gdb/i386-linux-nat.c

   1 /* Native-dependent code for Linux running on i386's, for GDB.
   2
   3 This file is part of GDB.
   4
   5 This program is free software; you can redistribute it and/or modify
   6 it under the terms of the GNU General Public License as published by
   7 the Free Software Foundation; either version 2 of the License, or
   8 (at your option) any later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program; if not, write to the Free Software
  17 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  18
  19 #include "defs.h"
  20 #include "inferior.h"
  21 #include "gdbcore.h"
  22
  23 /* For i386_linux_skip_solib_resolver */
  24 #include "symtab.h"
  25 #include "frame.h"
  26 #include "symfile.h"
  27 #include "objfiles.h"
  28
  29 #include <sys/ptrace.h>
  30 #include <sys/user.h>
  31 #include <sys/procfs.h>
  32
  33 #ifdef HAVE_SYS_REG_H
  34 #include <sys/reg.h>
  35 #endif
  36
  37 /* This is a duplicate of the table in i386-xdep.c. */
  38
  39 static int regmap[] =
  40 {
  41   EAX, ECX, EDX, EBX,
  42   UESP, EBP, ESI, EDI,
  43   EIP, EFL, CS, SS,
  44   DS, ES, FS, GS,
  45 };
  46
  47
  48 /* Which ptrace request retrieves which registers?
  49    These apply to the corresponding SET requests as well.  */
  50 #define GETREGS_SUPPLIES(regno) \
  51   (0 <= (regno) && (regno) <= 15)
  52 #define GETFPREGS_SUPPLIES(regno) \
  53   (FP0_REGNUM <= (regno) && (regno) <= LAST_FPU_CTRL_REGNUM)
  54 #define GETXFPREGS_SUPPLIES(regno) \
  55   (FP0_REGNUM <= (regno) && (regno) <= MXCSR_REGNUM)
  56
  57 /* Does the current host support the GETXFPREGS request?  The header
  58    file may or may not define it, and even if it is defined, the
  59    kernel will return EIO if it's running on a pre-SSE processor.
  60
  61    PTRACE_GETXFPREGS is a Cygnus invention, since we wrote our own
  62    Linux kernel patch for SSE support.  That patch may or may not
  63    actually make it into the official distribution.  If you find that
  64    years have gone by since this stuff was added, and Linux isn't
  65    using PTRACE_GETXFPREGS, that means that our patch didn't make it,
  66    and you can delete this, and the related code.
  67
  68    My instinct is to attach this to some architecture- or
  69    target-specific data structure, but really, a particular GDB
  70    process can only run on top of one kernel at a time.  So it's okay
  71    for this to be a simple variable.  */
  72 int have_ptrace_getxfpregs =
  73 #ifdef HAVE_PTRACE_GETXFPREGS
  74   1
  75 #else
  76   0
  77 #endif
  78 ;
  79
  80
  81 \f
  82 /* Transfering the general registers between GDB, inferiors and core files.  */
  83
  84 /* Given a pointer to a general register set in struct user format
  85    (gregset_t *), unpack the register contents and supply them as
  86    gdb's idea of the current register values. */
  87 void
  88 supply_gregset (gregsetp)
  89      gregset_t *gregsetp;
  90 {
  91   register int regi;
  92   register greg_t *regp = (greg_t *) gregsetp;
  93
  94   for (regi = 0; regi < NUM_GREGS; regi++)
  95     {
  96       supply_register (regi, (char *) (regp + regmap[regi]));
  97     }
  98 }
  99
 100
 101 /* Fill in a gregset_t object with selected data from a gdb-format
 102    register file.
 103    - GREGSETP points to the gregset_t object to be filled.
 104    - GDB_REGS points to the GDB-style register file providing the data.
