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
   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 2 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, write to the Free Software
  20    Foundation, Inc., 51 Franklin Street, Fifth Floor,
  21    Boston, MA 02110-1301, USA.  */
  22
  23 #include "defs.h"
  24 #include "inferior.h"
  25 #include "gdbcore.h"
  26 #include "regcache.h"
  27 #include "target.h"
  28 #include "linux-nat.h"
  29
  30 #include "gdb_assert.h"
  31 #include "gdb_string.h"
  32 #include <sys/ptrace.h>
  33 #include <sys/user.h>
  34 #include <sys/procfs.h>
  35
  36 #ifdef HAVE_SYS_REG_H
  37 #include <sys/reg.h>
  38 #endif
  39
  40 #ifndef ORIG_EAX
  41 #define ORIG_EAX -1
  42 #endif
  43
  44 #ifdef HAVE_SYS_DEBUGREG_H
  45 #include <sys/debugreg.h>
  46 #endif
  47
  48 #ifndef DR_FIRSTADDR
  49 #define DR_FIRSTADDR 0
  50 #endif
  51
  52 #ifndef DR_LASTADDR
  53 #define DR_LASTADDR 3
  54 #endif
  55
  56 #ifndef DR_STATUS
  57 #define DR_STATUS 6
  58 #endif
  59
  60 #ifndef DR_CONTROL
  61 #define DR_CONTROL 7
  62 #endif
  63
  64 /* Prototypes for supply_gregset etc.  */
  65 #include "gregset.h"
  66
  67 #include "i387-tdep.h"
  68 #include "i386-tdep.h"
  69 #include "i386-linux-tdep.h"
  70
  71 /* Defines ps_err_e, struct ps_prochandle.  */
  72 #include "gdb_proc_service.h"
  73 \f
  74
  75 /* The register sets used in GNU/Linux ELF core-dumps are identical to
  76    the register sets in `struct user' that is used for a.out
  77    core-dumps, and is also used by `ptrace'.  The corresponding types
  78    are `elf_gregset_t' for the general-purpose registers (with
  79    `elf_greg_t' the type of a single GP register) and `elf_fpregset_t'
  80    for the floating-point registers.
  81
  82    Those types used to be available under the names `gregset_t' and
  83    `fpregset_t' too, and this file used those names in the past.  But
  84    those names are now used for the register sets used in the
  85    `mcontext_t' type, and have a different size and layout.  */
  86
  87 /* Mapping between the general-purpose registers in `struct user'
  88    format and GDB's register array layout.  */
  89 static int regmap[] =
  90 {
  91   EAX, ECX, EDX, EBX,
  92   UESP, EBP, ESI, EDI,
  93   EIP, EFL, CS, SS,
  94   DS, ES, FS, GS,
  95   -1, -1, -1, -1,               /* st0, st1, st2, st3 */
  96   -1, -1, -1, -1,               /* st4, st5, st6, st7 */
  97   -1, -1, -1, -1,               /* fctrl, fstat, ftag, fiseg */
  98   -1, -1, -1, -1,               /* fioff, foseg, fooff, fop */
  99   -1, -1, -1, -1,               /* xmm0, xmm1, xmm2, xmm3 */
 100   -1, -1, -1, -1,               /* xmm4, xmm5, xmm6, xmm6 */
 101   -1,                           /* mxcsr */
 102   ORIG_EAX
 103 };
 104
 105 /* Which ptrace request retrieves which registers?
 106    These apply to the corresponding SET requests as well.  */
 107
 108 #define GETREGS_SUPPLIES(regno) \
 109   ((0 <= (regno) && (regno) <= 15) || (regno) == I386_LINUX_ORIG_EAX_REGNUM)
 110
 111 #define GETFPXREGS_SUPPLIES(regno) \
 112   (I386_ST0_REGNUM <= (regno) && (regno) < I386_SSE_NUM_REGS)
 113
 114 /* Does the current host support the GETREGS request?  */
 115 int have_ptrace_getregs =
 116 #ifdef HAVE_PTRACE_GETREGS
 117   1
 118 #else
 119   0
 120 #endif
 121 ;
 122
 123 /* Does the current host support the GETFPXREGS request?  The header
 124    file may or may not define it, and even if it is defined, the
 125    kernel will return EIO if it's running on a pre-SSE processor.
