linux-kernel - Re: [PATCH 5/5] x86_64 EFI support -v3: EFI document

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Message-ID: <m1r6mnnpj8.fsf@ebiederm.dsl.xmission.com>
Date:	Wed, 01 Aug 2007 11:16:43 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	ak@...e.de, akpm@...ux-foundation.org,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] x86_64 EFI support -v3: EFI document

"Huang, Ying" <ying.huang@...el.com> writes:

> On Mon, 2007-07-30 at 22:40 -0600, Eric W. Biederman wrote:
>> "Huang, Ying" <ying.huang@...el.com> writes:
>> 
>> > This patch adds document for EFI x86_64 support. The boot parameters
>> > added are documented in Documentation/i386/zero-page.txt. The setup
>> > and operation guide of EFI based system is documented in
>> > Documentation/x86_64/uefi.txt.
>> >
>> > Signed-off-by: Chandramouli Narayanan <mouli@...ux.intel.com>
>> > Signed-off-by: Huang Ying <ying.huang@...el.com>
>> >
>> > ---
>> >
>> >  i386/zero-page.txt |   18 ++++++++++++++----
>> >  x86_64/uefi.txt    |   42 ++++++++++++++++++++++++++++++++++++++++++
>> >  2 files changed, 56 insertions(+), 4 deletions(-)
>> >
>> > Index: linux-2.6.23-rc1/Documentation/i386/zero-page.txt
>> > ===================================================================
>> > --- linux-2.6.23-rc1.orig/Documentation/i386/zero-page.txt 2007-07-30
>> > 11:28:45.000000000 +0800
>> > +++ linux-2.6.23-rc1/Documentation/i386/zero-page.txt 2007-07-30
>> > 11:29:28.000000000 +0800
>> > @@ -31,11 +31,11 @@
>> > 0xb0 - 0x13f Free. Add more parameters here if you really need them.
>> >   0x140- 0x1be		EDID_INFO Video mode setup
>> >  
>> > -0x1c4	unsigned long	EFI system table pointer
>> > -0x1c8	unsigned long	EFI memory descriptor size
>> > -0x1cc	unsigned long	EFI memory descriptor version
>> > +0x1c4	unsigned long	EFI system table pointer*
>> > +0x1c8	unsigned long	EFI memory descriptor size*
>> > +0x1cc	unsigned long	EFI memory descriptor version*
>> >  0x1d0	unsigned long	EFI memory descriptor map pointer
>> > -0x1d4	unsigned long	EFI memory descriptor map size
>> > +0x1d4	unsigned long	EFI memory descriptor map size*
>> >  0x1e0	unsigned long	ALT_MEM_K, alternative mem check, in Kb
>> >  0x1e4	unsigned long	Scratch field for the kernel setup code
>> >  0x1e8	char		number of entries in E820MAP (below)
>> > @@ -87,3 +87,13 @@
>> >  0x2d0 - 0xd00		E820MAP
>> >  0xd00 - 0xeff		EDDBUF (edd.S) for disk signature read sector
>> >  0xd00 - 0xeeb		EDDBUF (edd.S) for edd data
>> > +
>> > +Changes for x86_64 implementation:
>> > +---------------------------------
>> > +For alignment purposes, the following parameters are rearranged.
>> > +
>> > +0x1b8	unsigned long	EFI system table pointer
>> > +0x1c0	unsigned long	EFI Loader signature
>> > +0x1c4	unsigned long	EFI memory descriptor size
>> > +0x1c8	unsigned long	EFI memory descriptor version
>> > +0x1cc	unsigned long	EFI memory descriptor map size
>> 
>> Huh?  It is the same protocol.  Unless there are specific issues such
>> as pointers being to small we should remain 100% the same for both
>> arch/i386 and arch/x86_64   This variation looks like a serious
>> bug.
>
> The parameters are rearranged, because the pointer is too small. For
> example, the EFI system table pointer is 8 bytes in x86_64, while it is
> 4 bytes in i386.

Ok.  I see what is happening.  When the documentation is for arch/i386
unsigned long is 4 bytes, and you are using unsigned long to mean 8
bytes.  For an 8 byte fields please just spell out the size as 8
bytes.

How does EFI handle 32bit/64bit compatibility?  In particular
how do I load a 32bit kernel on machine with a 64bit EFI?  Can
it be done?

Eric
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