574 lines
17 KiB
C
574 lines
17 KiB
C
/* DWARF 2 location expression support for GDB.
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Copyright 2003, 2005 Free Software Foundation, Inc.
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Contributed by Daniel Jacobowitz, MontaVista Software, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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This program is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include "defs.h"
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#include "ui-out.h"
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#include "value.h"
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#include "frame.h"
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#include "gdbcore.h"
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#include "target.h"
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#include "inferior.h"
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#include "ax.h"
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#include "ax-gdb.h"
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#include "regcache.h"
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#include "objfiles.h"
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#include "elf/dwarf2.h"
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#include "dwarf2expr.h"
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#include "dwarf2loc.h"
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#include "gdb_string.h"
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#ifndef DWARF2_REG_TO_REGNUM
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#define DWARF2_REG_TO_REGNUM(REG) (REG)
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#endif
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/* A helper function for dealing with location lists. Given a
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symbol baton (BATON) and a pc value (PC), find the appropriate
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location expression, set *LOCEXPR_LENGTH, and return a pointer
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to the beginning of the expression. Returns NULL on failure.
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For now, only return the first matching location expression; there
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can be more than one in the list. */
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static char *
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find_location_expression (struct dwarf2_loclist_baton *baton,
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size_t *locexpr_length, CORE_ADDR pc)
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{
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CORE_ADDR low, high;
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char *loc_ptr, *buf_end;
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unsigned int addr_size = TARGET_ADDR_BIT / TARGET_CHAR_BIT, length;
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CORE_ADDR base_mask = ~(~(CORE_ADDR)1 << (addr_size * 8 - 1));
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/* Adjust base_address for relocatable objects. */
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CORE_ADDR base_offset = ANOFFSET (baton->objfile->section_offsets,
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SECT_OFF_TEXT (baton->objfile));
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CORE_ADDR base_address = baton->base_address + base_offset;
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loc_ptr = baton->data;
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buf_end = baton->data + baton->size;
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while (1)
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{
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low = dwarf2_read_address (loc_ptr, buf_end, &length);
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loc_ptr += length;
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high = dwarf2_read_address (loc_ptr, buf_end, &length);
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loc_ptr += length;
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/* An end-of-list entry. */
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if (low == 0 && high == 0)
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return NULL;
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/* A base-address-selection entry. */
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if ((low & base_mask) == base_mask)
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{
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base_address = high;
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continue;
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}
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/* Otherwise, a location expression entry. */
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low += base_address;
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high += base_address;
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length = extract_unsigned_integer (loc_ptr, 2);
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loc_ptr += 2;
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if (pc >= low && pc < high)
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{
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*locexpr_length = length;
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return loc_ptr;
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}
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loc_ptr += length;
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}
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}
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/* This is the baton used when performing dwarf2 expression
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evaluation. */
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struct dwarf_expr_baton
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{
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struct frame_info *frame;
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struct objfile *objfile;
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};
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/* Helper functions for dwarf2_evaluate_loc_desc. */
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/* Using the frame specified in BATON, read register REGNUM. The lval
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type will be returned in LVALP, and for lval_memory the register
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save address will be returned in ADDRP. */
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static CORE_ADDR
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dwarf_expr_read_reg (void *baton, int dwarf_regnum)
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{
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struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
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CORE_ADDR result, save_addr;
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enum lval_type lval_type;
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char *buf;
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int optimized, regnum, realnum, regsize;
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regnum = DWARF2_REG_TO_REGNUM (dwarf_regnum);
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regsize = register_size (current_gdbarch, regnum);
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buf = (char *) alloca (regsize);
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frame_register (debaton->frame, regnum, &optimized, &lval_type, &save_addr,
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&realnum, buf);
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/* NOTE: cagney/2003-05-22: This extract is assuming that a DWARF 2
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address is always unsigned. That may or may not be true. */
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result = extract_unsigned_integer (buf, regsize);
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return result;
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}
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/* Read memory at ADDR (length LEN) into BUF. */
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static void
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dwarf_expr_read_mem (void *baton, char *buf, CORE_ADDR addr, size_t len)
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{
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read_memory (addr, buf, len);
