1 /* DWARF 2 location expression support for GDB.
2 Copyright 2003 Free Software Foundation, Inc.
3 Contributed by Daniel Jacobowitz, MontaVista Software, Inc.
5 This file is part of GDB.
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 2 of the License, or (at
10 your option) any later version.
12 This program is distributed in the hope that it will be useful, but
13 WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program; if not, write to the Free Software
19 Foundation, Inc., 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
34 #include "elf/dwarf2.h"
35 #include "dwarf2expr.h"
36 #include "dwarf2loc.h"
38 #include "gdb_string.h"
40 #ifndef DWARF2_REG_TO_REGNUM
41 #define DWARF2_REG_TO_REGNUM(REG) (REG)
44 /* A helper function for dealing with location lists. Given a
45 symbol baton (BATON) and a pc value (PC), find the appropriate
46 location expression, set *LOCEXPR_LENGTH, and return a pointer
47 to the beginning of the expression. Returns NULL on failure.
49 For now, only return the first matching location expression; there
50 can be more than one in the list. */
53 find_location_expression (struct dwarf2_loclist_baton *baton,
54 size_t *locexpr_length, CORE_ADDR pc)
57 char *loc_ptr, *buf_end;
58 unsigned int addr_size = TARGET_ADDR_BIT / TARGET_CHAR_BIT, length;
59 CORE_ADDR base_mask = ~(~(CORE_ADDR)1 << (addr_size * 8 - 1));
60 /* Adjust base_address for relocatable objects. */
61 CORE_ADDR base_offset = ANOFFSET (baton->objfile->section_offsets,
62 SECT_OFF_TEXT (baton->objfile));
63 CORE_ADDR base_address = baton->base_address + base_offset;
65 loc_ptr = baton->data;
66 buf_end = baton->data + baton->size;
70 low = dwarf2_read_address (loc_ptr, buf_end, &length);
72 high = dwarf2_read_address (loc_ptr, buf_end, &length);
75 /* An end-of-list entry. */
76 if (low == 0 && high == 0)
79 /* A base-address-selection entry. */
80 if ((low & base_mask) == base_mask)
86 /* Otherwise, a location expression entry. */
90 length = extract_unsigned_integer (loc_ptr, 2);
93 if (pc >= low && pc < high)
95 *locexpr_length = length;
103 /* This is the baton used when performing dwarf2 expression
105 struct dwarf_expr_baton
107 struct frame_info *frame;
108 struct objfile *objfile;
111 /* Helper functions for dwarf2_evaluate_loc_desc. */
113 /* Using the frame specified in BATON, read register REGNUM. The lval
114 type will be returned in LVALP, and for lval_memory the register
115 save address will be returned in ADDRP. */
117 dwarf_expr_read_reg (void *baton, int dwarf_regnum)
119 struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
120 CORE_ADDR result, save_addr;
121 enum lval_type lval_type;
123 int optimized, regnum, realnum, regsize;
125 regnum = DWARF2_REG_TO_REGNUM (dwarf_regnum);
126 regsize = register_size (current_gdbarch, regnum);
127 buf = (char *) alloca (regsize);
129 frame_register (debaton->frame, regnum, &optimized, &lval_type, &save_addr,
131 /* NOTE: cagney/2003-05-22: This extract is assuming that a DWARF 2
132 address is always unsigned. That may or may not be true. */
133 result = extract_unsigned_integer (buf, regsize);
138 /* Read memory at ADDR (length LEN) into BUF. */
141 dwarf_expr_read_mem (void *baton, char *buf, CORE_ADDR addr, size_t len)
143 read_memory (addr, buf, len);
146 /* Using the frame specified in BATON, find the location expression
147 describing the frame base. Return a pointer to it in START and
148 its length in LENGTH. */
150 dwarf_expr_frame_base (void *baton, unsigned char **start, size_t * length)
152 /* FIXME: cagney/2003-03-26: This code should be using
153 get_frame_base_address(), and then implement a dwarf2 specific
155 struct symbol *framefunc;
