Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong alignment

[Mark Wielaard <mark@klomp.org>]

Hi

On Thu, 2020-08-20 at 08:51 -0700, Yonghong Song wrote:
> > > Do you think we could skip these .debug_* sections somehow in elf
> > > parsing in resolve_btfids? resolve_btfids does not need to read
> > > these sections. This way, no need to change their alignment
> > > either.
> > 
> > The issue is that elfutils libelf will not allow writing out the
> > section when it notices the sh_addralign field is setup wrongly.
> 
> Maybe resolve_btfids can temporarily change sh_addralign to 4/8
> before elf manipulation (elf_write) to make libelf happy.
> After all elf_write is done, change back to whatever the
> original value (1). Does this work?

Unfortunately no, because there is no elf_write, elf_update is how you
write out the ELF image to disc.

Since the code is using ELF_F_LAYOUT this will not change the actual
layout of the ELF image if that is what you are worried about.

And the workaround to set sh_addralign correctly before calling
elf_update is precisely what the fix in elfutils libelf will do itself
in the next release. Also binutils ld has been fixed to setup
sh_addralign to 4/8 as appropriate now (in git).

Cheers,

Mark