gdb/ppc64-tdep.c

   1 /* Common target-dependent code for ppc64 GDB, the GNU debugger.
   2
   3    Copyright (C) 1986-2015 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "frame.h"
  22 #include "gdbcore.h"
  23 #include "infrun.h"
  24 #include "ppc-tdep.h"
  25 #include "ppc64-tdep.h"
  26 #include "elf-bfd.h"
  27
  28 /* Macros for matching instructions.  Note that, since all the
  29    operands are masked off before they're or-ed into the instruction,
  30    you can use -1 to make masks.  */
  31
  32 #define insn_d(opcd, rts, ra, d)                \
  33   ((((opcd) & 0x3f) << 26)                      \
  34    | (((rts) & 0x1f) << 21)                     \
  35    | (((ra) & 0x1f) << 16)                      \
  36    | ((d) & 0xffff))
  37
  38 #define insn_ds(opcd, rts, ra, d, xo)           \
  39   ((((opcd) & 0x3f) << 26)                      \
  40    | (((rts) & 0x1f) << 21)                     \
  41    | (((ra) & 0x1f) << 16)                      \
  42    | ((d) & 0xfffc)                             \
  43    | ((xo) & 0x3))
  44
  45 #define insn_xfx(opcd, rts, spr, xo)            \
  46   ((((opcd) & 0x3f) << 26)                      \
  47    | (((rts) & 0x1f) << 21)                     \
  48    | (((spr) & 0x1f) << 16)                     \
  49    | (((spr) & 0x3e0) << 6)                     \
  50    | (((xo) & 0x3ff) << 1))
  51
  52 /* If PLT is the address of a 64-bit PowerPC PLT entry,
  53    return the function's entry point.  */
  54
  55 static CORE_ADDR
  56 ppc64_plt_entry_point (struct gdbarch *gdbarch, CORE_ADDR plt)
  57 {
  58   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
  59   /* The first word of the PLT entry is the function entry point.  */
  60   return (CORE_ADDR) read_memory_unsigned_integer (plt, 8, byte_order);
  61 }
  62
  63 /* Patterns for the standard linkage functions.  These are built by
  64    build_plt_stub in bfd/elf64-ppc.c.  */
  65
  66 /* Old ELFv1 PLT call stub.  */
  67
  68 static struct ppc_insn_pattern ppc64_standard_linkage1[] =
  69   {
  70     /* addis r12, r2, <any> */
  71     { insn_d (-1, -1, -1, 0), insn_d (15, 12, 2, 0), 0 },
  72
  73     /* std r2, 40(r1) */
  74     { -1, insn_ds (62, 2, 1, 40, 0), 0 },
  75
  76     /* ld r11, <any>(r12) */
  77     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 0 },
  78
  79     /* addis r12, r12, 1 <optional> */
  80     { insn_d (-1, -1, -1, -1), insn_d (15, 12, 12, 1), 1 },
  81
  82     /* ld r2, <any>(r12) */
  83     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 12, 0, 0), 0 },
  84
  85     /* addis r12, r12, 1 <optional> */
  86     { insn_d (-1, -1, -1, -1), insn_d (15, 12, 12, 1), 1 },
  87
  88     /* mtctr r11 */
  89     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 11, 9, 467), 0 },
  90
  91     /* ld r11, <any>(r12) <optional> */
  92     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 1 },
  93
  94     /* bctr */
  95     { -1, 0x4e800420, 0 },
  96
  97     { 0, 0, 0 }
  98   };
  99
 100 /* ELFv1 PLT call stub to access PLT entries more than +/- 32k from r2.
