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From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: gexps
Date: Thu, 01 Sep 2016 14:59:28 +0200
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	(David Craven's message of "Thu, 1 Sep 2016 13:58:31 +0200")
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To: David Craven <david@craven.ch>
Cc: guix-devel <guix-devel@gnu.org>

David Craven <david@craven.ch> skribis:

>> If we force use of the host system type (say x86_64-linux), independent
>> of (%current-system) (say mips64el-linux), we approach what you want.
>> However, that would give us different derivations depending on the host
>> system type.  That is, =E2=80=98guix system build -s mips64el-linux -d=
=E2=80=99 on
>> x86_64 would return something different from =E2=80=98guix system build =
-d=E2=80=99 on
>> mips64.  This is not desirable.
>
> Maybe an option would be if %current-system !=3D host-system run guile
> using qemu-arm?

That would make it a different derivation.

>> An option would to have =E2=80=98gexp->file=E2=80=99 produce a fixed-out=
put derivation
>> (it can compute the hash of the output on the host side).
>>
>> Or maybe we need another mechanism similar to fixed-output derivations
>> to define equivalence classes of derivations.
>
> I'll have to read up on fixed-output derivations. Can you give me an
> example of where they are used currently?

For downloads (origins).  The manual mentions it briefly.

Ludo=E2=80=99.