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. 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 >