 101    Also supports older stub with different placement of std 2,40(1),
 102    a stub that omits the std 2,40(1), and both versions of power7
 103    thread safety read barriers.  Note that there are actually two more
 104    instructions following "cmpldi r2, 0", "bnectr+" and "b <glink_i>",
 105    but there isn't any need to match them.  */
 106
 107 static struct ppc_insn_pattern ppc64_standard_linkage2[] =
 108   {
 109     /* std r2, 40(r1) <optional> */
 110     { -1, insn_ds (62, 2, 1, 40, 0), 1 },
 111
 112     /* addis r12, r2, <any> */
 113     { insn_d (-1, -1, -1, 0), insn_d (15, 12, 2, 0), 0 },
 114
 115     /* std r2, 40(r1) <optional> */
 116     { -1, insn_ds (62, 2, 1, 40, 0), 1 },
 117
 118     /* ld r11, <any>(r12) */
 119     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 0 },
 120
 121     /* addi r12, r12, <any> <optional> */
 122     { insn_d (-1, -1, -1, 0), insn_d (14, 12, 12, 0), 1 },
 123
 124     /* mtctr r11 */
 125     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 11, 9, 467), 0 },
 126
 127     /* xor r11, r11, r11 <optional> */
 128     { -1, 0x7d6b5a78, 1 },
 129
 130     /* add r12, r12, r11 <optional> */
 131     { -1, 0x7d8c5a14, 1 },
 132
 133     /* ld r2, <any>(r12) */
 134     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 12, 0, 0), 0 },
 135
 136     /* ld r11, <any>(r12) <optional> */
 137     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 12, 0, 0), 1 },
 138
 139     /* bctr <optional> */
 140     { -1, 0x4e800420, 1 },
 141
 142     /* cmpldi r2, 0 <optional> */
 143     { -1, 0x28220000, 1 },
 144
 145     { 0, 0, 0 }
 146   };
 147
 148 /* ELFv1 PLT call stub to access PLT entries within +/- 32k of r2.  */
 149
 150 static struct ppc_insn_pattern ppc64_standard_linkage3[] =
 151   {
 152     /* std r2, 40(r1) <optional> */
 153     { -1, insn_ds (62, 2, 1, 40, 0), 1 },
 154
 155     /* ld r11, <any>(r2) */
 156     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 0 },
 157
 158     /* addi r2, r2, <any> <optional> */
 159     { insn_d (-1, -1, -1, 0), insn_d (14, 2, 2, 0), 1 },
 160
 161     /* mtctr r11 */
 162     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 11, 9, 467), 0 },
 163
 164     /* xor r11, r11, r11 <optional> */
 165     { -1, 0x7d6b5a78, 1 },
 166
 167     /* add r2, r2, r11 <optional> */
 168     { -1, 0x7c425a14, 1 },
 169
 170     /* ld r11, <any>(r2) <optional> */
 171     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 1 },
 172
 173     /* ld r2, <any>(r2) */
 174     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 2, 0, 0), 0 },
 175
 176     /* bctr <optional> */
 177     { -1, 0x4e800420, 1 },
 178
 179     /* cmpldi r2, 0 <optional> */
 180     { -1, 0x28220000, 1 },
 181
 182     { 0, 0, 0 }
 183   };
 184
 185 /* ELFv1 PLT call stub to access PLT entries more than +/- 32k from r2.
 186    A more modern variant of ppc64_standard_linkage2 differing in
 187    register usage.  */
 188
 189 static struct ppc_insn_pattern ppc64_standard_linkage4[] =
 190   {
 191     /* std r2, 40(r1) <optional> */
 192     { -1, insn_ds (62, 2, 1, 40, 0), 1 },
 193
 194     /* addis r11, r2, <any> */
 195     { insn_d (-1, -1, -1, 0), insn_d (15, 11, 2, 0), 0 },
 196
 197     /* ld r12, <any>(r11) */
 198     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 12, 11, 0, 0), 0 },
 199
 200     /* addi r11, r11, <any> <optional> */
 201     { insn_d (-1, -1, -1, 0), insn_d (14, 11, 11, 0), 1 },
 202
 203     /* mtctr r12 */
 204     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 12, 9, 467), 0 },
 205
 206     /* xor r2, r12, r12 <optional> */
 207     { -1, 0x7d826278, 1 },
 208
 209     /* add r11, r11, r2 <optional> */
 210     { -1, 0x7d6b1214, 1 },
 211
 212     /* ld r2, <any>(r11) */
 213     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 11, 0, 0), 0 },
 214
 215     /* ld r11, <any>(r11) <optional> */
 216     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 11, 0, 0), 1 },
 217
 218     /* bctr <optional> */
 219     { -1, 0x4e800420, 1 },
 220
 221     /* cmpldi r2, 0 <optional> */
 222     { -1, 0x28220000, 1 },
 223
 224     { 0, 0, 0 }
 225   };
 226
 227 /* ELFv1 PLT call stub to access PLT entries within +/- 32k of r2.