 105    - VALID is an array indicating which registers in GDB_REGS are
 106      valid; the parts of *GREGSETP that would hold registers marked
 107      invalid in GDB_REGS are left unchanged.  If VALID is zero, all
 108      registers are assumed to be valid.  */
 109 void
 110 convert_to_gregset (gregset_t *gregsetp,
 111                     char *gdb_regs,
 112                     signed char *valid)
 113 {
 114   int regi;
 115   register greg_t *regp = (greg_t *) gregsetp;
 116
 117   for (regi = 0; regi < NUM_GREGS; regi++)
 118     if (! valid || valid[regi])
 119       *(regp + regmap[regi]) = * (int *) &registers[REGISTER_BYTE (regi)];
 120 }
 121
 122
 123 /* Store GDB's value for REGNO in *GREGSETP.  If REGNO is -1, do all
 124    of them.  */
 125 void
 126 fill_gregset (gregset_t *gregsetp,
 127               int regno)
 128 {
 129   if (regno == -1)
 130     convert_to_gregset (gregsetp, registers, 0);
 131   else if (regno >= 0 && regno < NUM_GREGS)
 132     {
 133       signed char valid[NUM_GREGS];
 134       memset (valid, 0, sizeof (valid));
 135       valid[regno] = 1;
 136       convert_to_gregset (gregsetp, valid, valid);
 137     }
 138 }
 139
 140
 141 /* Read the general registers from the process, and store them
 142    in registers[].  */
 143 static void
 144 fetch_regs ()
 145 {
 146   int ret, regno;
 147   gregset_t buf;
 148
 149   ret = ptrace (PTRACE_GETREGS, inferior_pid, 0, (int) &buf);
 150   if (ret < 0)
 151     {
 152       warning ("Couldn't get registers");
 153       return;
 154     }
 155
 156   supply_gregset (&buf);
 157 }
 158
 159
 160 /* Set the inferior's general registers to the values in registers[]
 161    --- but only those registers marked as valid.  */
 162 static void
 163 store_regs ()
 164 {
 165   int ret, regno;
 166   gregset_t buf;
 167
 168   ret = ptrace (PTRACE_GETREGS, inferior_pid, 0, (int) &buf);
 169   if (ret < 0)
 170     {
 171       warning ("Couldn't get registers");
 172       return;
 173     }
 174
 175   convert_to_gregset (&buf, registers, register_valid);
 176
 177   ret = ptrace (PTRACE_SETREGS, inferior_pid, 0, (int)buf);
 178   if (ret < 0)
 179     {
 180       warning ("Couldn't write registers");
 181       return;
 182     }
 183 }
 184
 185
 186 \f
 187 /* Transfering floating-point registers between GDB, inferiors and cores.  */
 188
 189 /* What is the address of st(N) within the fpregset_t structure F?  */
 190 #define FPREGSET_T_FPREG_ADDR(f, n) \
 191   ((char *) &(f)->st_space + (n) * 10)
 192
 193 /* Fill GDB's register file with the floating-point register values in
 194    *FPREGSETP.  */
 195 void
 196 supply_fpregset (fpregset_t *fpregsetp)
 197 {
 198   int i;
 199
 200   /* Supply the floating-point registers.  */
 201   for (i = 0; i < 8; i++)
 202     supply_register (FP0_REGNUM + i, FPREGSET_T_FPREG_ADDR (fpregsetp, i));
 203
 204   supply_register (FCTRL_REGNUM, (char *) &fpregsetp->cwd);
 205   supply_register (FSTAT_REGNUM, (char *) &fpregsetp->swd);
 206   supply_register (FTAG_REGNUM,  (char *) &fpregsetp->twd);
 207   supply_register (FCOFF_REGNUM, (char *) &fpregsetp->fip);
 208   supply_register (FDS_REGNUM,   (char *) &fpregsetp->fos);
 209   supply_register (FDOFF_REGNUM, (char *) &fpregsetp->foo);
 210
 211   /* Extract the code segment and opcode from the  "fcs" member.  */
 212   {
 213     long l;
 214
 215     l = fpregsetp->fcs & 0xffff;
 216     supply_register (FCS_REGNUM, (char *) &l);
 217
 218     l = (fpregsetp->fcs >> 16) & ((1 << 11) - 1);
 219     supply_register (FOP_REGNUM, (char *) &l);
 220   }
 221 }
 222
 223
 224 /* Fill in an fpregset_t structure with selected data from a
 225    gdb-format register file.
 226    - FPREGSETP points to the structure to be filled.
 227    - GDB_REGS points to the GDB-style register file providing the data.
