Christophe Leroy <christophe.leroy@xxxxxx> writes: > I'm trying to implement TLS based stack protector in the Linux Kernel. > For that I need to give to GCC the offset at which it will find the > canary (register r2 is pointing to the current task struct). > > I have been able to do it with the below patch, but it only works when > include/generated/asm-offsets.h already exists from the start of the build. > > Is there a way to evaluate CANARY_OFFSET and add the stack-protector > flags to KBUILD_FLAGS only after include/generated/asm-offsets.h is built ? > > Or another way of add -mstack-protector-guard-offset=offsetof(struct > task_struct, stack_canary) ? This seems to work, at least I see the value in CFLAGS: diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index 07d9dce..39ee113 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -404,6 +394,11 @@ archclean: archprepare: checkbin +prepare: stack_protector_prepare + +stack_protector_prepare: prepare0 + $(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TSK_STACK_CANARY") print $$3;}' include/generated/asm-offsets.h)) + # Use the file '.tmp_gas_check' for binutils tests, as gas won't output # to stdout and these checks are run even on install targets. TOUT := .tmp_gas_check cheers