte *regp = (gdb_byte *) gregsetp;
  180.   int i;

  182.   for (i = 0; i < I386_NUM_GREGS; i++)
  183.     if (regno == -1 || regno == i)
  184.       regcache_raw_collect (regcache, i,
  185.                             regp + i386_linux_gregset_reg_offset[i]);

  187.   if ((regno == -1 || regno == I386_LINUX_ORIG_EAX_REGNUM)
  188.       && I386_LINUX_ORIG_EAX_REGNUM
  189.            < gdbarch_num_regs (get_regcache_arch (regcache)))
  190.     regcache_raw_collect (regcache, I386_LINUX_ORIG_EAX_REGNUM, regp
  191.                           + i386_linux_gregset_reg_offset[I386_LINUX_ORIG_EAX_REGNUM]);
  192. }

  194. #ifdef HAVE_PTRACE_GETREGS

  196. /* Fetch all general-purpose registers from process/thread TID and
  197.    store their values in GDB's register array.  */

  199. static void
  200. ‌fetch_regs (struct regcache *regcache, int tid)
  201. {
  202.   elf_gregset_t regs;
  203.   elf_gregset_t *regs_p = &regs;

  205.   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
  206.     {
  207.       if (errno == EIO)
  208.         {
  209.           /* The kernel we're running on doesn't support the GETREGS
  210.              request.  Reset `have_ptrace_getregs'.  */
  211.           have_ptrace_getregs = 0;
  212.           return;
  213.         }

  215.       perror_with_name (_("Couldn't get registers"));
  216.     }

  218.   supply_gregset (regcache, (const elf_gregset_t *) regs_p);
  219. }

  221. /* Store all valid general-purpose registers in GDB's register array
  222.    into the process/thread specified by TID.  */

  224. static void
  225. ‌store_regs (const struct regcache *regcache, int tid, int regno)
  226. {
  227.   elf_gregset_t regs;

  229.   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
  230.     perror_with_name (_("Couldn't get registers"));

  232.   fill_gregset (regcache, &regs, regno);

  234.   if (ptrace (PTRACE_SETREGS, tid, 0, (int) &regs) < 0)
  235.     perror_with_name (_("Couldn't write registers"));
  236. }

  238. #else

  240. ‌static void fetch_regs (struct regcache *regcache, int tid) {}
  241. ‌static void store_regs (const struct regcache *regcache, int tid, int regno) {}

  243. #endif


  246. /* Transfering floating-point registers between GDB, inferiors and cores.  */

  248. /* Fill GDB's register array with the floating-point register values in
  249.    *FPREGSETP.  */

  251. void
  252. ‌supply_fpregset (struct regcache *regcache, const elf_fpregset_t *fpregsetp)
  253. {
  254.   i387_supply_fsave (regcache, -1, fpregsetp);
  255. }

  257. /* Fill register REGNO (if it is a floating-point register) in
  258.    *FPREGSETP with the value in GDB's register array.  If REGNO is -1,
  259.    do this for all registers.  */

  261. void
  262. ‌fill_fpregset (const struct regcache *regcache,
  263.                elf_fpregset_t *fpregsetp, int regno)
  264. {
  265.   i387_collect_fsave (regcache, regno, fpregsetp);
  266. }

  268. #ifdef HAVE_PTRACE_GETREGS

  270. /* Fetch all floating-point registers from process/thread TID and store
  271.    thier values in GDB's register array.  */

  273. static void
  274. ‌fetch_fpregs (struct regcache *regcache, int tid)
  275. {
  276.   elf_fpregset_t fpregs;

  278.   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
  279.     perror_with_name (_("Couldn't get floating point status"));

  281.   supply_fpregset (regcache, (const elf_fpregset_t *) &fpregs);
  282. }

  284. /* Store all valid floating-point registers in GDB's register array
  285.    into the process/thread specified by TID.  */

  287. static void
  288. ‌store_fpregs (const struct regcache *regcache, int tid, int regno)
  289. {
  290.   elf_fpregset_t fpregs;

  292.   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
  293.     perror_with_name (_("Couldn't get floating point status"));

  295.   fill_fpregset (regcache, &fpregs, regno);

  297.   if (ptrace (PTRACE_SETFPREGS, tid, 0, (int) &fpregs) < 0)
  298.     perror_with_name (_("Couldn't write floating point status"));
  299. }

