Re: [PATCH dwarves] dwarf_loader: encode char type as signed

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Mon, Aug 8, 2022 at 3:52 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Sun, Aug 7, 2022 at 10:53 AM Yonghong Song <yhs@xxxxxx> 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@xxxxxx>
> > ---
>
> LGTM.

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>

>
> 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
> >



[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux