Re: [PATCH v4 3/7] bfd: Improve nm and objdump without section header

[Mark Wielaard <mark@klomp.org>]

Hi,

On Thu, Jul 13, 2023 at 02:32:25PM +0930, Alan Modra via Binutils wrote:
> > So, the program header of the .debug file describes the segments of the
> > main binary, not sure if that's expected.
> 
> No, that's not expected.  Program headers in a .debug file ought to
> describe the contents of the debug file.  You'll typically see many
> with p_filesz zero.  eu-strip appears to be broken in this respect.

It is by design that eu-strip -f copies over the program headers of
the main file into the .debug file. It would be nice to tag .debug
files as such, to prevent issues like this. There is a binutils bug
about it: https://sourceware.org/bugzilla/show_bug.cgi?id=22136

> There is another problem with the code added to elf_object_p:
> _bfd_elf_get_dynamic_symbols is told that it can access up to e_phnum
> program headers, but they very likely haven't all been swapped in.
> 
> I'm going to apply the following patch.
>
> ----
> 
> elf_object_p load of dynamic symbols
> 
> This fixes an uninitialised memory access on a fuzzed file:
> 0 0xf22e9b in offset_from_vma /src/binutils-gdb/bfd/elf.c:1899:2
> 1 0xf1e90f in _bfd_elf_get_dynamic_symbols /src/binutils-gdb/bfd/elf.c:2099:13
> 2 0x10e6a54 in bfd_elf32_object_p /src/binutils-gdb/bfd/elfcode.h:851:9
> 
> Hopefully it will also stop any attempt to load dynamic symbols from
> eu-strip debug files.
> 
> 	* elfcode.h (elf_object_p): Do not attempt to load dynamic
> 	symbols for a file with no section headers until all the
> 	program headers are swapped in.  Do not fail on eu-strip debug
> 	files.

Thanks! This does resolves an elfutils/debuginfod issue Ryan and I
were tracking down on debian-testing with using binutils objcopy
extracting sections from a .debug file. Debian testing ships with
binutils 2.40.90.20230705.

If possible could this go into 2.41 (and in an update for Debian
testing)?

Thanks,

Mark