From: George Guo <[email protected]>
On LoongArch, the klp relocation machinery redirects a livepatch's
reference to a core-kernel symbol through a GOT entry. klp-build extracts
the patched function into a separate module while the referenced symbol
stays in the core kernel, so the reference must be GOT-indirect for that
redirect to work. Two default compiler behaviours defeat this and make a
loaded livepatch module fault.
The first is a same-unit global (the syscall test patches sys_newuname()
in kernel/sys.c, which reads 'uts_sem', a rw_semaphore defined in the
same file). With CONFIG_RELOCATABLE=y the kernel is built -fPIE. For
a global defined in the same unit, -fPIE emits a direct PC-relative
reference (R_LARCH_PCALA_*) and skips the GOT, while -fPIC routes it
through the GOT (R_LARCH_GOT_PC_*). Once klp-build moves the patched
function into the livepatch module, the direct reference has no GOT
slot to redirect and faults.
The second is an extern global. -mdirect-extern-access replaces GOT-based
external symbol access with direct addressing. A livepatch reference to
such a symbol then has no GOT slot to fix up, and the wrong address faults
the kernel. This optimization was added by commit 38b10b269d04
("LoongArch: Tweak CFLAGS for Clang compatibility") as a nice-to-have that
reduces GOT accesses.
For LoongArch KLP builds, keep both forms GOT-indirect:
- Add -fPIC via KCFLAGS. -fPIE is not enough; it optimizes away the very
GOT indirection KLP relies on.
- Disable direct-extern-access: -mno-direct-extern-access for GCC,
-fno-direct-access-external-data for Clang.
Co-developed-by: Kexin Liu <[email protected]>
Signed-off-by: Kexin Liu <[email protected]>
Signed-off-by: George Guo <[email protected]>
---
scripts/livepatch/klp-build | 43 ++++++++++++++++++++++++++++++++++++-
1 file changed, 42 insertions(+), 1 deletion(-)
diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index e83973567c87..27463def08f8 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -278,6 +278,13 @@ validate_config() {
[[ -x "$OBJTOOL" ]] && "$OBJTOOL" klp 2>&1 | command grep -q "not
implemented" && \
die "objtool not built with KLP support; install
xxhash-devel/libxxhash-dev (version >= 0.8) and recompile"
+ if [[ -v CONFIG_LOONGARCH ]]; then
+ [[ -v CONFIG_AS_HAS_EXPLICIT_RELOCS ]] || \
+ die "LoongArch klp-build requires
CONFIG_AS_HAS_EXPLICIT_RELOCS=y"
+ [[ -v CONFIG_RELOCATABLE ]] || \
+ die "LoongArch klp-build requires CONFIG_RELOCATABLE=y"
+ fi
+
return 0
}
@@ -556,6 +563,31 @@ build_kernel() {
local log="$TMP_DIR/build.log"
local cmd=()
+ local ARCH_KBUILD_CFLAGS_KERNEL=""
+ local ARCH_KCFLAGS=""
+
+ # For KLP, LoongArch symbol references must stay GOT-indirect so the klp
+ # relocation machinery can redirect a cross-object reference through a
+ # GOT entry. Two default behaviours defeat that (CONFIG_RELOCATABLE and
+ # CONFIG_AS_HAS_EXPLICIT_RELOCS are checked in validate_config()):
+ #
+ # - -fPIE (added under CONFIG_RELOCATABLE) emits a direct PC-relative
+ # reference for a same-unit global and skips the GOT; -fPIC routes it
+ # through the GOT. Add -fPIC via KCFLAGS.
+ # - -mdirect-extern-access replaces GOT access for an extern global
with
+ # direct addressing. Disable it.
+ if [[ -v CONFIG_LOONGARCH ]]; then
+ ARCH_KCFLAGS="-fPIC"
+
+ if [[ "${CONFIG_CC_IS_CLANG:-}" == "y" ]]; then
+
ARCH_KBUILD_CFLAGS_KERNEL="-fno-direct-access-external-data"
+ else
+ ARCH_KBUILD_CFLAGS_KERNEL="-mno-direct-extern-access"
+ fi
+
+ status "LoongArch detected: adding $ARCH_KBUILD_CFLAGS_KERNEL
to KBUILD_CFLAGS_KERNEL"
+ fi
+
cmd=("make")
# When a patch to a kernel module references a newly created unexported
@@ -581,7 +613,16 @@ build_kernel() {
cmd+=("-s")
fi
cmd+=("-j$JOBS")
- cmd+=("KCFLAGS=-ffunction-sections -fdata-sections")
+ cmd+=("KCFLAGS=-ffunction-sections -fdata-sections${ARCH_KCFLAGS:+
$ARCH_KCFLAGS}")
+ # -fPIC is added for KLP via KCFLAGS above; the arch adds -fPIE via
+ # KBUILD_CFLAGS_KERNEL, which kbuild places after KCFLAGS on the
+ # built-in compile line. -fPIC/-fPIE is last-one-wins, so -fPIE would
+ # win. Setting KBUILD_CFLAGS_KERNEL on the command line replaces the
+ # arch value (not append), which drops -fPIE and lets -fPIC win. Only
+ # do this when an arch needs it (LoongArch).
+ if [[ -n "$ARCH_KBUILD_CFLAGS_KERNEL" ]]; then
+ cmd+=("KBUILD_CFLAGS_KERNEL=$ARCH_KBUILD_CFLAGS_KERNEL")
+ fi
cmd+=("vmlinux")
cmd+=("modules")
--
2.53.0
