Re: [PATCH 2/5] gcc: configure and Makefile changes needed by jit

[David Malcolm <dmalcolm@redhat.com>]

On Wed, 2014-10-15 at 11:36 -0600, Jeff Law wrote:
> On 10/13/14 11:45, David Malcolm wrote:
> > gcc/ChangeLog:
> > 	* configure.ac (gcc_version): Expose this value for use via
> > 	AC_SUBST, since the jit code needs it within the new file
> > 	libgccjit.pc.in.
> > 	(doc_build_sys): New variable, set to "sphinx" if
> > 	sphinx is installed, falling back to "texinfo" otherwise.
> > 	(gcc-driver-name.h): Generate a gcc-driver-name.h file containing
> > 	GCC_DRIVER_NAME for the benefit of jit/jit-playback.c.
> > 	* configure: Regenerate.
> > 	* Makefile.in (doc_build_sys): New.
> > 	(bindir): New.
> > 	(pkgconfigdir): New.
> > 	(installdirs): Add creation of $(DESTDIR)$(pkgconfigdir).
> > 	(site.exp): When constructing site.exp, add a line to set "bindir".
> Mostly OK.  Though a couple questions.
> 
> Why do we need pkgconfig and why do you need a bindir in site.exp?

I chose to provide a libgccjit.pc file in the install, so that client
code has the option of compiling and linking against the library like
this:

$ gcc jit-hello-world.c $(pkg-config libgccjit --cflags)
$ gcc jit-hello-world.o $(pkg-config libgccjit --libs)

relying on pkg-config to automatically supply the relevant flags for the
correct paths (for those people who want to use pkg-config).

To do this, we need to install the libgccjit.pc file into the correct
location for pkg-config to find it; hence we need to create
pkgconfigdir, so that the jit/Make-lang.in has somewhere to install it
to.

See https://gcc.gnu.org/ml/jit/2014-q3/msg00024.html for the commit that
added this.


As for the "bindir" in site.exp, Joseph asked me when the library
invokes a driver to convert from .s to .so to:

On Tue, 2014-09-23 at 23:27 +0000, Joseph S. Myers wrote:
> * use the $(target_noncanonical)-gcc-$(version) name for the
> driver rather than plain "gcc", to maximise the chance that it
> is actually the same compiler the JIT library was built for (I
> realise you may not actually depend on it being the same
> compiler, but that does seem best; in principle in future it
> should be possible to load multiple copies of the JIT library
> to JIT for different targets, so that code for an offload
> accelerator can go through the JIT).
( https://gcc.gnu.org/ml/jit/2014-q3/msg00033.html )

This full name is used when *installing* the driver, but doesn't exist
within the build directory.
Hence when running the library, the installation bindir needs to be in
the PATH.  In particular, (in
https://gcc.gnu.org/ml/jit/2014-q4/msg00005.html ) when running the jit
testsuite we rely on the driver having been installed, and in jit.exp we
need to temporarily prepend the installation bindir onto the front of
PATH when running test programs linked against libgccjit.so.  Hence we
need to know what bindir is from expect, hence we add it to site.exp.

Hope the above sounds sane
Dave