Christophe LEROY <christophe.leroy@xxxxxx> writes: > Le 24/09/2018 à 14:10, Michael Ellerman a écrit : >> 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)) >> + > > Great, it works ! > Thanks, I have sent v3 of the patches. Cool. It would be good to here from someone who knows Kbuild better than me if this is acceptable or just a gross hack :) cheers