Date: Wed, 23 Oct 2019 09:59:09 -0700 From: Sami Tolvanen <samitolvanen@...gle.com> To: Mark Rutland <mark.rutland@....com>, Masahiro Yamada <yamada.masahiro@...ionext.com> Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>, Nick Desaulniers <ndesaulniers@...gle.com>, clang-built-linux <clang-built-linux@...glegroups.com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 06/18] add support for Clang's Shadow Call Stack (SCS) On Tue, Oct 22, 2019 at 9:28 AM Mark Rutland <mark.rutland@....com> wrote: > I think it would be preferable to follow the example of CC_FLAGS_FTRACE > so that this can be filtered out, e.g. > > ifdef CONFIG_SHADOW_CALL_STACK > CFLAGS_SCS := -fsanitize=shadow-call-stack > KBUILD_CFLAGS += $(CFLAGS_SCS) > export CC_FLAGS_SCS > endif > > ... with removal being: > > CFLAGS_REMOVE := $(CC_FLAGS_SCS) > > ... or: > > CFLAGS_REMOVE_obj.o := $(CC_FLAGS_SCS) > > That way you only need to define the flags once, so the enable and > disable falgs remain in sync by construction. CFLAGS_REMOVE appears to be only implemented for objects, which means there's no convenient way to filter out flags for everything in arch/arm64/kvm/hyp, for example. I could add a CFLAGS_REMOVE separately for each object file, or we could add something like ccflags-remove-y to complement ccflags-y, which should be relatively simple. Masahiro, do you have any suggestions? Sami
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