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Subject[PATCH v2 RESEND] kbuild: Enable armthumb BCJ filter for Thumb-2 kernel
Date
xz_wrap.sh use $SRCARCH to detect the BCJ filter. However, assigning
arm BCJ filter to Thumb-2 kernel is not optimal. In my case, about 5%
decrease of image size is observed with armthumb BCJ filter:

Test results:
hardware: QEMU emulator version 3.1.0
config: vexpress_defconfig with THUMB2_KERNEL & KERNEL_XZ on
arm BCJ: 4029808
armthumb BCJ: 3827280

Choose armthumb BCJ filter for Thumb-2 kernel to make smaller images.

Signed-off-by: Jubin Zhong <zhongjubin@huawei.com>
Acked-by: Lasse Collin <lasse.collin@tukaani.org>

----
v1:
https://lore.kernel.org/lkml/1637323647-19988-1-git-send-email-zhongjubin@huawei.com/
---
lib/decompress_unxz.c | 6 +++++-
scripts/xz_wrap.sh | 6 ++++++
2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/decompress_unxz.c b/lib/decompress_unxz.c
index 9f4262e..9d9cb48 100644
--- a/lib/decompress_unxz.c
+++ b/lib/decompress_unxz.c
@@ -129,7 +129,11 @@
# define XZ_DEC_POWERPC
#endif
#ifdef CONFIG_ARM
-# define XZ_DEC_ARM
+# ifdef CONFIG_THUMB2_KERNEL
+# define XZ_DEC_ARMTHUMB
+# else
+# define XZ_DEC_ARM
+# endif
#endif
#ifdef CONFIG_IA64
# define XZ_DEC_IA64
diff --git a/scripts/xz_wrap.sh b/scripts/xz_wrap.sh
index 76e9cbc..3824fdf 100755
--- a/scripts/xz_wrap.sh
+++ b/scripts/xz_wrap.sh
@@ -9,6 +9,8 @@
# You can do whatever you want with this file.
#

+. include/config/auto.conf
+
BCJ=
LZMA2OPTS=

@@ -20,4 +22,8 @@ case $SRCARCH in
sparc) BCJ=--sparc ;;
esac

+if [ -n "${CONFIG_THUMB2_KERNEL}" ]; then
+ BCJ=--armthumb
+fi
+
exec $XZ --check=crc32 $BCJ --lzma2=$LZMA2OPTS,dict=32MiB
--
1.8.5.6
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