gdb/dwarf2expr.c

   1 /* DWARF 2 Expression Evaluator.
   2
   3    Copyright (C) 2001, 2002, 2003, 2005, 2007, 2008, 2009, 2010
   4    Free Software Foundation, Inc.
   5
   6    Contributed by Daniel Berlin (dan@dberlin.org)
   7
   8    This file is part of GDB.
   9
  10    This program is free software; you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation; either version 3 of the License, or
  13    (at your option) any later version.
  14
  15    This program is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  22
  23 #include "defs.h"
  24 #include "symtab.h"
  25 #include "gdbtypes.h"
  26 #include "value.h"
  27 #include "gdbcore.h"
  28 #include "dwarf2.h"
  29 #include "dwarf2expr.h"
  30 #include "gdb_assert.h"
  31
  32 /* Local prototypes.  */
  33
  34 static void execute_stack_op (struct dwarf_expr_context *,
  35                               const gdb_byte *, const gdb_byte *);
  36 static struct type *unsigned_address_type (struct gdbarch *, int);
  37
  38 /* Create a new context for the expression evaluator.  */
  39
  40 struct dwarf_expr_context *
  41 new_dwarf_expr_context (void)
  42 {
  43   struct dwarf_expr_context *retval;
  44
  45   retval = xcalloc (1, sizeof (struct dwarf_expr_context));
  46   retval->stack_len = 0;
  47   retval->stack_allocated = 10;
  48   retval->stack = xmalloc (retval->stack_allocated
  49                            * sizeof (struct dwarf_stack_value));
  50   retval->num_pieces = 0;
  51   retval->pieces = 0;
  52   retval->max_recursion_depth = 0x100;
  53   return retval;
  54 }
  55
  56 /* Release the memory allocated to CTX.  */
  57
  58 void
  59 free_dwarf_expr_context (struct dwarf_expr_context *ctx)
  60 {
  61   xfree (ctx->stack);
  62   xfree (ctx->pieces);
  63   xfree (ctx);
  64 }
  65
  66 /* Helper for make_cleanup_free_dwarf_expr_context.  */
  67
  68 static void
  69 free_dwarf_expr_context_cleanup (void *arg)
  70 {
  71   free_dwarf_expr_context (arg);
  72 }
  73
  74 /* Return a cleanup that calls free_dwarf_expr_context.  */
  75
  76 struct cleanup *
  77 make_cleanup_free_dwarf_expr_context (struct dwarf_expr_context *ctx)
  78 {
  79   return make_cleanup (free_dwarf_expr_context_cleanup, ctx);
  80 }
  81
  82 /* Expand the memory allocated to CTX's stack to contain at least
  83    NEED more elements than are currently used.  */
  84
  85 static void
  86 dwarf_expr_grow_stack (struct dwarf_expr_context *ctx, size_t need)
  87 {
  88   if (ctx->stack_len + need > ctx->stack_allocated)
  89     {
  90       size_t newlen = ctx->stack_len + need + 10;
  91
  92       ctx->stack = xrealloc (ctx->stack,
  93                              newlen * sizeof (struct dwarf_stack_value));
  94       ctx->stack_allocated = newlen;
  95     }
  96 }
  97
  98 /* Push VALUE onto CTX's stack.  */
  99
 100 void
 101 dwarf_expr_push (struct dwarf_expr_context *ctx, CORE_ADDR value,
 102                  int in_stack_memory)
 103 {
 104   struct dwarf_stack_value *v;
 105
 106   dwarf_expr_grow_stack (ctx, 1);
 107   v = &ctx->stack[ctx->stack_len++];
 108   v->value = value;
 109   v->in_stack_memory = in_stack_memory;
 110 }
 111
 112 /* Pop the top item off of CTX's stack.  */
 113
 114 void
 115 dwarf_expr_pop (struct dwarf_expr_context *ctx)
 116 {
 117   if (ctx->stack_len <= 0)
 118     error (_("dwarf expression stack underflow"));
 119   ctx->stack_len--;
 120 }
 121
 122 /* Retrieve the N'th item on CTX's stack.  */
 123
 124 CORE_ADDR
 125 dwarf_expr_fetch (struct dwarf_expr_context *ctx, int n)
 126 {
 127   if (ctx->stack_len <= n)
 128      error (_("Asked for position %d of stack, stack only has %d elements on it."),
 129             n, ctx->stack_len);
 130   return ctx->stack[ctx->stack_len - (1 + n)].value;
 131
 132 }
 133
 134 /* Retrieve the in_stack_memory flag of the N'th item on CTX's stack.  */
 135
 136 int
 137 dwarf_expr_fetch_in_stack_memory (struct dwarf_expr_context *ctx, int n)
 138 {
