Hi Cupertino,
A couple of comments inline.
On 11/13/23 14:37, Cupertino Miranda wrote:
> This patch fixes a BTF, which would become invalid when having
> smaller then 4 byte definitions of enums.
> For example, when using the __attribute__((mode(byte))) in the enum
> definition.
Please add a test for this case in the BTF testsuite.
>
> Two problems were identified:
> - it would incorrectly create an entry for enum64 when the size of the
> enum was different then 4.
> - it would allocate less then 4 bytes for the value entry in BTF, in
> case the type was smaller.
>
> BTF generated was validated against clang.
>
> gcc/ChangeLog:
> * bpfout.cc (btf_calc_num_vbytes): Fixed logic for enum64.
> (btf_asm_enum_const): Corrected logic for enum64 and smaller
> than 4 bytes values.
> ---
> gcc/btfout.cc | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
> index e07fed302c24..d2263ec6eec3 100644
> --- a/gcc/btfout.cc
> +++ b/gcc/btfout.cc
> @@ -299,7 +299,7 @@ btf_calc_num_vbytes (ctf_dtdef_ref dtd)
> break;
>
> case BTF_KIND_ENUM:
> - vlen_bytes += (dtd->dtd_data.ctti_size == 0x8)
> + vlen_bytes += (dtd->dtd_data.ctti_size > 4)
> ? vlen * sizeof (struct btf_enum64)
> : vlen * sizeof (struct btf_enum);
> break;
> @@ -914,13 +914,13 @@ btf_asm_enum_const (unsigned int size, ctf_dmdef_t *
> dmd, unsigned int idx)
> {
> dw2_asm_output_data (4, dmd->dmd_name_offset, "ENUM_CONST '%s' idx=%u",
> dmd->dmd_name, idx);
> - if (size == 4)
> - dw2_asm_output_data (size, dmd->dmd_value, "bte_value");
> - else
> + if (size > 4)
> {
> - dw2_asm_output_data (4, dmd->dmd_value & 0xffffffff, "bte_value_lo32");
> + dw2_asm_output_data (4, dmd->dmd_value & 0xfffffffe, "bte_value_lo32");
I don't understand the mask change here.
Why clear the low bit of the enum value?
> dw2_asm_output_data (4, (dmd->dmd_value >> 32) & 0xffffffff,
> "bte_value_hi32");
> }
> + else
> + dw2_asm_output_data (size < 4 ? 4 : size, dmd->dmd_value, "bte_value");
In the else case isn't size guaranteed <= 4?
In which case, 'size < 4 ? 4 : size' always evaluates to 4.
So I would suggest to just write a literal 4 to keep it simple.
> }
>
> /* Asm'out a function parameter description following a BTF_KIND_FUNC_PROTO.
> */