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}
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/* Using the frame specified in BATON, find the location expression
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describing the frame base. Return a pointer to it in START and
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its length in LENGTH. */
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static void
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dwarf_expr_frame_base (void *baton, unsigned char **start, size_t * length)
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{
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/* FIXME: cagney/2003-03-26: This code should be using
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get_frame_base_address(), and then implement a dwarf2 specific
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this_base method. */
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struct symbol *framefunc;
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struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
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framefunc = get_frame_function (debaton->frame);
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if (SYMBOL_OPS (framefunc) == &dwarf2_loclist_funcs)
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{
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struct dwarf2_loclist_baton *symbaton;
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symbaton = SYMBOL_LOCATION_BATON (framefunc);
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*start = find_location_expression (symbaton, length,
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get_frame_pc (debaton->frame));
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}
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else
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{
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struct dwarf2_locexpr_baton *symbaton;
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symbaton = SYMBOL_LOCATION_BATON (framefunc);
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*length = symbaton->size;
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*start = symbaton->data;
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}
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if (*start == NULL)
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error (_("Could not find the frame base for \"%s\"."),
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SYMBOL_NATURAL_NAME (framefunc));
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}
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/* Using the objfile specified in BATON, find the address for the
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current thread's thread-local storage with offset OFFSET. */
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static CORE_ADDR
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dwarf_expr_tls_address (void *baton, CORE_ADDR offset)
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{
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struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
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CORE_ADDR addr;
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if (target_get_thread_local_address_p ())
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addr = target_get_thread_local_address (inferior_ptid,
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debaton->objfile,
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offset);
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/* It wouldn't be wrong here to try a gdbarch method, too; finding
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TLS is an ABI-specific thing. But we don't do that yet. */
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else
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error (_("Cannot find thread-local variables on this target"));
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return addr;
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}
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/* Evaluate a location description, starting at DATA and with length
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SIZE, to find the current location of variable VAR in the context
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of FRAME. */
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static struct value *
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dwarf2_evaluate_loc_desc (struct symbol *var, struct frame_info *frame,
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unsigned char *data, unsigned short size,
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struct objfile *objfile)
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{
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struct gdbarch *arch = get_frame_arch (frame);
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struct value *retval;
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struct dwarf_expr_baton baton;
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struct dwarf_expr_context *ctx;
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if (size == 0)
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{
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retval = allocate_value (SYMBOL_TYPE (var));
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VALUE_LVAL (retval) = not_lval;
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set_value_optimized_out (retval, 1);
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}
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baton.frame = frame;
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baton.objfile = objfile;
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ctx = new_dwarf_expr_context ();
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ctx->baton = &baton;
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ctx->read_reg = dwarf_expr_read_reg;
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ctx->read_mem = dwarf_expr_read_mem;
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ctx->get_frame_base = dwarf_expr_frame_base;
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ctx->get_tls_address = dwarf_expr_tls_address;
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dwarf_expr_eval (ctx, data, size);
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if (ctx->num_pieces > 0)
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{
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/* We haven't implemented splicing together pieces from
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arbitrary sources yet. */
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error (_("The value of variable '%s' is distributed across several\n"
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"locations, and GDB cannot access its value.\n"),
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SYMBOL_NATURAL_NAME (var));
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}
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else if (ctx->in_reg)
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{
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CORE_ADDR dwarf_regnum = dwarf_expr_fetch (ctx, 0);
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int gdb_regnum = DWARF2_REG_TO_REGNUM (dwarf_regnum);
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retval = value_from_register (SYMBOL_TYPE (var), gdb_regnum, frame);
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}
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else
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{
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CORE_ADDR address = dwarf_expr_fetch (ctx, 0);
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retval = allocate_value (SYMBOL_TYPE (var));
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VALUE_LVAL (retval) = lval_memory;
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set_value_lazy (retval, 1);
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VALUE_ADDRESS (retval) = address;
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}
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free_dwarf_expr_context (ctx);
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return retval;
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}
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/* Helper functions and baton for dwarf2_loc_desc_needs_frame. */
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struct needs_frame_baton
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{
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int needs_frame;
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};