 139   if (ctx->stack_len <= n)
 140      error (_("Asked for position %d of stack, stack only has %d elements on it."),
 141             n, ctx->stack_len);
 142   return ctx->stack[ctx->stack_len - (1 + n)].in_stack_memory;
 143
 144 }
 145
 146 /* Return true if the expression stack is empty.  */
 147
 148 static int
 149 dwarf_expr_stack_empty_p (struct dwarf_expr_context *ctx)
 150 {
 151   return ctx->stack_len == 0;
 152 }
 153
 154 /* Add a new piece to CTX's piece list.  */
 155 static void
 156 add_piece (struct dwarf_expr_context *ctx, ULONGEST size, ULONGEST offset)
 157 {
 158   struct dwarf_expr_piece *p;
 159
 160   ctx->num_pieces++;
 161
 162   ctx->pieces = xrealloc (ctx->pieces,
 163                           (ctx->num_pieces
 164                            * sizeof (struct dwarf_expr_piece)));
 165
 166   p = &ctx->pieces[ctx->num_pieces - 1];
 167   p->location = ctx->location;
 168   p->size = size;
 169   p->offset = offset;
 170
 171   if (p->location == DWARF_VALUE_LITERAL)
 172     {
 173       p->v.literal.data = ctx->data;
 174       p->v.literal.length = ctx->len;
 175     }
 176   else if (dwarf_expr_stack_empty_p (ctx))
 177     {
 178       p->location = DWARF_VALUE_OPTIMIZED_OUT;
 179       /* Also reset the context's location, for our callers.  This is
 180          a somewhat strange approach, but this lets us avoid setting
 181          the location to DWARF_VALUE_MEMORY in all the individual
 182          cases in the evaluator.  */
 183       ctx->location = DWARF_VALUE_OPTIMIZED_OUT;
 184     }
 185   else
 186     {
 187       p->v.expr.value = dwarf_expr_fetch (ctx, 0);
 188       p->v.expr.in_stack_memory = dwarf_expr_fetch_in_stack_memory (ctx, 0);
 189     }
 190 }
 191
 192 /* Evaluate the expression at ADDR (LEN bytes long) using the context
 193    CTX.  */
 194
 195 void
 196 dwarf_expr_eval (struct dwarf_expr_context *ctx, const gdb_byte *addr,
 197                  size_t len)
 198 {
 199   int old_recursion_depth = ctx->recursion_depth;
 200
 201   execute_stack_op (ctx, addr, addr + len);
 202
 203   /* CTX RECURSION_DEPTH becomes invalid if an exception was thrown here.  */
 204
 205   gdb_assert (ctx->recursion_depth == old_recursion_depth);
 206 }
 207
 208 /* Decode the unsigned LEB128 constant at BUF into the variable pointed to
 209    by R, and return the new value of BUF.  Verify that it doesn't extend
 210    past BUF_END.  */
 211
 212 const gdb_byte *
 213 read_uleb128 (const gdb_byte *buf, const gdb_byte *buf_end, ULONGEST * r)
 214 {
 215   unsigned shift = 0;
 216   ULONGEST result = 0;
 217   gdb_byte byte;
 218
 219   while (1)
 220     {
 221       if (buf >= buf_end)
 222         error (_("read_uleb128: Corrupted DWARF expression."));
 223
 224       byte = *buf++;
 225       result |= (byte & 0x7f) << shift;
 226       if ((byte & 0x80) == 0)
 227         break;
 228       shift += 7;
 229     }
 230   *r = result;
 231   return buf;
 232 }
 233
 234 /* Decode the signed LEB128 constant at BUF into the variable pointed to
 235    by R, and return the new value of BUF.  Verify that it doesn't extend
 236    past BUF_END.  */
 237
 238 const gdb_byte *
 239 read_sleb128 (const gdb_byte *buf, const gdb_byte *buf_end, LONGEST * r)
 240 {
 241   unsigned shift = 0;
 242   LONGEST result = 0;
 243   gdb_byte byte;
 244
 245   while (1)
 246     {
 247       if (buf >= buf_end)
 248         error (_("read_sleb128: Corrupted DWARF expression."));
 249
 250       byte = *buf++;
 251       result |= (byte & 0x7f) << shift;
 252       shift += 7;
 253       if ((byte & 0x80) == 0)
 254         break;
 255     }
 256   if (shift < (sizeof (*r) * 8) && (byte & 0x40) != 0)
 257     result |= -(1 << shift);
 258
 259   *r = result;
 260   return buf;
 261 }
 262
 263 /* Read an address of size ADDR_SIZE from BUF, and verify that it
 264    doesn't extend past BUF_END.  */
 265
 266 CORE_ADDR
 267 dwarf2_read_address (struct gdbarch *gdbarch, const gdb_byte *buf,
