linux-kernel - Re: [PATCH] arm64: Adjust EFI libstub object include logic

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Date:	Mon, 16 Mar 2015 10:48:30 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Steve Capper <steve.capper@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] arm64: Adjust EFI libstub object include logic

On 16 March 2015 at 10:30, Steve Capper <steve.capper@...aro.org> wrote:
> Commit f4f75ad5 ("efi: efistub: Convert into static library")
> introduced a static library for EFI stub, libstub.
>
> The EFI libstub directory is referenced by the kernel build system via
> a obj subdirectory rule in:
> drivers/firmware/efi/Makefile
>
> Unfortunately, arm64 also references the EFI libstub via:
> libs-$(CONFIG_EFI_STUB) += drivers/firmware/efi/libstub/
>
> If we're unlucky, the kernel build system can enter libstub via two
> simultaneous threads resulting in build failures such as:
>
> fixdep: error opening depfile: drivers/firmware/efi/libstub/.efi-stub-helper.o.d: No such file or directory
> scripts/Makefile.build:257: recipe for target 'drivers/firmware/efi/libstub/efi-stub-helper.o' failed
> make[1]: *** [drivers/firmware/efi/libstub/efi-stub-helper.o] Error 2
> Makefile:939: recipe for target 'drivers/firmware/efi/libstub' failed
> make: *** [drivers/firmware/efi/libstub] Error 2
> make: *** Waiting for unfinished jobs....
>
> This patch adjusts the arm64 Makefile to reference the compiled library
> explicitly (as is currently done in x86), rather than the directory.
>

The thing to note here is that x86 links the stub into the
decompressor, which is a separate binary.

So rather than descending into the directory for the second time due
to it having been included in libs-y, we will now be relying on the
fact that vmlinux depends on the [empty]
drivers/firmware/efi/libstub/builtin.o, the building of which will
always have as a side effect that drivers/firmware/efi/libstub/lib.a
is also built.
I think that is fine, but it is subtly different from x86

> Fixes: f4f75ad5 efi: efistub: Convert into static library
> Signed-off-by: Steve Capper <steve.capper@...aro.org>
> ---
>  arch/arm64/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 0666888..da226de 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -51,7 +51,7 @@ core-$(CONFIG_XEN) += arch/arm64/xen/
>  core-$(CONFIG_CRYPTO) += arch/arm64/crypto/
>  libs-y         := arch/arm64/lib/ $(libs-y)
>  libs-y         += $(LIBGCC)
> -libs-$(CONFIG_EFI_STUB) += drivers/firmware/efi/libstub/
> +core-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
>
>  # Default target when executing plain make
>  KBUILD_IMAGE   := Image.gz
> --
> 2.1.0
>
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