From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Yonghong Song <yhs@fb.com>,
Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
dwarves@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
bpf@vger.kernel.org, Daniel Borkmann <daniel@iogearbox.net>,
kernel-team@fb.com
Subject: Re: [PATCH dwarves] dwarf_loader: encode char type as signed
Date: Wed, 10 Aug 2022 15:59:59 -0300 [thread overview]
Message-ID: <YvQAL+8Ah5J0hWAg@kernel.org> (raw)
In-Reply-To: <CAEf4BzYaWboRjHqewen71QZhvQyvtkeE5N43y=NvE+igw4RXYw@mail.gmail.com>
Em Mon, Aug 08, 2022 at 03:52:38PM -0700, Andrii Nakryiko escreveu:
> On Mon, Aug 8, 2022 at 3:52 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Sun, Aug 7, 2022 at 10:53 AM Yonghong Song <yhs@fb.com> wrote:
> > >
> > > Currently, the pahole treats 'char' or 'signed char' type
> > > as unsigned in BTF generation. The following is an example,
> > > $ cat t.c
> > > signed char a;
> > > char b;
> > > $ clang -O2 -g -c t.c
> > > $ pahole -JV t.o
> > > ...
> > > [1] INT signed char size=1 nr_bits=8 encoding=(none)
> > > [2] INT char size=1 nr_bits=8 encoding=(none)
> > > In the above encoding '(none)' implies unsigned type.
> > >
> > > But if the same program is compiled with bpf target,
> > > $ clang -target bpf -O2 -g -c t.c
> > > $ bpftool btf dump file t.o
> > > [1] INT 'signed char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
> > > [2] VAR 'a' type_id=1, linkage=global
> > > [3] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
> > > [4] VAR 'b' type_id=3, linkage=global
> > > [5] DATASEC '.bss' size=0 vlen=2
> > > type_id=2 offset=0 size=1 (VAR 'a')
> > > type_id=4 offset=0 size=1 (VAR 'b')
> > > the 'char' and 'signed char' are encoded as SIGNED integers.
> > >
> > > Encode 'char' and 'signed char' as SIGNED should be a right to
> > > do and it will be consistent with bpf implementation.
> > >
> > > With this patch,
> > > $ pahole -JV t.o
> > > ...
> > > [1] INT signed char size=1 nr_bits=8 encoding=SIGNED
> > > [2] INT char size=1 nr_bits=8 encoding=SIGNED
> > >
> > > Signed-off-by: Yonghong Song <yhs@fb.com>
> > > ---
> >
> > LGTM.
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
Thanks, tested before/after, applied.
Pushing out next for CI testing.
- Arnaldo
next prev parent reply other threads:[~2022-08-10 19:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-07 17:53 [PATCH dwarves] dwarf_loader: encode char type as signed Yonghong Song
2022-08-08 22:52 ` Andrii Nakryiko
2022-08-08 22:52 ` Andrii Nakryiko
2022-08-10 18:59 ` Arnaldo Carvalho de Melo [this message]
2022-08-09 6:33 ` Yonghong Song
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