[U-Boot] [PATCH v2 3/5] ARM: enable Thumb build

[Aneesh V]

On Thursday 23 February 2012 11:34 PM, Mike Frysinger wrote:
> On Thursday 23 February 2012 12:28:36 Aneesh V wrote:
>> On Thursday 23 February 2012 08:27 PM, Mike Frysinger wrote:
>>> On Thursday 23 February 2012 08:39:43 Aneesh V wrote:
>>>> --- a/arch/arm/config.mk
>>>> +++ b/arch/arm/config.mk
>>>>
>>>> -# Explicitly specifiy 32-bit ARM ISA since toolchain default can be
>>>> -mthumb: +# Choose between ARM/Thumb instruction sets
>>>> +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
>>>> +PF_CPPFLAGS_ARM := $(call cc-option, -mthumb -mthumb-interwork,\
>>>> +			$(call cc-option,-marm,)\
>>>> +			$(call cc-option,-mno-thumb-interwork,)\
>>>> +		)
>>>> +else
>>>>
>>>>    PF_CPPFLAGS_ARM := $(call cc-option,-marm,)
>>>>
>>>> +PF_CPPFLAGS_ARM += $(call cc-option,-mno-thumb-interwork,)
>>>
>>> this 2nd part is no good.  "+=" is not the same thing as ":=".
>>
>> I don't understand the difference. '+=' is done after ':=' right?
>>
>>> might be simpler to do:
>>> PF_CPPFLAGS_MARM := $(call cc-option,-marm)
>>> PF_CPPFLAGS_THUMB := $(call cc-option,-mthumb -mthumb-interwork)
>>> PF_CPPFLAGS_NO_THUMB := $(call cc-option,-mno-thumb-interwork)
>>>
>>> ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
>>> PF_CPPFLAGS_ARM = $(PF_CPPFLAGS_THUMB)
>>> else
>>> PF_CPPFLAGS_ARM = $(PF_CPPFLAGS_MARM) $(PF_CPPFLAGS_NO_THUMB)
>>> endif
>>
>> Are you trying to avoid all '+='. If so, why?
>
> "+=" does delayed evaluation and is the whole reason we started using ":=" in
> makefiles for *computed* values
>
> when you do:
> 	FOO := $(call cc-option,-marm)
> you're storing the result of the computation in $(FOO)
>
> if you do:
> 	FOO += $(call cc-option,-marm)
> you're appending "$(call cc-option,-marm)" to $(FOO) and that won't actually
> get computed until $(FOO) gets used
>
> so if you append $(call ...) to $(CPPFLAGS), then you end up doing the cc-
> option computation every time you compile a file that uses $(CPPFLAGS)

Get it. Thanks for explaining. I missed the computation part.

br,
Aneesh


> -mike