[PATCH 4/8] livepatch/klp-build: disable direct-extern-access for LoongArch to fix kernel panic

[George Guo <dongtai.guo@linux.dev>]

From: George Guo <guodongtai@kylinos.cn>

On LoongArch systems, livepatch modules containing references to
EXTERNAL global variables trigger kernel panics when the core kernel is
built with the -mdirect-extern-access optimization.

Root cause:
The -mdirect-extern-access optimization replaces GOT-based external
symbol access with direct addressing for improved performance. However,
this breaks the kernel module loading mechanism, which relies on GOT
entries for proper relocation of EXTERNAL symbol references. Direct
access to global variables from livepatch modules causes invalid memory
accesses and kernel panics.

Solution:
For LoongArch klp builds, conditionally disable direct-extern-access by
adding:
- -mno-direct-extern-access for GCC builds
- -fno-direct-access-external-data for Clang builds

See also commit 38b10b269d04 ("LoongArch: Tweak CFLAGS for Clang
compatibility"), which added -mdirect-extern-access to the kernel as a
nice-to-have optimization that reduces GOT accesses.

Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 scripts/livepatch/klp-build | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index e83973567c87..529437d75346 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -542,6 +542,17 @@ fix_patches() {
 
 clean_kernel() {
 	local cmd=()
+	local ARCH_KBUILD_CFLAGS_KERNEL=""
+
+	if [[ -v CONFIG_LOONGARCH && "$CONFIG_LOONGARCH" == "y" ]]; then
+		if [[ -n "$CONFIG_CC_IS_CLANG" ]]; then
+			ARCH_KBUILD_CFLAGS_KERNEL="-fno-direct-access-external-data"
+		else
+			ARCH_KBUILD_CFLAGS_KERNEL="-mno-direct-extern-access"
+		fi
+
+		status "LoongArch detected: adding $ARCH_KBUILD_CFLAGS_KERNEL to KBUILD_CFLAGS_KERNEL"
+	fi
 
 	cmd=("make")
 	cmd+=("--silent")
@@ -582,6 +593,7 @@ build_kernel() {
 	fi
 	cmd+=("-j$JOBS")
 	cmd+=("KCFLAGS=-ffunction-sections -fdata-sections")
+	cmd+=("KBUILD_CFLAGS_KERNEL=$ARCH_KBUILD_CFLAGS_KERNEL")
 	cmd+=("vmlinux")
 	cmd+=("modules")
 
-- 
2.25.1