 228    - VALID is an array indicating which registers in GDB_REGS are
 229      valid; the parts of *FPREGSETP that would hold registers marked
 230      invalid in GDB_REGS are left unchanged.  If VALID is zero, all
 231      registers are assumed to be valid.  */
 232 void
 233 convert_to_fpregset (fpregset_t *fpregsetp,
 234                      char *gdb_regs,
 235                      signed char *valid)
 236 {
 237   int i;
 238
 239   /* Fill in the floating-point registers.  */
 240   for (i = 0; i < 8; i++)
 241     if (!valid || valid[i])
 242       memcpy (FPREGSET_T_FPREG_ADDR (fpregsetp, i),
 243               &registers[REGISTER_BYTE (FP0_REGNUM + i)],
 244               REGISTER_RAW_SIZE(FP0_REGNUM + i));
 245
 246 #define fill(MEMBER, REGNO)                                             \
 247   if (! valid || valid[(REGNO)])                                        \
 248     memcpy (&fpregsetp->MEMBER, &registers[REGISTER_BYTE (REGNO)],      \
 249             sizeof (fpregsetp->MEMBER))
 250
 251   fill (cwd, FCTRL_REGNUM);
 252   fill (swd, FSTAT_REGNUM);
 253   fill (twd, FTAG_REGNUM);
 254   fill (fip, FCOFF_REGNUM);
 255   fill (foo, FDOFF_REGNUM);
 256   fill (fos, FDS_REGNUM);
 257
 258 #undef fill
 259
 260   if (! valid || valid[FCS_REGNUM])
 261     fpregsetp->fcs
 262       = ((fpregsetp->fcs & ~0xffff)
 263          | (* (int *) &registers[REGISTER_BYTE (FCS_REGNUM)] & 0xffff));
 264
 265   if (! valid || valid[FOP_REGNUM])
 266     fpregsetp->fcs
 267       = ((fpregsetp->fcs & 0xffff)
 268          | ((*(int *) &registers[REGISTER_BYTE (FOP_REGNUM)] & ((1 << 11) - 1))
 269             << 16));
 270 }
 271
 272
 273 /* Given a pointer to a floating point register set in (fpregset_t *)
 274    format, update all of the registers from gdb's idea of the current
 275    floating point register set.  */
 276
 277 void
 278 fill_fpregset (fpregset_t *fpregsetp,
 279                int regno)
 280 {
 281   convert_to_fpregset (fpregsetp, registers, 0);
 282 }
 283
 284
 285 /* Get the whole floating point state of the process and store the
 286    floating point stack into registers[].  */
 287 static void
 288 fetch_fpregs ()
 289 {
 290   int ret, regno;
 291   fpregset_t buf;
 292
 293   ret = ptrace (PTRACE_GETFPREGS, inferior_pid, 0, (int) &buf);
 294   if (ret < 0)
 295     {
 296       warning ("Couldn't get floating point status");
 297       return;
 298     }
 299
 300   /* ptrace fills an fpregset_t, so we can use the same function we do
 301      for core files.  */
 302   supply_fpregset (&buf);
 303 }
 304
 305
 306 /* Set the inferior's floating-point registers to the values in
 307    registers[] --- but only those registers marked valid.  */
 308 static void
 309 store_fpregs ()
 310 {
 311   int ret;
 312   fpregset_t buf;
 313
 314   ret = ptrace (PTRACE_GETFPREGS, inferior_pid, 0, (int) &buf);
 315   if (ret < 0)
 316     {
 317       warning ("Couldn't get floating point status");
 318       return;
 319     }
 320
 321   convert_to_fpregset (&buf, registers, register_valid);
 322
 323   ret = ptrace (PTRACE_SETFPREGS, inferior_pid, 0, (int) &buf);
 324   if (ret < 0)
 325     {
 326       warning ("Couldn't write floating point status");
 327       return;
 328     }
 329 }
 330
 331 \f
 332 /* Transfering floating-point and SSE registers to and from GDB.  */
 333
 334
 335 /* PTRACE_GETXFPREGS is a Cygnus invention, since we wrote our own
 336    Linux kernel patch for SSE support.  That patch may or may not
 337    actually make it into the official distribution.  If you find that
 338    years have gone by since this code was added, and Linux isn't using
 339    PTRACE_GETXFPREGS, that means that our patch didn't make it, and