156 struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
158 framefunc = get_frame_function (debaton->frame);
160 if (SYMBOL_OPS (framefunc) == &dwarf2_loclist_funcs)
162 struct dwarf2_loclist_baton *symbaton;
163 symbaton = SYMBOL_LOCATION_BATON (framefunc);
164 *start = find_location_expression (symbaton, length,
165 get_frame_pc (debaton->frame));
169 struct dwarf2_locexpr_baton *symbaton;
170 symbaton = SYMBOL_LOCATION_BATON (framefunc);
171 *length = symbaton->size;
172 *start = symbaton->data;
176 error ("Could not find the frame base for \"%s\".",
177 SYMBOL_NATURAL_NAME (framefunc));
180 /* Using the objfile specified in BATON, find the address for the
181 current thread's thread-local storage with offset OFFSET. */
183 dwarf_expr_tls_address (void *baton, CORE_ADDR offset)
185 struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
188 if (target_get_thread_local_address_p ())
189 addr = target_get_thread_local_address (inferior_ptid,
192 /* It wouldn't be wrong here to try a gdbarch method, too; finding
193 TLS is an ABI-specific thing. But we don't do that yet. */
195 error ("Cannot find thread-local variables on this target");
200 /* Evaluate a location description, starting at DATA and with length
201 SIZE, to find the current location of variable VAR in the context
203 static struct value *
204 dwarf2_evaluate_loc_desc (struct symbol *var, struct frame_info *frame,
205 unsigned char *data, unsigned short size,
206 struct objfile *objfile)
209 struct gdbarch *arch = get_frame_arch (frame);
210 struct value *retval;
211 struct dwarf_expr_baton baton;
212 struct dwarf_expr_context *ctx;
216 retval = allocate_value (SYMBOL_TYPE (var));
217 VALUE_LVAL (retval) = not_lval;
218 VALUE_OPTIMIZED_OUT (retval) = 1;
222 baton.objfile = objfile;
224 ctx = new_dwarf_expr_context ();
226 ctx->read_reg = dwarf_expr_read_reg;
227 ctx->read_mem = dwarf_expr_read_mem;
228 ctx->get_frame_base = dwarf_expr_frame_base;
229 ctx->get_tls_address = dwarf_expr_tls_address;
231 dwarf_expr_eval (ctx, data, size);
232 result = dwarf_expr_fetch (ctx, 0);
234 if (ctx->num_pieces > 0)
240 retval = allocate_value (SYMBOL_TYPE (var));
241 contents = VALUE_CONTENTS_RAW (retval);
242 for (i = 0; i < ctx->num_pieces; i++)
244 struct dwarf_expr_piece *p = &ctx->pieces[i];
247 bfd_byte regval[MAX_REGISTER_SIZE];
248 int gdb_regnum = DWARF2_REG_TO_REGNUM (p->value);
249 get_frame_register (frame, gdb_regnum, regval);
250 memcpy (contents + offset, regval, p->size);
252 else /* In memory? */
254 read_memory (p->value, contents + offset, p->size);
259 else if (ctx->in_reg)
261 int regnum = DWARF2_REG_TO_REGNUM (result);
262 retval = value_from_register (SYMBOL_TYPE (var), regnum, frame);
266 retval = allocate_value (SYMBOL_TYPE (var));
267 VALUE_BFD_SECTION (retval) = SYMBOL_BFD_SECTION (var);
269 VALUE_LVAL (retval) = lval_memory;
270 VALUE_LAZY (retval) = 1;
271 VALUE_ADDRESS (retval) = result;
274 set_value_initialized (retval, ctx->initialized);
276 free_dwarf_expr_context (ctx);
285 /* Helper functions and baton for dwarf2_loc_desc_needs_frame. */
287 struct needs_frame_baton
292 /* Reads from registers do require a frame. */
294 needs_frame_read_reg (void *baton, int regnum)
296 struct needs_frame_baton *nf_baton = baton;
297 nf_baton->needs_frame = 1;
301 /* Reads from memory do not require a frame. */
303 needs_frame_read_mem (void *baton, char *buf, CORE_ADDR addr, size_t len)
305 memset (buf, 0, len);
308 /* Frame-relative accesses do require a frame. */
310 needs_frame_frame_base (void *baton, unsigned char **start, size_t * length)
312 static char lit0 = DW_OP_lit0;
313 struct needs_frame_baton *nf_baton = baton;
318 nf_baton->needs_frame = 1;
321 /* Thread-local accesses do require a frame. */