 268                      const gdb_byte *buf_end, int addr_size)
 269 {
 270   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 271
 272   if (buf_end - buf < addr_size)
 273     error (_("dwarf2_read_address: Corrupted DWARF expression."));
 274
 275   /* For most architectures, calling extract_unsigned_integer() alone
 276      is sufficient for extracting an address.  However, some
 277      architectures (e.g. MIPS) use signed addresses and using
 278      extract_unsigned_integer() will not produce a correct
 279      result.  Make sure we invoke gdbarch_integer_to_address()
 280      for those architectures which require it.
 281
 282      The use of `unsigned_address_type' in the code below refers to
 283      the type of buf and has no bearing on the signedness of the
 284      address being returned.  */
 285
 286   if (gdbarch_integer_to_address_p (gdbarch))
 287     return gdbarch_integer_to_address
 288              (gdbarch, unsigned_address_type (gdbarch, addr_size), buf);
 289
 290   return extract_unsigned_integer (buf, addr_size, byte_order);
 291 }
 292
 293 /* Return the type of an address of size ADDR_SIZE,
 294    for unsigned arithmetic.  */
 295
 296 static struct type *
 297 unsigned_address_type (struct gdbarch *gdbarch, int addr_size)
 298 {
 299   switch (addr_size)
 300     {
 301     case 2:
 302       return builtin_type (gdbarch)->builtin_uint16;
 303     case 4:
 304       return builtin_type (gdbarch)->builtin_uint32;
 305     case 8:
 306       return builtin_type (gdbarch)->builtin_uint64;
 307     default:
 308       internal_error (__FILE__, __LINE__,
 309                       _("Unsupported address size.\n"));
 310     }
 311 }
 312
 313 /* Return the type of an address of size ADDR_SIZE,
 314    for signed arithmetic.  */
 315
 316 static struct type *
 317 signed_address_type (struct gdbarch *gdbarch, int addr_size)
 318 {
 319   switch (addr_size)
 320     {
 321     case 2:
 322       return builtin_type (gdbarch)->builtin_int16;
 323     case 4:
 324       return builtin_type (gdbarch)->builtin_int32;
 325     case 8:
 326       return builtin_type (gdbarch)->builtin_int64;
 327     default:
 328       internal_error (__FILE__, __LINE__,
 329                       _("Unsupported address size.\n"));
 330     }
 331 }
 332 \f
 333
 334 /* Check that the current operator is either at the end of an
 335    expression, or that it is followed by a composition operator.  */
 336
 337 static void
 338 require_composition (const gdb_byte *op_ptr, const gdb_byte *op_end,
 339                      const char *op_name)
 340 {
 341   /* It seems like DW_OP_GNU_uninit should be handled here.  However,
 342      it doesn't seem to make sense for DW_OP_*_value, and it was not
 343      checked at the other place that this function is called.  */
 344   if (op_ptr != op_end && *op_ptr != DW_OP_piece && *op_ptr != DW_OP_bit_piece)
 345     error (_("DWARF-2 expression error: `%s' operations must be "
 346              "used either alone or in conjuction with DW_OP_piece "
 347              "or DW_OP_bit_piece."),
 348            op_name);
 349 }
 350
 351 /* The engine for the expression evaluator.  Using the context in CTX,
 352    evaluate the expression between OP_PTR and OP_END.  */
 353
 354 static void
 355 execute_stack_op (struct dwarf_expr_context *ctx,
 356                   const gdb_byte *op_ptr, const gdb_byte *op_end)
 357 {
 358   enum bfd_endian byte_order = gdbarch_byte_order (ctx->gdbarch);
 359
 360   ctx->location = DWARF_VALUE_MEMORY;
 361   ctx->initialized = 1;  /* Default is initialized.  */
 362
 363   if (ctx->recursion_depth > ctx->max_recursion_depth)
 364     error (_("DWARF-2 expression error: Loop detected (%d)."),
 365            ctx->recursion_depth);
 366   ctx->recursion_depth++;
 367
 368   while (op_ptr < op_end)
 369     {
 370       enum dwarf_location_atom op = *op_ptr++;
 371       CORE_ADDR result;
 372       /* Assume the value is not in stack memory.
