gdb/i386-linux-nat.c

   1 /* Native-dependent code for GNU/Linux i386.
   2
   3    Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004, 2005
   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 /* Support for the user struct.  */
 141
 142 /* Return the address of register REGNUM.  BLOCKEND is the value of
 143    u.u_ar0, which should point to the registers.  */
 144
 145 CORE_ADDR
 146 register_u_addr (CORE_ADDR blockend, int regnum)
 147 {
 148   return (blockend + 4 * regmap[regnum]);
 149 }
 150
 151 /* Return the size of the user struct.  */
 152
 153 int
 154 kernel_u_size (void)
 155 {
 156   return (sizeof (struct user));
 157 }
 158 \f
 159
 160 /* Accessing registers through the U area, one at a time.  */
 161
 162 /* Fetch one register.  */
 163
 164 static void
 165 fetch_register (int regno)
 166 {
 167   int tid;
 168   int val;
 169
 170   gdb_assert (!have_ptrace_getregs);
 171   if (cannot_fetch_register (regno))
 172     {
 173       regcache_raw_supply (current_regcache, regno, NULL);
 174       return;
 175     }
 176
 177   /* GNU/Linux LWP ID's are process ID's.  */
 178   tid = TIDGET (inferior_ptid);
 179   if (tid == 0)
 180     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 181
 182   errno = 0;
 183   val = ptrace (PTRACE_PEEKUSER, tid, register_addr (regno, 0), 0);
 184   if (errno != 0)
 185     error (_("Couldn't read register %s (#%d): %s."), REGISTER_NAME (regno),
 186            regno, safe_strerror (errno));
 187
 188   regcache_raw_supply (current_regcache, regno, &val);
 189 }
 190
 191 /* Store one register. */
 192
 193 static void
 194 store_register (int regno)
 195 {
 196   int tid;
 197   int val;
 198
 199   gdb_assert (!have_ptrace_getregs);
 200   if (cannot_store_register (regno))
 201     return;
 202
 203   /* GNU/Linux LWP ID's are process ID's.  */
 204   tid = TIDGET (inferior_ptid);
 205   if (tid == 0)
 206     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 207
 208   errno = 0;
 209   regcache_raw_collect (current_regcache, regno, &val);
 210   ptrace (PTRACE_POKEUSER, tid, register_addr (regno, 0), val);
 211   if (errno != 0)
 212     error (_("Couldn't write register %s (#%d): %s."), REGISTER_NAME (regno),
 213            regno, safe_strerror (errno));
 214 }
 215 \f
 216
 217 /* Transfering the general-purpose registers between GDB, inferiors
 218    and core files.  */
 219
 220 /* Fill GDB's register array with the general-purpose register values
 221    in *GREGSETP.  */
 222
 223 void
 224 supply_gregset (elf_gregset_t *gregsetp)
 225 {
 226   elf_greg_t *regp = (elf_greg_t *) gregsetp;
 227   int i;
 228
 229   for (i = 0; i < I386_NUM_GREGS; i++)
 230     regcache_raw_supply (current_regcache, i, regp + regmap[i]);
 231
 232   if (I386_LINUX_ORIG_EAX_REGNUM < NUM_REGS)
 233     regcache_raw_supply (current_regcache, I386_LINUX_ORIG_EAX_REGNUM,
 234                          regp + ORIG_EAX);
 235 }
 236
 237 /* Fill register REGNO (if it is a general-purpose register) in
 238    *GREGSETPS with the value in GDB's register array.  If REGNO is -1,
 239    do this for all registers.  */
 240
 241 void
 242 fill_gregset (elf_gregset_t *gregsetp, int regno)
 243 {
 244   elf_greg_t *regp = (elf_greg_t *) gregsetp;
 245   int i;
 246
 247   for (i = 0; i < I386_NUM_GREGS; i++)
 248     if (regno == -1 || regno == i)
 249       regcache_raw_collect (current_regcache, i, regp + regmap[i]);
 250
 251   if ((regno == -1 || regno == I386_LINUX_ORIG_EAX_REGNUM)
 252       && I386_LINUX_ORIG_EAX_REGNUM < NUM_REGS)
 253     regcache_raw_collect (current_regcache, I386_LINUX_ORIG_EAX_REGNUM,
 254                           regp + ORIG_EAX);
 255 }
 256
 257 #ifdef HAVE_PTRACE_GETREGS
 258
 259 /* Fetch all general-purpose registers from process/thread TID and
 260    store their values in GDB's register array.  */
 261