 126
 127    My instinct is to attach this to some architecture- or
 128    target-specific data structure, but really, a particular GDB
 129    process can only run on top of one kernel at a time.  So it's okay
 130    for this to be a simple variable.  */
 131 int have_ptrace_getfpxregs =
 132 #ifdef HAVE_PTRACE_GETFPXREGS
 133   1
 134 #else
 135   0
 136 #endif
 137 ;
 138 \f
 139
 140 /* Accessing registers through the U area, one at a time.  */
 141
 142 /* Fetch one register.  */
 143
 144 static void
 145 fetch_register (struct regcache *regcache, int regno)
 146 {
 147   int tid;
 148   int val;
 149
 150   gdb_assert (!have_ptrace_getregs);
 151   if (regmap[regno] == -1)
 152     {
 153       regcache_raw_supply (regcache, regno, NULL);
 154       return;
 155     }
 156
 157   /* GNU/Linux LWP ID's are process ID's.  */
 158   tid = TIDGET (inferior_ptid);
 159   if (tid == 0)
 160     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 161
 162   errno = 0;
 163   val = ptrace (PTRACE_PEEKUSER, tid, 4 * regmap[regno], 0);
 164   if (errno != 0)
 165     error (_("Couldn't read register %s (#%d): %s."),
 166            gdbarch_register_name (current_gdbarch, regno),
 167            regno, safe_strerror (errno));
 168
 169   regcache_raw_supply (regcache, regno, &val);
 170 }
 171
 172 /* Store one register. */
 173
 174 static void
 175 store_register (const struct regcache *regcache, int regno)
 176 {
 177   int tid;
 178   int val;
 179
 180   gdb_assert (!have_ptrace_getregs);
 181   if (regmap[regno] == -1)
 182     return;
 183
 184   /* GNU/Linux LWP ID's are process ID's.  */
 185   tid = TIDGET (inferior_ptid);
 186   if (tid == 0)
 187     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 188
 189   errno = 0;
 190   regcache_raw_collect (regcache, regno, &val);
 191   ptrace (PTRACE_POKEUSER, tid, 4 * regmap[regno], val);
 192   if (errno != 0)
 193     error (_("Couldn't write register %s (#%d): %s."),
 194            gdbarch_register_name (current_gdbarch, regno),
 195            regno, safe_strerror (errno));
 196 }
 197 \f
 198
 199 /* Transfering the general-purpose registers between GDB, inferiors
 200    and core files.  */
 201
 202 /* Fill GDB's register array with the general-purpose register values
 203    in *GREGSETP.  */
 204
 205 void
 206 supply_gregset (struct regcache *regcache, const elf_gregset_t *gregsetp)
 207 {
 208   const elf_greg_t *regp = (const elf_greg_t *) gregsetp;
 209   int i;
 210
 211   for (i = 0; i < I386_NUM_GREGS; i++)
 212     regcache_raw_supply (regcache, i, regp + regmap[i]);
 213
 214   if (I386_LINUX_ORIG_EAX_REGNUM < gdbarch_num_regs (current_gdbarch))
 215     regcache_raw_supply (regcache, I386_LINUX_ORIG_EAX_REGNUM,
 216                          regp + ORIG_EAX);
 217 }
 218
 219 /* Fill register REGNO (if it is a general-purpose register) in
 220    *GREGSETPS with the value in GDB's register array.  If REGNO is -1,
 221    do this for all registers.  */
 222
 223 void
 224 fill_gregset (const struct regcache *regcache,
 225               elf_gregset_t *gregsetp, int regno)
 226 {
 227   elf_greg_t *regp = (elf_greg_t *) gregsetp;
 228   int i;
 229
 230   for (i = 0; i < I386_NUM_GREGS; i++)
 231     if (regno == -1 || regno == i)
 232       regcache_raw_collect (regcache, i, regp + regmap[i]);
 233
 234   if ((regno == -1 || regno == I386_LINUX_ORIG_EAX_REGNUM)
 235       && I386_LINUX_ORIG_EAX_REGNUM < gdbarch_num_regs (current_gdbarch))
 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 (current_gdbarch); 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 (current_gdbarch); 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
 585 i386_linux_dr_get (int regnum)
 586 {
 587   int tid;
 588   unsigned long value;
 589
 590   /* FIXME: kettenis/2001-01-29: It's not clear what we should do with
 591      multi-threaded processes here.  For now, pretend there is just
 592      one thread.  */
 593   tid = PIDGET (inferior_ptid);
 594
