[Intel-gfx] [PATCH] igt: tests/Android.mk: fix LOCAL_PATH usage

[Damien Lespiau]

On Tue, Jan 14, 2014 at 06:29:48PM +0000, Beckett, Robert wrote:
> In Makefile language, rule and dependency definitions use immediate
> expansions of variables, so they get expanded as soon as the rule is
> created (1st pass). Rule implementation (a.k.a recipe) use deferred
> expansion (2nd pass).

I had forgotten that the rules are expanded in the first pass, makes it
clear. Thanks.

Pushed, with this blob attached and a direct link the "how make reads a
Makefile section", that makes a much better commit message!

-- 
Damien

> 
> Android effectively makes all Android.mk files a single makefile by
> including them all in a big tree from the toplevel makefile. The rules
> are all evaluated in the first pass and targets are generated. Then
> the 2nd pass happens and the required target's recipes are run. At
> this point, LOCAL_PATH has been assigned the value from the last
> evaluated Android.mk in the 1st phase that defined LOCAL_PATH (most
> Android.mk use this variable). In my particular case, it was the
> bootloader's Android.mk that was evaluated last and had defined
> LOCAL_PATH to it's path. The errors are rather misleading due to it
> looking like a bug in another module's Android.mk rather than this one
> :)
> 
> Basically, if you want to use a variable that any other Android.mk
> defines, then you can only use it in an immediate expansion context,
> not a deferred expansion context as it will likely be re-defined by
> the time the 2nd pass happens.
> 
> This patch stores it in a unique variable that should not be being
> used by other Android.mk files. An alternative fix would be to use $@
> and $< as the files in question are target and dependency, but I never
> like using those as they can easily break if dependencies are added
> etc. I prefer variable to be explicitly named to make them obvious.
> 
> (see gnu make manual for explanation of deferred vs immediate
> expansion of variables :
> http://www.gnu.org/software/make/manual/make.html )