 373          Code that knows otherwise sets this to 1.
 374          Some arithmetic on stack addresses can probably be assumed to still
 375          be a stack address, but we skip this complication for now.
 376          This is just an optimization, so it's always ok to punt
 377          and leave this as 0.  */
 378       int in_stack_memory = 0;
 379       ULONGEST uoffset, reg;
 380       LONGEST offset;
 381
 382       switch (op)
 383         {
 384         case DW_OP_lit0:
 385         case DW_OP_lit1:
 386         case DW_OP_lit2:
 387         case DW_OP_lit3:
 388         case DW_OP_lit4:
 389         case DW_OP_lit5:
 390         case DW_OP_lit6:
 391         case DW_OP_lit7:
 392         case DW_OP_lit8:
 393         case DW_OP_lit9:
 394         case DW_OP_lit10:
 395         case DW_OP_lit11:
 396         case DW_OP_lit12:
 397         case DW_OP_lit13:
 398         case DW_OP_lit14:
 399         case DW_OP_lit15:
 400         case DW_OP_lit16:
 401         case DW_OP_lit17:
 402         case DW_OP_lit18:
 403         case DW_OP_lit19:
 404         case DW_OP_lit20:
 405         case DW_OP_lit21:
 406         case DW_OP_lit22:
 407         case DW_OP_lit23:
 408         case DW_OP_lit24:
 409         case DW_OP_lit25:
 410         case DW_OP_lit26:
 411         case DW_OP_lit27:
 412         case DW_OP_lit28:
 413         case DW_OP_lit29:
 414         case DW_OP_lit30:
 415         case DW_OP_lit31:
 416           result = op - DW_OP_lit0;
 417           break;
 418
 419         case DW_OP_addr:
 420           result = dwarf2_read_address (ctx->gdbarch,
 421                                         op_ptr, op_end, ctx->addr_size);
 422           op_ptr += ctx->addr_size;
 423           break;
 424
 425         case DW_OP_const1u:
 426           result = extract_unsigned_integer (op_ptr, 1, byte_order);
 427           op_ptr += 1;
 428           break;
 429         case DW_OP_const1s:
 430           result = extract_signed_integer (op_ptr, 1, byte_order);
 431           op_ptr += 1;
 432           break;
 433         case DW_OP_const2u:
 434           result = extract_unsigned_integer (op_ptr, 2, byte_order);
 435           op_ptr += 2;
 436           break;
 437         case DW_OP_const2s:
 438           result = extract_signed_integer (op_ptr, 2, byte_order);
 439           op_ptr += 2;
 440           break;
 441         case DW_OP_const4u:
 442           result = extract_unsigned_integer (op_ptr, 4, byte_order);
 443           op_ptr += 4;
 444           break;
 445         case DW_OP_const4s:
 446           result = extract_signed_integer (op_ptr, 4, byte_order);
 447           op_ptr += 4;
 448           break;
 449         case DW_OP_const8u:
 450           result = extract_unsigned_integer (op_ptr, 8, byte_order);
 451           op_ptr += 8;
 452           break;
 453         case DW_OP_const8s:
 454           result = extract_signed_integer (op_ptr, 8, byte_order);
 455           op_ptr += 8;
 456           break;
 457         case DW_OP_constu:
 458           op_ptr = read_uleb128 (op_ptr, op_end, &uoffset);
 459           result = uoffset;
 460           break;
 461         case DW_OP_consts:
 462           op_ptr = read_sleb128 (op_ptr, op_end, &offset);
 463           result = offset;
 464           break;
 465
 466         /* The DW_OP_reg operations are required to occur alone in
 467            location expressions.  */
 468         case DW_OP_reg0:
 469         case DW_OP_reg1:
 470         case DW_OP_reg2:
 471         case DW_OP_reg3:
 472         case DW_OP_reg4:
 473         case DW_OP_reg5:
 474         case DW_OP_reg6:
 475         case DW_OP_reg7:
 476         case DW_OP_reg8:
 477         case DW_OP_reg9:
 478         case DW_OP_reg10:
 479         case DW_OP_reg11:
 480         case DW_OP_reg12:
 481         case DW_OP_reg13:
 482         case DW_OP_reg14:
 483         case DW_OP_reg15:
 484         case DW_OP_reg16:
 485         case DW_OP_reg17:
 486         case DW_OP_reg18:
 487         case DW_OP_reg19:
 488         case DW_OP_reg20:
 489         case DW_OP_reg21:
 490         case DW_OP_reg22:
 491         case DW_OP_reg23:
