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SubjectRe: [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@linux.vnet.ibm.com>
>Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>


This patch looks good for me too,

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

I think Michal will take this into kbuild tree.

Thanks!


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