 228    A more modern variant of ppc64_standard_linkage3 differing in
 229    register usage.  */
 230
 231 static struct ppc_insn_pattern ppc64_standard_linkage5[] =
 232   {
 233     /* std r2, 40(r1) <optional> */
 234     { -1, insn_ds (62, 2, 1, 40, 0), 1 },
 235
 236     /* ld r12, <any>(r2) */
 237     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 12, 2, 0, 0), 0 },
 238
 239     /* addi r2, r2, <any> <optional> */
 240     { insn_d (-1, -1, -1, 0), insn_d (14, 2, 2, 0), 1 },
 241
 242     /* mtctr r12 */
 243     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 12, 9, 467), 0 },
 244
 245     /* xor r11, r12, r12 <optional> */
 246     { -1, 0x7d8b6278, 1 },
 247
 248     /* add r2, r2, r11 <optional> */
 249     { -1, 0x7c425a14, 1 },
 250
 251     /* ld r11, <any>(r2) <optional> */
 252     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 11, 2, 0, 0), 1 },
 253
 254     /* ld r2, <any>(r2) */
 255     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 2, 2, 0, 0), 0 },
 256
 257     /* bctr <optional> */
 258     { -1, 0x4e800420, 1 },
 259
 260     /* cmpldi r2, 0 <optional> */
 261     { -1, 0x28220000, 1 },
 262
 263     { 0, 0, 0 }
 264   };
 265
 266 /* ELFv2 PLT call stub to access PLT entries more than +/- 32k from r2.  */
 267
 268 static struct ppc_insn_pattern ppc64_standard_linkage6[] =
 269   {
 270     /* std r2, 24(r1) <optional> */
 271     { -1, insn_ds (62, 2, 1, 24, 0), 1 },
 272
 273     /* addis r11, r2, <any> */
 274     { insn_d (-1, -1, -1, 0), insn_d (15, 11, 2, 0), 0 },
 275
 276     /* ld r12, <any>(r11) */
 277     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 12, 11, 0, 0), 0 },
 278
 279     /* mtctr r12 */
 280     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 12, 9, 467), 0 },
 281
 282     /* bctr */
 283     { -1, 0x4e800420, 0 },
 284
 285     { 0, 0, 0 }
 286   };
 287
 288 /* ELFv2 PLT call stub to access PLT entries within +/- 32k of r2.  */
 289
 290 static struct ppc_insn_pattern ppc64_standard_linkage7[] =
 291   {
 292     /* std r2, 24(r1) <optional> */
 293     { -1, insn_ds (62, 2, 1, 24, 0), 1 },
 294
 295     /* ld r12, <any>(r2) */
 296     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 12, 2, 0, 0), 0 },
 297
 298     /* mtctr r12 */
 299     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 12, 9, 467), 0 },
 300
 301     /* bctr */
 302     { -1, 0x4e800420, 0 },
 303
 304     { 0, 0, 0 }
 305   };
 306
 307 /* ELFv2 PLT call stub to access PLT entries more than +/- 32k from r2,
 308    supporting fusion.  */
 309
 310 static struct ppc_insn_pattern ppc64_standard_linkage8[] =
 311   {
 312     /* std r2, 24(r1) <optional> */
 313     { -1, insn_ds (62, 2, 1, 24, 0), 1 },
 314
 315     /* addis r12, r2, <any> */
 316     { insn_d (-1, -1, -1, 0), insn_d (15, 12, 2, 0), 0 },
 317
 318     /* ld r12, <any>(r12) */
 319     { insn_ds (-1, -1, -1, 0, -1), insn_ds (58, 12, 12, 0, 0), 0 },
 320
 321     /* mtctr r12 */
 322     { insn_xfx (-1, -1, -1, -1), insn_xfx (31, 12, 9, 467), 0 },
 323
 324     /* bctr */
 325     { -1, 0x4e800420, 0 },
 326
 327     { 0, 0, 0 }
 328   };
 329
 330 /* When the dynamic linker is doing lazy symbol resolution, the first
 331    call to a function in another object will go like this:
 332
 333    - The user's function calls the linkage function:
 334
 335         100003d4:   4b ff ff ad     bl      10000380 <nnnn.plt_call.printf>
 336         100003d8:   e8 41 00 28     ld      r2,40(r1)
 337
 338    - The linkage function loads the entry point and toc pointer from
 339      the function descriptor in the PLT, and jumps to it:
 340
 341      <nnnn.plt_call.printf>:
 342         10000380:   f8 41 00 28     std     r2,40(r1)
 343         10000384:   e9 62 80 78     ld      r11,-32648(r2)
 344         10000388:   7d 69 03 a6     mtctr   r11
 345         1000038c:   e8 42 80 80     ld      r2,-32640(r2)
 346         10000390:   28 22 00 00     cmpldi  r2,0
 347         10000394:   4c e2 04 20     bnectr+
 348         10000398:   48 00 03 a0     b       10000738 <printf@plt>
 349
 350    - But since this is the first time that PLT entry has been used, it
 351      sends control to its glink entry.  That loads the number of the