 492         case DW_OP_reg24:
 493         case DW_OP_reg25:
 494         case DW_OP_reg26:
 495         case DW_OP_reg27:
 496         case DW_OP_reg28:
 497         case DW_OP_reg29:
 498         case DW_OP_reg30:
 499         case DW_OP_reg31:
 500           if (op_ptr != op_end
 501               && *op_ptr != DW_OP_piece
 502               && *op_ptr != DW_OP_bit_piece
 503               && *op_ptr != DW_OP_GNU_uninit)
 504             error (_("DWARF-2 expression error: DW_OP_reg operations must be "
 505                      "used either alone or in conjuction with DW_OP_piece "
 506                      "or DW_OP_bit_piece."));
 507
 508           result = op - DW_OP_reg0;
 509           ctx->location = DWARF_VALUE_REGISTER;
 510           break;
 511
 512         case DW_OP_regx:
 513           op_ptr = read_uleb128 (op_ptr, op_end, &reg);
 514           require_composition (op_ptr, op_end, "DW_OP_regx");
 515
 516           result = reg;
 517           ctx->location = DWARF_VALUE_REGISTER;
 518           break;
 519
 520         case DW_OP_implicit_value:
 521           {
 522             ULONGEST len;
 523
 524             op_ptr = read_uleb128 (op_ptr, op_end, &len);
 525             if (op_ptr + len > op_end)
 526               error (_("DW_OP_implicit_value: too few bytes available."));
 527             ctx->len = len;
 528             ctx->data = op_ptr;
 529             ctx->location = DWARF_VALUE_LITERAL;
 530             op_ptr += len;
 531             require_composition (op_ptr, op_end, "DW_OP_implicit_value");
 532           }
 533           goto no_push;
 534
 535         case DW_OP_stack_value:
 536           ctx->location = DWARF_VALUE_STACK;
 537           require_composition (op_ptr, op_end, "DW_OP_stack_value");
 538           goto no_push;
 539
 540         case DW_OP_breg0:
 541         case DW_OP_breg1:
 542         case DW_OP_breg2:
 543         case DW_OP_breg3:
 544         case DW_OP_breg4:
 545         case DW_OP_breg5:
 546         case DW_OP_breg6:
 547         case DW_OP_breg7:
 548         case DW_OP_breg8:
 549         case DW_OP_breg9:
 550         case DW_OP_breg10:
 551         case DW_OP_breg11:
 552         case DW_OP_breg12:
 553         case DW_OP_breg13:
 554         case DW_OP_breg14:
 555         case DW_OP_breg15:
 556         case DW_OP_breg16:
 557         case DW_OP_breg17:
 558         case DW_OP_breg18:
 559         case DW_OP_breg19:
 560         case DW_OP_breg20:
 561         case DW_OP_breg21:
 562         case DW_OP_breg22:
 563         case DW_OP_breg23:
 564         case DW_OP_breg24:
 565         case DW_OP_breg25:
 566         case DW_OP_breg26:
 567         case DW_OP_breg27:
 568         case DW_OP_breg28:
 569         case DW_OP_breg29:
 570         case DW_OP_breg30:
 571         case DW_OP_breg31:
 572           {
 573             op_ptr = read_sleb128 (op_ptr, op_end, &offset);
 574             result = (ctx->read_reg) (ctx->baton, op - DW_OP_breg0);
 575             result += offset;
 576           }
 577           break;
 578         case DW_OP_bregx:
 579           {
 580             op_ptr = read_uleb128 (op_ptr, op_end, &reg);
 581             op_ptr = read_sleb128 (op_ptr, op_end, &offset);
 582             result = (ctx->read_reg) (ctx->baton, reg);
 583             result += offset;
 584           }
 585           break;
 586         case DW_OP_fbreg:
 587           {
 588             const gdb_byte *datastart;
 589             size_t datalen;
 590             unsigned int before_stack_len;
 591
 592             op_ptr = read_sleb128 (op_ptr, op_end, &offset);
 593             /* Rather than create a whole new context, we simply
 594                record the stack length before execution, then reset it
 595                afterwards, effectively erasing whatever the recursive
 596                call put there.  */
 597             before_stack_len = ctx->stack_len;
 598             /* FIXME: cagney/2003-03-26: This code should be using
 599                get_frame_base_address(), and then implement a dwarf2
 600                specific this_base method.  */