 262 static void
 263 fetch_regs (int tid)
 264 {
 265   elf_gregset_t regs;
 266
 267   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
 268     {
 269       if (errno == EIO)
 270         {
 271           /* The kernel we're running on doesn't support the GETREGS
 272              request.  Reset `have_ptrace_getregs'.  */
 273           have_ptrace_getregs = 0;
 274           return;
 275         }
 276
 277       perror_with_name (_("Couldn't get registers"));
 278     }
 279
 280   supply_gregset (&regs);
 281 }
 282
 283 /* Store all valid general-purpose registers in GDB's register array
 284    into the process/thread specified by TID.  */
 285
 286 static void
 287 store_regs (int tid, int regno)
 288 {
 289   elf_gregset_t regs;
 290
 291   if (ptrace (PTRACE_GETREGS, tid, 0, (int) &regs) < 0)
 292     perror_with_name (_("Couldn't get registers"));
 293
 294   fill_gregset (&regs, regno);
 295
 296   if (ptrace (PTRACE_SETREGS, tid, 0, (int) &regs) < 0)
 297     perror_with_name (_("Couldn't write registers"));
 298 }
 299
 300 #else
 301
 302 static void fetch_regs (int tid) {}
 303 static void store_regs (int tid, int regno) {}
 304
 305 #endif
 306 \f
 307
 308 /* Transfering floating-point registers between GDB, inferiors and cores.  */
 309
 310 /* Fill GDB's register array with the floating-point register values in
 311    *FPREGSETP.  */
 312
 313 void
 314 supply_fpregset (elf_fpregset_t *fpregsetp)
 315 {
 316   i387_supply_fsave (current_regcache, -1, fpregsetp);
 317 }
 318
 319 /* Fill register REGNO (if it is a floating-point register) in
 320    *FPREGSETP with the value in GDB's register array.  If REGNO is -1,
 321    do this for all registers.  */
 322
 323 void
 324 fill_fpregset (elf_fpregset_t *fpregsetp, int regno)
 325 {
 326   i387_fill_fsave ((char *) fpregsetp, regno);
 327 }
 328
 329 #ifdef HAVE_PTRACE_GETREGS
 330
 331 /* Fetch all floating-point registers from process/thread TID and store
 332    thier values in GDB's register array.  */
 333
 334 static void
 335 fetch_fpregs (int tid)
 336 {
 337   elf_fpregset_t fpregs;
 338
 339   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
 340     perror_with_name (_("Couldn't get floating point status"));
 341
 342   supply_fpregset (&fpregs);
 343 }
 344
 345 /* Store all valid floating-point registers in GDB's register array
 346    into the process/thread specified by TID.  */
 347
 348 static void
 349 store_fpregs (int tid, int regno)
 350 {
 351   elf_fpregset_t fpregs;
 352
 353   if (ptrace (PTRACE_GETFPREGS, tid, 0, (int) &fpregs) < 0)
 354     perror_with_name (_("Couldn't get floating point status"));
 355
 356   fill_fpregset (&fpregs, regno);
 357
 358   if (ptrace (PTRACE_SETFPREGS, tid, 0, (int) &fpregs) < 0)
 359     perror_with_name (_("Couldn't write floating point status"));
 360 }
 361
 362 #else
 363
 364 static void fetch_fpregs (int tid) {}
 365 static void store_fpregs (int tid, int regno) {}
 366
 367 #endif
 368 \f
 369
 370 /* Transfering floating-point and SSE registers to and from GDB.  */
 371
 372 #ifdef HAVE_PTRACE_GETFPXREGS
 373
 374 /* Fill GDB's register array with the floating-point and SSE register
 375    values in *FPXREGSETP.  */
 376
 377 void
 378 supply_fpxregset (elf_fpxregset_t *fpxregsetp)
 379 {
 380   i387_supply_fxsave (current_regcache, -1, fpxregsetp);
 381 }
 382
 383 /* Fill register REGNO (if it is a floating-point or SSE register) in
 384    *FPXREGSETP with the value in GDB's register array.  If REGNO is
 385    -1, do this for all registers.  */
 386
 387 void
 388 fill_fpxregset (elf_fpxregset_t *fpxregsetp, int regno)
 389 {
 390   i387_fill_fxsave ((char *) fpxregsetp, regno);
 391 }
 392
 393 /* Fetch all registers covered by the PTRACE_GETFPXREGS request from
 394    process/thread TID and store their values in GDB's register array.
