1 /* DWARF 2 location expression support for GDB.
3 Copyright (C) 2003, 2005, 2007 Free Software Foundation, Inc.
5 Contributed by Daniel Jacobowitz, MontaVista Software, Inc.
7 This file is part of GDB.
9 This program is free software; you can redistribute it and/or modify
10 it under the terms of the GNU General Public License as published by
11 the Free Software Foundation; either version 3 of the License, or
12 (at your option) any later version.
14 This program is distributed in the hope that it will be useful,
15 but WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 GNU General Public License for more details.
19 You should have received a copy of the GNU General Public License
20 along with this program. If not, see <http://www.gnu.org/licenses/>. */
33 #include "exceptions.h"
35 #include "elf/dwarf2.h"
36 #include "dwarf2expr.h"
37 #include "dwarf2loc.h"
39 #include "gdb_string.h"
41 /* A helper function for dealing with location lists. Given a
42 symbol baton (BATON) and a pc value (PC), find the appropriate
43 location expression, set *LOCEXPR_LENGTH, and return a pointer
44 to the beginning of the expression. Returns NULL on failure.
46 For now, only return the first matching location expression; there
47 can be more than one in the list. */
50 find_location_expression (struct dwarf2_loclist_baton
*baton
,
51 size_t *locexpr_length
, CORE_ADDR pc
)
54 gdb_byte
*loc_ptr
, *buf_end
;
56 unsigned int addr_size
= gdbarch_addr_bit (current_gdbarch
) / TARGET_CHAR_BIT
;
57 CORE_ADDR base_mask
= ~(~(CORE_ADDR
)1 << (addr_size
* 8 - 1));
58 /* Adjust base_address for relocatable objects. */
59 CORE_ADDR base_offset
= ANOFFSET (baton
->objfile
->section_offsets
,
60 SECT_OFF_TEXT (baton
->objfile
));
61 CORE_ADDR base_address
= baton
->base_address
+ base_offset
;
63 loc_ptr
= baton
->data
;
64 buf_end
= baton
->data
+ baton
->size
;
68 low
= dwarf2_read_address (loc_ptr
, buf_end
, &length
);
70 high
= dwarf2_read_address (loc_ptr
, buf_end
, &length
);
73 /* An end-of-list entry. */
74 if (low
== 0 && high
== 0)
77 /* A base-address-selection entry. */
78 if ((low
& base_mask
) == base_mask
)
84 /* Otherwise, a location expression entry. */
88 length
= extract_unsigned_integer (loc_ptr
, 2);
91 if (pc
>= low
&& pc
< high
)
93 *locexpr_length
= length
;
101 /* This is the baton used when performing dwarf2 expression
103 struct dwarf_expr_baton
105 struct frame_info
*frame
;
106 struct objfile
*objfile
;
109 /* Helper functions for dwarf2_evaluate_loc_desc. */
111 /* Using the frame specified in BATON, return the value of register
112 REGNUM, treated as a pointer. */
114 dwarf_expr_read_reg (void *baton
, int dwarf_regnum
)
116 struct dwarf_expr_baton
*debaton
= (struct dwarf_expr_baton
*) baton
;
120 regnum
= gdbarch_dwarf2_reg_to_regnum (current_gdbarch
, dwarf_regnum
);
121 result
= address_from_register (builtin_type_void_data_ptr
,
122 regnum
, debaton
->frame
);
126 /* Read memory at ADDR (length LEN) into BUF. */
129 dwarf_expr_read_mem (void *baton
, gdb_byte
*buf
, CORE_ADDR addr
, size_t len
)
131 read_memory (addr
, buf
, len
);
134 /* Using the frame specified in BATON, find the location expression
135 describing the frame base. Return a pointer to it in START and
136 its length in LENGTH. */
138 dwarf_expr_frame_base (void *baton
, gdb_byte
**start
, size_t * length
)
140 /* FIXME: cagney/2003-03-26: This code should be using
141 get_frame_base_address(), and then implement a dwarf2 specific
143 struct symbol
*framefunc
;
144 struct dwarf_expr_baton
*debaton
= (struct dwarf_expr_baton
*) baton
;
146 framefunc
= get_frame_function (debaton
->frame
);
148 if (SYMBOL_OPS (framefunc
) == &dwarf2_loclist_funcs
)
150 struct dwarf2_loclist_baton
*symbaton
;
151 struct frame_info
*frame
= debaton
->frame
;
153 symbaton
= SYMBOL_LOCATION_BATON (framefunc
);
154 *start