 601             (ctx->get_frame_base) (ctx->baton, &datastart, &datalen);
 602             dwarf_expr_eval (ctx, datastart, datalen);
 603             if (ctx->location == DWARF_VALUE_LITERAL
 604                 || ctx->location == DWARF_VALUE_STACK)
 605               error (_("Not implemented: computing frame base using explicit value operator"));
 606             result = dwarf_expr_fetch (ctx, 0);
 607             if (ctx->location == DWARF_VALUE_REGISTER)
 608               result = (ctx->read_reg) (ctx->baton, result);
 609             result = result + offset;
 610             in_stack_memory = 1;
 611             ctx->stack_len = before_stack_len;
 612             ctx->location = DWARF_VALUE_MEMORY;
 613           }
 614           break;
 615
 616         case DW_OP_dup:
 617           result = dwarf_expr_fetch (ctx, 0);
 618           in_stack_memory = dwarf_expr_fetch_in_stack_memory (ctx, 0);
 619           break;
 620
 621         case DW_OP_drop:
 622           dwarf_expr_pop (ctx);
 623           goto no_push;
 624
 625         case DW_OP_pick:
 626           offset = *op_ptr++;
 627           result = dwarf_expr_fetch (ctx, offset);
 628           in_stack_memory = dwarf_expr_fetch_in_stack_memory (ctx, offset);
 629           break;
 630
 631         case DW_OP_swap:
 632           {
 633             struct dwarf_stack_value t1, t2;
 634
 635             if (ctx->stack_len < 2)
 636                error (_("Not enough elements for DW_OP_swap. Need 2, have %d."),
 637                       ctx->stack_len);
 638             t1 = ctx->stack[ctx->stack_len - 1];
 639             t2 = ctx->stack[ctx->stack_len - 2];
 640             ctx->stack[ctx->stack_len - 1] = t2;
 641             ctx->stack[ctx->stack_len - 2] = t1;
 642             goto no_push;
 643           }
 644
 645         case DW_OP_over:
 646           result = dwarf_expr_fetch (ctx, 1);
 647           in_stack_memory = dwarf_expr_fetch_in_stack_memory (ctx, 1);
 648           break;
 649
 650         case DW_OP_rot:
 651           {
 652             struct dwarf_stack_value t1, t2, t3;
 653
 654             if (ctx->stack_len < 3)
 655                error (_("Not enough elements for DW_OP_rot. Need 3, have %d."),
 656                       ctx->stack_len);
 657             t1 = ctx->stack[ctx->stack_len - 1];
 658             t2 = ctx->stack[ctx->stack_len - 2];
 659             t3 = ctx->stack[ctx->stack_len - 3];
 660             ctx->stack[ctx->stack_len - 1] = t2;
 661             ctx->stack[ctx->stack_len - 2] = t3;
 662             ctx->stack[ctx->stack_len - 3] = t1;
 663             goto no_push;
 664           }
 665
 666         case DW_OP_deref:
 667         case DW_OP_deref_size:
 668         case DW_OP_abs:
 669         case DW_OP_neg:
 670         case DW_OP_not:
 671         case DW_OP_plus_uconst:
 672           /* Unary operations.  */
 673           result = dwarf_expr_fetch (ctx, 0);
 674           dwarf_expr_pop (ctx);
 675
 676           switch (op)
 677             {
 678             case DW_OP_deref:
 679               {
 680                 gdb_byte *buf = alloca (ctx->addr_size);
 681
 682                 (ctx->read_mem) (ctx->baton, buf, result, ctx->addr_size);
 683                 result = dwarf2_read_address (ctx->gdbarch,
 684                                               buf, buf + ctx->addr_size,
 685                                               ctx->addr_size);
 686               }
 687               break;
 688
 689             case DW_OP_deref_size:
 690               {
 691                 int addr_size = *op_ptr++;
 692                 gdb_byte *buf = alloca (addr_size);
 693
 694                 (ctx->read_mem) (ctx->baton, buf, result, addr_size);
 695                 result = dwarf2_read_address (ctx->gdbarch,
 696                                               buf, buf + addr_size,
 697                                               addr_size);
 698               }
 699               break;
 700
 701             case DW_OP_abs:
 702               if ((signed int) result < 0)
 703                 result = -result;
 704               break;
 705             case DW_OP_neg:
