From: George Guo <[email protected]> On LoongArch, klp-build livepatch modules panic when a patched function references a global defined in the same compilation unit (e.g. SYSCALL_DEFINE1(newuname) -> 'uts_sem' in kernel/sys.c).
With CONFIG_RELOCATABLE=y the kernel is already -fPIE, so this is not absolute addressing; the problem is GOT indirection. For a same-unit global, -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_*). klp-build extracts the patched function into a separate module while 'uts_sem' stays in the core kernel, and the klp relocation machinery can only redirect such a cross-object reference through a GOT entry. The direct -fPIE reference has no GOT slot to fix up, so once the function is relocated its target is wrong and it faults. Force -fPIC for LoongArch KLP builds; -fPIE is not enough, as it optimizes away the very GOT indirection KLP relies on. This depends on the preceding patch: -fPIC is passed via KCFLAGS, but the arch adds -fPIE via KBUILD_CFLAGS_KERNEL, which kbuild applies after KCFLAGS (so -fPIE would win). That patch's command-line KBUILD_CFLAGS_KERNEL= assignment replaces the arch value and drops -fPIE, letting -fPIC take effect. The two patches must stay together. 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 | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build index 27fe8824ef12..42cd58aff3d8 100755 --- a/scripts/livepatch/klp-build +++ b/scripts/livepatch/klp-build @@ -557,8 +557,15 @@ build_kernel() { local cmd=() local ARCH_KBUILD_CFLAGS_KERNEL="" + local ARCH_KCFLAGS="" if [[ -v CONFIG_LOONGARCH && "$CONFIG_LOONGARCH" == "y" ]]; then + # -fPIC replaces the kernel's -fPIE (added under CONFIG_RELOCATABLE); + # without that config there is no -fPIE to replace. + [[ "${CONFIG_RELOCATABLE:-}" == "y" ]] || \ + die "LoongArch klp-build requires CONFIG_RELOCATABLE=y" + ARCH_KCFLAGS="-fPIC" + # -mdirect-extern-access only exists under explicit relocs, and this # function replaces KBUILD_CFLAGS_KERNEL wholesale (safe only then; # the non-explicit build puts -Wa,-mla-global-with-pcrel there). @@ -599,8 +606,16 @@ build_kernel() { cmd+=("-s") fi cmd+=("-j$JOBS") - cmd+=("KCFLAGS=-ffunction-sections -fdata-sections") - cmd+=("KBUILD_CFLAGS_KERNEL=$ARCH_KBUILD_CFLAGS_KERNEL") + 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") -- 2.25.1
