linux-kernel - Re: [PATCH 2/2] initramfs: Fix initramfs size calculation

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Date:	Wed, 1 Sep 2010 15:47:21 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Cc:	mmarek@...e.cz, Sam Ravnborg <sam@...nborg.org>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	tabbott@...lice.com, vda.linux@...glemail.com, hpa@...ux.intel.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	heiko.carstens@...ibm.com, schwidefsky@...ibm.com
Subject: Re: [PATCH 2/2] initramfs: Fix initramfs size calculation

On Tue, Aug 31, 2010 at 10:23:09AM +0200, Hendrik Brueckner wrote:
>The size of a built-in initramfs is calculated in init/initramfs.c by 
>"__initramfs_end - __initramfs_start".  Those symbols are defined in the
>linker script include/asm-generic/vmlinux.lds.h:
>
>#define INIT_RAM_FS                                                     \
>        . = ALIGN(PAGE_SIZE);                                           \
>        VMLINUX_SYMBOL(__initramfs_start) = .;                          \
>        *(.init.ramfs)                                                  \
>        VMLINUX_SYMBOL(__initramfs_end) = .;
>
>If the initramfs file has an odd number of bytes, the "__initramfs_end"
>symbol points to an odd address, for example, the symbols in the System.map
>might look like:
>
>    0000000000572000 T __initramfs_start
>    00000000005bcd05 T __initramfs_end	  <-- odd address
>
>At least on s390 this causes a problem:
>
>Certain s390 instructions, especially instructions for loading addresses
>(larl) or branch addresses must be on even addresses. 
>The compiler loads the symbol addresses with the "larl" instruction. This
>instruction sets the last bit to 0 and, therefore, for odd size files, the
>calculated size is one byte less than it should be:
>
>    0000000000540a9c <populate_rootfs>:
>      540a9c:     eb cf f0 78 00 24       stmg    %r12,%r15,120(%r15),
>      540aa2:     c0 10 00 01 8a af       larl    %r1,572000 <__initramfs_start>
>      540aa8:     c0 c0 00 03 e1 2e       larl    %r12,5bcd04 <initramfs_end>
>                                                  (Instead of  5bcd05)
>      ...
>      540abe:     1b c1                   sr      %r12,%r1
>
>To fix the problem, this patch introduces the global variable
>__initramfs_size, which is calculated in the "usr/initramfs_data.S" file.
>The populate_rootfs() function can then use the start marker of the
>.init.ramfs section and the value of __initramfs_size for loading the
>initramfs.  Because the start marker and size is sufficient, the
>__initramfs_end symbol is no longer needed and is removed.
>
>Signed-off-by: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
>Signed-off-by: Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>


This patch looks good for me too,

Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>

I think Michal will take this into kbuild tree.

Thanks!
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