Created attachment 53614 [details]
objdump output for dwarf-4

GCC 12 now defaults to outputting debug information via dwarf-5. Compared to dwarf-4 (which works), gdb's interpretation of dwarf-5 seems to show that we're missing the correct line information, which causes gdb to not be able to correctly find and evaluate a macro on the command line due to being in the wrong context. It's not clear whether gcc is not correctly emitting all the information, or if gdb is not correctly reading all the information.

Breaking at the "main" function and attempting to run "info macro X" produces the error message, "The symbol `X' has no definition as a C/C++ preprocessor macro at macro.c:-1".

The same behavior happens when breaking at any other point in a C program, and not just at "main".

In both examples below, the breakpoint output shows we're at line 5 in macro.c:

$ cat macro.c
#define TEST_MACRO 42

int main()
{
  return 0;
}

### DWARF-4 Example ###

$ gcc -O3 -ggdb3 -gdwarf-4 macro.c -o macro
$ gdb macro 
GNU gdb (Gentoo 12.1 vanilla) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://bugs.gentoo.org/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from macro...
(gdb) break main
Breakpoint 1 at 0x401020: file macro.c, line 5.
(gdb) run
Starting program: /g/macro 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at macro.c:5
5         return 0;
(gdb) info macro TEST_MACRO
Defined at /g/macro.c:1
#define TEST_MACRO 42
(gdb) p TEST_MACRO
$1 = 42
(gdb) quit

### DWARF-5 EXAMPLE ###

$ gcc -O3 -ggdb3 -gdwarf-5 macro.c -o macro
$ gdb macro
GNU gdb (Gentoo 12.1 vanilla) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://bugs.gentoo.org/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from macro...
(gdb) break main
Breakpoint 1 at 0x401020: file macro.c, line 5.
(gdb) run
Starting program: /g/macro 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at macro.c:5
5         return 0;
(gdb) info macro TEST_MACRO
The symbol `TEST_MACRO' has no definition as a C/C++ preprocessor macro
at /g/macro.c:-1
(gdb) p TEST_MACRO
No symbol "TEST_MACRO" in current context.
(gdb) quit


Software versions:

$ gdb -v
GNU gdb (Gentoo 12.1 vanilla) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/12.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-12.2.0/work/gcc-12.2.0/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/12.2.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/12.2.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/12.2.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/12.2.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include/g++-v12 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/12.2.0/python --enable-languages=c,c++ --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --disable-nls --disable-libunwind-exceptions --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 12.2.0 p1' --disable-esp --enable-libstdcxx-time --disable-libstdcxx-pch --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-multilib --with-multilib-list=m32,m64 --disable-fixed-point --enable-targets=all --enable-libgomp --disable-libssp --disable-libada --disable-cet --disable-systemtap --disable-valgrind-annotations --disable-vtable-verify --disable-libvtv --with-zstd --enable-lto --without-isl --disable-libsanitizer --disable-default-pie --disable-default-ssp
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.0 (Gentoo 12.2.0 p1) 

I've attached the output of "objdump -g macro" for both dwarf-4 and dwarf-5.

Thanks!