Re: libgccjit 5.2 on Mac OSX Yosemite

[David Malcolm <dmalcolm@redhat.com>]

On Mon, 2015-08-10 at 21:36 +0100, Dibyendu Majumdar wrote:
> Hi
> 
> I tried building gcc 5.2 on Mac OSX but could not get the linking to
> work. Then fortunately found that homebrew has a formula for deploy
> gcc 5.2 with jit enabled.


Aha.  Thanks.  This would seem to be:
 https://github.com/Homebrew/homebrew/blob/master/Library/Formula/gcc.rb

which I see slightly patches
  gcc/jit/Make-lang.in
to avoid an assumption that we're building using the GNU linker.



> All installed and then built Ravi successfully. But when I try to run
> Ravi any attempt to invoke the JIT fails with:
> 
> Lua 5.3.1  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> 
> > function x() return end
> 
> > ravi.compile(x)
> 
> Undefined symbols for architecture x86_64:
> 
>   "_luaD_poscall", referenced from:
> 
>       _ravif1 in cczhNq92.o
> 
>   "_luaF_close", referenced from:
> 
>       _ravif1 in cczhNq92.o
> 
> ld: symbol(s) not found for architecture x86_64
> 
> collect2: error: ld returned 1 exit status
> 
> libgccjit.so: error: error invoking gcc driver: exit_status: 256 err: 0
> 
> libgccjit.so: error: whilst attempting to run a driver named:
> x86_64-apple-darwin14.4.0-gcc-5.2.0
> 
> libgccjit.so: error: PATH was:
> /Users/username/github/ravi/build:/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/git/bin:/Library/TeX/texbin
> 
> aborting due to JIT error: error invoking gcc driver: exit_status: 256 err: 0
> 
> Abort trap: 6
> 
> Any clues?
> 
> I had set PATH and LD_LIBRARY_PATH.

Presumably "luaD_poscall" and "luaF_close" are symbols that you're
exporting from ravi for use by the JIT-generated code, via:
https://github.com/dibyendumajumdar/ravi/blob/master/src/ravi_gcctypes.c#L802

  t->luaD_poscallT = gcc_jit_context_new_function(
      ravi->context, NULL, GCC_JIT_FUNCTION_IMPORTED, t->C_intT,
"luaD_poscall",
      3, params, 0);

I'm not quite sure exactly where the leading underscore came from.

This appears to be a linker error from the static link that creates the
jit-generated .so file.  If I'm reading things right, it's complaining
that the code is using luaD_poscall, but it doesn't have a definition
for it.

My guess is that "ld" on OS X has slightly different behavior from the
GNU "ld" I've been developing against, and that it defaults to a
stricter linkage model where it wants to see those symbols upfront, when
we want to defer them until the later dynamic link phase (when we dlopen
the generated .so file).  This is a guess though.

What does "ld --version" print?

It may be easiest to try to work from a minimal reproducer for this.
To that end, what happens if you try building and running
  gcc/testsuite/jit.dg/test-calling-external-function.c
from the jit testsuite, using the homebrew build?


Thanks
Dave