linux-kernel - Re: [PATCH 4/6] arm64: add EFI stub

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Message-ID: <CAFECyb_S8-n_rAKgKOzc9c6uiSo3oiLe=TfNWBsH=uynJo4pkA@mail.gmail.com>
Date:	Tue, 14 Jan 2014 11:26:58 -0800
From:	Roy Franz <roy.franz@...aro.org>
To:	Mark Salter <msalter@...hat.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Matt Fleming <matt.fleming@...el.com>,
	Patch Tracking <patches@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>
Subject: Re: [PATCH 4/6] arm64: add EFI stub

On Tue, Jan 14, 2014 at 6:44 AM, Mark Salter <msalter@...hat.com> wrote:
> On Mon, 2014-01-13 at 19:49 +0100, Arnd Bergmann wrote:
>> On Friday 10 January 2014, Mark Salter wrote:
>> > This patch adds PE/COFF header fields to the start of the Image
>> > so that it appears as an EFI application to EFI firmware. An EFI
>> > stub is included to allow direct booting of the kernel Image. Due
>> > to EFI firmware limitations, only little endian kernels with 4K
>> > page sizes are supported at this time. Support in the COFF header
>> > for signed images was provided by Ard Biesheuvel.
>> >
>> > Signed-off-by: Mark Salter <msalter@...hat.com>
>> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>>
>> You got the ordering of the S-o-b lines wrong. Since you send the
>> patch, your name should come last.
>
> Yes.
>
>>
>> > +config EFI_STUB
>> > +     bool "EFI stub support"
>> > +     depends on !ARM64_64K_PAGES && OF
>> > +     select LIBFDT
>> > +     default y
>> > +     help
>> > +       This kernel feature allows an Image to be loaded directly
>> > +       by EFI firmware without the use of a bootloader.
>> > +       See Documentation/efi-stub.txt for more information.
>> > +
>> >  endmenu
>>
>> Why not ARM64_64K_PAGES? I thought that it was going to be the
>> default for a lot of distros that would need to run on UEFI systems.
>
> The UEFI spec currently mandates 4k page size. We may be able to work
> around that or get the spec changed, but for now it is just 4k pages.
>
>>
>> >  menu "Userspace binary formats"
>> > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
>> > index 5ba2fd4..1c52b84 100644
>> > --- a/arch/arm64/kernel/Makefile
>> > +++ b/arch/arm64/kernel/Makefile
>> > @@ -4,6 +4,8 @@
>> >
>> >  CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET)
>> >  AFLAGS_head.o                := -DTEXT_OFFSET=$(TEXT_OFFSET)
>> > +CFLAGS_efi-stub.o    := -DTEXT_OFFSET=$(TEXT_OFFSET) \
>> > +                        -I$(src)/../../../scripts/dtc/libfdt
>>
>> Hmm, this is pretty ugly. I notice the same has been done on MIPS
>> as well, but I'd hope we can find a proper way to do it.
>
> Yes, I just copied that from mips. I can look into some more.
>
>>
>> > diff --git a/arch/arm64/kernel/efi-stub.c b/arch/arm64/kernel/efi-stub.c
>> > new file mode 100644
>> > index 0000000..10d02bf
>> > --- /dev/null
>> > +++ b/arch/arm64/kernel/efi-stub.c
>> > +
>> > +/* Include shared EFI stub code */
>> > +#include "../../../drivers/firmware/efi/efi-stub-helper.c"
>> > +#include "../../../drivers/firmware/efi/fdt.c"
>>
>> It gets worse here.
>
> Well, I'm open to suggestions here. The shared code has to work with
> stubs which are built into kernel (arm64) and which are part of the
> compressed image wrapper.
>

The decompression algorithms are shared among the compressed image
wrappers using #include of C code, so this is
following that convention.  The only other mechanism that I saw for
sharing code with the compressed image wrappers was
copying of files, as is done with the FDT files for the ARM compressed
wrapper.  I agree that neither of these is elegant, but
whatever we do needs to work for compiling into the decompression
wrapper (arm) and the kernel proper (arm64).

Roy
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