Re: [PATCH bpf-next] bpf: Add config for skipping BTF enum64s

[Jiri Olsa <olsajiri@gmail.com>]

On Sun, Aug 28, 2022 at 01:51:24PM -0300, Martin Reboredo wrote:
> From: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> 
> After the release of pahole 1.24 some people in the dwarves mailing list
> notified issues related to building the kernel with the BTF_DEBUG_INFO
> option toggled. They seem to be happenning due to the kernel and
> resolve_btfids interpreting btf types erroneously. In the dwarves list
> I've proposed a change to the scripts that I've written while testing
> the Rust kernel, it simply passes the --skip_encoding_btf_enum64 to
> pahole if it has version 1.24, but it might be desirable to have the
> option to pass said flag.

as I wrote in the original thread, I think we need to do this just for
stable kernels that don't have enum64 support and use pahole 1.24

I think we should switch it off there by default without config option

jirka

> 
> Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> ---
>  lib/Kconfig.debug       | 14 ++++++++++++++
>  scripts/pahole-flags.sh |  7 +++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 072e4b289c13..638a33cf9e57 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -356,6 +356,20 @@ config PAHOLE_HAS_BTF_TAG
>  	  btf_decl_tag) or not. Currently only clang compiler implements
>  	  these attributes, so make the config depend on CC_IS_CLANG.
>  
> +config PAHOLE_HAS_SKIP_ENCODING_BTF_ENUM64
> +	def_bool PAHOLE_VERSION >= 124
> +	help
> +	  Encoding BTF enum64s can be skipped with the
> +	  --skip_encoding_btf_enum64 pahole option.
> +
> +config DEBUG_INFO_BTF_SKIP_ENCODING_ENUM64
> +	def_bool n
> +	depends on DEBUG_INFO_BTF && PAHOLE_HAS_SKIP_ENCODING_BTF_ENUM64
> +	help
> +	  Omit the encoding of 64 bits enum values with pahole. With certain
> +	  kernel configurations having ENUM64s enabled may result in malformed
> +	  output binaries.
> +
>  config DEBUG_INFO_BTF_MODULES
>  	def_bool y
>  	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> index 0d99ef17e4a5..e44bc2a947ce 100755
> --- a/scripts/pahole-flags.sh
> +++ b/scripts/pahole-flags.sh
> @@ -9,6 +9,10 @@ fi
>  
>  pahole_ver=$($(dirname $0)/pahole-version.sh ${PAHOLE})
>  
> +is_enabled() {
> +	grep -q "^$1=y" include/config/auto.conf
> +}
> +
>  if [ "${pahole_ver}" -ge "118" ] && [ "${pahole_ver}" -le "121" ]; then
>  	# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
>  	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_vars"
> @@ -19,5 +23,8 @@ fi
>  if [ "${pahole_ver}" -ge "122" ]; then
>  	extra_paholeopt="${extra_paholeopt} -j"
>  fi
> +if is_enabled DEBUG_INFO_BTF_SKIP_ENCODING_ENUM64; then
> +	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_enum64"
> +fi
>  
>  echo ${extra_paholeopt}
> -- 
> 2.37.2
>