  301. #else

  303. static void
  304. ‌fetch_fpregs (struct regcache *regcache, int tid)
  305. {
  306. }

  308. static void
  309. ‌store_fpregs (const struct regcache *regcache, int tid, int regno)
  310. {
  311. }

  313. #endif


  316. /* Transfering floating-point and SSE registers to and from GDB.  */

  318. /* Fetch all registers covered by the PTRACE_GETREGSET request from
  319.    process/thread TID and store their values in GDB's register array.
  320.    Return non-zero if successful, zero otherwise.  */

  322. static int
  323. ‌fetch_xstateregs (struct regcache *regcache, int tid)
  324. {
  325.   char xstateregs[X86_XSTATE_MAX_SIZE];
  326.   struct iovec iov;

  328.   if (!have_ptrace_getregset)
  329.     return 0;

  331.   iov.iov_base = xstateregs;
  332.   iov.iov_len = sizeof(xstateregs);
  333.   if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE,
  334.               &iov) < 0)
  335.     perror_with_name (_("Couldn't read extended state status"));

  337.   i387_supply_xsave (regcache, -1, xstateregs);
  338.   return 1;
  339. }

  341. /* Store all valid registers in GDB's register array covered by the
  342.    PTRACE_SETREGSET request into the process/thread specified by TID.
  343.    Return non-zero if successful, zero otherwise.  */

  345. static int
  346. ‌store_xstateregs (const struct regcache *regcache, int tid, int regno)
  347. {
  348.   char xstateregs[X86_XSTATE_MAX_SIZE];
  349.   struct iovec iov;

  351.   if (!have_ptrace_getregset)
  352.     return 0;

  354.   iov.iov_base = xstateregs;
  355.   iov.iov_len = sizeof(xstateregs);
  356.   if (ptrace (PTRACE_GETREGSET, tid, (unsigned int) NT_X86_XSTATE,
  357.               &iov) < 0)
  358.     perror_with_name (_("Couldn't read extended state status"));

  360.   i387_collect_xsave (regcache, regno, xstateregs, 0);

  362.   if (ptrace (PTRACE_SETREGSET, tid, (unsigned int) NT_X86_XSTATE,
  363.               (int) &iov) < 0)
  364.     perror_with_name (_("Couldn't write extended state status"));

  366.   return 1;
  367. }

  369. #ifdef HAVE_PTRACE_GETFPXREGS

  371. /* Fetch all registers covered by the PTRACE_GETFPXREGS request from
  372.    process/thread TID and store their values in GDB's register array.
  373.    Return non-zero if successful, zero otherwise.  */

  375. static int
  376. ‌fetch_fpxregs (struct regcache *regcache, int tid)
  377. {
  378.   elf_fpxregset_t fpxregs;

  380.   if (! have_ptrace_getfpxregs)
  381.     return 0;

  383.   if (ptrace (PTRACE_GETFPXREGS, tid, 0, (int) &fpxregs) < 0)
  384.     {
  385.       if (errno == EIO)
  386.         {
  387.           have_ptrace_getfpxregs = 0;
  388.           return 0;
  389.         }

  391.       perror_with_name (_("Couldn't read floating-point and SSE registers"));
  392.     }

  394.   i387_supply_fxsave (regcache, -1, (const elf_fpxregset_t *) &fpxregs);
  395.   return 1;
  396. }

  398. /* Store all valid registers in GDB's register array covered by the
  399.    PTRACE_SETFPXREGS request into the process/thread specified by TID.
  400.    Return non-zero if successful, zero otherwise.  */

  402. static int
  403. ‌store_fpxregs (const struct regcache *regcache, int tid, int regno)
  404. {
  405.   elf_fpxregset_t fpxregs;

  407.   if (! have_ptrace_getfpxregs)
  408.     return 0;

  410.   if (ptrace (PTRACE_GETFPXREGS, tid, 0, &fpxregs) == -1)
  411.     {
  412.       if (errno == EIO)
  413.         {
  414.           have_ptrace_getfpxregs = 0;
  415.           return 0;
  416.         }

  418.       perror_with_name (_("Couldn't read floating-point and SSE registers"));
  419.     }

  421.   i387_collect_fxsave (regcache, regno, &fpxregs);

