[PATCH v2] kheaders: make it possible to override TAR

[Michał Górny]

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@xxxxxxxxxx>
Tested-by: Sam James <sam@xxxxxxxxxx>
Co-developed-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Michał Górny <mgorny@xxxxxxxxxx>
---
 Makefile               | 3 ++-
 kernel/gen_kheaders.sh | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 5aeea3d98..50045059c 100644
--- a/Makefile
+++ b/Makefile
@@ -520,6 +520,7 @@ LZMA		= lzma
 LZ4		= lz4c
 XZ		= xz
 ZSTD		= zstd
+TAR		= tar
 
 PAHOLE_FLAGS	= $(shell PAHOLE=$(PAHOLE) $(srctree)/scripts/pahole-flags.sh)
 
@@ -599,7 +600,7 @@ export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN CARGO
 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 LDFLAGS_MODULE
 export KBUILD_USERCFLAGS KBUILD_USERLDFLAGS
 
diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
index 1ef9a8751..82d539648 100755
--- a/kernel/gen_kheaders.sh
+++ b/kernel/gen_kheaders.sh
@@ -86,7 +86,7 @@ find $cpio_dir -type f -print0 |
 # For compatibility with older versions of tar, files are fed to tar
 # pre-sorted, as --sort=name might not be available.
 find $cpio_dir -printf "./%P\n" | LC_ALL=C sort | \
-    tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
+    ${TAR:-tar} "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
     --owner=0 --group=0 --numeric-owner --no-recursion \
     -I $XZ -cf $tarfile -C $cpio_dir/ -T - > /dev/null
 
-- 
2.40.0