aboutsummaryrefslogtreecommitdiff
path: root/gdb/dwarf2loc.c
blob: 027e13588794405ad6142087f1a40af0b004649a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
/* DWARF 2 location expression support for GDB.

   Copyright (C) 2003, 2005, 2007, 2008, 2009 Free Software Foundation, Inc.

   Contributed by Daniel Jacobowitz, MontaVista Software, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "ui-out.h"
#include "value.h"
#include "frame.h"
#include "gdbcore.h"
#include "target.h"
#include "inferior.h"
#include "ax.h"
#include "ax-gdb.h"
#include "regcache.h"
#include "objfiles.h"
#include "exceptions.h"
#include "block.h"

#include "elf/dwarf2.h"
#include "dwarf2expr.h"
#include "dwarf2loc.h"

#include "gdb_string.h"
#include "gdb_assert.h"

/* A helper function for dealing with location lists.  Given a
   symbol baton (BATON) and a pc value (PC), find the appropriate
   location expression, set *LOCEXPR_LENGTH, and return a pointer
   to the beginning of the expression.  Returns NULL on failure.

   For now, only return the first matching location expression; there
   can be more than one in the list.  */

static gdb_byte *
find_location_expression (struct dwarf2_loclist_baton *baton,
			  size_t *locexpr_length, CORE_ADDR pc)
{
  CORE_ADDR low, high;
  gdb_byte *loc_ptr, *buf_end;
  int length;
  struct objfile *objfile = dwarf2_per_cu_objfile (baton->per_cu);
  struct gdbarch *gdbarch = get_objfile_arch (objfile);
  unsigned int addr_size = dwarf2_per_cu_addr_size (baton->per_cu);
  CORE_ADDR base_mask = ~(~(CORE_ADDR)1 << (addr_size * 8 - 1));
  /* Adjust base_address for relocatable objects.  */
  CORE_ADDR base_offset = ANOFFSET (objfile->section_offsets,
				    SECT_OFF_TEXT (objfile));
  CORE_ADDR base_address = baton->base_address + base_offset;

  loc_ptr = baton->data;
  buf_end = baton->data + baton->size;

  while (1)
    {
      low = dwarf2_read_address (gdbarch, loc_ptr, buf_end, addr_size);
      loc_ptr += addr_size;
      high = dwarf2_read_address (gdbarch, loc_ptr, buf_end, addr_size);
      loc_ptr += addr_size;

      /* An end-of-list entry.  */
      if (low == 0 && high == 0)
	return NULL;

      /* A base-address-selection entry.  */
      if ((low & base_mask) == base_mask)
	{
	  base_address = high;
	  continue;
	}

      /* Otherwise, a location expression entry.  */
      low += base_address;
      high += base_address;

      length = extract_unsigned_integer (loc_ptr, 2);
      loc_ptr += 2;

      if (pc >= low && pc < high)
	{
	  *locexpr_length = length;
	  return loc_ptr;
	}

      loc_ptr += length;
    }
}

/* This is the baton used when performing dwarf2 expression
   evaluation.  */
struct dwarf_expr_baton
{
  struct frame_info *frame;
  struct objfile *objfile;
};

/* Helper functions for dwarf2_evaluate_loc_desc.  */

/* Using the frame specified in BATON, return the value of register
   REGNUM, treated as a pointer.  */
static CORE_ADDR
dwarf_expr_read_reg (void *baton, int dwarf_regnum)
{
  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
  struct gdbarch *gdbarch = get_frame_arch (debaton->frame);
  CORE_ADDR result;
  int regnum;

  regnum = gdbarch_dwarf2_reg_to_regnum (gdbarch, dwarf_regnum);
  result = address_from_register (builtin_type (gdbarch)->builtin_data_ptr,
				  regnum, debaton->frame);
  return result;
}

/* Read memory at ADDR (length LEN) into BUF.  */

static void
dwarf_expr_read_mem (void *baton, gdb_byte *buf, CORE_ADDR addr, size_t len)
{
  read_memory (addr, buf, len);
}