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/* Reads from registers do require a frame. */
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static CORE_ADDR
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needs_frame_read_reg (void *baton, int regnum)
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{
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struct needs_frame_baton *nf_baton = baton;
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nf_baton->needs_frame = 1;
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return 1;
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}
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/* Reads from memory do not require a frame. */
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static void
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needs_frame_read_mem (void *baton, char *buf, CORE_ADDR addr, size_t len)
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{
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memset (buf, 0, len);
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}
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/* Frame-relative accesses do require a frame. */
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static void
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needs_frame_frame_base (void *baton, unsigned char **start, size_t * length)
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{
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static char lit0 = DW_OP_lit0;
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struct needs_frame_baton *nf_baton = baton;
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*start = &lit0;
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*length = 1;
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nf_baton->needs_frame = 1;
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}
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/* Thread-local accesses do require a frame. */
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static CORE_ADDR
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needs_frame_tls_address (void *baton, CORE_ADDR offset)
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{
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struct needs_frame_baton *nf_baton = baton;
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nf_baton->needs_frame = 1;
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return 1;
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}
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/* Return non-zero iff the location expression at DATA (length SIZE)
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requires a frame to evaluate. */
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static int
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dwarf2_loc_desc_needs_frame (unsigned char *data, unsigned short size)
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{
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struct needs_frame_baton baton;
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struct dwarf_expr_context *ctx;
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int in_reg;
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baton.needs_frame = 0;
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ctx = new_dwarf_expr_context ();
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ctx->baton = &baton;
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ctx->read_reg = needs_frame_read_reg;
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ctx->read_mem = needs_frame_read_mem;
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ctx->get_frame_base = needs_frame_frame_base;
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ctx->get_tls_address = needs_frame_tls_address;
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dwarf_expr_eval (ctx, data, size);
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in_reg = ctx->in_reg;
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if (ctx->num_pieces > 0)
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{
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int i;
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/* If the location has several pieces, and any of them are in
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registers, then we will need a frame to fetch them from. */
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for (i = 0; i < ctx->num_pieces; i++)
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if (ctx->pieces[i].in_reg)
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in_reg = 1;
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}
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free_dwarf_expr_context (ctx);
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return baton.needs_frame || in_reg;
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}
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static void
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dwarf2_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,
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struct axs_value * value, unsigned char *data,
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int size)
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{
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if (size == 0)
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error (_("Symbol \"%s\" has been optimized out."),
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SYMBOL_PRINT_NAME (symbol));
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if (size == 1
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&& data[0] >= DW_OP_reg0
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&& data[0] <= DW_OP_reg31)
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{
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value->kind = axs_lvalue_register;
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value->u.reg = data[0] - DW_OP_reg0;
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}
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else if (data[0] == DW_OP_regx)
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{
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ULONGEST reg;
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read_uleb128 (data + 1, data + size, ®);
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value->kind = axs_lvalue_register;
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value->u.reg = reg;
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}
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else if (data[0] == DW_OP_fbreg)
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{
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/* And this is worse than just minimal; we should honor the frame base
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as above. */
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int frame_reg;
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LONGEST frame_offset;
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unsigned char *buf_end;
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buf_end = read_sleb128 (data + 1, data + size, &frame_offset);
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if (buf_end != data + size)
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error (_("Unexpected opcode after DW_OP_fbreg for symbol \"%s\"."),
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SYMBOL_PRINT_NAME (symbol));
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TARGET_VIRTUAL_FRAME_POINTER (ax->scope, &frame_reg, &frame_offset);
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ax_reg (ax, frame_reg);
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ax_const_l (ax, frame_offset);
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ax_simple (ax, aop_add);
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ax_const_l (ax, frame_offset);
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ax_simple (ax, aop_add);
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value->kind = axs_lvalue_memory;
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}
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else
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error (_("Unsupported DWARF opcode in the location of \"%s\"."),
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SYMBOL_PRINT_NAME (symbol));
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}
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/* Return the value of SYMBOL in FRAME using the DWARF-2 expression
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evaluator to calculate the location. */
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static struct value *