 340    you can delete this code.  */
 341
 342 #ifdef HAVE_PTRACE_GETXFPREGS
 343 static void
 344 supply_xfpregset (struct user_xfpregs_struct *xfpregs)
 345 {
 346   int reg;
 347
 348   /* Supply the floating-point registers.  */
 349   for (reg = 0; reg < 8; reg++)
 350     supply_register (FP0_REGNUM + reg, (char *) &xfpregs->st_space[reg]);
 351
 352   {
 353     supply_register (FCTRL_REGNUM, (char *) &xfpregs->cwd);
 354     supply_register (FSTAT_REGNUM, (char *) &xfpregs->swd);
 355     supply_register (FTAG_REGNUM,  (char *) &xfpregs->twd);
 356     supply_register (FCOFF_REGNUM, (char *) &xfpregs->fip);
 357     supply_register (FDS_REGNUM,   (char *) &xfpregs->fos);
 358     supply_register (FDOFF_REGNUM, (char *) &xfpregs->foo);
 359
 360     /* Extract the code segment and opcode from the  "fcs" member.  */
 361     {
 362       long l;
 363
 364       l = xfpregs->fcs & 0xffff;
 365       supply_register (FCS_REGNUM, (char *) &l);
 366
 367       l = (xfpregs->fcs >> 16) & ((1 << 11) - 1);
 368       supply_register (FOP_REGNUM, (char *) &l);
 369     }
 370   }
 371
 372   /* Supply the SSE registers.  */
 373   for (reg = 0; reg < 8; reg++)
 374     supply_register (XMM0_REGNUM + reg, (char *) &xfpregs->xmm_space[reg]);
 375   supply_register (MXCSR_REGNUM, (char *) &xfpregs->mxcsr);
 376 }
 377
 378
 379 static void
 380 convert_to_xfpregset (struct user_xfpregs_struct *xfpregs,
 381                       char *gdb_regs,
 382                       signed char *valid)
 383 {
 384   int reg;
 385
 386   /* Fill in the floating-point registers.  */
 387   for (reg = 0; reg < 8; reg++)
 388     if (!valid || valid[reg])
 389       memcpy (&xfpregs->st_space[reg],
 390               &registers[REGISTER_BYTE (FP0_REGNUM + reg)],
 391               REGISTER_RAW_SIZE(FP0_REGNUM + reg));
 392
 393 #define fill(MEMBER, REGNO)                                             \
 394   if (! valid || valid[(REGNO)])                                        \
 395     memcpy (&xfpregs->MEMBER, &registers[REGISTER_BYTE (REGNO)],        \
 396             sizeof (xfpregs->MEMBER))
 397
 398   fill (cwd, FCTRL_REGNUM);
 399   fill (swd, FSTAT_REGNUM);
 400   fill (twd, FTAG_REGNUM);
 401   fill (fip, FCOFF_REGNUM);
 402   fill (foo, FDOFF_REGNUM);
 403   fill (fos, FDS_REGNUM);
 404
 405 #undef fill
 406
 407   if (! valid || valid[FCS_REGNUM])
 408     xfpregs->fcs
 409       = ((xfpregs->fcs & ~0xffff)
 410          | (* (int *) &registers[REGISTER_BYTE (FCS_REGNUM)] & 0xffff));
 411
 412   if (! valid || valid[FOP_REGNUM])
 413     xfpregs->fcs
 414       = ((xfpregs->fcs & 0xffff)
 415          | ((*(int *) &registers[REGISTER_BYTE (FOP_REGNUM)] & ((1 << 11) - 1))
 416             << 16));
 417
 418   /* Fill in the XMM registers.  */
 419   for (reg = 0; reg < 8; reg++)
 420     if (! valid || valid[reg])
 421       memcpy (&xfpregs->xmm_space[reg],
 422               &registers[REGISTER_BYTE (XMM0_REGNUM + reg)],
 423               REGISTER_RAW_SIZE (XMM0_REGNUM + reg));
 424 }
 425
 426
 427 /* Make a PTRACE_GETXFPREGS request, and supply all the register
 428    values that yields to GDB.  */
 429 static int
 430 fetch_xfpregs ()
 431 {
 432   int ret;
 433   struct user_xfpregs_struct xfpregs;
 434
 435   if (! have_ptrace_getxfpregs)
 436     return 0;
 437
 438   ret = ptrace (PTRACE_GETXFPREGS, inferior_pid, 0, &xfpregs);
 439   if (ret == -1)
 440     {
 441       if (errno == EIO)
 442         {
 443           have_ptrace_getxfpregs = 0;
 444           return 0;
 445         }
 446
 447       warning ("couldn't read floating-point and SSE registers.");
 448       return 0;
 449     }
 450
