[U-Boot] Making U-Boot smaller

[Eugeniu Rosca]

Hi Tom,

On Wed, May 22, 2019 at 11:09:54AM -0400, Tom Rini wrote:
> On Wed, May 22, 2019 at 04:15:47PM +0200, Eugeniu Rosca wrote:
> > cc: Yamada-san
> > 
> > I dream of a (Kconfig/Kbuild-assisted) bloaty-like output [1] which
> > would point out the culprit configs. This is hardly achievable, but
> > looks good on the paper!
> > 
> >       CONFIG           FILE SIZE
> >   ------------       --------------
> >   CONFIG_FEATURE_A    10.7Mi  37.1%
> >   CONFIG_FEATURE_B    5.39Mi  18.6%
> >   CONFIG_FEATURE_C    4.48Mi  15.5%
> >   CONFIG_FEATURE_D    1.86Mi   6.4%
> >   CONFIG_FEATURE_E    1.67Mi   5.8%
> >   CONFIG_FEATURE_F    1.61Mi   5.6%
> >   CONFIG_FEATURE_G     856Ki   2.9%
> >   CONFIG_FEATURE_H     470Ki   1.6%
> >   ....
> >   TOTAL               28.9Mi 100.0%
> > 
> > [1] https://github.com/google/bloaty
> 
> This is relatively easy to do today, with buildman and a local commit to
> enable/disable CONFIG_FEATURE_A.

Being a valid choice doesn't make it necessarily appealing, especially
with 512 [1] configurations enabled in sandbox and knowing that U-Boot
is not really randconfig-grade [2] (the latter is being improved).

What I was alluding to is embedding the Kconfig symbol names into the
ELF objects, such that utilities like 'nm' (currently producing a nice
output of symbol sizes [3]) can also be made capable to report the exact
Kconfig symbols contributing to the size of the objects passed as input.
That would be, in my opinion, mind-blowingly useful.

[1] grep "CONFIG.*=" .config | wc -l
512

[2] https://patchwork.ozlabs.org/patch/1074420/

[3] nm --print-size --size-sort --radix=d ./drivers/clk/clk-uclass.o
0000000000000421 0000000000000024 T clk_free
0000000000000961 0000000000000027 T clk_disable
0000000000000888 0000000000000027 T clk_enable
0000000000000000 0000000000000027 T clk_request
0000000000000503 0000000000000027 T clk_set_parent
0000000000000445 0000000000000029 T clk_get_rate
0000000000000474 0000000000000029 T clk_set_rate
...

-- 
Best regards,
Eugeniu.