Re: [PATCH 1/2] btf: be clear when record size/type is not used

[Indu Bhagat <indu.bhagat@oracle.com>]

On 5/30/23 11:27, David Faust wrote:
> [Changes from v1: split this change into own commit.]
> 
> All BTF type records have a 4-byte field used to encode a size or link
> to another type, depending on the type kind. But BTF_KIND_ARRAY and
> BTF_KIND_FWD do not use this field at all, and should write zero.
> 
> GCC already correctly writes zero in this field for these type kinds,
> but the process is not straightforward and results in the -dA comment
> claiming the field is a reference to another type. This patch makes
> the behavior explicit and updates the assembler comment to state
> clearly that the field is unused.
> 

LGTM.

Thanks

> gcc/
> 
> 	* btfout.cc (btf_asm_type): Add dedicated cases for BTF_KIND_ARRAY
> 	and BTF_KIND_FWD which do not use the size/type field at all.
> ---
>   gcc/btfout.cc | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
> index 497c1ca06e6..ae9855716eb 100644
> --- a/gcc/btfout.cc
> +++ b/gcc/btfout.cc
> @@ -705,6 +705,12 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>         dw2_asm_output_data (4, dtd->dtd_data.ctti_size, "btt_size: %uB",
>   			   dtd->dtd_data.ctti_size);
>         return;
> +    case BTF_KIND_ARRAY:
> +    case BTF_KIND_FWD:
> +      /* These types do not encode any information in the size/type field
> +	 and should write 0.  */
> +      dw2_asm_output_data (4, 0, "(unused)");
> +      return;
>       default:
>         break;
>       }