 595   /* FIXME: kettenis/2001-03-27: Calling perror_with_name if the
 596      ptrace call fails breaks debugging remote targets.  The correct
 597      way to fix this is to add the hardware breakpoint and watchpoint
 598      stuff to the target vector.  For now, just return zero if the
 599      ptrace call fails.  */
 600   errno = 0;
 601   value = ptrace (PTRACE_PEEKUSER, tid,
 602                   offsetof (struct user, u_debugreg[regnum]), 0);
 603   if (errno != 0)
 604 #if 0
 605     perror_with_name (_("Couldn't read debug register"));
 606 #else
 607     return 0;
 608 #endif
 609
 610   return value;
 611 }
 612
 613 static void
 614 i386_linux_dr_set (int regnum, unsigned long value)
 615 {
 616   int tid;
 617
 618   /* FIXME: kettenis/2001-01-29: It's not clear what we should do with
 619      multi-threaded processes here.  For now, pretend there is just
 620      one thread.  */
 621   tid = PIDGET (inferior_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   i386_linux_dr_set (DR_CONTROL, control);
 634 }
 635
 636 void
 637 i386_linux_dr_set_addr (int regnum, CORE_ADDR addr)
 638 {
 639   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 640
 641   i386_linux_dr_set (DR_FIRSTADDR + regnum, addr);
 642 }
 643
 644 void
 645 i386_linux_dr_reset_addr (int regnum)
 646 {
 647   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 648
 649   i386_linux_dr_set (DR_FIRSTADDR + regnum, 0L);
 650 }
 651
 652 unsigned long
 653 i386_linux_dr_get_status (void)
 654 {
 655   return i386_linux_dr_get (DR_STATUS);
 656 }
 657 \f
 658
 659 /* Called by libthread_db.  Returns a pointer to the thread local
 660    storage (or its descriptor).  */
 661
 662 ps_err_e
 663 ps_get_thread_area (const struct ps_prochandle *ph,
 664                     lwpid_t lwpid, int idx, void **base)
 665 {
 666   /* NOTE: cagney/2003-08-26: The definition of this buffer is found
 667      in the kernel header <asm-i386/ldt.h>.  It, after padding, is 4 x
 668      4 byte integers in size: `entry_number', `base_addr', `limit',
 669      and a bunch of status bits.
 670
 671      The values returned by this ptrace call should be part of the
 672      regcache buffer, and ps_get_thread_area should channel its
 673      request through the regcache.  That way remote targets could
 674      provide the value using the remote protocol and not this direct
 675      call.
 676
 677      Is this function needed?  I'm guessing that the `base' is the
 678      address of a a descriptor that libthread_db uses to find the
 679      thread local address base that GDB needs.  Perhaps that
 680      descriptor is defined by the ABI.  Anyway, given that
 681      libthread_db calls this function without prompting (gdb
 682      requesting tls base) I guess it needs info in there anyway.  */
 683   unsigned int desc[4];
 684   gdb_assert (sizeof (int) == 4);
 685
 686 #ifndef PTRACE_GET_THREAD_AREA
 687 #define PTRACE_GET_THREAD_AREA 25
 688 #endif
 689
 690   if (ptrace (PTRACE_GET_THREAD_AREA, lwpid,
 691               (void *) idx, (unsigned long) &desc) < 0)
 692     return PS_ERR;
 693
 694   *(int *)base = desc[1];
 695   return PS_OK;
 696 }
 697 \f
 698
 699 /* The instruction for a GNU/Linux system call is:
 700        int $0x80
 701    or 0xcd 0x80.  */
 702
 703 static const unsigned char linux_syscall[] = { 0xcd, 0x80 };
 704
 705 #define LINUX_SYSCALL_LEN (sizeof linux_syscall)
 706
 707 /* The system call number is stored in the %eax register.  */
 708 #define LINUX_SYSCALL_REGNUM I386_EAX_REGNUM
 709
 710 /* We are specifically interested in the sigreturn and rt_sigreturn
 711    system calls.  */
 712
 713 #ifndef SYS_sigreturn
 714 #define SYS_sigreturn           0x77
 715 #endif
 716 #ifndef SYS_rt_sigreturn
 717 #define SYS_rt_sigreturn        0xad
 718 #endif
 719
 720 /* Offset to saved processor flags, from <asm/sigcontext.h>.  */
 721 #define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64)
 722
 723 /* Resume execution of the inferior process.