  423.   if (ptrace (PTRACE_SETFPXREGS, tid, 0, &fpxregs) == -1)
  424.     perror_with_name (_("Couldn't write floating-point and SSE registers"));

  426.   return 1;
  427. }

  429. #else

  431. static int
  432. ‌fetch_fpxregs (struct regcache *regcache, int tid)
  433. {
  434.   return 0;
  435. }

  437. static int
  438. ‌store_fpxregs (const struct regcache *regcache, int tid, int regno)
  439. {
  440.   return 0;
  441. }

  443. #endif /* HAVE_PTRACE_GETFPXREGS */


  446. /* Transferring arbitrary registers between GDB and inferior.  */

  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).  */

  452. static void
  453. ‌i386_linux_fetch_inferior_registers (struct target_ops *ops,
  454.                                      struct regcache *regcache, int regno)
  455. {
  456.   int tid;

  458.   /* Use the old method of peeking around in `struct user' if the
  459.      GETREGS request isn't available.  */
  460.   if (!have_ptrace_getregs)
  461.     {
  462.       int i;

  464.       for (i = 0; i < gdbarch_num_regs (get_regcache_arch (regcache)); i++)
  465.         if (regno == -1 || regno == i)
  466.           fetch_register (regcache, i);

  468.       return;
  469.     }

  471.   /* GNU/Linux LWP ID's are process ID's.  */
  472.   tid = ptid_get_lwp (inferior_ptid);
  473.   if (tid == 0)
  474.     tid = ptid_get_pid (inferior_ptid); /* Not a threaded program.  */

  476.   /* Use the PTRACE_GETFPXREGS request whenever possible, since it
  477.      transfers more registers in one system call, and we'll cache the
  478.      results.  But remember that fetch_fpxregs can fail, and return
  479.      zero.  */
  480.   if (regno == -1)
  481.     {
  482.       fetch_regs (regcache, tid);

  484.       /* The call above might reset `have_ptrace_getregs'.  */
  485.       if (!have_ptrace_getregs)
  486.         {
  487.           i386_linux_fetch_inferior_registers (ops, regcache, regno);
  488.           return;
  489.         }

  491.       if (fetch_xstateregs (regcache, tid))
  492.         return;
  493.       if (fetch_fpxregs (regcache, tid))
  494.         return;
  495.       fetch_fpregs (regcache, tid);
  496.       return;
  497.     }

  499.   if (GETREGS_SUPPLIES (regno))
  500.     {
  501.       fetch_regs (regcache, tid);
  502.       return;
  503.     }

  505.   if (GETXSTATEREGS_SUPPLIES (regno))
  506.     {
  507.       if (fetch_xstateregs (regcache, tid))
  508.         return;
  509.     }

  511.   if (GETFPXREGS_SUPPLIES (regno))
  512.     {
  513.       if (fetch_fpxregs (regcache, tid))
  514.         return;

  516.       /* Either our processor or our kernel doesn't support the SSE
  517.          registers, so read the FP registers in the traditional way,
  518.          and fill the SSE registers with dummy values.  It would be
  519.          more graceful to handle differences in the register set using
  520.          gdbarch.  Until then, this will at least make things work
  521.          plausibly.  */
  522.       fetch_fpregs (regcache, tid);
  523.       return;
  524.     }

  526.   internal_error (__FILE__, __LINE__,
  527.                   _("Got request for bad register number %d."), regno);
  528. }

  530. /* Store register REGNO back into the child process.  If REGNO is -1,
  531.    do this for all registers (including the floating point and SSE
  532.    registers).  */
  533. static void
  534. ‌i386_linux_store_inferior_registers (struct target_ops *ops,
  535.                                      struct regcache *regcache, int regno)
  536. {
  537.   int tid;

  539.   /* Use the old method of poking around in `struct user' if the
  540.      SETREGS request isn't available.  */
  541.   if (!have_ptrace_getregs)
  542.     {
  543.       int i;

  545.       for (i = 0; i < gdbarch_num_regs (get_regcache_arch (regcache)); i++)
  546.         if (regno == -1 || regno == i)
  547.           store_register (regcache, i);

  549.       return;
  550.     }

  552.   /* GNU/Linux LWP ID's are process ID's.  */
  553.   tid = ptid_get_lwp (inferior_ptid);
  554.   if (tid == 0)
  555.     tid = ptid_get_pid (inferior_ptid); /* Not a threaded program.  */