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locexpr_read_variable (struct symbol *symbol, struct frame_info *frame)
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{
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struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
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struct value *val;
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val = dwarf2_evaluate_loc_desc (symbol, frame, dlbaton->data, dlbaton->size,
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dlbaton->objfile);
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return val;
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}
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/* Return non-zero iff we need a frame to evaluate SYMBOL. */
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static int
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locexpr_read_needs_frame (struct symbol *symbol)
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{
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struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
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return dwarf2_loc_desc_needs_frame (dlbaton->data, dlbaton->size);
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}
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/* Print a natural-language description of SYMBOL to STREAM. */
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static int
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locexpr_describe_location (struct symbol *symbol, struct ui_file *stream)
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{
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/* FIXME: be more extensive. */
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struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
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if (dlbaton->size == 1
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&& dlbaton->data[0] >= DW_OP_reg0
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&& dlbaton->data[0] <= DW_OP_reg31)
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{
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int regno = DWARF2_REG_TO_REGNUM (dlbaton->data[0] - DW_OP_reg0);
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fprintf_filtered (stream,
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"a variable in register %s", REGISTER_NAME (regno));
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return 1;
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}
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/* The location expression for a TLS variable looks like this (on a
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64-bit LE machine):
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DW_AT_location : 10 byte block: 3 4 0 0 0 0 0 0 0 e0
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(DW_OP_addr: 4; DW_OP_GNU_push_tls_address)
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0x3 is the encoding for DW_OP_addr, which has an operand as long
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as the size of an address on the target machine (here is 8
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bytes). 0xe0 is the encoding for DW_OP_GNU_push_tls_address.
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The operand represents the offset at which the variable is within
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the thread local storage. */
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if (dlbaton->size > 1
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&& dlbaton->data[dlbaton->size - 1] == DW_OP_GNU_push_tls_address)
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if (dlbaton->data[0] == DW_OP_addr)
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{
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int bytes_read;
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CORE_ADDR offset = dwarf2_read_address (&dlbaton->data[1],
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&dlbaton->data[dlbaton->size - 1],
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&bytes_read);
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fprintf_filtered (stream,
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"a thread-local variable at offset %s in the "
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"thread-local storage for `%s'",
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paddr_nz (offset), dlbaton->objfile->name);
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return 1;
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}
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fprintf_filtered (stream,
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"a variable with complex or multiple locations (DWARF2)");
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return 1;
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}
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/* Describe the location of SYMBOL as an agent value in VALUE, generating
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any necessary bytecode in AX.
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NOTE drow/2003-02-26: This function is extremely minimal, because
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doing it correctly is extremely complicated and there is no
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publicly available stub with tracepoint support for me to test
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against. When there is one this function should be revisited. */
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static void
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locexpr_tracepoint_var_ref (struct symbol * symbol, struct agent_expr * ax,
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struct axs_value * value)
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{
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struct dwarf2_locexpr_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
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dwarf2_tracepoint_var_ref (symbol, ax, value, dlbaton->data, dlbaton->size);
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}
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/* The set of location functions used with the DWARF-2 expression
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evaluator. */
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const struct symbol_ops dwarf2_locexpr_funcs = {
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locexpr_read_variable,
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locexpr_read_needs_frame,
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locexpr_describe_location,
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locexpr_tracepoint_var_ref
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};
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/* Wrapper functions for location lists. These generally find
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the appropriate location expression and call something above. */
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/* Return the value of SYMBOL in FRAME using the DWARF-2 expression
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evaluator to calculate the location. */
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static struct value *
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loclist_read_variable (struct symbol *symbol, struct frame_info *frame)
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{
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struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
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struct value *val;
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unsigned char *data;
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size_t size;
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data = find_location_expression (dlbaton, &size,
|
||
frame ? get_frame_pc (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->objfile);
|
||
|
||
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 agent_expr * ax,
|
||
struct axs_value * value)
|
||
{
|
||
struct dwarf2_loclist_baton *dlbaton = SYMBOL_LOCATION_BATON (symbol);
|
||
unsigned char *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, ax, value, data, size);
|
||
}
|
||
|
||
/* The set of location functions used with the DWARF-2 expression
|
||
evaluator and location lists. */
|
||
const struct symbol_ops dwarf2_loclist_funcs = {
|
||
loclist_read_variable,
|
||
loclist_read_needs_frame,
|
||
loclist_describe_location,
|
||
loclist_tracepoint_var_ref
|
||
};
|