From: Markus Fritsche Date: Mon, 18 May 2026 11:42:00 +0200 Subject: [PATCH] arm64: xor-neon: restore -ffixed-x18 when SHADOW_CALL_STACK=y (GCC 15+ build fix) GCC 15.2.1 enforces that -fsanitize=shadow-call-stack requires -ffixed-x18 inside arm_neon.h's #pragma GCC target() blocks. The existing CFLAGS_REMOVE_xor-neon.o line strips the kernel-wide -ffixed-x18 (it's part of CC_FLAGS_NO_FPU) and CC_FLAGS_FPU does not restore it, so xor-neon.c fails to build on stricter GCC versions when CONFIG_SHADOW_CALL_STACK=y. Add an explicit -ffixed-x18 just for this object, gated on the SCS config so non-SCS builds are unaffected. Build environment workaround; not a kernel-runtime bug. --- arch/arm64/lib/Makefile | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile index 1234567..2345678 100644 --- a/arch/arm64/lib/Makefile +++ b/arch/arm64/lib/Makefile @@ -9,6 +9,10 @@ ifeq ($(CONFIG_KERNEL_MODE_NEON), y) obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o CFLAGS_xor-neon.o += $(CC_FLAGS_FPU) CFLAGS_REMOVE_xor-neon.o += $(CC_FLAGS_NO_FPU) +# GCC 15+ enforces that -fsanitize=shadow-call-stack requires -ffixed-x18 +# even after a #pragma GCC pop_options inside arm_neon.h. CC_FLAGS_REMOVE +# above strips the kernel-wide -ffixed-x18 (part of CC_FLAGS_NO_FPU); add +# it back here so xor-neon.c still compiles when SHADOW_CALL_STACK=y. +CFLAGS_xor-neon.o += $(if $(CONFIG_SHADOW_CALL_STACK),-ffixed-x18) endif lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o