 395    Return non-zero if successful, zero otherwise.  */
 396
 397 static int
 398 fetch_fpxregs (int tid)
 399 {
 400   elf_fpxregset_t fpxregs;
 401
 402   if (! have_ptrace_getfpxregs)
 403     return 0;
 404
 405   if (ptrace (PTRACE_GETFPXREGS, tid, 0, (int) &fpxregs) < 0)
 406     {
 407       if (errno == EIO)
 408         {
 409           have_ptrace_getfpxregs = 0;
 410           return 0;
 411         }
 412
 413       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 414     }
 415
 416   supply_fpxregset (&fpxregs);
 417   return 1;
 418 }
 419
 420 /* Store all valid registers in GDB's register array covered by the
 421    PTRACE_SETFPXREGS request into the process/thread specified by TID.
 422    Return non-zero if successful, zero otherwise.  */
 423
 424 static int
 425 store_fpxregs (int tid, int regno)
 426 {
 427   elf_fpxregset_t fpxregs;
 428
 429   if (! have_ptrace_getfpxregs)
 430     return 0;
 431
 432   if (ptrace (PTRACE_GETFPXREGS, tid, 0, &fpxregs) == -1)
 433     {
 434       if (errno == EIO)
 435         {
 436           have_ptrace_getfpxregs = 0;
 437           return 0;
 438         }
 439
 440       perror_with_name (_("Couldn't read floating-point and SSE registers"));
 441     }
 442
 443   fill_fpxregset (&fpxregs, regno);
 444
 445   if (ptrace (PTRACE_SETFPXREGS, tid, 0, &fpxregs) == -1)
 446     perror_with_name (_("Couldn't write floating-point and SSE registers"));
 447
 448   return 1;
 449 }
 450
 451 #else
 452
 453 static int fetch_fpxregs (int tid) { return 0; }
 454 static int store_fpxregs (int tid, int regno) { return 0; }
 455
 456 #endif /* HAVE_PTRACE_GETFPXREGS */
 457 \f
 458
 459 /* Transferring arbitrary registers between GDB and inferior.  */
 460
 461 /* Check if register REGNO in the child process is accessible.
 462    If we are accessing registers directly via the U area, only the
 463    general-purpose registers are available.
 464    All registers should be accessible if we have GETREGS support.  */
 465
 466 int
 467 cannot_fetch_register (int regno)
 468 {
 469   gdb_assert (regno >= 0 && regno < NUM_REGS);
 470   return (!have_ptrace_getregs && regmap[regno] == -1);
 471 }
 472
 473 int
 474 cannot_store_register (int regno)
 475 {
 476   gdb_assert (regno >= 0 && regno < NUM_REGS);
 477   return (!have_ptrace_getregs && regmap[regno] == -1);
 478 }
 479
 480 /* Fetch register REGNO from the child process.  If REGNO is -1, do
 481    this for all registers (including the floating point and SSE
 482    registers).  */
 483
 484 static void
 485 i386_linux_fetch_inferior_registers (int regno)
 486 {
 487   int tid;
 488
 489   /* Use the old method of peeking around in `struct user' if the
 490      GETREGS request isn't available.  */
 491   if (!have_ptrace_getregs)
 492     {
 493       int i;
 494
 495       for (i = 0; i < NUM_REGS; i++)
 496         if (regno == -1 || regno == i)
 497           fetch_register (i);
 498
 499       return;
 500     }
 501
 502   /* GNU/Linux LWP ID's are process ID's.  */
 503   tid = TIDGET (inferior_ptid);
 504   if (tid == 0)
 505     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 506
 507   /* Use the PTRACE_GETFPXREGS request whenever possible, since it
 508      transfers more registers in one system call, and we'll cache the
 509      results.  But remember that fetch_fpxregs can fail, and return
 510      zero.  */
 511   if (regno == -1)
 512     {
 513       fetch_regs (tid);
 514
 515       /* The call above might reset `have_ptrace_getregs'.  */
 516       if (!have_ptrace_getregs)
 517         {
 518           i386_linux_fetch_inferior_registers (regno);
 519           return;
 520         }
 521
 522       if (fetch_fpxregs (tid))
