There are two methods to factor out type information in a dwarf4 executable: - use -fdebug-info-types to generate type units in a .debug_types section, and - use dwz to create partial units. The dwz method has an extra benefit: it also allows to factor out information between executables into a newly created .dwz file, pointed to by a .gnu_debugaltlink section. There is nothing prohibiting a .gnu_debugaltlink file to contain a .debug_types section. It's just not generated by dwz atm, and consequently gdb has no support for it.
Created attachment 15107 [details] partial patch The patch contains a test-case, and some fixes in the dwarf reader, which allow the test-case to pass. It doesn't fix the target board cc-with-gdb-index case though. The test-case passes, but the .gdb_index section in the exec is quietly ignored, because there's no .gdb_index section in the dwz file.
I'm not sure it makes sense at this point to explore this further, given that there's no regular way to generate dwarf like this, but I'd like this PR to stay open, such that I can reference it from the source code when throwing an error to say this is unsupported.
(In reply to Tom de Vries from comment #2) > when > throwing an error to say this is unsupported. https://sourceware.org/pipermail/gdb-patches/2023-September/202354.html
The master branch has been updated by Tom de Vries <vries@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=973db6fae304c2bcafff5f169610f663adc9e817 commit 973db6fae304c2bcafff5f169610f663adc9e817 Author: Tom de Vries <tdevries@suse.de> Date: Wed Sep 20 16:05:55 2023 +0200 [gdb/symtab] Error out for .debug_types section in dwz file There are two methods to factor out type information in a dwarf4 executable: - use -fdebug-info-types to generate type units in a .debug_types section, and - use dwz to create partial units. The dwz method has an extra benefit: it also allows to factor out information between executables into a newly created .dwz file, pointed to by a .gnu_debugaltlink section. There is nothing prohibiting a .gnu_debugaltlink file to contain a .debug_types section. It's just not generated by dwz or any other tool atm, and consequently gdb has no support for it. Enhancement PR symtab/30838 is open about the lack of support. Make the current situation explicit by emitting a dwarf error: ... (gdb) file struct-with-sig-2^M Reading symbols from struct-with-sig-2...^M Dwarf Error: .debug_types section not supported in dwz file^M ... and add an assert in write_gdbindex: ... + /* See enhancement PR symtab/30838. */ + gdb_assert (!(per_cu->is_dwz && per_cu->is_debug_types)); ... to clarify why we can use: ... data_buf &cu_list = (per_cu->is_debug_types ? types_cu_list : per_cu->is_dwz ? dwz_cu_list : objfile_cu_list); ... The test-case is a modified copy from gdb.dwarf2/struct-with-sig.exp, so it keeps the copyright years range. Tested on x86_64-linux. Tested-By: Guinevere Larsen <blarsen@redhat.com> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30838