= find_location_expression (symbaton
, length
,
155 get_frame_address_in_block (frame
));
159 struct dwarf2_locexpr_baton
*symbaton
;
160 symbaton
= SYMBOL_LOCATION_BATON (framefunc
);
161 *length
= symbaton
->size
;
162 *start
= symbaton
->data
;
166 error (_("Could not find the frame base for \"%s\"."),
167 SYMBOL_NATURAL_NAME (framefunc
));
170 /* Using the objfile specified in BATON, find the address for the
171 current thread's thread-local storage with offset OFFSET. */
173 dwarf_expr_tls_address (void *baton
, CORE_ADDR offset
)
175 struct dwarf_expr_baton
*debaton
= (struct dwarf_expr_baton
*) baton
;
177 return target_translate_tls_address (debaton
->objfile
, offset
);
180 /* Evaluate a location description, starting at DATA and with length
181 SIZE, to find the current location of variable VAR in the context
183 static struct value
*
184 dwarf2_evaluate_loc_desc (struct symbol
*var
, struct frame_info
*frame
,
185 gdb_byte
*data
, unsigned short size
,
186 struct objfile
*objfile
)
188 struct gdbarch
*arch
= get_frame_arch (frame
);
189 struct value
*retval
;
190 struct dwarf_expr_baton baton
;
191 struct dwarf_expr_context
*ctx
;
195 retval
= allocate_value (SYMBOL_TYPE (var
));
196 VALUE_LVAL (retval
) = not_lval
;
197 set_value_optimized_out (retval
, 1);
202 baton
.objfile
= objfile
;
204 ctx
= new_dwarf_expr_context ();
206 ctx
->read_reg
= dwarf_expr_read_reg
;
207 ctx
->read_mem
= dwarf_expr_read_mem
;
208 ctx
->get_frame_base
= dwarf_expr_frame_base
;
209 ctx
->get_tls_address
= dwarf_expr_tls_address
;
211 dwarf_expr_eval (ctx
, data
, size
);
212 if (ctx
->num_pieces
> 0)
218 retval
= allocate_value (SYMBOL_TYPE (var
));
219 contents
= value_contents_raw (retval
);
220 for (i
= 0; i
< ctx
->num_pieces
; i
++)
222 struct dwarf_expr_piece
*p
= &ctx
->pieces
[i
];
225 bfd_byte regval
[MAX_REGISTER_SIZE
];
226 int gdb_regnum
= gdbarch_dwarf2_reg_to_regnum
227 (current_gdbarch
, p
->value
);
228 get_frame_register (frame
, gdb_regnum
, regval
);
229 memcpy (contents
+ offset
, regval
, p
->size
);
231 else /* In memory? */
233 read_memory (p
->value
, contents
+ offset
, p
->size
);
238 else if (ctx
->in_reg
)
240 CORE_ADDR dwarf_regnum
= dwarf_expr_fetch (ctx
, 0);
241 int gdb_regnum
= gdbarch_dwarf2_reg_to_regnum
242 (current_gdbarch
, dwarf_regnum
);
243 retval
= value_from_register (SYMBOL_TYPE (var
), gdb_regnum
, frame
);
247 CORE_ADDR address
= dwarf_expr_fetch (ctx
, 0);
249 retval
= allocate_value (SYMBOL_TYPE (var
));
250 VALUE_LVAL (retval
) = lval_memory
;
251 set_value_lazy (retval
, 1);
252 VALUE_ADDRESS (retval
) = address
;
255 set_value_initialized (retval
, ctx
->initialized
);
257 free_dwarf_expr_context (ctx
);
266 /* Helper functions and baton for dwarf2_loc_desc_needs_frame. */
268 struct needs_frame_baton
273 /* Reads from registers do require a frame. */
275 needs_frame_read_reg (void *baton
, int regnum
)
277 struct needs_frame_baton
*nf_baton
= baton
;
278 nf_baton
->needs_frame
= 1;
282 /* Reads from memory do not require a frame. */
284 needs_frame_read_mem (void *baton
, gdb_byte
*buf
, CORE_ADDR addr
, size_t len
)
286 memset (buf
, 0, len
);
289 /* Frame-relative accesses do require a frame. */
291 needs_frame_frame_base (void *baton
, gdb_byte
**start
, size_t * length
)
293 static gdb_byte lit0
= DW_OP_lit0
;
294 struct needs_frame_baton
*nf_baton
= baton
;
299 nf_baton
->needs_frame
= 1;
302 /* Thread-local accesses do require a frame. */
304 needs_frame_tls_address (void *baton
, CORE_ADDR offset
)
306 struct needs_frame_baton
*nf_baton
= baton
;
307 nf_baton
->needs_frame
= 1;
311 /* Return non-zero iff the location expression at DATA (length SIZE)
312 requires a frame to evaluate. */
315 dwarf2_loc_desc_needs_frame (gdb_byte
*data
, unsigned short size
)
317 struct needs_frame_baton baton
;
318 struct dwarf_expr_context
*ctx
;
321 baton
.needs_frame