 523         return;
 524       fetch_fpregs (tid);
 525       return;
 526     }
 527
 528   if (GETREGS_SUPPLIES (regno))
 529     {
 530       fetch_regs (tid);
 531       return;
 532     }
 533
 534   if (GETFPXREGS_SUPPLIES (regno))
 535     {
 536       if (fetch_fpxregs (tid))
 537         return;
 538
 539       /* Either our processor or our kernel doesn't support the SSE
 540          registers, so read the FP registers in the traditional way,
 541          and fill the SSE registers with dummy values.  It would be
 542          more graceful to handle differences in the register set using
 543          gdbarch.  Until then, this will at least make things work
 544          plausibly.  */
 545       fetch_fpregs (tid);
 546       return;
 547     }
 548
 549   internal_error (__FILE__, __LINE__,
 550                   _("Got request for bad register number %d."), regno);
 551 }
 552
 553 /* Store register REGNO back into the child process.  If REGNO is -1,
 554    do this for all registers (including the floating point and SSE
 555    registers).  */
 556 static void
 557 i386_linux_store_inferior_registers (int regno)
 558 {
 559   int tid;
 560
 561   /* Use the old method of poking around in `struct user' if the
 562      SETREGS request isn't available.  */
 563   if (!have_ptrace_getregs)
 564     {
 565       int i;
 566
 567       for (i = 0; i < NUM_REGS; i++)
 568         if (regno == -1 || regno == i)
 569           store_register (i);
 570
 571       return;
 572     }
 573
 574   /* GNU/Linux LWP ID's are process ID's.  */
 575   tid = TIDGET (inferior_ptid);
 576   if (tid == 0)
 577     tid = PIDGET (inferior_ptid); /* Not a threaded program.  */
 578
 579   /* Use the PTRACE_SETFPXREGS requests whenever possible, since it
 580      transfers more registers in one system call.  But remember that
 581      store_fpxregs can fail, and return zero.  */
 582   if (regno == -1)
 583     {
 584       store_regs (tid, regno);
 585       if (store_fpxregs (tid, regno))
 586         return;
 587       store_fpregs (tid, regno);
 588       return;
 589     }
 590
 591   if (GETREGS_SUPPLIES (regno))
 592     {
 593       store_regs (tid, regno);
 594       return;
 595     }
 596
 597   if (GETFPXREGS_SUPPLIES (regno))
 598     {
 599       if (store_fpxregs (tid, regno))
 600         return;
 601
 602       /* Either our processor or our kernel doesn't support the SSE
 603          registers, so just write the FP registers in the traditional
 604          way.  */
 605       store_fpregs (tid, regno);
 606       return;
 607     }
 608
 609   internal_error (__FILE__, __LINE__,
 610                   _("Got request to store bad register number %d."), regno);
 611 }
 612 \f
 613
 614 /* Support for debug registers.  */
 615
 616 static unsigned long
 617 i386_linux_dr_get (int regnum)
 618 {
 619   int tid;
 620   unsigned long value;
 621
 622   /* FIXME: kettenis/2001-01-29: It's not clear what we should do with
 623      multi-threaded processes here.  For now, pretend there is just
 624      one thread.  */
 625   tid = PIDGET (inferior_ptid);
 626
 627   /* FIXME: kettenis/2001-03-27: Calling perror_with_name if the
 628      ptrace call fails breaks debugging remote targets.  The correct
 629      way to fix this is to add the hardware breakpoint and watchpoint
 630      stuff to the target vector.  For now, just return zero if the
 631      ptrace call fails.  */
 632   errno = 0;
 633   value = ptrace (PTRACE_PEEKUSER, tid,
 634                   offsetof (struct user, u_debugreg[regnum]), 0);
 635   if (errno != 0)
 636 #if 0
 637     perror_with_name (_("Couldn't read debug register"));
 638 #else