323 needs_frame_tls_address (void *baton, CORE_ADDR offset)
325 struct needs_frame_baton *nf_baton = baton;
326 nf_baton->needs_frame = 1;
330 /* Return non-zero iff the location expression at DATA (length SIZE)
331 requires a frame to evaluate. */
334 dwarf2_loc_desc_needs_frame (unsigned char *data, unsigned short size)
336 struct needs_frame_baton baton;
337 struct dwarf_expr_context *ctx;
340 baton.needs_frame = 0;
342 ctx = new_dwarf_expr_context ();
344 ctx->read_reg = needs_frame_read_reg;
345 ctx->read_mem = needs_frame_read_mem;
346 ctx->get_frame_base = needs_frame_frame_base;
347 ctx->get_tls_address = needs_frame_tls_address;
349 dwarf_expr_eval (ctx, data, size);
351 in_reg = ctx->in_reg;
353 if (ctx->num_pieces > 0)
357 /* If the location has several pieces, and any of them are in
358 registers, then we will need a frame to fetch them from. */
359 for (i = 0; i < ctx->num_pieces; i++)
360 if (ctx->pieces[i].in_reg)
364 free_dwarf_expr_context (ctx);
366 return baton.needs_frame || in_reg;
370 dwarf2_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,
371 struct axs_value * value, unsigned char *data,
375 error ("Symbol \"%s\" has been optimized out.",
376 SYMBOL_PRINT_NAME (symbol));
379 && data[0] >= DW_OP_reg0
380 && data[0] <= DW_OP_reg31)
382 value->kind = axs_lvalue_register;
383 value->u.reg = data[0] - DW_OP_reg0;
385 else if (data[0] == DW_OP_regx)
388 read_uleb128 (data + 1, data + size, ®);
389 value->kind = axs_lvalue_register;
392 else if (data[0] == DW_OP_fbreg)
394 /* And this is worse than just minimal; we should honor the frame base
397 LONGEST frame_offset;
398 unsigned char *buf_end;
400 buf_end = read_sleb128 (data + 1, data + size, &frame_offset);
401 if (buf_end != data + size)
402 error ("Unexpected opcode after DW_OP_fbreg for symbol \"%s\".",
403 SYMBOL_PRINT_NAME (symbol));
405 TARGET_VIRTUAL_FRAME_POINTER (ax->scope, &frame_reg, &frame_offset);
406 ax_reg (ax, frame_reg);
407 ax_const_l (ax, frame_offset);
408 ax_simple (ax, aop_add);
410 ax_const_l (ax, frame_offset);
411 ax_simple (ax, aop_add);
412 value->kind = axs_lvalue_memory;
415 error ("Unsupported DWARF opcode in the location of \"%s\".",
416 SYMBOL_PRINT_NAME (symbol));
419 /* Return the value of SYMBOL in FRAME using the DWARF-2 expression
420 evaluator to calculate the location. */
421 static struct value *
422 locexpr_read_variable (struct symbol *symbol, struct frame_info *frame)
424 struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
426 val = dwarf2_evaluate_loc_desc (symbol, frame, dlbaton->data, dlbaton->size,
432 /* Return non-zero iff we need a frame to evaluate SYMBOL. */
434 locexpr_read_needs_frame (struct symbol *symbol)
436 struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
437 return dwarf2_loc_desc_needs_frame (dlbaton->data, dlbaton->size);
440 /* Print a natural-language description of SYMBOL to STREAM. */
442 locexpr_describe_location (struct symbol *symbol, struct ui_file *stream)
444 /* FIXME: be more extensive. */
445 struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
447 if (dlbaton->size == 1
448 && dlbaton->data[0] >= DW_OP_reg0
449 && dlbaton->data[0] <= DW_OP_reg31)
451 int regno = DWARF2_REG_TO_REGNUM (dlbaton->data[0] - DW_OP_reg0);
452 fprintf_filtered (stream,
453 "a variable in register %s", REGISTER_NAME (regno));
457 /* The location expression for a TLS variable looks like this (on a
460 DW_AT_location : 10 byte block: 3 4 0 0 0 0 0 0 0 e0
461 (DW_OP_addr: 4; DW_OP_GNU_push_tls_address)
463 0x3 is the encoding for DW_OP_addr, which has an operand as long
464 as the size of an address on the target machine (here is 8
465 bytes). 0xe0 is the encoding for DW_OP_GNU_push_tls_address.