 352      PLT entry and jumps to the common glink0 code:
 353
 354      <printf@plt>:
 355         10000738:   38 00 00 01     li      r0,1
 356         1000073c:   4b ff ff bc     b       100006f8 <__glink_PLTresolve>
 357
 358    - The common glink0 code then transfers control to the dynamic
 359      linker's fixup code:
 360
 361         100006f0:   0000000000010440 .quad plt0 - (. + 16)
 362      <__glink_PLTresolve>:
 363         100006f8:   7d 88 02 a6     mflr    r12
 364         100006fc:   42 9f 00 05     bcl     20,4*cr7+so,10000700
 365         10000700:   7d 68 02 a6     mflr    r11
 366         10000704:   e8 4b ff f0     ld      r2,-16(r11)
 367         10000708:   7d 88 03 a6     mtlr    r12
 368         1000070c:   7d 82 5a 14     add     r12,r2,r11
 369         10000710:   e9 6c 00 00     ld      r11,0(r12)
 370         10000714:   e8 4c 00 08     ld      r2,8(r12)
 371         10000718:   7d 69 03 a6     mtctr   r11
 372         1000071c:   e9 6c 00 10     ld      r11,16(r12)
 373         10000720:   4e 80 04 20     bctr
 374
 375    Eventually, this code will figure out how to skip all of this,
 376    including the dynamic linker.  At the moment, we just get through
 377    the linkage function.  */
 378
 379 /* If the current thread is about to execute a series of instructions
 380    at PC matching the ppc64_standard_linkage pattern, and INSN is the result
 381    from that pattern match, return the code address to which the
 382    standard linkage function will send them.  (This doesn't deal with
 383    dynamic linker lazy symbol resolution stubs.)  */
 384
 385 static CORE_ADDR
 386 ppc64_standard_linkage1_target (struct frame_info *frame,
 387                                 CORE_ADDR pc, unsigned int *insn)
 388 {
 389   struct gdbarch *gdbarch = get_frame_arch (frame);
 390   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 391
 392   /* The address of the PLT entry this linkage function references.  */
 393   CORE_ADDR plt
 394     = ((CORE_ADDR) get_frame_register_unsigned (frame,
 395                                                 tdep->ppc_gp0_regnum + 2)
 396        + (ppc_insn_d_field (insn[0]) << 16)
 397        + ppc_insn_ds_field (insn[2]));
 398
 399   return ppc64_plt_entry_point (gdbarch, plt);
 400 }
 401
 402 static CORE_ADDR
 403 ppc64_standard_linkage2_target (struct frame_info *frame,
 404                                 CORE_ADDR pc, unsigned int *insn)
 405 {
 406   struct gdbarch *gdbarch = get_frame_arch (frame);
 407   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 408
 409   /* The address of the PLT entry this linkage function references.  */
 410   CORE_ADDR plt
 411     = ((CORE_ADDR) get_frame_register_unsigned (frame,
 412                                                 tdep->ppc_gp0_regnum + 2)
 413        + (ppc_insn_d_field (insn[1]) << 16)
 414        + ppc_insn_ds_field (insn[3]));
 415
 416   return ppc64_plt_entry_point (gdbarch, plt);
 417 }
 418
 419 static CORE_ADDR
 420 ppc64_standard_linkage3_target (struct frame_info *frame,
 421                                 CORE_ADDR pc, unsigned int *insn)
 422 {
 423   struct gdbarch *gdbarch = get_frame_arch (frame);
 424   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 425
 426   /* The address of the PLT entry this linkage function references.  */
 427   CORE_ADDR plt
 428     = ((CORE_ADDR) get_frame_register_unsigned (frame,
 429                                                 tdep->ppc_gp0_regnum + 2)
 430        + ppc_insn_ds_field (insn[1]));
 431
 432   return ppc64_plt_entry_point (gdbarch, plt);
 433 }
 434
 435 static CORE_ADDR
 436 ppc64_standard_linkage4_target (struct frame_info *frame,
 437                                 CORE_ADDR pc, unsigned int *insn)
 438 {
 439   struct gdbarch *gdbarch = get_frame_arch (frame);
 440   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 441
 442   CORE_ADDR plt
 443     = ((CORE_ADDR) get_frame_register_unsigned (frame, tdep->ppc_gp0_regnum + 2)
 444        + (ppc_insn_d_field (insn[1]) << 16)
 445        + ppc_insn_ds_field (insn[2]));
 446
 447   return ppc64_plt_entry_point (gdbarch, plt);
 448 }
 449
