[PATCH] ppc boot: replace string labels with numbers
Jerry Van Baren
gerald.vanbaren at smiths-aerospace.com
Fri Nov 18 09:54:25 EST 2005
Olaf Hering wrote:
> Replacing the string labels with numbers saves 117 bytes in the final zImage.
> These local labels are not discared.
> Signed-off-by: Olaf Hering <olh at suse.de>
> arch/powerpc/boot/crt0.S | 23 +++++++++++------------
> 1 files changed, 11 insertions(+), 12 deletions(-)
> Index: linux-2.6.15-rc1-olh/arch/powerpc/boot/crt0.S
> --- linux-2.6.15-rc1-olh.orig/arch/powerpc/boot/crt0.S
> +++ linux-2.6.15-rc1-olh/arch/powerpc/boot/crt0.S
> @@ -14,43 +14,42 @@
> .globl _zimage_start
> - bl reloc_offset
> + bl 1f
> mflr r0
> - lis r9,reloc_offset at ha
> - addi r9,r9,reloc_offset at l
> + lis r9,1b at ha
> + addi r9,r9,1b at l
> subf. r0,r9,r0
> - beq clear_caches
> + beq 3f
OK, I've waited for someone dumber than me to ask, but I guess I'm the
bottom guy on the totem pole here.
How does changing a local ascii label to a temporary label _but using
the same machine instructions_ affect the output image size???? Why
would "lis r9,reloc_offset at ha" generate a smaller (!) instruction than
"lis r9,1b at ha"????
My first thought was that the symbol section of the ELF output is
bigger, but the labels are not globals. Even if the local labels end up
in the symbol section (which the comment on the original patch message
sort of implies), that isn't going to make a (stripped) binary any
bigger. If that is the case, isn't a better cure to strip the ELF file?
While I'm being dumb, I gotta ask, how big is zImage and why does 117
bytes make a difference?
My 2c: if you are going to use inscrutable labels (1,2,3,4), please put
comments in. At least the previous labels gave hints as to what was
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