/* Using the frame specified in BATON, find the location expression
   describing the frame base.  Return a pointer to it in START and
   its length in LENGTH.  */
static void
dwarf_expr_frame_base (void *baton, gdb_byte **start, size_t * length)
{
  /* FIXME: cagney/2003-03-26: This code should be using
     get_frame_base_address(), and then implement a dwarf2 specific
     this_base method.  */
  struct symbol *framefunc;
  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;

  /* Use block_linkage_function, which returns a real (not inlined)
     function, instead of get_frame_function, which may return an
     inlined function.  */
  framefunc = block_linkage_function (get_frame_block (debaton->frame, NULL));

  /* If we found a frame-relative symbol then it was certainly within
     some function associated with a frame. If we can't find the frame,
     something has gone wrong.  */
  gdb_assert (framefunc != NULL);

  if (SYMBOL_LOCATION_BATON (framefunc) == NULL)
    *start = NULL;
  else if (SYMBOL_COMPUTED_OPS (framefunc) == &dwarf2_loclist_funcs)
    {
      struct dwarf2_loclist_baton *symbaton;
      struct frame_info *frame = debaton->frame;

      symbaton = SYMBOL_LOCATION_BATON (framefunc);
      *start = find_location_expression (symbaton, length,
					 get_frame_address_in_block (frame));
    }
  else
    {
      struct dwarf2_locexpr_baton *symbaton;
      symbaton = SYMBOL_LOCATION_BATON (framefunc);
      if (symbaton != NULL)
	{
	  *length = symbaton->size;
	  *start = symbaton->data;
	}
      else
	*start = NULL;
    }

  if (*start == NULL)
    error (_("Could not find the frame base for \"%s\"."),
	   SYMBOL_NATURAL_NAME (framefunc));
}

/* Using the objfile specified in BATON, find the address for the
   current thread's thread-local storage with offset OFFSET.  */
static CORE_ADDR
dwarf_expr_tls_address (void *baton, CORE_ADDR offset)
{
  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;

  return target_translate_tls_address (debaton->objfile, offset);
}

/* Evaluate a location description, starting at DATA and with length
   SIZE, to find the current location of variable VAR in the context
   of FRAME.  */
static struct value *
dwarf2_evaluate_loc_desc (struct symbol *var, struct frame_info *frame,
			  gdb_byte *data, unsigned short size,
			  struct dwarf2_per_cu_data *per_cu)
{
  struct value *retval;
  struct dwarf_expr_baton baton;
  struct dwarf_expr_context *ctx;

  if (size == 0)
    {
      retval = allocate_value (SYMBOL_TYPE (var));
      VALUE_LVAL (retval) = not_lval;
      set_value_optimized_out (retval, 1);
      return retval;
    }

  baton.frame = frame;
  baton.objfile = dwarf2_per_cu_objfile (per_cu);

  ctx = new_dwarf_expr_context ();
  ctx->gdbarch = get_objfile_arch (baton.objfile);
  ctx->addr_size = dwarf2_per_cu_addr_size (per_cu);
  ctx->baton = &baton;
  ctx->read_reg = dwarf_expr_read_reg;
  ctx->read_mem = dwarf_expr_read_mem;
  ctx->get_frame_base = dwarf_expr_frame_base;
  ctx->get_tls_address = dwarf_expr_tls_address;

  dwarf_expr_eval (ctx, data, size);
  if (ctx->num_pieces > 0)
    {
      int i;
      long offset = 0;
      bfd_byte *contents;

      retval = allocate_value (SYMBOL_TYPE (var));
      contents = value_contents_raw (retval);
      for (i = 0; i < ctx->num_pieces; i++)
	{
	  struct dwarf_expr_piece *p = &ctx->pieces[i];
	  if (p->in_reg)
	    {
	      struct gdbarch *arch = get_frame_arch (frame);
	      bfd_byte regval[MAX_REGISTER_SIZE];
	      int gdb_regnum = gdbarch_dwarf2_reg_to_regnum (arch, p->value);
	      get_frame_register (frame, gdb_regnum, regval);
	      memcpy (contents + offset, regval, p->size);
	    }
	  else /* In memory?  */
	    {
	      read_memory (p->value, contents + offset, p->size);
	    }
	  offset += p->size;
	}
    }
  else if (ctx->in_reg)
    {
      struct gdbarch *arch = get_frame_arch (frame);
      CORE_ADDR dwarf_regnum = dwarf_expr_fetch (ctx, 0);
      int gdb_regnum = gdbarch_dwarf2_reg_to_regnum (arch, dwarf_regnum);
      retval = value_from_register (SYMBOL_TYPE (var), gdb_regnum, frame);
    }
  else
    {
      CORE_ADDR address = dwarf_expr_fetch (ctx, 0);

