Re: Using cross-compiled packages (e.g. x86_64-linux-gnux32 on x86_64-linux-gnu)

[Csepp]

Sven Hartrumpf <hartrumpf@gmx.net> writes:

> Hello.
>
>> Sven Hartrumpf writes:
>>
>>> Hello.
>>>
>>> I want to cross-compile some packages for the x32 ABI
>>> (because it can speed up one of my performance-critical applications).
>>> Thanks to Efraim’s recent changes, I can simply use
>>>
>>>   # guix build lz4 –target=x86_64-linux-gnux32
>>> (lz4 is only a simple example, not the one which is important for me :-)
>>>
>>> What is a good or simple way to use the resulting binaries
>>> (which I find under /gnu/store/…/bin/lz4)?
>>> My user-land binaries are mainly x86_64-linux-gnu, only few will be
>>> x86_64-linux-gnux32.
>>>
>>> Greetings
>>> Sven
>
> Csepp wrote, 2024-01-26:
>
>> Don’t they run as normal?
>
> They do.
> I was looking for a way to prefer some x32 binaries over the 64bit ones.
>
>> If the question is about installing them in a profile, you could put them
>> in a manifest. Or you could try grafting them into existing packages if you
>> want them to use them in scripts. But be careful that you don’t mix
>> libraries into that.
>
> For many packages, I will have two builds in /gnu/store , e.g.
>
>   # file /gnu/store/*zstd*/bin/zstd
> /gnu/store/p61ifh74s4n4jg7c1j1f2gw2c235lna0-zstd-1.5.5/bin/zstd: ELF 64-bit 
> LSB
> executable, x86-64, version 1 (SYSV), dynamically linked, interpreter
> /gnu/store/ln6hxqjvz6m9gdd9s97pivlqck7hzs99-glibc-2.35/lib/ld-linux-x86-64.so.2,
> for GNU/Linux 2.6.32, stripped
> /gnu/store/yf15abzz51wfapi699g1xp02lklkis5z-zstd-1.5.5/bin/zstd: ELF 32-bit 
> LSB
> executable, x86-64, version 1 (SYSV), dynamically linked, interpreter
> /gnu/store/dxxbn44p9lfy7pbpj82kj68rk2mixn89-glibc-cross-x86_64-linux-gnux32-2.35/lib/ld-linux-x32.so.2,
> for GNU/Linux 2.6.32, stripped
>
>> But as far as using them goes, I’m pretty sure you can just run them. Guix
>> is actually really nice for this use case, because you don’t have to
>> manually manage a different sysroot for every ABI. I’ve used this property
>> at work to cross-build an ARM package and transfer it to a Raspberry Pi. It
>> just worked.
>
> Yes.
> But thhe use of –target for building x32 binaries is somewhat different from 
> cross-compilation
> because the resulting binaries can (and should) be run on the host system. 
> And of course,
> a profile can only referenced one version and that will be the 64bit version.
>
> I came up with a naive solution which works for me (as a Guix System 
> beginner).
> I explicitly put links in ~/.local/bin/x86_64-linux-gnux32/ to the x32 
> binaries I prefer.
> (~/.local/bin/x86_64-linux-gnux32/ is the first element in my PATH).
>
> Greetings
> Sven

I recommend looking into package transformations (especially how grafts work) 
and/or managing multiple profiles.
If you want to have the x32 variants in your profile, I think you can do that 
with a manual graft.