[LLVMdev] strace for whole-program bitcodes

[Daniel Dunbar]

On Thu, Oct 15, 2009 at 7:14 AM, Timo Juhani Lindfors
<timo.lindfors at iki.fi> wrote:
> Tianwei <tianwei.sheng at gmail.com> writes:
>> someone suggested me to use gold-plugin, I know nothing about it yet, I will
>> have a try later.  Does anyone have a good solution for this problem?
>
> Afaik gold does not help here. I tried it and managed to only generate
> native code.

"Just" gold isn't quite good enough, because at the last final link
steps gold will still generate native code. However, it should be
possible to find a way to get gold to leave the merged bitcode around
somewhere, or perhaps do something like llvm-ld. Nicholas?

The advantage of this approach is that it will potentially work with
build systems that call ar/ld directly.

> I'm currently investigating an alternative approach to produce
> whole-program bitcodes:
>
> 1) add /tmp/wrap to PATH
> 2) create /tmp/wrap/gcc with the following contents
>
> #!/bin/sh
> exec llvm-gcc -specs /tmp/wrap/gcc.specs "$@"
>
> 3) llvm-gcc -dumpspecs > /tmp/wrap/gcc.specs
> 4) modify /tmp/wrap/gcc.specs so that it always passes -emit-llvm to cc1
> 5) modify /tmp/wrap/gcc.specs so that it calls llvm-ld* instead of real
>   ld and does not pass any unknown flags to it.
>
> With this approach I was able to compile and run airstrike (a 2d
> dogfighting game) in bitcode form very transparently with:
>
> $ make-bitcode fakeroot apt-get --build source airstrike
> $ sudo dpkg -i airstrike*.deb
> $ airstrike

Very clever though. :)

 - Daniel

> If you are interested I can try to rework my scripts to a shape where
> they could be used by somebody else.
>
> (*) I am not actually calling llvm-ld directly. Instead I have an
>    "llvm-ld-exe" wrapper that calls llvm-ld and then uses "anytoexe" to
>    pack the resulting bitcode to a shell script that can execute itself with
>    lli and use the correct -load options.
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