binutils-gdb/gdb/testsuite/gdb.dwarf2/loclists-sec-offset.c

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/* Copyright (C) 2021 Free Software Foundation, 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/>. */
static int
func1 (void)
{
asm ("func1_label: .global func1_label\n");
return 1;
}
static int
func2 (void)
{
asm ("func2_label: .global func2_label\n");
return 2;
}
gdb/dwarf: split dwarf2_cu::ranges_base in two 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
2021-02-02 23:41:59 +08:00
static int
func3 (void)
{
asm ("func3_label: .global func3_label\n");
return 3;
}
static int
func4 (void)
{
asm ("func4_label: .global func4_label\n");
return 4;
}
int
main (void)
{
func1 ();
func2 ();
gdb/dwarf: split dwarf2_cu::ranges_base in two 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
2021-02-02 23:41:59 +08:00
func3 ();
func4 ();
}