On Thu, 2021-08-19 at 14:54 +0100, Colin Ian King wrote:
On 19/08/2021 14:51, Joe Perches wrote:
On Thu, 2021-08-19 at 14:38 +0100, Colin King wrote:
From: Colin Ian King colin.king@canonical.com
Don't populate the array ext_div on the stack but instead it static const. Makes the object code smaller by 118 bytes:
Before: text data bss dec hex filename 39449 17500 128 57077 def5 ./drivers/gpu/drm/bridge/tc358767.o
After: text data bss dec hex filename 39235 17596 128 56959 de7f ./drivers/gpu/drm/bridge/tc358767.o
Why is text smaller and data larger with this change?
There are less instructions being used with the change since it's not shoving the array data onto the stack at run time. Instead the array is being stored in the data section and there is less object code required to access the data.
Ah. It's really because it's not a minimal compilation ala defconfig.
I think you should really stop making these size comparisons with .config uses that are not based on a defconfig as a whole lot of other things are going on.
Please notice that the object sizes are significantly smaller below:
So with an x86-64 defconfig and this compilation unit enabled with CONFIG_OF enabled and CONFIG_DRM_TOSHIBA_TC358767=y, with gcc 10.3 and this change the object size actually increases a bit.
$ size drivers/gpu/drm/bridge/tc358767.o* text data bss dec hex filename 13554 268 1 13823 35ff drivers/gpu/drm/bridge/tc358767.o.new 13548 268 1 13817 35f9 drivers/gpu/drm/bridge/tc358767.o.old
objdump -h shows these differences:
.old: 0 .text 00001e1f 0000000000000000 0000000000000000 00000040 2**4 CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE [...] 14 .rodata 000005ae 0000000000000000 0000000000000000 000046e0 2**5 CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
.new: 0 .text 00001e05 0000000000000000 0000000000000000 00000040 2**4 CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE [...] 11 .rodata 000005ce 0000000000000000 0000000000000000 00004600 2**5 CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
cheers, Joe