 450
 451 /* Given that we've begun executing a call trampoline at PC, return
 452    the entry point of the function the trampoline will go to.  */
 453
 454 CORE_ADDR
 455 ppc64_skip_trampoline_code (struct frame_info *frame, CORE_ADDR pc)
 456 {
 457 #define MAX(a,b) ((a) > (b) ? (a) : (b))
 458   unsigned int insns[MAX (MAX (MAX (ARRAY_SIZE (ppc64_standard_linkage1),
 459                                     ARRAY_SIZE (ppc64_standard_linkage2)),
 460                                MAX (ARRAY_SIZE (ppc64_standard_linkage3),
 461                                     ARRAY_SIZE (ppc64_standard_linkage4))),
 462                           MAX (MAX (ARRAY_SIZE (ppc64_standard_linkage5),
 463                                     ARRAY_SIZE (ppc64_standard_linkage6)),
 464                                MAX (ARRAY_SIZE (ppc64_standard_linkage7),
 465                                     ARRAY_SIZE (ppc64_standard_linkage8))))
 466                      - 1];
 467   CORE_ADDR target;
 468   int scan_limit, i;
 469
 470   scan_limit = 1;
 471   /* When reverse-debugging, scan backward to check whether we are
 472      in the middle of trampoline code.  */
 473   if (execution_direction == EXEC_REVERSE)
 474     scan_limit = ARRAY_SIZE (insns) - 1;
 475
 476   for (i = 0; i < scan_limit; i++)
 477     {
 478       if (i < ARRAY_SIZE (ppc64_standard_linkage8) - 1
 479           && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage8, insns))
 480         pc = ppc64_standard_linkage4_target (frame, pc, insns);
 481       else if (i < ARRAY_SIZE (ppc64_standard_linkage7) - 1
 482                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage7,
 483                                            insns))
 484         pc = ppc64_standard_linkage3_target (frame, pc, insns);
 485       else if (i < ARRAY_SIZE (ppc64_standard_linkage6) - 1
 486                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage6,
 487                                            insns))
 488         pc = ppc64_standard_linkage4_target (frame, pc, insns);
 489       else if (i < ARRAY_SIZE (ppc64_standard_linkage5) - 1
 490                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage5,
 491                                            insns)
 492                && (insns[8] != 0 || insns[9] != 0))
 493         pc = ppc64_standard_linkage3_target (frame, pc, insns);
 494       else if (i < ARRAY_SIZE (ppc64_standard_linkage4) - 1
 495                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage4,
 496                                            insns)
 497                && (insns[9] != 0 || insns[10] != 0))
 498         pc = ppc64_standard_linkage4_target (frame, pc, insns);
 499       else if (i < ARRAY_SIZE (ppc64_standard_linkage3) - 1
 500                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage3,
 501                                            insns)
 502                && (insns[8] != 0 || insns[9] != 0))
 503         pc = ppc64_standard_linkage3_target (frame, pc, insns);
 504       else if (i < ARRAY_SIZE (ppc64_standard_linkage2) - 1
 505                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage2,
 506                                            insns)
 507                && (insns[10] != 0 || insns[11] != 0))
 508         pc = ppc64_standard_linkage2_target (frame, pc, insns);
 509       else if (i < ARRAY_SIZE (ppc64_standard_linkage1) - 1
 510                && ppc_insns_match_pattern (frame, pc, ppc64_standard_linkage1,
 511                                            insns))
 512         pc = ppc64_standard_linkage1_target (frame, pc, insns);
 513       else
 514         {
 515           /* Scan backward one more instructions if doesn't match.  */
 516           pc -= 4;
 517           continue;
 518         }
 519
 520       /* The PLT descriptor will either point to the already resolved target
 521          address, or else to a glink stub.  As the latter carry synthetic @plt
 522          symbols, find_solib_trampoline_target should be able to resolve them.  */
 523       target = find_solib_trampoline_target (frame, pc);
 524       return target ? target : pc;
 525   }
 526
 527   return 0;
