From: "Fāng-ruì Sòng" <maskray@google.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Yonghong Song <yhs@fb.com>, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
Lorenz Bauer <lmb@cloudflare.com>
Subject: Re: [PATCH bpf-next v2] docs/bpf: add llvm_reloc.rst to explain llvm bpf relocations
Date: Tue, 8 Jun 2021 09:33:28 -0700 [thread overview]
Message-ID: <CAFP8O3KayCgP6OqF1Vx8afav==jkL038m0rK66b7jJ0DOO=uJQ@mail.gmail.com> (raw)
In-Reply-To: <CAADnVQ+sD7ELvEwKf5Ui1dVkXPYEyjkwFxogxP5_4vrH3nMhPA@mail.gmail.com>
On Tue, Jun 8, 2021 at 8:49 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Jun 7, 2021 at 10:51 PM Fāng-ruì Sòng <maskray@google.com> wrote:
> >
> > You can rename R_BPF_64_64 to something more meaningful, e.g. R_BPF_64_LDIMM64.
> > Then I am fine that such a relocation type applies inconsecutive bytes.
> >
> > See below. Just change every occurrence of the old name in llvm-project.
>
> No. We cannot rename them, because certain gnu tools resolve relos by name
> and not by number.
How do the GNU tools resolve relocations by name instead of by
relocation type number?
I don't think this should and can be supported.
Most tools should do:
if (type == R_BPF_64_64) do_something();
You are free to change them to
if (type == R_BPF_64_LDIMM64) do_something();
as long as R_BPF_64_LDIMM64 is defined as the number.
> The only thing we can do is to document why such a name was picked in
> the first place.
> Back then 64_64 meant that it applied to 64-bit field in 16-byte insn.
> Whereas 64_32 meant that it applied to 32-bit field in 8-byte insn.
> 64_64 used to be called 64_MAPFD relo, but was renamed early enough
> while we still had time to do such rename. Now backward compatibility
> is more important than odd looking names.
next prev parent reply other threads:[~2021-06-08 16:33 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-25 3:33 [PATCH bpf-next v2] docs/bpf: add llvm_reloc.rst to explain llvm bpf relocations Yonghong Song
2021-05-25 18:29 ` Fangrui Song
2021-05-25 18:52 ` Yonghong Song
2021-06-05 21:03 ` Fāng-ruì Sòng
2021-06-07 21:06 ` Yonghong Song
2021-06-07 22:08 ` Fāng-ruì Sòng
2021-06-08 4:22 ` Andrii Nakryiko
2021-06-08 4:32 ` Yonghong Song
2021-06-08 5:51 ` Fāng-ruì Sòng
2021-06-08 15:49 ` Alexei Starovoitov
2021-06-08 16:33 ` Fāng-ruì Sòng [this message]
2021-06-08 18:32 ` Alexei Starovoitov
2021-06-08 23:10 ` Fāng-ruì Sòng
2021-06-08 23:23 ` Alexei Starovoitov
2021-05-25 15:25 Yonghong Song
2021-05-25 15:31 ` Yonghong Song
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