      retval = allocate_value (SYMBOL_TYPE (var));
      VALUE_LVAL (retval) = lval_memory;
      set_value_lazy (retval, 1);
      set_value_address (retval, address);
    }

  set_value_initialized (retval, ctx->initialized);

  free_dwarf_expr_context (ctx);

  return retval;
}





/* Helper functions and baton for dwarf2_loc_desc_needs_frame.  */

struct needs_frame_baton
{
  int needs_frame;
};

/* Reads from registers do require a frame.  */
static CORE_ADDR
needs_frame_read_reg (void *baton, int regnum)
{
  struct needs_frame_baton *nf_baton = baton;
  nf_baton->needs_frame = 1;
  return 1;
}

/* Reads from memory do not require a frame.  */
static void
needs_frame_read_mem (void *baton, gdb_byte *buf, CORE_ADDR addr, size_t len)
{
  memset (buf, 0, len);
}

/* Frame-relative accesses do require a frame.  */
static void
needs_frame_frame_base (void *baton, gdb_byte **start, size_t * length)
{
  static gdb_byte lit0 = DW_OP_lit0;
  struct needs_frame_baton *nf_baton = baton;

  *start = &lit0;
  *length = 1;

  nf_baton->needs_frame = 1;
}

/* Thread-local accesses do require a frame.  */
static CORE_ADDR
needs_frame_tls_address (void *baton, CORE_ADDR offset)
{
  struct needs_frame_baton *nf_baton = baton;
  nf_baton->needs_frame = 1;
  return 1;
}

/* Return non-zero iff the location expression at DATA (length SIZE)
   requires a frame to evaluate.  */

static int
dwarf2_loc_desc_needs_frame (gdb_byte *data, unsigned short size,
			     struct dwarf2_per_cu_data *per_cu)
{
  struct needs_frame_baton baton;
  struct dwarf_expr_context *ctx;
  int in_reg;

  baton.needs_frame = 0;

  ctx = new_dwarf_expr_context ();
  ctx->gdbarch = get_objfile_arch (dwarf2_per_cu_objfile (per_cu));
  ctx->addr_size = dwarf2_per_cu_addr_size (per_cu);
  ctx->baton = &baton;
  ctx->read_reg = needs_frame_read_reg;
  ctx->read_mem = needs_frame_read_mem;
  ctx->get_frame_base = needs_frame_frame_base;
  ctx->get_tls_address = needs_frame_tls_address;

  dwarf_expr_eval (ctx, data, size);

  in_reg = ctx->in_reg;

  if (ctx->num_pieces > 0)
    {
      int i;

      /* If the location has several pieces, and any of them are in
         registers, then we will need a frame to fetch them from.  */
      for (i = 0; i < ctx->num_pieces; i++)
        if (ctx->pieces[i].in_reg)
          in_reg = 1;
    }

  free_dwarf_expr_context (ctx);

  return baton.needs_frame || in_reg;
}

static void
dwarf2_tracepoint_var_ref (struct symbol *symbol, struct gdbarch *gdbarch,
			   struct agent_expr *ax, struct axs_value *value,
			   gdb_byte *data, int size)
{
  if (size == 0)
    error (_("Symbol \"%s\" has been optimized out."),
	   SYMBOL_PRINT_NAME (symbol));