 528 }
 529
 530 /* Support for convert_from_func_ptr_addr (ARCH, ADDR, TARG) on PPC64
 531    GNU/Linux.
 532
 533    Usually a function pointer's representation is simply the address
 534    of the function.  On GNU/Linux on the PowerPC however, a function
 535    pointer may be a pointer to a function descriptor.
 536
 537    For PPC64, a function descriptor is a TOC entry, in a data section,
 538    which contains three words: the first word is the address of the
 539    function, the second word is the TOC pointer (r2), and the third word
 540    is the static chain value.
 541
 542    Throughout GDB it is currently assumed that a function pointer contains
 543    the address of the function, which is not easy to fix.  In addition, the
 544    conversion of a function address to a function pointer would
 545    require allocation of a TOC entry in the inferior's memory space,
 546    with all its drawbacks.  To be able to call C++ virtual methods in
 547    the inferior (which are called via function pointers),
 548    find_function_addr uses this function to get the function address
 549    from a function pointer.
 550
 551    If ADDR points at what is clearly a function descriptor, transform
 552    it into the address of the corresponding function, if needed.  Be
 553    conservative, otherwise GDB will do the transformation on any
 554    random addresses such as occur when there is no symbol table.  */
 555
 556 CORE_ADDR
 557 ppc64_convert_from_func_ptr_addr (struct gdbarch *gdbarch,
 558                                         CORE_ADDR addr,
 559                                         struct target_ops *targ)
 560 {
 561   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 562   struct target_section *s = target_section_by_addr (targ, addr);
 563
 564   /* Check if ADDR points to a function descriptor.  */
 565   if (s && strcmp (s->the_bfd_section->name, ".opd") == 0)
 566     {
 567       /* There may be relocations that need to be applied to the .opd
 568          section.  Unfortunately, this function may be called at a time
 569          where these relocations have not yet been performed -- this can
 570          happen for example shortly after a library has been loaded with
 571          dlopen, but ld.so has not yet applied the relocations.
 572
 573          To cope with both the case where the relocation has been applied,
 574          and the case where it has not yet been applied, we do *not* read
 575          the (maybe) relocated value from target memory, but we instead
 576          read the non-relocated value from the BFD, and apply the relocation
 577          offset manually.
 578
 579          This makes the assumption that all .opd entries are always relocated
 580          by the same offset the section itself was relocated.  This should
 581          always be the case for GNU/Linux executables and shared libraries.
 582          Note that other kind of object files (e.g. those added via
 583          add-symbol-files) will currently never end up here anyway, as this
 584          function accesses *target* sections only; only the main exec and
 585          shared libraries are ever added to the target.  */
 586
 587       gdb_byte buf[8];
 588       int res;
 589
 590       res = bfd_get_section_contents (s->the_bfd_section->owner,
 591                                       s->the_bfd_section,
 592                                       &buf, addr - s->addr, 8);
 593       if (res != 0)
 594         return extract_unsigned_integer (buf, 8, byte_order)
 595                 - bfd_section_vma (s->bfd, s->the_bfd_section) + s->addr;
 596    }
 597
 598   return addr;
 599 }
 600
 601 /* A synthetic 'dot' symbols on ppc64 has the udata.p entry pointing
 602    back to the original ELF symbol it was derived from.  Get the size
 603    from that symbol.  */
 604
 605 void
 606 ppc64_elf_make_msymbol_special (asymbol *sym, struct minimal_symbol *msym)
 607 {
 608   if ((sym->flags & BSF_SYNTHETIC) != 0 && sym->udata.p != NULL)
 609     {
 610       elf_symbol_type *elf_sym = (elf_symbol_type *) sym->udata.p;
 611       SET_MSYMBOL_SIZE (msym, elf_sym->internal_elf_sym.st_size);
 612     }
 613 }