https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91968
Bug ID: 91968
Summary: DW_AT_low_pc missing for DW_TAG_label with LTO
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: keiths at redhat dot com
Target Milestone: ---
Compilers tested: gcc version 10.0.0 20190930, several Fedora system compilers,
e.g., Fedora 29 (gcc version 9.2.1 20190827 (Red Hat 9.2.1-1).
Consider the simple program (from GDB's test suite,
gdb/testsuite/gdb.base/label.c):
#include <stdio.h>
int
main (int argc, char **argv)
{
int i = 0;
goto there;
here:
printf("not here\n");
i = 1;
there:
printf("but here\n");
if (i == 0)
goto here;
done:
return 0;
}
If this is compiled with LTO (gcc -g -flto label.c)[1], GDB is unable to set a
breakpoint at any of the labels. This is because GDB is looking for
DW_AT_low_pc, but this attribute is missing from the DIEs for the labels:
<2><f7>: Abbrev Number: 8 (DW_TAG_label)
<f8> DW_AT_name : (indirect string, offset: 0xfe): there
<fc> DW_AT_decl_file : 1
<fd> DW_AT_decl_line : 13
<fe> DW_AT_decl_column : 1
<2><ff>: Abbrev Number: 8 (DW_TAG_label)
<100> DW_AT_name : (indirect string, offset: 0xff): here
<104> DW_AT_decl_file : 1
<105> DW_AT_decl_line : 9
<106> DW_AT_decl_column : 1
<2><107>: Abbrev Number: 8 (DW_TAG_label)
<108> DW_AT_name : (indirect string, offset: 0xc6): done
<10c> DW_AT_decl_file : 1
<10d> DW_AT_decl_line : 18
<10e> DW_AT_decl_column : 1
Is GDB supposed to deal with this in some other way?
[1] Alternatively, if you have a GDB build lying around:
$ make check RUNTESTFLAGS="--target_board unix/-flto" \
TESTS=gdb.base/label.exp
That test will show several internal errors (assertion failures) as a result of
this.