  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.     }

  571.   if (GETREGS_SUPPLIES (regno))
  572.     {
  573.       store_regs (regcache, tid, regno);
  574.       return;
  575.     }

  577.   if (GETXSTATEREGS_SUPPLIES (regno))
  578.     {
  579.       if (store_xstateregs (regcache, tid, regno))
  580.         return;
  581.     }

  583.   if (GETFPXREGS_SUPPLIES (regno))
  584.     {
  585.       if (store_fpxregs (regcache, tid, regno))
  586.         return;

  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.     }

  595.   internal_error (__FILE__, __LINE__,
  596.                   _("Got request to store bad register number %d."), regno);
  597. }


  600. /* Called by libthread_db.  Returns a pointer to the thread local
  601.    storage (or its descriptor).  */

  603. ps_err_e
  604. ‌ps_get_thread_area (const struct ps_prochandle *ph,
  605.                     lwpid_t lwpid, int idx, void **base)
  606. {
  607.   unsigned int base_addr;
  608.   ps_err_e result;

  610.   result = x86_linux_get_thread_area (lwpid, (void *) idx, &base_addr);

  612.   if (result == PS_OK)
  613.     *(int *) base = base_addr;

  615.   return result;
  616. }


  619. /* The instruction for a GNU/Linux system call is:
  620.        int $0x80
  621.    or 0xcd 0x80.  */

  623. ‌static const unsigned char linux_syscall[] = { 0xcd, 0x80 };

  625. ‌#define LINUX_SYSCALL_LEN (sizeof linux_syscall)

  627. /* The system call number is stored in the %eax register.  */
  628. ‌#define LINUX_SYSCALL_REGNUM I386_EAX_REGNUM

  630. /* We are specifically interested in the sigreturn and rt_sigreturn
  631.    system calls.  */

  633. #ifndef SYS_sigreturn
  634. ‌#define SYS_sigreturn                0x77
  635. #endif
  636. #ifndef SYS_rt_sigreturn
  637. ‌#define SYS_rt_sigreturn        0xad
  638. #endif

  640. /* Offset to saved processor flags, from <asm/sigcontext.h>.  */
  641. ‌#define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64)

  643. /* Resume execution of the inferior process.
  644.    If STEP is nonzero, single-step it.
  645.    If SIGNAL is nonzero, give it that signal.  */

  647. static void
  648. ‌i386_linux_resume (struct target_ops *ops,
  649.                    ptid_t ptid, int step, enum gdb_signal signal)
  650. {
  651.   int pid = ptid_get_pid (ptid);

  653.   int request;

  655.   if (catch_syscall_enabled () > 0)
  656.    request = PTRACE_SYSCALL;
  657.   else
  658.     request = PTRACE_CONT;

  660.   if (step)
  661.     {
  662.       struct regcache *regcache = get_thread_regcache (pid_to_ptid (pid));
  663.       struct gdbarch *gdbarch = get_regcache_arch (regcache);
  664.       enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
  665.       ULONGEST pc;
  666.       gdb_byte buf[LINUX_SYSCALL_LEN];

  668.       request = PTRACE_SINGLESTEP;

  670.       regcache_cooked_read_unsigned (regcache,
  671.                                      gdbarch_pc_regnum (gdbarch), &pc);

  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.  */

  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);

  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;

  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;

  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.     }

  712.   if (ptrace (request, pid, 0, gdb_signal_to_host (signal)) == -1)
  713.     perror_with_name (("ptrace"));
  714. }


  717. /* -Wmissing-prototypes */
  718. extern initialize_file_ftype _initialize_i386_linux_nat;

  720. void
  721. ‌_initialize_i386_linux_nat (void)
  722. {
  723.   /* Create a generic x86 GNU/Linux target.  */
  724.   struct target_ops *t = x86_linux_create_target ();

  726.   /* Override the default ptrace resume method.  */
  727.   t->to_resume = i386_linux_resume;

  729.   /* Add our register access methods.  */
  730.   t->to_fetch_registers = i386_linux_fetch_inferior_registers;
  731.   t->to_store_registers = i386_linux_store_inferior_registers;

  733.   /* Add the target.  */
  734.   x86_linux_add_target (t);
  735. }