Re: tweak for documentation of how to create universal binaries

[Peter O'Gorman]

Ralf Wildenhues wrote:

> Well, if Bruno has run the latter command only (without going through
> the depcomp wrapper), and got inconsistent results, then that indicates
> a bug in this gcc.  Peter, would you file a bug report with Apple for us?

Well, if you put the multiple -arch flags in CFLAGS/CXXFLAGS instead of
CC/CXX then configure will set depmode to gcc3 rather than gcc, and the
first compile will error out with:

gcc-4.0: -E, -S, -save-temps and -M options are not allowed with
multiple -arch flags

When depmode is set to gcc, it looks like that check is avoided by
quoting -MD with -Wp, - so I'm pretty sure that if I file a bug, it will
be rejected.

Dependency output is quite likely to be different for different
architectures anyway...

If it were up to me, I'd just document the restriction as Bruno suggests.

For recent versions of Apple's gcc, you can pass -Xarch_<arch> to pass
flags to one architecture compile. So configure could check for multiple
-arch flags, choose one, and quote every dependency flag etc with
-Xarch_<arch>. e.g. -Xarch_i386 -MT -Xarch_i386 file.o -Xarch_i386  -MD
-Xarch_i386 -MP -Xarch_i386 -MF -Xarch_i386 .deps/file.Tpo

I doubt that the effort is worth it.

If you're curious, the wrapper for gcc that apple uses is here:
http://www.opensource.apple.com/darwinsource/DevToolsOct2008/gcc_42-5566/driverdriver.c

Peter