Re: powerpc-eabism, strategy for finding crt0.o

[Geoff Keating <geoffk at geoffk dot org>]

Benjamin Kosnik <bkoz@redhat.com> writes:

> Geoff, powerpc-eabism targets use libgloss to deal with crt0.o. If I'm
> going to get libstdc++-v3's testsuite working correctly with the
> target, I'm going to have to find crt0.o so that it can be linked in
> to resolve things like _start, and __eabi. I don't see an existent way
> to do this, please correct me if I'm wrong.
> 
> One option is linking 
> (builddir)/powerpc-eabism/libgloss/rs6000/crt0.o
> to
> (builddir)/powerpc-eabism/newlib/crt0.o
> 
> Another option is to pass down NEWLIB_SUPPORT_DIRS from the toplevel
> makefile, thus allowing target libs to know that libgloss is in
> play. Then the trick is finding crt0.o: for a --target=powerpc-eabism,
> the holding directory is 'rs6000'. 
> 
> it would be nice to just be able to do
> 
> (builddir)/powerpc-eabism/NEWLIB_SUPPORT_DIRS/$(target_cpu)/crt0.o
> 
> can't do that now though, but I suppose a sym-link could be made at
> build time that allowed this.
> 
> 
> What seems like the best approach?

How about doing it the way the g++ testsuite does it (whatever that
is)?  I think that dejagnu knows about libgloss in various special
ways, see for instance this code:

set_board_info cflags  "[libgloss_include_flags] [newlib_include_flags]"
set_board_info ldflags  "-msim [libgloss_link_flags] [newlib_link_flags]"

in powerpc-sim.exp.  So in theory if you just build and link
"properly" (using cflags and ldflags), everything should work.  Note
that -msim is required, and for other boards other flags will be
needed (it's very common to require some linker script option, for
instance "-Tidt.ld" on mips for IDT boards.)

(I was going to ask 'what's wrong with doing it...', but I immediately
thought of dozens of ways the current way is wrong.)

Yes, I agree that the _best_ way to do it would be to simply do

g++ -B $builddir/ -L $builddir/lib -L $builddir/$target/lib foo.cc -o foo
./foo

and arrange things so that $builddir/lib and $builddir/$target contain
the right things: crt*, linker scripts, libc.a, libstdc++.a, header
files, and whatever else is needed to compile and link a program.
That way, lots and lots of crud could be removed from dejagnu and
makefiles.

-- 
- Geoffrey Keating <geoffk@geoffk.org>