  if (size == 1
      && data[0] >= DW_OP_reg0
      && data[0] <= DW_OP_reg31)
    {
      value->kind = axs_lvalue_register;
      value->u.reg = data[0] - DW_OP_reg0;
    }
  else if (data[0] == DW_OP_regx)
    {
      ULONGEST reg;
      read_uleb128 (data + 1, data + size, &reg);
      value->kind = axs_lvalue_register;
      value->u.reg = reg;
    }
  else if (data[0] == DW_OP_fbreg)
    {
      /* And this is worse than just minimal; we should honor the frame base
	 as above.  */
      int frame_reg;
      LONGEST frame_offset;
      gdb_byte *buf_end;

      buf_end = read_sleb128 (data + 1, data + size, &frame_offset);
      if (buf_end != data + size)
	error (_("Unexpected opcode after DW_OP_fbreg for symbol \"%s\"."),
	       SYMBOL_PRINT_NAME (symbol));

      gdbarch_virtual_frame_pointer (gdbarch,
				     ax->scope, &frame_reg, &frame_offset);
      ax_reg (ax, frame_reg);
      ax_const_l (ax, frame_offset);
      ax_simple (ax, aop_add);

      value->kind = axs_lvalue_memory;
    }
  else if (data[0] >= DW_OP_breg0
	   && data[0] <= DW_OP_breg31)
    {
      unsigned int reg;
      LONGEST offset;
      gdb_byte *buf_end;

      reg = data[0] - DW_OP_breg0;
      buf_end = read_sleb128 (data + 1, data + size, &offset);
      if (buf_end != data + size)
	error (_("Unexpected opcode after DW_OP_breg%u for symbol \"%s\"."),
	       reg, SYMBOL_PRINT_NAME (symbol));

      ax_reg (ax, reg);
      ax_const_l (ax, offset);
      ax_simple (ax, aop_add);

      value->kind = axs_lvalue_memory;
    }
  else
    error (_("Unsupported DWARF opcode 0x%x in the location of \"%s\"."),
	   data[0], SYMBOL_PRINT_NAME (symbol));
}

/* Return the value of SYMBOL in FRAME using the DWARF-2 expression
   evaluator to calculate the location.  */
static struct value *
locexpr_read_variable (struct symbol *symbol, struct frame_info *frame)
{
  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
  struct value *val;
  val = dwarf2_evaluate_loc_desc (symbol, frame, dlbaton->data, dlbaton->size,
				  dlbaton->per_cu);

  return val;
}

/* Return non-zero iff we need a frame to evaluate SYMBOL.  */
static int
locexpr_read_needs_frame (struct symbol *symbol)
{
  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
  return dwarf2_loc_desc_needs_frame (dlbaton->data, dlbaton->size,
				      dlbaton->per_cu);
}

/* Print a natural-language description of SYMBOL to STREAM.  */
static int
locexpr_describe_location (struct symbol *symbol, struct ui_file *stream)
{
  /* FIXME: be more extensive.  */
  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
  int addr_size = dwarf2_per_cu_addr_size (dlbaton->per_cu);

  if (dlbaton->size == 1
      && dlbaton->data[0] >= DW_OP_reg0
      && dlbaton->data[0] <= DW_OP_reg31)
    {
      struct objfile *objfile = dwarf2_per_cu_objfile (dlbaton->per_cu);
      struct gdbarch *gdbarch = get_objfile_arch (objfile);
      int regno = gdbarch_dwarf2_reg_to_regnum (gdbarch,
						dlbaton->data[0] - DW_OP_reg0);
      fprintf_filtered (stream,
			"a variable in register %s",
			gdbarch_register_name (gdbarch, regno));
      return 1;
    }

  /* The location expression for a TLS variable looks like this (on a
     64-bit LE machine):

     DW_AT_location    : 10 byte block: 3 4 0 0 0 0 0 0 0 e0
                        (DW_OP_addr: 4; DW_OP_GNU_push_tls_address)
     
