[bug#54239] [PATCH v2 1/5] gnu: Add cross-llvm.

[Pierre Langlois <pierre.langlois@gmx.com>]

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Julien Lepiller <julien@lepiller.eu> writes:

> Le Fri, 04 Mar 2022 19:34:07 +0000,
> Pierre Langlois <pierre.langlois@gmx.com> a écrit :
>
>> Hi Julien,
>> 
>> Julien Lepiller <julien@lepiller.eu> writes:
>> 
>> > * gnu/packages/llvm.scm (cross-llvm): New variable.  
>> 
>> Do you really need to define a cross package for LLVM? In my
>> experience it was possible to use the same llvm libraries for native
>> and cross compilation. By default LLVM builds support for all
>> supported targets (provided they are not "experimental" IIRC).
>
> No, I don't think it's required.  I only need it so I can define a
> default target that's different from the host.
>
>> 
>> Whereas for the clang package, at the moment it does have to be built
>> for a specific target IIUC. I hope that one day we could have the same
>> clang for native and cross compilation in Guix, but I don't think it
>> can work without some serious re-design of how cross-compilation
>> works. I've been trying to think about it but I don't yet have a good
>> understanding of it.
>
> You can use --target to control which target clang builds for (although
> I don't know if our clang package can work like that). I wanted to have
> a default target though, because passing --target all the time is
> cumbersome and we would have to adjust all recipes to pass the flag.
> With the default target set appropriately, (clang-for-target) will
> always produce binaries for the correct architecture, whether
> cross-compiling or not.
>

Ah I see, that makes sense!  I suppose a possible alternative could be
to define a wrapper around clang to pass the `--target=<triplet>' option
by default, but that might be a bit ugly (although we already have a
ld-wrapper).

Thanks,
Pierre


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