llvm dev - Oct 2009 - [LLVMdev] fudging the top-level Makefile

Currently, to get LLVM to build "Apple-style," it's necessary to
copy
two files (utils/buildit/GNUmakefile and utils/buildit/build_llvm)  
into the top-level directory.  This is generally a PITA inside of  
Apple.  (I'll spare you the gory details.  :-)

I'd like to fix this for Apple, and I want to avoid compromising  
anybody else's build system.  I've never used CMAKE, so I would be  
very grateful if a Windows/CMAKE developer would look this over.

I'm proposing to rename the top-level Makefile to
"Makefile.standard",
and add a new, trivial top-level "Makefile" that detects the Apple  
build environment.  Every Apple-style build happens in the presence of  
an environment variable named "$RC_ARCHS".  If the magic $RC_ARCHS is
detected, the new Makefile arranges for an Apple-style build.  If the  
magic environment variable is absent, "Makefile.standard" is included,
and everything proceeds as usual.

I've tested this by building LLVM on OS/X:
1) with a separate build directory, e.g. "cd llvm.obj ; ../llvm/ 
configure ; make"
2) building inside the LLVM source directory, e.g. "cd llvm ; ./ 
configure ; make"
3) Apple-style (too ugly and frightening to reproduce here :-)

I've also tested this by building LLVM on my home Linux system:
1) with a separate build directory, e.g. "cd llvm.obj ; ../llvm/ 
configure ; make"
2) building inside the LLVM source directory, e.g. "cd llvm ; ./ 
configure ; make"

Comments or suggestions (or better approaches) are greatly appreciated.

Here is the patch.  I was obliged to change autoconf/configure.ac; I  
have omitted the corresponding diffs from the top-level configure  
shellscript for brevity:

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Note that the existing top-level Makefile will be renamed to  
"Makefile.standard".  (This doesn't show up very well in a simple
SVN
diff.)  Here is the new top-level Makefile:

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Thank you very much in advance!

stuart

On Oct 8, 2009, at 4:52 PM, Stuart Hastings wrote:
> Currently, to get LLVM to build "Apple-style," it's necessary
to
> copy two files (utils/buildit/GNUmakefile and utils/buildit/ 
> build_llvm) into the top-level directory.
Why not:

$ RC_ARCHS="x86" make
echo Apple Build.
Apple Build.
$ make
echo Standard Build
Standard Build
$ cat Makefile
ifneq ($(RC_ARCHS),)
include Makefile.apple
else
all:
	echo Standard Build
endif
mrs $ cat Makefile.apple
all:
	echo Apple Build.

It leaves Makefile mostly alone, all except for three lines at the top  
and one line at the end of it.

Stuart Hastings <stuart at apple.com> writes:
> I'd like to fix this for Apple, and I want to avoid compromising
> anybody else's build system.  I've never used CMAKE, so I would be
> very grateful if a Windows/CMAKE developer would look this over.
As the LLVM cmake build specification completely ignores the makefiles
provided with LLVM, no problem here.

-- 
Óscar

On Oct 8, 2009, at 5:18 PM, Mike Stump wrote:
> On Oct 8, 2009, at 4:52 PM, Stuart Hastings wrote:
>> Currently, to get LLVM to build "Apple-style," it's
necessary to
>> copy two files (utils/buildit/GNUmakefile and utils/buildit/ 
>> build_llvm) into the top-level directory.
>
> Why not:
>
> $ RC_ARCHS="x86" make
> echo Apple Build.
> Apple Build.
> $ make
> echo Standard Build
> Standard Build
> $ cat Makefile
> ifneq ($(RC_ARCHS),)
> include Makefile.apple
> else
> all:
> 	echo Standard Build
> endif
> mrs $ cat Makefile.apple
> all:
> 	echo Apple Build.
>
> It leaves Makefile mostly alone, all except for three lines at the  
> top and one line at the end of it.
Because the existing top-level Makefile includes "Makefile.config".   
In a normal build, the configure step creates "Makefile.config".   
"Apple-style" builds don't run the configure script (I have filed
a
bug about this :-).

stuart

On Thursday 08 October 2009 19:18, Mike Stump wrote:
> On Oct 8, 2009, at 4:52 PM, Stuart Hastings wrote:
> > Currently, to get LLVM to build "Apple-style," it's
necessary to
> > copy two files (utils/buildit/GNUmakefile and utils/buildit/
> > build_llvm) into the top-level directory.
>
> Why not:
>
> It leaves Makefile mostly alone, all except for three lines at the top
> and one line at the end of it.
Absolutely.  Third-party build systems should impact the public LLVM as little 
as possible.

                                  -Dave