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

[Mike Frysinger]

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)
-mike
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