[U-Boot] [PATCH 2/2] SPL: Allow ARM926EJS to avoid compiling in the CPU support code

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Le 22/10/2011 03:20, Marek Vasut a ?crit :
> On Saturday, October 22, 2011 02:41:54 AM Albert ARIBAUD wrote:
>> Le 22/10/2011 02:19, Marek Vasut a ?crit :
>>> On Saturday, October 22, 2011 02:04:52 AM Tom Rini wrote:
>>>> On Fri, Oct 21, 2011 at 4:45 PM, Marek Vasut<marek.vasut@gmail.com>   wrote:
>>>>> On Saturday, October 22, 2011 01:08:43 AM Albert ARIBAUD wrote:
>>>>>> Le 22/10/2011 00:46, Marek Vasut a ?crit :
>>>>>>> On Saturday, October 22, 2011 12:44:06 AM Albert ARIBAUD wrote:
>>>>>>>> Le 22/10/2011 00:00, Marek Vasut a ?crit :
>>>>>>>>> On Friday, October 21, 2011 11:52:23 PM Albert ARIBAUD wrote:
>>>>>>>>>> Hi Marek,
>>>>>>>>>>
>>>>>>>>>> Le 21/10/2011 22:44, Marek Vasut a ?crit :
>>>>>>>>>>> On Thursday, October 06, 2011 02:13:26 AM Marek Vasut wrote:
>>>>>>>>>>>> This allows the SPL to avoid compiling in the CPU support code.
>>>>>>>>>>>>
>>>>>>>>>>>> Signed-off-by: Marek Vasut<marek.vasut@gmail.com>
>>>>>>>>>>>> Cc: Stefano Babic<sbabic@denx.de>
>>>>>>>>>>>> Cc: Wolfgang Denk<wd@denx.de>
>>>>>>>>>>>> Cc: Detlev Zundel<dzu@denx.de>
>>>>>>>>>>>> Cc: Scott Wood<scottwood@freescale.com>
>>>>>>>>>>>> ---
>>>>>>>>>>>>
>>>>>>>>>>>>       arch/arm/cpu/arm926ejs/Makefile |    7 +++++++
>>>>>>>>>>>>       1 files changed, 7 insertions(+), 0 deletions(-)
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/arch/arm/cpu/arm926ejs/Makefile
>>>>>>>>>>>> b/arch/arm/cpu/arm926ejs/Makefile index 930e0d1..3f9b0f1 100644
>>>>>>>>>>>> --- a/arch/arm/cpu/arm926ejs/Makefile
>>>>>>>>>>>> +++ b/arch/arm/cpu/arm926ejs/Makefile
>>>>>>>>>>>> @@ -28,6 +28,13 @@ LIB = $(obj)lib$(CPU).o
>>>>>>>>>>>>
>>>>>>>>>>>>       START      = start.o
>>>>>>>>>>>>       COBJS      = cpu.o
>>>>>>>>>>>>
>>>>>>>>>>>> +ifdef CONFIG_SPL_BUILD
>>>>>>>>>>>> +ifdef CONFIG_SPL_NO_CPU_SUPPORT_CODE
>>>>>>>>>>>> +START :=
>>>>>>>>>>>> +COBJS :=
>>>>>>>>>>>> +endif
>>>>>>>>>>>> +endif
>>>>>>>>>>>> +
>>>>>>>>>>>>
>>>>>>>>>>>>       SRCS       := $(START:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c)
>>>>>>>>>>>>       OBJS       := $(addprefix $(obj),$(COBJS) $(SOBJS))
>>>>>>>>>>>>       START      := $(addprefix $(obj),$(START))
>>>>>>>>>>>
>>>>>>>>>>> Hi Albert,
>>>>>>>>>>>
>>>>>>>>>>> can we get this applied please?
>>>>>>>>>>
>>>>>>>>>> I still don't understand what this is supposed to do -- why not
>>>>>>>>>> linking this code is required.
>>>>>>>>>>
>>>>>>>>>> Amicalement,
>>>>>>>>>
>>>>>>>>> Hi Albert,
>>>>>>>>>
>>>>>>>>> I use very different start.S in SPL. And I don't need cpu.o at all.
>>>>>>>>
>>>>>>>> That I understand; but is there a /problem/ in linking cpu.o in?
>>>>>>>
>>>>>>> I suppose it'll be optimized out at link time ?
>>>>>>
>>>>>> That indirectly answers my question: what you want to achieve is
>>>>>> removing dead code.
>>>>>
>>>>> The code IS USED in U-Boot, but IS NOT USED in SPL !
>>>>
>>>> Right, but linked and unused code in SPL is (or should be!) thrown
>>>> away, is what's
>>>> trying to be driven home right now.  If the file is going to go away,
>>>> and it's compiled
>>>> thrown away at final link of SPL, lets just ignore that it exists for
>>>> a little longer, and
>>>> then it won't.
>>>
>>> My distrust towards compiler abilities to optimize such stuff out tells
>>> me it's better to avoid it even to be compiled in at all.
>>
>> Optimizing unused functions is a rather simple and reliable ability in
>> tolchains. The issue is not really whether the toolchain is able to do
>> the removal (it is); rather, the issue is whether the linker command
>> line will cause the removal (it will IMO as long as -gc-sections is
>> specified).
>>
>> Amicalement,
>
> So what you suggest is to leave cpu.o compiling and drop only start.S ?

Yes -- once you're sure that -gc-sections is there.

> Cheers

Amicalement,
-- 
Albert.