 639     return 0;
 640 #endif
 641
 642   return value;
 643 }
 644
 645 static void
 646 i386_linux_dr_set (int regnum, unsigned long value)
 647 {
 648   int tid;
 649
 650   /* FIXME: kettenis/2001-01-29: It's not clear what we should do with
 651      multi-threaded processes here.  For now, pretend there is just
 652      one thread.  */
 653   tid = PIDGET (inferior_ptid);
 654
 655   errno = 0;
 656   ptrace (PTRACE_POKEUSER, tid,
 657           offsetof (struct user, u_debugreg[regnum]), value);
 658   if (errno != 0)
 659     perror_with_name (_("Couldn't write debug register"));
 660 }
 661
 662 void
 663 i386_linux_dr_set_control (unsigned long control)
 664 {
 665   i386_linux_dr_set (DR_CONTROL, control);
 666 }
 667
 668 void
 669 i386_linux_dr_set_addr (int regnum, CORE_ADDR addr)
 670 {
 671   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 672
 673   i386_linux_dr_set (DR_FIRSTADDR + regnum, addr);
 674 }
 675
 676 void
 677 i386_linux_dr_reset_addr (int regnum)
 678 {
 679   gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);
 680
 681   i386_linux_dr_set (DR_FIRSTADDR + regnum, 0L);
 682 }
 683
 684 unsigned long
 685 i386_linux_dr_get_status (void)
 686 {
 687   return i386_linux_dr_get (DR_STATUS);
 688 }
 689 \f
 690
 691 /* Called by libthread_db.  Returns a pointer to the thread local
 692    storage (or its descriptor).  */
 693
 694 ps_err_e
 695 ps_get_thread_area (const struct ps_prochandle *ph,
 696                     lwpid_t lwpid, int idx, void **base)
 697 {
 698   /* NOTE: cagney/2003-08-26: The definition of this buffer is found
 699      in the kernel header <asm-i386/ldt.h>.  It, after padding, is 4 x
 700      4 byte integers in size: `entry_number', `base_addr', `limit',
 701      and a bunch of status bits.
 702
 703      The values returned by this ptrace call should be part of the
 704      regcache buffer, and ps_get_thread_area should channel its
 705      request through the regcache.  That way remote targets could
 706      provide the value using the remote protocol and not this direct
 707      call.
 708
 709      Is this function needed?  I'm guessing that the `base' is the
 710      address of a a descriptor that libthread_db uses to find the
 711      thread local address base that GDB needs.  Perhaps that
 712      descriptor is defined by the ABI.  Anyway, given that
 713      libthread_db calls this function without prompting (gdb
 714      requesting tls base) I guess it needs info in there anyway.  */
 715   unsigned int desc[4];
 716   gdb_assert (sizeof (int) == 4);
 717
 718 #ifndef PTRACE_GET_THREAD_AREA
 719 #define PTRACE_GET_THREAD_AREA 25
 720 #endif
 721
 722   if (ptrace (PTRACE_GET_THREAD_AREA, lwpid,
 723               (void *) idx, (unsigned long) &desc) < 0)
 724     return PS_ERR;
 725
 726   *(int *)base = desc[1];
 727   return PS_OK;
 728 }
 729 \f
 730
 731 /* The instruction for a GNU/Linux system call is:
 732        int $0x80
 733    or 0xcd 0x80.  */
 734
 735 static const unsigned char linux_syscall[] = { 0xcd, 0x80 };
 736
 737 #define LINUX_SYSCALL_LEN (sizeof linux_syscall)
 738
 739 /* The system call number is stored in the %eax register.  */
 740 #define LINUX_SYSCALL_REGNUM I386_EAX_REGNUM
 741
 742 /* We are specifically interested in the sigreturn and rt_sigreturn
 743    system calls.  */
 744
 745 #ifndef SYS_sigreturn
 746 #define SYS_sigreturn           0x77
 747 #endif
 748 #ifndef SYS_rt_sigreturn
 749 #define SYS_rt_sigreturn        0xad
 750 #endif
 751
 752 /* Offset to saved processor flags, from <asm/sigcontext.h>.  */
 753 #define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64)
 754
 755 /* Resume execution of the inferior process.
