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From: Mark Wielaard <mark@klomp.org>
To: "Yonghong Song" <yhs@fb.com>,
	"Fāng-ruì Sòng" <maskray@google.com>,
	"Jiri Olsa" <jolsa@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Nick Clifton <nickc@redhat.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Network Development <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>, Martin KaFai Lau <kafai@fb.com>,
	Song Liu <songliubraving@fb.com>,
	Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH bpf-next] tools/resolve_btfids: Fix sections with wrong alignment
Date: Thu, 20 Aug 2020 19:36:37 +0200	[thread overview]
Message-ID: <a6f1d7be73ca5d9f767a746927e7872ddcf18244.camel@klomp.org> (raw)
In-Reply-To: <7029ff8f-77d3-584b-2e7e-388c001cd648@fb.com>

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

  reply	other threads:[~2020-08-20 17:36 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19  9:23 Jiri Olsa
2020-08-19 15:31 ` Yonghong Song
2020-08-19 17:36   ` Jiri Olsa
2020-08-19 18:16     ` Nick Desaulniers
2020-08-19 21:30       ` Yonghong Song
2020-08-20  2:27         ` Fāng-ruì Sòng
2020-08-20  3:23           ` Yonghong Song
2020-08-20 10:18             ` Jiri Olsa
2020-08-20 10:18             ` Mark Wielaard
2020-08-20 15:51               ` Yonghong Song
2020-08-20 17:36                 ` Mark Wielaard [this message]
2020-08-20 17:54                   ` Yonghong Song
2020-08-20 21:24                     ` Alexei Starovoitov
2020-08-19 17:02 ` Jesper Dangaard Brouer
2020-08-19 21:32 ` Yonghong Song

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