https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101431
Bug ID: 101431
Summary: gcc-generated DWARF5 .debug_line directory entries
violate the DWARF5 spec
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: roc at ocallahan dot org
Target Milestone: ---
For the "Line Number Program Header" "directories" field, the DWARF5 spec says
"The first entry is the current directory of the compilation. Each additional
path entry is either a full path name or is relative to the current directory
of
the compilation."
In a simple testcase (see below) I get the following tables emitted (gcc
11.1.1):
The Directory Table:
0 out
1 out
2 /usr/include
The File Name Table
Entry Dir Time Size Name
0 0 0 0 file.c
1 1 0 0 file.c
2 1 0 0 message.h
3 2 0 0 stdio.h
The compilation unit info from .debug_info is
UNIT<header overall offset = 0x0000006a>:
dwo_id = 0x6ef97fe679ccccda
< 0><0x00000014> DW_TAG_skeleton_unit
DW_AT_low_pc 0x00201728
DW_AT_high_pc <offset-from-lowpc>21
DW_AT_stmt_list <.debug_line+0x000000bd>
DW_AT_dwo_name out/main.dwo
DW_AT_comp_dir /tmp/pernosco-submit-test
DW_AT_GNU_pubnames yes
DW_AT_addr_base <.debug_addr+0x00000030>
The correct path for 'file.c' is /tmp/pernosco-submit-test/out/file.c.
Clearly, treating directory entry 1 as relative to directory entry 0 would give
the wrong file path (something containing 'out/out'). It looks like gcc intends
all directory entries to be treated as relative to the DW_AT_comp_dir from the
.debug_info unit?
Note that if the latter is true, then that violates the intent of the new
behavior in DWARF5:
> In DWARF Version 5, the current directory is explicitly present in the
directories field. This is needed to support the common practice of stripping
all but the line number sections ( .debug_line and .debug_line_str ) from an
executable.
To reproduce this bug:
git clone --recurse-submodules https://github.com/Pernosco/pernosco-submit-test
cd pernosco-submit-test
./build.sh
dwarfdump -l out/main.debug