= 0;
323 ctx
= new_dwarf_expr_context ();
325 ctx
->read_reg
= needs_frame_read_reg
;
326 ctx
->read_mem
= needs_frame_read_mem
;
327 ctx
->get_frame_base
= needs_frame_frame_base
;
328 ctx
->get_tls_address
= needs_frame_tls_address
;
330 dwarf_expr_eval (ctx
, data
, size
);
332 in_reg
= ctx
->in_reg
;
334 if (ctx
->num_pieces
> 0)
338 /* If the location has several pieces, and any of them are in
339 registers, then we will need a frame to fetch them from. */
340 for (i
= 0; i
< ctx
->num_pieces
; i
++)
341 if (ctx
->pieces
[i
].in_reg
)
345 free_dwarf_expr_context (ctx
);
347 return baton
.needs_frame
|| in_reg
;
351 dwarf2_tracepoint_var_ref (struct symbol
*symbol
, struct agent_expr
*ax
,
352 struct axs_value
*value
, gdb_byte
*data
,
356 error (_("Symbol \"%s\" has been optimized out."),
357 SYMBOL_PRINT_NAME (symbol
));
360 && data
[0] >= DW_OP_reg0
361 && data
[0] <= DW_OP_reg31
)
363 value
->kind
= axs_lvalue_register
;
364 value
->u
.reg
= data
[0] - DW_OP_reg0
;
366 else if (data
[0] == DW_OP_regx
)
369 read_uleb128 (data
+ 1, data
+ size
, ®
);
370 value
->kind
= axs_lvalue_register
;
373 else if (data
[0] == DW_OP_fbreg
)
375 /* And this is worse than just minimal; we should honor the frame base
378 LONGEST frame_offset
;
381 buf_end
= read_sleb128 (data
+ 1, data
+ size
, &frame_offset
);
382 if (buf_end
!= data
+ size
)
383 error (_("Unexpected opcode after DW_OP_fbreg for symbol \"%s\"."),
384 SYMBOL_PRINT_NAME (symbol
));
386 gdbarch_virtual_frame_pointer (current_gdbarch
,
387 ax
->scope
, &frame_reg
, &frame_offset
);
388 ax_reg (ax
, frame_reg
);
389 ax_const_l (ax
, frame_offset
);
390 ax_simple (ax
, aop_add
);
392 value
->kind
= axs_lvalue_memory
;
394 else if (data
[0] >= DW_OP_breg0
395 && data
[0] <= DW_OP_breg31
)
401 reg
= data
[0] - DW_OP_breg0
;
402 buf_end
= read_sleb128 (data
+ 1, data
+ size
, &offset
);
403 if (buf_end
!= data
+ size
)
404 error (_("Unexpected opcode after DW_OP_breg%u for symbol \"%s\"."),
405 reg
, SYMBOL_PRINT_NAME (symbol
));
408 ax_const_l (ax
, offset
);
409 ax_simple (ax
, aop_add
);
411 value
->kind
= axs_lvalue_memory
;
414 error (_("Unsupported DWARF opcode 0x%x in the location of \"%s\"."),
415 data
[0], SYMBOL_PRINT_NAME (symbol
));
418 /* Return the value of SYMBOL in FRAME using the DWARF-2 expression
419 evaluator to calculate the location. */
420 static struct value
*
421 locexpr_read_variable (struct symbol
*symbol
, struct frame_info
*frame
)
423 struct dwarf2_locexpr_baton
*dlbaton
= SYMBOL_LOCATION_BATON (symbol
);
425 val
= dwarf2_evaluate_loc_desc (symbol
, frame
, dlbaton
->data
, dlbaton
->size
,
431 /* Return non-zero iff we need a frame to evaluate SYMBOL. */
433 locexpr_read_needs_frame (struct symbol
*symbol
)
435 struct dwarf2_locexpr_baton
*dlbaton
= SYMBOL_LOCATION_BATON (symbol
);
436 return dwarf2_loc_desc_needs_frame (dlbaton
->data
, dlbaton
->size
);
439 /* Print a natural-language description of SYMBOL to STREAM. */
441 locexpr_describe_location (struct symbol
*symbol
, struct ui_file
*stream
)
443 /* FIXME: be more extensive. */
444 struct dwarf2_locexpr_baton
*dlbaton
= SYMBOL_LOCATION_BATON (symbol
);
446 if (dlbaton
->size
== 1
447 && dlbaton
->data
[0] >= DW_OP_reg0
448 && dlbaton
->data
[0] <= DW_OP_reg31
)
450 int regno
= gdbarch_dwarf2_reg_to_regnum
451 (current_gdbarch
, dlbaton
->data
[0] - DW_OP_reg0
);
452 fprintf_filtered (stream
,
453 "a variable in register %s",
454 gdbarch_register_name (current_gdbarch
, regno
));
458 /* The location expression for a TLS variable looks like this (on a
461 DW_AT_location : 10 byte block: 3 4 0 0 0 0 0 0 0 e0
462 (DW_OP_addr: 4; DW_OP_GNU_push_tls_address)
464 0x3 is the encoding for DW_OP_addr, which has an operand as long
465 as the size of an address on the target machine (here is 8
466 bytes). 0xe0 is the encoding for DW_OP_GNU_push_tls_address.
