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Consider the test case added in this patch. It defines a compilation unit with a DW_AT_rnglists_base attribute (used for attributes of form DW_FORM_rnglistx), but also uses DW_AT_ranges of form DW_FORM_sec_offset: 0x00000027: DW_TAG_compile_unit DW_AT_ranges [DW_FORM_sec_offset] (0x0000004c [0x0000000000005000, 0x0000000000006000)) DW_AT_rnglists_base [DW_FORM_sec_offset] (0x00000044) The DW_AT_rnglists_base does not play a role in reading the DW_AT_ranges of form DW_FORM_sec_offset, but it should also not do any harm. This case is currently not handled correctly by GDB. This is not something that a compiler is likely to emit, but in my opinion there's no reason why GDB should fail reading it. The problem is that in partial_die_info::read and a few other places where the same logic is replicated, the cu->ranges_base value, containing the DW_AT_rnglists_base value, is wrongfully added to the DW_AT_ranges value. It is quite messy how to decide whether cu->ranges_base should be added to the attribute's value or not. But to summarize, the only time we want to add it is when the attribute comes from a pre-DWARF 5 split unit file (a .dwo) [1]. In this case, the DW_AT_ranges attribute from the split unit file will have form DW_FORM_sec_offset, pointing somewhere in the linked file's .debug_ranges section. *But* it's not a "true" DW_FORM_sec_offset, in that it's an offset relative to the beginning of that CU's contribution in the section, not relative to the beginning of the section. So in that case, and only that case, do we want to add the ranges base value, which we found from the DW_AT_GNU_ranges_base attribute on the skeleton unit. Almost all instances of the DW_AT_ranges attribute will be found in the split unit (on DW_TAG_subprogram, for example), and therefore need to have the ranges base added. However, the DW_TAG_compile_unit DIE in the skeleton may also have a DW_AT_ranges attribute. For that one, the ranges base must not be added. Once the DIEs have been loaded in GDB, however, the distinction between what's coming from the skeleton and what's coming from the split unit is not clear. It is all merged in one big happy tree. So how do we know if a given attribute comes from the split unit or not? We use the fact that in pre-DWARF 5 split DWARF, DW_AT_ranges is found on the skeleton's DW_TAG_compile_unit (in the linked file) and never in the split unit's DW_TAG_compile_unit. This is why you have this in partial_die_info::read: int need_ranges_base = (tag != DW_TAG_compile_unit && attr.form != DW_FORM_rnglistx); However, with the corner case described above (where we have a DW_AT_rnglists_base attribute and a DW_AT_ranges attribute of form DW_FORM_sec_offset) the condition gets it wrong when it encounters an attribute like DW_TAG_subprogram with a DW_AT_ranges attribute of DW_FORM_sec_offset form: it thinks that it is necessary to add the base, when it reality it is not. The problem boils down to failing to differentiate these cases: - a DW_AT_ranges attribute of form DW_FORM_sec_offset in a pre-DWARF 5 split unit (in which case we need to add the base) - a DW_AT_ranges attribute of form DW_FORM_sec_offset in a DWARF 5 non-split unit (in which case we must not add the base) What makes it unnecessarily complex is that the cu->ranges_base field is overloaded, used to hold the pre-DWARF 5, non-standard DW_AT_GNU_ranges_base and the DWARF 5 DW_AT_rnglists_base. In reality, these two are called "bases" but are not the same thing. The result is that we need twisted conditions to try to determine whether or not we should add the base to the attribute's value. To fix it, split the field in two distinct fields. I renamed everything related to the "old" ranges base to "gnu_ranges_base", to make it clear that it's about the non-standard, pre-DWARF 5 thing. And everything related to the DWARF 5 thing gets renamed "rnglists". I think it becomes much easier to reason this way. The issue described above gets fixed by the fact that the DW_AT_rnglists_base value does not end up in cu->gnu_ranges_base, so cu->gnu_ranges_base stays 0. The condition to determine whether gnu_ranges_base should be added can therefore be simplified back to: tag != DW_TAG_compile_unit ... as it was before rnglistx support was added. Extend the gdb.dwarf2/rnglists-sec-offset.exp to cover this case. I also extended the test case for loclists similarly, just to see if there would be some similar problem. There wasn't, but I think it's not a bad idea to test that case for loclists as well, so I left it in the patch. [1] https://gcc.gnu.org/wiki/DebugFission gdb/ChangeLog: * dwarf2/die.h (struct die_info) <ranges_base>: Split in... <gnu_ranges_base>: ... this... <rnglists_base>: ... and this. * dwarf2/read.c (struct dwarf2_cu) <ranges_base>: Split in... <gnu_ranges_base>: ... this... <rnglists_base>: ... and this. (read_cutu_die_from_dwo): Adjust (dwarf2_get_pc_bounds): Adjust (dwarf2_record_block_ranges): Adjust. (read_full_die_1): Adjust (partial_die_info::read): Adjust. (read_rnglist_index): Adjust. gdb/testsuite/ChangeLog: * gdb.dwarf2/rnglists-sec-offset.exp: Add test for DW_AT_ranges of DW_FORM_sec_offset form plus DW_AT_rnglists_base attribute. * gdb.dwarf2/loclists-sec-offset.exp: Add test for DW_AT_location of DW_FORM_sec_offset plus DW_AT_loclists_base attribute Change-Id: Icd109038634b75d0e6e9d7d1dcb62fb9eb951d83
130 lines
3.9 KiB
C
130 lines
3.9 KiB
C
/* DWARF DIEs
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Copyright (C) 2003-2021 Free Software Foundation, 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 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU 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, see <http://www.gnu.org/licenses/>. */
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#ifndef GDB_DWARF2_DIE_H
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#define GDB_DWARF2_DIE_H
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#include "complaints.h"
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/* This data structure holds a complete die structure. */
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struct die_info
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{
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/* Return the named attribute or NULL if not there, but do not
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follow DW_AT_specification, etc. */
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struct attribute *attr (dwarf_attribute name)
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{
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for (unsigned i = 0; i < num_attrs; ++i)
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if (attrs[i].name == name)
