[LLVMdev] getting gold plugin to work?

[Sandeep Patel]

On Mon, Oct 5, 2009 at 2:21 PM, Rafael Espindola <espindola at google.com> wrote:
> 2009/10/4 Sandeep Patel <deeppatel1987 at gmail.com>:
>> There needs to be a build step
>> somewhere in llvm-gcc that copies it into libexec/<gcc
>> poop>/libLLVMgold.so, but I've been doing that manually for now.
>
> Yes, this is bad. The problem is that we build the plugin in llvm, not
> llvm-gcc. Another option is to add a new search directory to llvm-gcc.
> That way you could configure llvm-gcc with a --gold-plugin-dir=<path>
> and the resulting binary would search there. This would work nicely
> when using an already installed llvm copy.

That would work for gold, but what about nm, etc.?

>> It doesn't seem that simple use of -O4 results in the plugin learning
>> what subtarget is desired. I presume that the llvm-gcc driver needs to
>> pass -mcpu down through collect2 into ld somehow. Has anybody solved
>> this already? Perhaps we should finally just put the feature string
>> into the bitcode?
>
> Interesting. It is probably better to pass it via the command line. I
> will try to take a look at it. Do you have a small testcase?

I have no idea how to reduce this.

Configure llvm-gcc for "arm-eabi" and use "--with-cpu=cortex-a8
--with-fpu=neon --with-abi=aapcs --with-float=hard". The triple in the
bitcode will be "armv7-eabi" but the actual CPU subtarget won't be
known to the gold plugin. I'd think the same would be true for any
cross-compiler. Note that self-hosting X86 will eventually use a CPUID
instruction to determine the proper subtarget on the fly so it will
usually be correct.

deep