Re: [RFC][gomp4] Offloading patches (3/3): Add invocation of target compiler

["Michael V. Zolotukhin" <michael.v.zolotukhin@gmail.com>]

> This patch seems to make rather too many assumptions about host and
> target compilers. Certainly code like this can't go into
> target-independent code like lto-wrapper.
That's true.  The point of this patch was to show what is needed to support
x86->MIC OpenMP offloading, as we currently see it.  We are ready to extend
existing code making it more versatile, but keeping this needed functionality.

> Also, I'm not sure you can
> assume you'll get ELF files out of the OpenACC target compiler; I'd very
> prefer a solution that doesn't rely on objcopy.
Yep, that's an issue I suspected but wasn't sure of.

The idea was to prepare an image in the following steps:
  1. Compile with target compiler.
  2. Post-process it (in our case, call objcopy and perform partial linking).
  3. Pass it to the host linker as a usual object file with the image and its
size placed in the known symbols with defined names (e.g.
_omp_<target-name>_image).

I would like to keep step 3 unchanged, while the steps 1 and 2 could be easily
combined into a single one.

In that case we could say that output of a target compiler should be an object
file for host linker with several symbols defined: _omp_<target-name>_image,
_omp_<target-name>_size, etc.

For x86->MIC one would use gcc+objcopy for this, and for OpenACC offloading one
could use gcc+some of other target-specific utils (if any of them needed).

Will this scheme work for OpenACC?

Michael
> Bernd