linux-kernel - Re: [PATCH v5 03/19] x86, boot: Simplify run

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Date:	Mon, 23 Mar 2015 00:12:13 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Baoquan He <bhe@...hat.com>
Cc:	Matt Fleming <matt.fleming@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Junjie Mao <eternal.n08@...il.com>,
	Josh Triplett <josh@...htriplett.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 03/19] x86, boot: Simplify run_size calculation

On Sun, Mar 22, 2015 at 8:25 PM, Baoquan He <bhe@...hat.com> wrote:
>
> This may not be correct. In commit e602336
> runsize = offset(.bss) + size(.bss) + size(.brk), why this formula comes
> out can be checked from discussion between Kees and Junjie:
> https://lkml.org/lkml/2014/10/30/612
>
> And in my one kernel build the related values are:
> -) objdump -h vmlinux
> vmlinux:     file format elf64-x86-64
>
> Sections:
> Idx Name          Size      VMA               LMA               File off
> Algn
>  27 .bss          00167000  ffffffff81e92000  0000000001e92000  01292000
> 2**12
>                   ALLOC
>  28 .brk          00027000  ffffffff81ff9000  0000000001ff9000  01292000
> 2**0
>                   ALLOC
>
> run_size on old calculation is
> 0x01292000+0x00167000+0x00027000=0x1420000
>
> -) nm vmlinux
> ffffffff81000000 T _text
> ffffffff82020000 B _end
>
> run_size on your method is 0x82020000 - 0x81000000 = 0x1020000
>
> So if output_len which is the length of vmlinux.bin + vmlinux.relocs is
> between the old run_size and your new run_size, the problem Junjie tried
> to fix will happen again.

no. We should not use file offset in the elf for run_size.
when the section can not fill 2M, use file offset will get not needed
extra size.

parse_elf will move sections forward according to program headers.

Thanks

Yinghai
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