linux-kernel - Re: [PATCH -v6 0/3] x86 boot: 32-bit boot protocol

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Date:	Tue, 23 Oct 2007 10:28:35 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <ak@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH -v6 0/3] x86 boot: 32-bit boot protocol

Hi, Peter,

On Mon, 2007-10-22 at 11:42 -0700, H. Peter Anvin wrote:
> This patchset should be rebased on top of Rusty's changes; the rebase is 
>   fairly trivial and I was originally intending to simply commit the 
> rebase as-is, with the boot protocol version bumped to 2.08.
> 
> However, the documentation section is simply wrong in a number of 
> places.  In particular:
> 
> +In 32-bit boot protocol, the first step in loading a Linux kernel
> +should still be to load the real-mode code and then examine the kernel
> +header at offset 0x01f1. But, it is not necessary to load all
> +real-mode code, just first 4K bytes traditionally known as "zero page"
> +is needed.
> 
> This is incorrect.  The zeropage (which really is better referred to as 
> struct boot_param) should be initialized to all zero, except for the 
> setup header (starting at offset 0x1f0 or 0x1f1(*)) to the length 
> specified either by boot protocol version or by the byte at offset 0x201.

I will change this.

> +At entry, the CPU must be in 32-bit protected mode with paging
> +disabled; the CS and DS must be 4G flat segments; %esi holds the base
> +address of the "zero page"; %esp, %ebp, %edi should be zero.
> 
> You also need to have a GDT loaded with the selectors for __BOOT_CS 
> (0x10) and __BOOT_DS (0x18) containing appropriate values, and you 
> should enter with interrupts disabled.  For safety, set up ES and SS as 
> well as DS.
> 
> The bit about %esp, %ebp and %edi being zero is nonsense, although 
> specifying at least %ebp == %edi == 0 for future use isn't a bad idea. 
> On the other hand, %ebx *is* supposed to be zero.

I will change this.

> The documentation in zero-page.txt is wrong when it comes to protocol 
> versions.  Most of these fields are ancient, and only a handful of the 
> remainder can be tied to specific protocol versions.

So, should the protocol of current fields be set to "ALL" as that of
setup header.

> +  struct setup_data {
> +	  u64 next;
> +	  u32 type;
> +	  u32 len;
> +	  u8  data[0];
> +  } __attribute__((packed));
> 
> Why packed?

I will change this.

> Time permitting, I might rewrite this myself, but it may be quicker for 
> you to update it.

OK, I will update it as soon as possible.

Best Regards,
Huang Ying
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