467 The operand represents the offset at which the variable is within
468 the thread local storage. */
470 if (dlbaton
->size
> 1
471 && dlbaton
->data
[dlbaton
->size
- 1] == DW_OP_GNU_push_tls_address
)
472 if (dlbaton
->data
[0] == DW_OP_addr
)
475 CORE_ADDR offset
= dwarf2_read_address (&dlbaton
->data
[1],
476 &dlbaton
->data
[dlbaton
->size
- 1],
478 fprintf_filtered (stream
,
479 "a thread-local variable at offset %s in the "
480 "thread-local storage for `%s'",
481 paddr_nz (offset
), dlbaton
->objfile
->name
);
486 fprintf_filtered (stream
,
487 "a variable with complex or multiple locations (DWARF2)");
492 /* Describe the location of SYMBOL as an agent value in VALUE, generating
493 any necessary bytecode in AX.
495 NOTE drow/2003-02-26: This function is extremely minimal, because
496 doing it correctly is extremely complicated and there is no
497 publicly available stub with tracepoint support for me to test
498 against. When there is one this function should be revisited. */
501 locexpr_tracepoint_var_ref (struct symbol
* symbol
, struct agent_expr
* ax
,
502 struct axs_value
* value
)
504 struct dwarf2_locexpr_baton
*dlbaton
= SYMBOL_LOCATION_BATON (symbol
);
506 dwarf2_tracepoint_var_ref (symbol
, ax
, value
, dlbaton
->data
, dlbaton
->size
);
509 /* The set of location functions used with the DWARF-2 expression
511 const struct symbol_ops dwarf2_locexpr_funcs
= {
512 locexpr_read_variable
,
513 locexpr_read_needs_frame
,
514 locexpr_describe_location
,
515 locexpr_tracepoint_var_ref
519 /* Wrapper functions for location lists. These generally find
520 the appropriate location expression and call something above. */
522 /* Return the value of SYMBOL in FRAME using the DWARF-2 expression
523 evaluator to calculate the location. */
524 static struct value
*
525 loclist_read_variable (struct symbol
*symbol
, struct frame_info
*frame
)
527 struct dwarf2_loclist_baton
*dlbaton
= SYMBOL_LOCATION_BATON (symbol
);
532 data
= find_location_expression (dlbaton
, &size
,
533 frame
? get_frame_address_in_block (frame
)
537 val
= allocate_value (SYMBOL_TYPE (symbol
));
538 VALUE_LVAL (val
) = not_lval
;
539 set_value_optimized_out (val
, 1);
542 val
= dwarf2_evaluate_loc_desc (symbol
, frame
, data
, size
,
548 /* Return non-zero iff we need a frame to evaluate SYMBOL. */
550 loclist_read_needs_frame (struct symbol
*symbol
)
552 /* If there's a location list, then assume we need to have a frame
553 to choose the appropriate location expression. With tracking of
554 global variables this is not necessarily true, but such tracking
555 is disabled in GCC at the moment until we figure out how to
561 /* Print a natural-language description of SYMBOL to STREAM. */
563 loclist_describe_location (struct symbol
*symbol
, struct ui_file
*stream
)
565 /* FIXME: Could print the entire list of locations. */
566 fprintf_filtered (stream
, "a variable with multiple locations");
570 /* Describe the location of SYMBOL as an agent value in VALUE, generating
571 any necessary bytecode in AX. */
573 loclist_tracepoint_var_ref (struct symbol
* symbol
, struct agent_expr
* ax
,
574 struct axs_value
* value
)
576 struct dwarf2_loclist_baton
*dlbaton
= SYMBOL_LOCATION_BATON (symbol
);
580 data
= find_location_expression (dlbaton
, &size
, ax
->scope
);
582 error (_("Variable \"%s\" is not available."), SYMBOL_NATURAL_NAME (symbol
));
584 dwarf2_tracepoint_var_ref (symbol
, ax
, value
, data
, size
);
587 /* The set of location functions used with the DWARF-2 expression
588 evaluator and location lists. */
589 const struct symbol_ops dwarf2_loclist_funcs
= {
590 loclist_read_variable
,
591 loclist_read_needs_frame
,
592 loclist_describe_location
,
593 loclist_tracepoint_var_ref