* [PATCH dwarves] dwarf_loader: encode char type as signed
@ 2022-08-07 17:53 Yonghong Song
2022-08-08 22:52 ` Andrii Nakryiko
0 siblings, 1 reply; 5+ messages in thread
From: Yonghong Song @ 2022-08-07 17:53 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, Daniel Borkmann,
kernel-team
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
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH dwarves] dwarf_loader: encode char type as signed
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
2022-08-09 6:33 ` Yonghong Song
0 siblings, 2 replies; 5+ messages in thread
From: Andrii Nakryiko @ 2022-08-08 22:52 UTC (permalink / raw)
To: Yonghong Song
Cc: Arnaldo Carvalho de Melo, dwarves, Alexei Starovoitov,
Andrii Nakryiko, bpf, Daniel Borkmann, kernel-team
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.
Is there a plan to also add CHAR encoding bit?
> 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
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH dwarves] dwarf_loader: encode char type as signed
2022-08-08 22:52 ` 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
1 sibling, 1 reply; 5+ messages in thread
From: Andrii Nakryiko @ 2022-08-08 22:52 UTC (permalink / raw)
To: Yonghong Song
Cc: Arnaldo Carvalho de Melo, dwarves, Alexei Starovoitov,
Andrii Nakryiko, bpf, Daniel Borkmann, kernel-team
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>
>
> Is there a plan to also add CHAR encoding bit?
>
>
> > 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
> >
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH dwarves] dwarf_loader: encode char type as signed
2022-08-08 22:52 ` Andrii Nakryiko
@ 2022-08-10 18:59 ` Arnaldo Carvalho de Melo
0 siblings, 0 replies; 5+ messages in thread
From: Arnaldo Carvalho de Melo @ 2022-08-10 18:59 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: Yonghong Song, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, Daniel Borkmann,
kernel-team
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH dwarves] dwarf_loader: encode char type as signed
2022-08-08 22:52 ` Andrii Nakryiko
2022-08-08 22:52 ` Andrii Nakryiko
@ 2022-08-09 6:33 ` Yonghong Song
1 sibling, 0 replies; 5+ messages in thread
From: Yonghong Song @ 2022-08-09 6:33 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: Arnaldo Carvalho de Melo, dwarves, Alexei Starovoitov,
Andrii Nakryiko, bpf, Daniel Borkmann, kernel-team
On 8/8/22 3:52 PM, Andrii Nakryiko 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.
>
> Is there a plan to also add CHAR encoding bit?
Not yet... Need more thinking about use cases and backward comparability
issues.
>
>
>> 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
>>
^ permalink raw reply [flat|nested] 5+ messages in thread
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Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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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
2022-08-09 6:33 ` Yonghong Song
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