linux-kernel - Re: [PATCH v3] kheaders: make it possible to override TAR

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Message-ID: <20250719201002.GA3285766@ax162>
Date: Sat, 19 Jul 2025 16:10:02 -0400
From: Nathan Chancellor <nathan@...nel.org>
To: Sam James <sam@...too.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	linux-kbuild@...r.kernel.org,
	Michał Górny <mgorny@...too.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] kheaders: make it possible to override TAR

On Sat, Jul 19, 2025 at 04:24:05PM +0100, Sam James wrote:
> From: Michał Górny <mgorny@...too.org>
> 
> Commit 86cdd2fdc4e39c388d39c7ba2396d1a9dfd66226 ("kheaders: make headers
> archive reproducible") introduced a number of options specific to GNU
> tar to the `tar` invocation in `gen_kheaders.sh` script.  This causes
> the script to fail to work on systems where `tar` is not GNU tar.  This
> can occur e.g. on recent Gentoo Linux installations that support using
> bsdtar from libarchive instead.
> 
> Add a `TAR` make variable to make it possible to override the tar
> executable used, e.g. by specifying:
> 
>   make TAR=gtar
> 
> Link: https://bugs.gentoo.org/884061
> Reported-by: Sam James <sam@...too.org>
> Tested-by: Sam James <sam@...too.org>
> Co-developed-by: Masahiro Yamada <masahiroy@...nel.org>
> Signed-off-by: Michał Górny <mgorny@...too.org>
> Signed-off-by: Sam James <sam@...too.org>
> ---

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

I assume that other places that call tar within the build process are
not problematic because they do not use GNU specific options, such as
scripts/Makefile.package and scripts/package/install-extmod-build, or
maybe that people just have not tried building those packages with
bsdtar?

> v3: Rebase, cover more tar instances.
> 
>  Makefile               | 3 ++-
>  kernel/gen_kheaders.sh | 6 +++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index c09766beb7eff..22d6037d738fe 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -543,6 +543,7 @@ LZMA		= lzma
>  LZ4		= lz4
>  XZ		= xz
>  ZSTD		= zstd
> +TAR		= tar
>  
>  CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
>  		  -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)
> @@ -622,7 +623,7 @@ export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN
>  export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
>  export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
>  export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
> -export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD
> +export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD TAR
>  export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS KBUILD_PROCMACROLDFLAGS LDFLAGS_MODULE
>  export KBUILD_USERCFLAGS KBUILD_USERLDFLAGS
>  
> diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
> index c9e5dc068e854..bb609a9ed72b4 100755
> --- a/kernel/gen_kheaders.sh
> +++ b/kernel/gen_kheaders.sh
> @@ -66,13 +66,13 @@ if [ "$building_out_of_srctree" ]; then
>  		cd $srctree
>  		for f in $dir_list
>  			do find "$f" -name "*.h";
> -		done | tar -c -f - -T - | tar -xf - -C "${tmpdir}"
> +		done | ${TAR:-tar} -c -f - -T - | ${TAR:-tar} -xf - -C "${tmpdir}"
>  	)
>  fi
>  
>  for f in $dir_list;
>  	do find "$f" -name "*.h";
> -done | tar -c -f - -T - | tar -xf - -C "${tmpdir}"
> +done | ${TAR:-tar} -c -f - -T - | ${TAR:-tar} -xf - -C "${tmpdir}"
>  
>  # Always exclude include/generated/utsversion.h
>  # Otherwise, the contents of the tarball may vary depending on the build steps.
> @@ -88,7 +88,7 @@ xargs -0 -P8 -n1 \
>  rm -f "${tmpdir}.contents.txt"
>  
>  # Create archive and try to normalize metadata for reproducibility.
> -tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
> +${TAR:-tar} "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
>      --owner=0 --group=0 --sort=name --numeric-owner --mode=u=rw,go=r,a+X \
>      -I $XZ -cf $tarfile -C "${tmpdir}/" . > /dev/null
>  
> -- 
> 2.50.1
>