     0x3 is the encoding for DW_OP_addr, which has an operand as long
     as the size of an address on the target machine (here is 8
     bytes).  0xe0 is the encoding for DW_OP_GNU_push_tls_address.
     The operand represents the offset at which the variable is within
     the thread local storage.  */

  if (dlbaton->size > 1 
      && dlbaton->data[dlbaton->size - 1] == DW_OP_GNU_push_tls_address)
    if (dlbaton->data[0] == DW_OP_addr)
      {
	struct objfile *objfile = dwarf2_per_cu_objfile (dlbaton->per_cu);
	struct gdbarch *gdbarch = get_objfile_arch (objfile);
	CORE_ADDR offset = dwarf2_read_address (gdbarch,
						&dlbaton->data[1],
						&dlbaton->data[dlbaton->size - 1],
						addr_size);
	fprintf_filtered (stream, 
			  "a thread-local variable at offset %s in the "
			  "thread-local storage for `%s'",
			  paddress (gdbarch, offset), objfile->name);
	return 1;
      }
  

  fprintf_filtered (stream,
		    "a variable with complex or multiple locations (DWARF2)");
  return 1;
}


/* Describe the location of SYMBOL as an agent value in VALUE, generating
   any necessary bytecode in AX.

   NOTE drow/2003-02-26: This function is extremely minimal, because
   doing it correctly is extremely complicated and there is no
   publicly available stub with tracepoint support for me to test
   against.  When there is one this function should be revisited.  */

static void
locexpr_tracepoint_var_ref (struct symbol *symbol, struct gdbarch *gdbarch,
			    struct agent_expr *ax, struct axs_value *value)
{
  struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);

  dwarf2_tracepoint_var_ref (symbol, gdbarch, ax, value,
			     dlbaton->data, dlbaton->size);
}

/* The set of location functions used with the DWARF-2 expression
   evaluator.  */
const struct symbol_computed_ops dwarf2_locexpr_funcs = {
  locexpr_read_variable,
  locexpr_read_needs_frame,
  locexpr_describe_location,
  locexpr_tracepoint_var_ref
};


/* Wrapper functions for location lists.  These generally find
   the appropriate location expression and call something above.  */

/* Return the value of SYMBOL in FRAME using the DWARF-2 expression
   evaluator to calculate the location.  */
static struct value *
loclist_read_variable (struct symbol *symbol, struct frame_info *frame)
{
  struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
  struct value *val;
  gdb_byte *data;
  size_t size;

  data = find_location_expression (dlbaton, &size,
				   frame ? get_frame_address_in_block (frame)
				   : 0);
  if (data == NULL)
    {
      val = allocate_value (SYMBOL_TYPE (symbol));
      VALUE_LVAL (val) = not_lval;
      set_value_optimized_out (val, 1);
    }
  else
    val = dwarf2_evaluate_loc_desc (symbol, frame, data, size,
				    dlbaton->per_cu);

  return val;
}

/* Return non-zero iff we need a frame to evaluate SYMBOL.  */
static int
loclist_read_needs_frame (struct symbol *symbol)
{
  /* If there's a location list, then assume we need to have a frame
     to choose the appropriate location expression.  With tracking of
     global variables this is not necessarily true, but such tracking
     is disabled in GCC at the moment until we figure out how to
     represent it.  */

  return 1;
}

/* Print a natural-language description of SYMBOL to STREAM.  */
static int
loclist_describe_location (struct symbol *symbol, struct ui_file *stream)
{
  /* FIXME: Could print the entire list of locations.  */
  fprintf_filtered (stream, "a variable with multiple locations");
  return 1;
}

/* Describe the location of SYMBOL as an agent value in VALUE, generating
   any necessary bytecode in AX.  */
static void
loclist_tracepoint_var_ref (struct symbol *symbol, struct gdbarch *gdbarch,
			    struct agent_expr *ax, struct axs_value *value)
{
  struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
  gdb_byte *data;
  size_t size;

  data = find_location_expression (dlbaton, &size, ax->scope);
  if (data == NULL)
    error (_("Variable \"%s\" is not available."), SYMBOL_NATURAL_NAME (symbol));

  dwarf2_tracepoint_var_ref (symbol, gdbarch, ax, value, data, size);
}

/* The set of location functions used with the DWARF-2 expression
   evaluator and location lists.  */
const struct symbol_computed_ops dwarf2_loclist_funcs = {
  loclist_read_variable,
  loclist_read_needs_frame,
  loclist_describe_location,
  loclist_tracepoint_var_ref
};