 451   supply_xfpregset (&xfpregs);
 452   return 1;
 453 }
 454
 455
 456 /* Send all the valid register values in GDB's register file covered
 457    by the PTRACE_SETXFPREGS request to the inferior.  */
 458 static int
 459 store_xfpregs ()
 460 {
 461   int ret;
 462   struct user_xfpregs_struct xfpregs;
 463
 464   if (! have_ptrace_getxfpregs)
 465     return 0;
 466
 467   ret = ptrace (PTRACE_GETXFPREGS, inferior_pid, 0, &xfpregs);
 468   if (ret == -1)
 469     {
 470       if (errno == EIO)
 471         {
 472           have_ptrace_getxfpregs = 0;
 473           return 0;
 474         }
 475
 476       warning ("couldn't read floating-point and SSE registers.");
 477       return 0;
 478     }
 479
 480   convert_to_xfpregset (&xfpregs, registers, register_valid);
 481
 482   if (ptrace (PTRACE_SETXFPREGS, inferior_pid, 0, &xfpregs) < 0)
 483     {
 484       warning ("Couldn't write floating-point and SSE registers.");
 485       return 0;
 486     }
 487
 488   return 1;
 489 }
 490
 491
 492 /* Fill the XMM registers in the register file with dummy values.  For
 493    cases where we don't have access to the XMM registers.  I think
 494    this is cleaner than printing a warning.  For a cleaner solution,
 495    we should gdbarchify the i386 family.  */
 496 static void
 497 dummy_sse_values ()
 498 {
 499   /* C doesn't have a syntax for NaN's, so write it out as an array of
 500      longs.  */
 501   static long dummy[4] = { 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff };
 502   static long mxcsr = 0x1f80;
 503   int reg;
 504
 505   for (reg = 0; reg < 8; reg++)
 506     supply_register (XMM0_REGNUM + reg, (char *) dummy);
 507   supply_register (MXCSR_REGNUM, (char *) &mxcsr);
 508 }
 509
 510 #else
 511
 512 /* Stub versions of the above routines, for systems that don't have
 513    PTRACE_GETXFPREGS.  */
 514 static int store_xfpregs () { return 0; }
 515 static int fetch_xfpregs () { return 0; }
 516 static void dummy_sse_values () {}
 517
 518 #endif
 519
 520 \f
 521 /* Transferring arbitrary registers between GDB and inferior.  */
 522
 523 /* Fetch registers from the child process.
 524    Fetch all if regno == -1, otherwise fetch all ordinary
 525    registers or all floating point registers depending
 526    upon the value of regno. */
 527
 528 void
 529 fetch_inferior_registers (int regno)
 530 {
 531   /* Use the xfpregs requests whenever possible, since they transfer
 532      more registers in one system call, and we'll cache the results.
 533      But remember that fetch_xfpregs can fail, and return zero.  */
 534   if (regno == -1)
 535     {
 536       fetch_regs ();
 537       if (fetch_xfpregs ())
 538         return;
 539       fetch_fpregs ();
 540       return;
 541     }
 542
 543   if (GETREGS_SUPPLIES (regno))
 544     {
 545       fetch_regs ();
 546       return;
 547     }
 548
 549   if (GETXFPREGS_SUPPLIES (regno))
 550     {
 551       if (fetch_xfpregs ())
 552         return;
 553
 554       /* Either our processor or our kernel doesn't support the SSE
 555          registers, so read the FP registers in the traditional way,
 556          and fill the SSE registers with dummy values.  It would be
 557          more graceful to handle differences in the register set using
 558          gdbarch.  Until then, this will at least make things work
 559          plausibly.  */
 560       fetch_fpregs ();
 561       dummy_sse_values ();
 562       return;
 563     }
 564
 565   internal_error ("i386-linux-nat.c (fetch_inferior_registers): "
 566                   "got request for bad register number %d", regno);
 567 }
 568
 569
 570 /* Store our register values back into the inferior.
