linux-kernel - Re: [PATCH] x86: tell the world boot

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Date:	Fri, 08 May 2015 09:26:49 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Borislav Petkov <bp@...en8.de>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: tell the world boot_params is 16-byte aligned

NAK.  This could break in the case of careless bootloaders...

On May 8, 2015 9:23:52 AM PDT, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
>On Fri, May 08 2015, Borislav Petkov <bp@...en8.de> wrote:
>
>> On Fri, May 08, 2015 at 03:42:33PM +0200, Rasmus Villemoes wrote:
>>> It doesn't matter much, but this disassembly makes me cry a little
>bit:
>>> 
>>> ffffffff81f21223 <copy_bootdata>:
>>> ffffffff81f21223:       55                      push   %rbp
>>> ffffffff81f21224:       48 c7 c0 40 c2 02 82    mov   
>$0xffffffff8202c240,%rax
>>> ffffffff81f2122b:       48 89 fe                mov    %rdi,%rsi
>>> ffffffff81f2122e:       a8 01                   test   $0x1,%al
>>> 
>>> The reason is that boot_params is defined with
>>> __attribute__((aligned(16))) in boot/main.c, but other translation
>>> units only see the packed attribute on the definition of struct
>>> boot_params, so assume the worst. Making the de facto alignment
>public
>>
>> Wouldn't it be better if we put both attributes together, i.e.:
>
>Sure, putting it on the type works as well. Either way is fine with me.
>
>Rasmus

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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