 706               result = -result;
 707               break;
 708             case DW_OP_not:
 709               result = ~result;
 710               break;
 711             case DW_OP_plus_uconst:
 712               op_ptr = read_uleb128 (op_ptr, op_end, &reg);
 713               result += reg;
 714               break;
 715             }
 716           break;
 717
 718         case DW_OP_and:
 719         case DW_OP_div:
 720         case DW_OP_minus:
 721         case DW_OP_mod:
 722         case DW_OP_mul:
 723         case DW_OP_or:
 724         case DW_OP_plus:
 725         case DW_OP_shl:
 726         case DW_OP_shr:
 727         case DW_OP_shra:
 728         case DW_OP_xor:
 729         case DW_OP_le:
 730         case DW_OP_ge:
 731         case DW_OP_eq:
 732         case DW_OP_lt:
 733         case DW_OP_gt:
 734         case DW_OP_ne:
 735           {
 736             /* Binary operations.  Use the value engine to do computations in
 737                the right width.  */
 738             CORE_ADDR first, second;
 739             enum exp_opcode binop;
 740             struct value *val1 = NULL, *val2 = NULL;
 741             struct type *stype, *utype;
 742
 743             second = dwarf_expr_fetch (ctx, 0);
 744             dwarf_expr_pop (ctx);
 745
 746             first = dwarf_expr_fetch (ctx, 0);
 747             dwarf_expr_pop (ctx);
 748
 749             utype = unsigned_address_type (ctx->gdbarch, ctx->addr_size);
 750             stype = signed_address_type (ctx->gdbarch, ctx->addr_size);
 751
 752             switch (op)
 753               {
 754               case DW_OP_and:
 755                 binop = BINOP_BITWISE_AND;
 756                 break;
 757               case DW_OP_div:
 758                 binop = BINOP_DIV;
 759                 val1 = value_from_longest (stype, first);
 760                 val2 = value_from_longest (stype, second);
 761                 break;
 762               case DW_OP_minus:
 763                 binop = BINOP_SUB;
 764                 break;
 765               case DW_OP_mod:
 766                 binop = BINOP_MOD;
 767                 break;
 768               case DW_OP_mul:
 769                 binop = BINOP_MUL;
 770                 break;
 771               case DW_OP_or:
 772                 binop = BINOP_BITWISE_IOR;
 773                 break;
 774               case DW_OP_plus:
 775                 binop = BINOP_ADD;
 776                 break;
 777               case DW_OP_shl:
 778                 binop = BINOP_LSH;
 779                 break;
 780               case DW_OP_shr:
 781                 binop = BINOP_RSH;
 782                 break;
 783               case DW_OP_shra:
 784                 binop = BINOP_RSH;
 785                 val1 = value_from_longest (stype, first);
 786                 break;
 787               case DW_OP_xor:
 788                 binop = BINOP_BITWISE_XOR;
 789                 break;
 790               case DW_OP_le:
 791                 binop = BINOP_LEQ;
 792                 val1 = value_from_longest (stype, first);
 793                 val2 = value_from_longest (stype, second);
 794                 break;
 795               case DW_OP_ge:
 796                 binop = BINOP_GEQ;
 797                 val1 = value_from_longest (stype, first);
 798                 val2 = value_from_longest (stype, second);
 799                 break;
 800               case DW_OP_eq:
 801                 binop = BINOP_EQUAL;
 802                 val1 = value_from_longest (stype, first);
 803                 val2 = value_from_longest (stype, second);
 804                 break;
 805               case DW_OP_lt:
 806                 binop = BINOP_LESS;
 807                 val1 = value_from_longest (stype, first);
 808                 val2 = value_from_longest (stype, second);
 809                 break;
 810               case DW_OP_gt:
 811                 binop = BINOP_GTR;
 812                 val1 = value_from_longest (stype, first);
 813                 val2 = value_from_longest (stype, second);
 814                 break;
 815               case DW_OP_ne:
