Re: How to define some additional KBUILD_CFLAGS after building include/generated/asm-offsets.h ?
From: Christophe LEROY <hidden>
Date: 2018-09-24 15:26:22
Also in:
linux-kbuild, lkml
Le 24/09/2018 à 14:10, Michael Ellerman a écrit :
quoted hunk ↗ jump to hunk
Christophe Leroy [off-list ref] writes:quoted
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. Christophe
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