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SubjectRe: [PATCH] arch/x86/boot: use prefix map to avoid embedded paths
Don't forget to CC: lkml and x86@kernel.org on x86 patches.

On Thu, Sep 26, 2019 at 10:11:32AM +0100, Ross Burton wrote:
> From: Bruce Ashfield <bruce.ashfield@gmail.com>
>
> It was observed that the kernel embeds the path in the x86 boot
> artifacts.
>
> From https://bugzilla.yoctoproject.org/show_bug.cgi?id=13458:
>
> [
> If you turn on the buildpaths QA test, or try a reproducible build, you
> discover that the kernel image contains build paths.
>
> $ strings bzImage-5.0.19-yocto-standard |grep tmp/
> out of pgt_buf in
> /data/poky-tmp/reproducible/tmp/work-shared/qemux86-64/kernel-source/arch/x86/boot/compressed/kaslr_64.c!?
>
> But what's this in the top-level Makefile:
>
> $ git grep prefix-map
> Makefile:KBUILD_CFLAGS += $(call
> cc-option,-fmacro-prefix-map=$(srctree)/=)
>
> So the __FILE__ shouldn't be using the full path. However
> arch/x86/boot/compressed/Makefile has this:
>
> KBUILD_CFLAGS := -m$(BITS) -O2
>
> So that clears KBUILD_FLAGS, removing the -fmacro-prefix-map option.
> ]
>
> Other architectures do not clear the flags, but instead prune before
> adding boot or specific options. There's no obvious reason why x86 isn't
> doing the same thing (pruning vs clearing) and no build or boot issues
> have been observed.
>
> So we make x86 can do the same thing, and we no longer have embedded paths.
>
> Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
> Signed-off-by: Ross Burton <ross.burton@intel.com>
> ---
> arch/x86/boot/compressed/Makefile | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 6b84afdd7538..b246f18c5857 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -38,6 +38,7 @@ KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
> KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> KBUILD_CFLAGS += -Wno-pointer-sign
> +KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
>
> KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> GCOV_PROFILE := n
> --

What about arch/x86/boot/Makefile ?

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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