 816                 binop = BINOP_NOTEQUAL;
 817                 val1 = value_from_longest (stype, first);
 818                 val2 = value_from_longest (stype, second);
 819                 break;
 820               default:
 821                 internal_error (__FILE__, __LINE__,
 822                                 _("Can't be reached."));
 823               }
 824
 825             /* We use unsigned operands by default.  */
 826             if (val1 == NULL)
 827               val1 = value_from_longest (utype, first);
 828             if (val2 == NULL)
 829               val2 = value_from_longest (utype, second);
 830
 831             result = value_as_long (value_binop (val1, val2, binop));
 832           }
 833           break;
 834
 835         case DW_OP_call_frame_cfa:
 836           result = (ctx->get_frame_cfa) (ctx->baton);
 837           in_stack_memory = 1;
 838           break;
 839
 840         case DW_OP_GNU_push_tls_address:
 841           /* Variable is at a constant offset in the thread-local
 842           storage block into the objfile for the current thread and
 843           the dynamic linker module containing this expression. Here
 844           we return returns the offset from that base.  The top of the
 845           stack has the offset from the beginning of the thread
 846           control block at which the variable is located.  Nothing
 847           should follow this operator, so the top of stack would be
 848           returned.  */
 849           result = dwarf_expr_fetch (ctx, 0);
 850           dwarf_expr_pop (ctx);
 851           result = (ctx->get_tls_address) (ctx->baton, result);
 852           break;
 853
 854         case DW_OP_skip:
 855           offset = extract_signed_integer (op_ptr, 2, byte_order);
 856           op_ptr += 2;
 857           op_ptr += offset;
 858           goto no_push;
 859
 860         case DW_OP_bra:
 861           offset = extract_signed_integer (op_ptr, 2, byte_order);
 862           op_ptr += 2;
 863           if (dwarf_expr_fetch (ctx, 0) != 0)
 864             op_ptr += offset;
 865           dwarf_expr_pop (ctx);
 866           goto no_push;
 867
 868         case DW_OP_nop:
 869           goto no_push;
 870
 871         case DW_OP_piece:
 872           {
 873             ULONGEST size;
 874
 875             /* Record the piece.  */
 876             op_ptr = read_uleb128 (op_ptr, op_end, &size);
 877             add_piece (ctx, 8 * size, 0);
 878
 879             /* Pop off the address/regnum, and reset the location
 880                type.  */
 881             if (ctx->location != DWARF_VALUE_LITERAL
 882                 && ctx->location != DWARF_VALUE_OPTIMIZED_OUT)
 883               dwarf_expr_pop (ctx);
 884             ctx->location = DWARF_VALUE_MEMORY;
 885           }
 886           goto no_push;
 887
 888         case DW_OP_bit_piece:
 889           {
 890             ULONGEST size, offset;
 891
 892             /* Record the piece.  */
 893             op_ptr = read_uleb128 (op_ptr, op_end, &size);
 894             op_ptr = read_uleb128 (op_ptr, op_end, &offset);
 895             add_piece (ctx, size, offset);
 896
 897             /* Pop off the address/regnum, and reset the location
 898                type.  */
 899             if (ctx->location != DWARF_VALUE_LITERAL
 900                 && ctx->location != DWARF_VALUE_OPTIMIZED_OUT)
 901               dwarf_expr_pop (ctx);
 902             ctx->location = DWARF_VALUE_MEMORY;
 903           }
 904           goto no_push;
 905
 906         case DW_OP_GNU_uninit:
 907           if (op_ptr != op_end)
 908             error (_("DWARF-2 expression error: DW_OP_GNU_uninit must always "
 909                    "be the very last op."));
 910
 911           ctx->initialized = 0;
 912           goto no_push;
 913
 914         default:
 915           error (_("Unhandled dwarf expression opcode 0x%x"), op);
 916         }
 917
 918       /* Most things push a result value.  */
 919       dwarf_expr_push (ctx, result, in_stack_memory);
 920     no_push:;
 921     }
 922
 923   ctx->recursion_depth--;
 924   gdb_assert (ctx->recursion_depth >= 0);
 925 }