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@xxxxxxxxxxxxx>
> > >
> > > 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
