Re: [PATCH v2 2/3] btf_loader.c: Refactor class__fixup_btf_bitfields

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Oct 18, 2021 at 02:16:20PM +0100, Douglas RAILLARD escreveu:
> From: Douglas Raillard <douglas.raillard@arm.com>
> 
> Refactor class__fixup_btf_bitfields to remove a "continue" statement, to
> prepare the ground for alignment fixup that is relevant for some types
> matching:
> 
>     type->tag != DW_TAG_base_type && type->tag != DW_TAG_enumeration_type

Thanks, applied.

    Committer testing:

    btfdiff passes for a x86_64 kernel built with gcc and for a clang
    thin-LTO vmlinux build.


- Arnaldo

 
> Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
> ---
>  btf_loader.c | 29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)
> 
> diff --git a/btf_loader.c b/btf_loader.c
> index 3e5a945..9c2daee 100644
> --- a/btf_loader.c
> +++ b/btf_loader.c
> @@ -486,28 +486,27 @@ static int class__fixup_btf_bitfields(struct tag *tag, struct cu *cu)
>  		pos->byte_size = tag__size(type, cu);
>  		pos->bit_size = pos->byte_size * 8;
>  
> -		/* bitfield fixup is needed for enums and base types only */
> -		if (type->tag != DW_TAG_base_type && type->tag != DW_TAG_enumeration_type)
> -			continue;
> -
>  		/* if BTF data is incorrect and has size == 0, skip field,
>  		 * instead of crashing */
>  		if (pos->byte_size == 0) {
>  			continue;
>  		}
>  
> -		if (pos->bitfield_size) {
> -			/* bitfields seem to be always aligned, no matter the packing */
> -			pos->byte_offset = pos->bit_offset / pos->bit_size * pos->bit_size / 8;
> -			pos->bitfield_offset = pos->bit_offset - pos->byte_offset * 8;
> -			/* re-adjust bitfield offset if it is negative */
> -			if (pos->bitfield_offset < 0) {
> -				pos->bitfield_offset += pos->bit_size;
> -				pos->byte_offset -= pos->byte_size;
> -				pos->bit_offset = pos->byte_offset * 8 + pos->bitfield_offset;
> +		/* bitfield fixup is needed for enums and base types only */
> +		if (type->tag == DW_TAG_base_type || type->tag == DW_TAG_enumeration_type) {
> +			if (pos->bitfield_size) {
> +				/* bitfields seem to be always aligned, no matter the packing */
> +				pos->byte_offset = pos->bit_offset / pos->bit_size * pos->bit_size / 8;
> +				pos->bitfield_offset = pos->bit_offset - pos->byte_offset * 8;
> +				/* re-adjust bitfield offset if it is negative */
> +				if (pos->bitfield_offset < 0) {
> +					pos->bitfield_offset += pos->bit_size;
> +					pos->byte_offset -= pos->byte_size;
> +					pos->bit_offset = pos->byte_offset * 8 + pos->bitfield_offset;
> +				}
> +			} else {
> +				pos->byte_offset = pos->bit_offset / 8;
>  			}
> -		} else {
> -			pos->byte_offset = pos->bit_offset / 8;
>  		}
>  	}
>  
> -- 
> 2.25.1

-- 

- Arnaldo