 756    If STEP is nonzero, single-step it.
 757    If SIGNAL is nonzero, give it that signal.  */
 758
 759 static void
 760 i386_linux_resume (ptid_t ptid, int step, enum target_signal signal)
 761 {
 762   int pid = PIDGET (ptid);
 763
 764   int request = PTRACE_CONT;
 765
 766   if (pid == -1)
 767     /* Resume all threads.  */
 768     /* I think this only gets used in the non-threaded case, where "resume
 769        all threads" and "resume inferior_ptid" are the same.  */
 770     pid = PIDGET (inferior_ptid);
 771
 772   if (step)
 773     {
 774       CORE_ADDR pc = read_pc_pid (pid_to_ptid (pid));
 775       gdb_byte buf[LINUX_SYSCALL_LEN];
 776
 777       request = PTRACE_SINGLESTEP;
 778
 779       /* Returning from a signal trampoline is done by calling a
 780          special system call (sigreturn or rt_sigreturn, see
 781          i386-linux-tdep.c for more information).  This system call
 782          restores the registers that were saved when the signal was
 783          raised, including %eflags.  That means that single-stepping
 784          won't work.  Instead, we'll have to modify the signal context
 785          that's about to be restored, and set the trace flag there.  */
 786
 787       /* First check if PC is at a system call.  */
 788       if (deprecated_read_memory_nobpt (pc, buf, LINUX_SYSCALL_LEN) == 0
 789           && memcmp (buf, linux_syscall, LINUX_SYSCALL_LEN) == 0)
 790         {
 791           int syscall = read_register_pid (LINUX_SYSCALL_REGNUM,
 792                                            pid_to_ptid (pid));
 793
 794           /* Then check the system call number.  */
 795           if (syscall == SYS_sigreturn || syscall == SYS_rt_sigreturn)
 796             {
 797               CORE_ADDR sp = read_register (I386_ESP_REGNUM);
 798               CORE_ADDR addr = sp;
 799               unsigned long int eflags;
 800
 801               if (syscall == SYS_rt_sigreturn)
 802                 addr = read_memory_integer (sp + 8, 4) + 20;
 803
 804               /* Set the trace flag in the context that's about to be
 805                  restored.  */
 806               addr += LINUX_SIGCONTEXT_EFLAGS_OFFSET;
 807               read_memory (addr, (gdb_byte *) &eflags, 4);
 808               eflags |= 0x0100;
 809               write_memory (addr, (gdb_byte *) &eflags, 4);
 810             }
 811         }
 812     }
 813
 814   if (ptrace (request, pid, 0, target_signal_to_host (signal)) == -1)
 815     perror_with_name (("ptrace"));
 816 }
 817
 818 static void (*super_post_startup_inferior) (ptid_t ptid);
 819
 820 static void
 821 i386_linux_child_post_startup_inferior (ptid_t ptid)
 822 {
 823   i386_cleanup_dregs ();
 824   super_post_startup_inferior (ptid);
 825 }
 826
 827 void
 828 _initialize_i386_linux_nat (void)
 829 {
 830   struct target_ops *t;
 831
 832   /* Fill in the generic GNU/Linux methods.  */
 833   t = linux_target ();
 834
 835   /* Override the default ptrace resume method.  */
 836   t->to_resume = i386_linux_resume;
 837
 838   /* Override the GNU/Linux inferior startup hook.  */
 839   super_post_startup_inferior = t->to_post_startup_inferior;
 840   t->to_post_startup_inferior = i386_linux_child_post_startup_inferior;
 841
 842   /* Add our register access methods.  */
 843   t->to_fetch_registers = i386_linux_fetch_inferior_registers;
 844   t->to_store_registers = i386_linux_store_inferior_registers;
 845
 846   /* Register the target.  */
 847   add_target (t);
 848 }