466 The operand represents the offset at which the variable is within
467 the thread local storage. */
469 if (dlbaton->size > 1
470 && dlbaton->data[dlbaton->size - 1] == DW_OP_GNU_push_tls_address)
471 if (dlbaton->data[0] == DW_OP_addr)
474 CORE_ADDR offset = dwarf2_read_address (&dlbaton->data[1],
475 &dlbaton->data[dlbaton->size - 1],
477 fprintf_filtered (stream,
478 "a thread-local variable at offset %s in the "
479 "thread-local storage for `%s'",
480 paddr_nz (offset), dlbaton->objfile->name);
485 fprintf_filtered (stream,
486 "a variable with complex or multiple locations (DWARF2)");
491 /* Describe the location of SYMBOL as an agent value in VALUE, generating
492 any necessary bytecode in AX.
494 NOTE drow/2003-02-26: This function is extremely minimal, because
495 doing it correctly is extremely complicated and there is no
496 publicly available stub with tracepoint support for me to test
497 against. When there is one this function should be revisited. */
500 locexpr_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,
501 struct axs_value * value)
503 struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
505 dwarf2_tracepoint_var_ref (symbol, ax, value, dlbaton->data, dlbaton->size);
508 /* The set of location functions used with the DWARF-2 expression
510 const struct symbol_ops dwarf2_locexpr_funcs = {
511 locexpr_read_variable,
512 locexpr_read_needs_frame,
513 locexpr_describe_location,
514 locexpr_tracepoint_var_ref
518 /* Wrapper functions for location lists. These generally find
519 the appropriate location expression and call something above. */
521 /* Return the value of SYMBOL in FRAME using the DWARF-2 expression
522 evaluator to calculate the location. */
523 static struct value *
524 loclist_read_variable (struct symbol *symbol, struct frame_info *frame)
526 struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
531 data = find_location_expression (dlbaton, &size,
532 frame ? get_frame_pc (frame) : 0);
535 val = allocate_value (SYMBOL_TYPE (symbol));
536 VALUE_LVAL (val) = not_lval;
537 VALUE_OPTIMIZED_OUT (val) = 1;
540 val = dwarf2_evaluate_loc_desc (symbol, frame, data, size,
546 /* Return non-zero iff we need a frame to evaluate SYMBOL. */
548 loclist_read_needs_frame (struct symbol *symbol)
550 /* If there's a location list, then assume we need to have a frame
551 to choose the appropriate location expression. With tracking of
552 global variables this is not necessarily true, but such tracking
553 is disabled in GCC at the moment until we figure out how to
559 /* Print a natural-language description of SYMBOL to STREAM. */
561 loclist_describe_location (struct symbol *symbol, struct ui_file *stream)
563 /* FIXME: Could print the entire list of locations. */
564 fprintf_filtered (stream, "a variable with multiple locations");
568 /* Describe the location of SYMBOL as an agent value in VALUE, generating
569 any necessary bytecode in AX. */
571 loclist_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,
572 struct axs_value * value)
574 struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
578 data = find_location_expression (dlbaton, &size, ax->scope);
580 error ("Variable \"%s\" is not available.", SYMBOL_NATURAL_NAME (symbol));
582 dwarf2_tracepoint_var_ref (symbol, ax, value, data, size);
585 /* The set of location functions used with the DWARF-2 expression
586 evaluator and location lists. */
587 const struct symbol_ops dwarf2_loclist_funcs = {
588 loclist_read_variable,
589 loclist_read_needs_frame,
590 loclist_describe_location,
591 loclist_tracepoint_var_ref