Hi. 2018-09-25 10:16 GMT+09:00 Michael Ellerman <mpe@xxxxxxxxxxxxxx>: > 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 :) I am fine with this solution. Thanks. -- Best Regards Masahiro Yamada