 571    If REGNO is -1, do this for all registers.
 572    Otherwise, REGNO specifies which register, which
 573    then determines whether we store all ordinary
 574    registers or all of the floating point registers. */
 575
 576 void
 577 store_inferior_registers (regno)
 578      int regno;
 579 {
 580   /* Use the xfpregs requests whenever possible, since they transfer
 581      more registers in one system call.  But remember that
 582      fetch_xfpregs can fail, and return zero.  */
 583   if (regno == -1)
 584     {
 585       store_regs ();
 586       if (store_xfpregs ())
 587         return;
 588       store_fpregs ();
 589       return;
 590     }
 591
 592   if (GETREGS_SUPPLIES (regno))
 593     {
 594       store_regs ();
 595       return;
 596     }
 597
 598   if (GETXFPREGS_SUPPLIES (regno))
 599     {
 600       if (store_xfpregs ())
 601         return;
 602
 603       /* Either our processor or our kernel doesn't support the SSE
 604          registers, so just write the FP registers in the traditional way.  */
 605       store_fpregs ();
 606       return;
 607     }
 608
 609   internal_error ("i386-linux-nat.c (store_inferior_registers): "
 610                   "got request to store bad register number %d", regno);
 611 }
 612
 613
 614 \f
 615 /* Calling functions in shared libraries.  */
 616
 617 /* Find the minimal symbol named NAME, and return both the minsym
 618    struct and its objfile.  This probably ought to be in minsym.c, but
 619    everything there is trying to deal with things like C++ and
 620    SOFUN_ADDRESS_MAYBE_TURQUOISE, ...  Since this is so simple, it may
 621    be considered too special-purpose for general consumption.  */
 622
 623 static struct minimal_symbol *
 624 find_minsym_and_objfile (char *name, struct objfile **objfile_p)
 625 {
 626   struct objfile *objfile;
 627
 628   ALL_OBJFILES (objfile)
 629     {
 630       struct minimal_symbol *msym;
 631
 632       ALL_OBJFILE_MSYMBOLS (objfile, msym)
 633         {
 634           if (SYMBOL_NAME (msym)
 635               && STREQ (SYMBOL_NAME (msym), name))
 636             {
 637               *objfile_p = objfile;
 638               return msym;
 639             }
 640         }
 641     }
 642
 643   return 0;
 644 }
 645
 646
 647 static CORE_ADDR
 648 skip_hurd_resolver (CORE_ADDR pc)
 649 {
 650   /* The HURD dynamic linker is part of the GNU C library, so many
 651      GNU/Linux distributions use it.  (All ELF versions, as far as I
 652      know.)  An unresolved PLT entry points to "_dl_runtime_resolve",
 653      which calls "fixup" to patch the PLT, and then passes control to
 654      the function.
 655
 656      We look for the symbol `_dl_runtime_resolve', and find `fixup' in
 657      the same objfile.  If we are at the entry point of `fixup', then
 658      we set a breakpoint at the return address (at the top of the
 659      stack), and continue.
 660
 661      It's kind of gross to do all these checks every time we're
 662      called, since they don't change once the executable has gotten
 663      started.  But this is only a temporary hack --- upcoming versions
 664      of Linux will provide a portable, efficient interface for
 665      debugging programs that use shared libraries.  */
 666
 667   struct objfile *objfile;
 668   struct minimal_symbol *resolver
 669     = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile);
 670
 671   if (resolver)
 672     {
 673       struct minimal_symbol *fixup
 674         = lookup_minimal_symbol ("fixup", 0, objfile);
 675
 676       if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc)
 677         return (SAVED_PC_AFTER_CALL (get_current_frame ()));
 678     }
 679
 680   return 0;
 681 }
 682
 683
 684 /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.
 685    This function:
 686    1) decides whether a PLT has sent us into the linker to resolve
 687       a function reference, and
 688    2) if so, tells us where to set a temporary breakpoint that will
 689       trigger when the dynamic linker is done.  */
 690
 691 CORE_ADDR
 692 i386_linux_skip_solib_resolver (CORE_ADDR pc)
 693 {
 694   CORE_ADDR result;
 695
 696   /* Plug in functions for other kinds of resolvers here.  */
 697   result = skip_hurd_resolver (pc);
 698   if (result)
 699     return result;
 700
 701   return 0;
 702 }