Xen devel - Jan 2009 - [PATCH] xen/Rules.mk: Do not dance about pointlessly with CFLAGS_tmp

It is usually better to use `='' in Makefiles than `:=''.  The
expansion
rules for `:='' are simpler - so simple in fact that they don''t
work if
any part of the expansion depends on the source or target filenames.

In this patch we remove the shuffling of the value of CFLAGS between
:= and = flavour variables.  This was previously `necessary'' because
otherwise it would run the seddery for removing -fomit-frame-pointer
once for each rule.

However this seddery is not actually necessary because there is plenty
of other machinery for (a) only setting -fomit-frame-frame-pointer
when applicable AND (b) passing -fno-omit-frame-pointer later on the
command line if it''s not applicable.  So we already have belt and
braces and can remove the safety pins.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>



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On 12/01/2009 17:05, "Ian Jackson" <Ian.Jackson@eu.citrix.com>
wrote:
> It is usually better to use `='' in Makefiles than `:=''. 
The expansion
> rules for `:='' are simpler - so simple in fact that they
don''t work if
> any part of the expansion depends on the source or target filenames.
> 
> In this patch we remove the shuffling of the value of CFLAGS between
> := and = flavour variables.  This was previously `necessary''
because
> otherwise it would run the seddery for removing -fomit-frame-pointer
> once for each rule.
> 
> However this seddery is not actually necessary because there is plenty
> of other machinery for (a) only setting -fomit-frame-frame-pointer
> when applicable AND (b) passing -fno-omit-frame-pointer later on the
> command line if it''s not applicable.  So we already have belt and
> braces and can remove the safety pins.
You missed a := in arch/x86/Rules.mk. Can that one be avoided so easily?

 -- Keir



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On 12/01/2009 18:55, "Keir Fraser" <keir.fraser@eu.citrix.com>
wrote:
>> However this seddery is not actually necessary because there is plenty
>> of other machinery for (a) only setting -fomit-frame-frame-pointer
>> when applicable AND (b) passing -fno-omit-frame-pointer later on the
>> command line if it''s not applicable.  So we already have belt
and
>> braces and can remove the safety pins.
> 
> You missed a := in arch/x86/Rules.mk. Can that one be avoided so easily?
Ah, well the answer is rather obviously yes. I''ll fix this one up
myself and
check it in.

I''ll also adjust cc-option to run $(CC) immediately and add the
resulting
appropriate option correctly even to a recursively-expanded variable. So
$(CC) execution is not delayed and does not occur multiple times even if
CFLAGS is expanded multiple times.

 -- Keir



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