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Merge pull request #22387 from Ericson2314/cross-3-platforms

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cross stdenv: let build package's build deps resolve to native packages
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John Ericson 2017-02-05 17:41:31 -05:00 committed by GitHub
commit f6ef6b56fe
2 changed files with 7 additions and 7 deletions
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11
doc/cross-compilation.xml
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@ -105,14 +105,15 @@
This is the most important guiding principle behind cross-compilation with Nixpkgs, and will be called the <wordasword>sliding window principle</wordasword>.
In this manner, given the 3 platforms for one package, we can determine the three platforms for all its transitive dependencies.
</para>
<para>
Some examples will probably make this clearer.
If a package is being built with a <literal>(build, host, target)</literal> platform triple of <literal>(foo, bar, bar)</literal>, then its build-time dependencies would have a triple of <literal>(foo, foo, bar)</literal>, and <emphasis>those packages'</emphasis> build-time dependencies would have triple of <literal>(foo, foo, foo)</literal>.
In other words, it should take two "rounds" of following build-time dependency edges before one reaches a fixed point where, by the sliding window principle, the platform triple no longer changes.
Indeed, this happens with cross compilation, where only rounds of native dependencies starting with the second necessarily coincide with native packages.
</para>
<note><para>
The depending package's target platform is unconstrained by the sliding window principle, which makes sense in that one can in principle build cross compilers targeting arbitrary platforms.
</para></note>
<warning><para>
From the above, one would surmise that if a package is being built with a <literal>(build, host, target)</literal> platform triple of <literal>(foo, bar, bar)</literal>, then its build-time dependencies would have a triple of <literal>(foo, foo, bar)</literal>, and <emphasis>those packages'</emphasis> build-time dependencies would have triple of <literal>(foo, foo, foo)</literal>.
In other words, it should take two "rounds" of following build-time dependency edges before one reaches a fixed point where, by the sliding window principle, the platform triple no longer changes.
Unfortunately, at the moment, we do <emphasis>not</emphasis> implement this correctly, and after only one round of following build-time dependencies is the fixed point reached, with target incorrectly kept different than the others.
</para></warning>
<para>
How does this work in practice? Nixpkgs is now structured so that build-time dependencies are taken from from <varname>buildPackages</varname>, whereas run-time dependencies are taken from the top level attribute set.
For example, <varname>buildPackages.gcc</varname> should be used at build time, while <varname>gcc</varname> should be used at run time.

3
pkgs/stdenv/cross/default.nix
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@ -18,8 +18,7 @@ in bootStages ++ [
hostPlatform = localSystem;
targetPlatform = crossSystem;
inherit config overlays;
# Should be false, but we're trying to preserve hashes for now
selfBuild = true;
selfBuild = false;
# It's OK to change the built-time dependencies
allowCustomOverrides = true;
stdenv = vanillaPackages.stdenv // {