On 8/8/22 3:52 PM, Andrii Nakryiko 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. 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
