linux-kernel - Re: [PATCH 1/2] kbuild: remove cc-option test of -fno-stack-protector

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Date:   Fri, 26 Jun 2020 13:37:00 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kbuild: remove cc-option test of -fno-stack-protector

On Fri, Jun 26, 2020 at 01:25:27PM -0700, Nick Desaulniers wrote:
> Ah, right. Thanks for pointing that out.  I'm still curious if the
> CFLAGS_<file>.o rules get appended or overwrite all flags for that
> translation unit?

CFLAGS_file.o gets appended to the CFLAGS. For example, after my updated
patch[1], the command line for syscall_64.o looks like this:

gcc -Wp,-MMD,arch/x86/entry/.syscall_64.o.d  -nostdinc -isystem \
...
-Wframe-larger-than=2048 -fstack-protector-strong \
...
-fno-stack-protector -Wno-override-init \
-DKBUILD_MODFILE='"arch/x86/entry/syscall_64"' \
-DKBUILD_BASENAME='"syscall_64"' \
-DKBUILD_MODNAME='"syscall_64"' \
-c -o arch/x86/entry/syscall_64.o \
arch/x86/entry/syscall_64.c

-Kees

[1] https://lore.kernel.org/lkml/202006261333.585319CA6B@keescook/

-- 
Kees Cook