Re: [PATCH bpf-next] kbuild, bpf: reproducible BTF from pahole when KBUILD_BUILD_TIMESTAMP set

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Jul 01, 2024 at 06:31:33PM +0100, Alan Maguire wrote:
> Reproducible builds [1] require that the same source code with
> the same set of tools can build identical objects each time,
> but pahole in parallel mode was non-deterministic in
> BTF generation prior to
> 
> dba7b5e ("pahole: Encode BTF serially in a reproducible build")
> 
> This was a problem since said BTF is baked into kernels and modules in
> .BTF sections, so parallel pahole was causing non-reproducible binary
> generation.  Now with the above commit we have support for parallel
> reproducible BTF generation in pahole.
> 
> KBUILD_BUILD_TIMESTAMP is set for reproducible builds, so if it
> is set, add reproducible_build to --btf_features.
> 
> [1] Documentation/kbuild/reproducible-builds.rst
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

makes sense

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  scripts/Makefile.btf | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
> index b75f09f3f424..40bb72662967 100644
> --- a/scripts/Makefile.btf
> +++ b/scripts/Makefile.btf
> @@ -21,6 +21,10 @@ else
>  # Switch to using --btf_features for v1.26 and later.
>  pahole-flags-$(call test-ge, $(pahole-ver), 126)  = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs
>  
> +ifneq ($(KBUILD_BUILD_TIMESTAMP),)
> +pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=reproducible_build
> +endif
> +
>  ifneq ($(KBUILD_EXTMOD),)
>  module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base
>  endif
> -- 
> 2.31.1
>