[RFC PATCH] bfd: Handle objcopy --only-keep-debug in _bfd_elf_init_private_section_data()
Nick Clifton
nickc@redhat.com
Fri Jan 28 12:42:08 GMT 2022
Hi Peilin,
> objcopy's --only-keep-debug option has been broken for ELF files since
> commit 8c803a2dd7d3 ("elf_backend_section_flags and
> _bfd_elf_init_private_section_data"):
>
> 1. binutils/objcopy.c:setup_section() marks non-debug sections as
> SHT_NOBITS, then calls bfd_copy_private_section_data(), see
> "mark_nobits";
> 2. If ISEC and OSEC share the same section flags,
> bfd/elf.c:_bfd_elf_init_private_section_data() restores OSEC's
> section type back to ISEC's section type, effectively undoing
> "mark_nobits".
>
> This makes objcopy's --only-keep-debug a no-op. As an example, Linux's
> scripts/package/builddeb script depends on this option to generate
> debug-info-only kernel modules.
>
> Handle this special case by checking OSEC's size in addition to its
> type (similar to bfd/elf.c:elf_fake_sections()). A non-debug section
> marked as SHT_NOBITS by --only-keep-debug should have a non-zero size.
I have a feeling that this change is going to have wider repercussions
than simply fixing this problem. It is going to affect those sections
created by elf_fake_sections() for example, and I bet that there will
be other scenarios that have not occurred to me.
Possibly a better fix would be to change objcopy instead so that it can
cope with the behaviour of bfd_copy_private_section_data(). For example,
please could you try out this patch and see if it fixes the problem ?
diff --git a/binutils/objcopy.c b/binutils/objcopy.c
index d16d8ee67e4..14b76d8a65a 100644
--- a/binutils/objcopy.c
+++ b/binutils/objcopy.c
@@ -4180,6 +4180,10 @@ setup_section (bfd *ibfd, sec_ptr isection, void *obfdarg)
err = _("failed to copy private data");
goto loser;
}
+ /* Since isec.flags == osec.flags, bfd_copy_private_section_data()
+ will reset the section type. */
+ if (make_nobits)
+ elf_section_type (osection) = SHT_NOBITS;
/* All went well. */
return;
> This patch is manually tested only. Which testsuite(s)
> should I use to test this patch?
Please run the binutils testsuite. ie:
cd <build-dir>/binutils
make check
Cheers
Nick
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