 724    If STEP is nonzero, single-step it.
 725    If SIGNAL is nonzero, give it that signal.  */
 726
 727 static void
 728 i386_linux_resume (ptid_t ptid, int step, enum target_signal signal)
 729 {
 730   int pid = PIDGET (ptid);
 731
 732   int request = PTRACE_CONT;
 733
 734   if (pid == -1)
 735     /* Resume all threads.  */
 736     /* I think this only gets used in the non-threaded case, where "resume
 737        all threads" and "resume inferior_ptid" are the same.  */
 738     pid = PIDGET (inferior_ptid);
 739
 740   if (step)
 741     {
 742       struct regcache *regcache = get_thread_regcache (pid_to_ptid (pid));
 743       ULONGEST pc;
 744       gdb_byte buf[LINUX_SYSCALL_LEN];
 745
 746       request = PTRACE_SINGLESTEP;
 747
 748       regcache_cooked_read_unsigned (regcache,
 749                                      gdbarch_pc_regnum (current_gdbarch), &pc);
 750
 751       /* Returning from a signal trampoline is done by calling a
 752          special system call (sigreturn or rt_sigreturn, see
 753          i386-linux-tdep.c for more information).  This system call
 754          restores the registers that were saved when the signal was
 755          raised, including %eflags.  That means that single-stepping
 756          won't work.  Instead, we'll have to modify the signal context
 757          that's about to be restored, and set the trace flag there.  */
 758
 759       /* First check if PC is at a system call.  */
 760       if (read_memory_nobpt (pc, buf, LINUX_SYSCALL_LEN) == 0
 761           && memcmp (buf, linux_syscall, LINUX_SYSCALL_LEN) == 0)
 762         {
 763           ULONGEST syscall;
 764           regcache_cooked_read_unsigned (regcache,
 765                                          LINUX_SYSCALL_REGNUM, &syscall);
 766
 767           /* Then check the system call number.  */
 768           if (syscall == SYS_sigreturn || syscall == SYS_rt_sigreturn)
 769             {
 770               ULONGEST sp, addr;
 771               unsigned long int eflags;
 772
 773               regcache_cooked_read_unsigned (regcache, I386_ESP_REGNUM, &sp);
 774               if (syscall == SYS_rt_sigreturn)
 775                 addr = read_memory_integer (sp + 8, 4) + 20;
 776               else
 777                 addr = sp;
 778
 779               /* Set the trace flag in the context that's about to be
 780                  restored.  */
 781               addr += LINUX_SIGCONTEXT_EFLAGS_OFFSET;
 782               read_memory (addr, (gdb_byte *) &eflags, 4);
 783               eflags |= 0x0100;
 784               write_memory (addr, (gdb_byte *) &eflags, 4);
 785             }
 786         }
 787     }
 788
 789   if (ptrace (request, pid, 0, target_signal_to_host (signal)) == -1)
 790     perror_with_name (("ptrace"));
 791 }
 792
 793 static void (*super_post_startup_inferior) (ptid_t ptid);
 794
 795 static void
 796 i386_linux_child_post_startup_inferior (ptid_t ptid)
 797 {
 798   i386_cleanup_dregs ();
 799   super_post_startup_inferior (ptid);
 800 }
 801
 802 void
 803 _initialize_i386_linux_nat (void)
 804 {
 805   struct target_ops *t;
 806
 807   /* Fill in the generic GNU/Linux methods.  */
 808   t = linux_target ();
 809
 810   /* Override the default ptrace resume method.  */
 811   t->to_resume = i386_linux_resume;
 812
 813   /* Override the GNU/Linux inferior startup hook.  */
 814   super_post_startup_inferior = t->to_post_startup_inferior;
 815   t->to_post_startup_inferior = i386_linux_child_post_startup_inferior;
 816
 817   /* Add our register access methods.  */
 818   t->to_fetch_registers = i386_linux_fetch_inferior_registers;
 819   t->to_store_registers = i386_linux_store_inferior_registers;
 820
 821   /* Register the target.  */
 822   linux_nat_add_target (t);
 823 }