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return &attrs[i];
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return NULL;
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}
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/* Return the address base of the compile unit, which, if exists, is
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stored either at the attribute DW_AT_GNU_addr_base, or
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DW_AT_addr_base. */
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gdb::optional<ULONGEST> addr_base ()
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{
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for (unsigned i = 0; i < num_attrs; ++i)
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if (attrs[i].name == DW_AT_addr_base
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|| attrs[i].name == DW_AT_GNU_addr_base)
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{
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if (attrs[i].form_is_unsigned ())
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{
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/* If both exist, just use the first one. */
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return attrs[i].as_unsigned ();
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}
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complaint (_("address base attribute (offset %s) as wrong form"),
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sect_offset_str (sect_off));
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}
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return gdb::optional<ULONGEST> ();
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}
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/* Return the base address of the compile unit into the .debug_ranges section,
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which, if exists, is stored in the DW_AT_GNU_ranges_base attribute. This
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value is only relevant in pre-DWARF 5 split-unit scenarios. */
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ULONGEST gnu_ranges_base ()
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{
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for (unsigned i = 0; i < num_attrs; ++i)
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if (attrs[i].name == DW_AT_GNU_ranges_base)
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{
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if (attrs[i].form_is_unsigned ())
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return attrs[i].as_unsigned ();
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complaint (_("ranges base attribute (offset %s) has wrong form"),
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sect_offset_str (sect_off));
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}
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return 0;
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}
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/* Return the rnglists base of the compile unit, which, if exists, is stored
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in the DW_AT_rnglists_base attribute. */
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ULONGEST rnglists_base ()
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{
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for (unsigned i = 0; i < num_attrs; ++i)
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if (attrs[i].name == DW_AT_rnglists_base)
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{
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if (attrs[i].form_is_unsigned ())
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return attrs[i].as_unsigned ();
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complaint (_("rnglists base attribute (offset %s) has wrong form"),
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sect_offset_str (sect_off));
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}
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return 0;
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}
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/* DWARF-2 tag for this DIE. */
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ENUM_BITFIELD(dwarf_tag) tag : 16;
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/* Number of attributes */
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unsigned char num_attrs;
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/* True if we're presently building the full type name for the
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type derived from this DIE. */
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unsigned char building_fullname : 1;
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/* True if this die is in process. PR 16581. */
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unsigned char in_process : 1;
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/* True if this DIE has children. */
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unsigned char has_children : 1;
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/* Abbrev number */
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unsigned int abbrev;
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/* Offset in .debug_info or .debug_types section. */
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sect_offset sect_off;
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/* The dies in a compilation unit form an n-ary tree. PARENT
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points to this die's parent; CHILD points to the first child of
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this node; and all the children of a given node are chained
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together via their SIBLING fields. */
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struct die_info *child; /* Its first child, if any. */
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struct die_info *sibling; /* Its next sibling, if any. */
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struct die_info *parent; /* Its parent, if any. */
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/* An array of attributes, with NUM_ATTRS elements. There may be
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zero, but it's not common and zero-sized arrays are not
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sufficiently portable C. */
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struct attribute attrs[1];
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};
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#endif /* GDB_DWARF2_DIE_H */
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