From: Yonghong Song <yhs@fb.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
<dwarves@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>, <bpf@vger.kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>, <kernel-team@fb.com>
Subject: [PATCH dwarves] dwarf_loader: encode char type as signed
Date: Sun, 7 Aug 2022 10:53:09 -0700 [thread overview]
Message-ID: <20220807175309.4186342-1-yhs@fb.com> (raw)
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>
---
dwarf_loader.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index d892bc3..c2ad2a0 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -560,7 +560,7 @@ static struct base_type *base_type__new(Dwarf_Die *die, struct cu *cu, struct co
bt->bit_size = attr_numeric(die, DW_AT_byte_size) * 8;
uint64_t encoding = attr_numeric(die, DW_AT_encoding);
bt->is_bool = encoding == DW_ATE_boolean;
- bt->is_signed = encoding == DW_ATE_signed;
+ bt->is_signed = (encoding == DW_ATE_signed) || (encoding == DW_ATE_signed_char);
bt->is_varargs = false;
bt->name_has_encoding = true;
bt->float_type = encoding_to_float_type(encoding);
--
2.30.2
next reply other threads:[~2022-08-07 17:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-07 17:53 Yonghong Song [this message]
2022-08-08 22:52 ` [PATCH dwarves] dwarf_loader: encode char type as signed Andrii Nakryiko
2022-08-08 22:52 ` Andrii Nakryiko
2022-08-10 18:59 ` Arnaldo Carvalho de Melo
2022-08-09 6:33 ` Yonghong Song
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220807175309.4186342-1-yhs@fb.com \
--to=yhs@fb.com \
--cc=andrii@kernel.org \
--cc=arnaldo.melo@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=dwarves@vger.kernel.org \
--cc=kernel-team@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).