[PATCH] kheaders: prefer gtar over tar for better compatibility

[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.

To achieve better portability, try using `gtar` over `tar` if the former
is available.  This is the name frequently used on systems featuring
support for installing GNU tar alongside another tar implementation.
If `gtar` is not present, `tar` is used for compatibility with regular
systems.

Link: https://bugs.gentoo.org/884061
Reported-by: Sam James <sam@xxxxxxxxxx>
Tested-by: Sam James <sam@xxxxxxxxxx>
Signed-off-by: Michał Górny <mgorny@xxxxxxxxxx>
---
 kernel/gen_kheaders.sh | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
index 473036b43..d2445af7f 100755
--- a/kernel/gen_kheaders.sh
+++ b/kernel/gen_kheaders.sh
@@ -80,11 +80,20 @@ done | cpio --quiet -pdu $cpio_dir >/dev/null 2>&1
 find $cpio_dir -type f -print0 |
 	xargs -0 -P8 -n1 perl -pi -e 'BEGIN {undef $/;}; s/\/\*((?!SPDX).)*?\*\///smg;'
 
+# The following tar invocations use options specific to GNU tar. On some
+# systems (e.g. Gentoo), `tar` can be a different tool (e.g. bsdtar), and GNU
+# tar can be found as `gtar`.
+if [ -x "$(command -v gtar)" ]; then
+	tar=gtar
+else
+	tar=tar
+fi
+
 # Create archive and try to normalize metadata for reproducibility.
 # 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}" \
+    $tar "${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
 
-- 
2.39.0