| 31 Dec 2024 |
 Maxim Moseychuk | Hi, Happy New Year!
Using pkgs.pkgsCross, I can compile a package from nixpkgs for another platform. For example:
# nix-build '<nixpkgs>' -A pkgs.pkgsCross.aarch64-multiplatform.hello
I have a local repository with a package. For example, let’s say it’s a simple hello world.
default.nix:
{ pkgs ? import <nixpkgs> { } }:
{
myhello = pkgs.callPackage ./pkgs/myhello { };
}
However, I can't build it the same way:
# nix-build -A pkgs.pkgsCross.aarch64-multiplatform.myhello
error: attribute 'pkgs' in selection path 'pkgs.pkgsCross.aarch64-multiplatform.myhello' not found
I can change pkgs.callPackage in default.nix to pkgs.pkgsCross.aarch64-multiplatform.callPackage. Then the package builds:
# nix-build -A myhello
this derivation will be built:
/nix/store/3mbcklrdg4dc90qg47fvakv6zv9gwqm2-myhello-1.0-aarch64-unknown-linux-gnu.drv
...
How can I properly test cross-compilation without adding the repository via a channel or flake?
I’d like to test building for different platforms without modifying nix files, as if the package were part of nixpkgs.
| 09:05:36 |
| Maxim Moseychuk | * Hi, Happy New Year!
Using pkgs.pkgsCross, I can compile a package from nixpkgs for another platform. For example:
# nix-build '<nixpkgs>' -A pkgs.pkgsCross.aarch64-multiplatform.hello
I have a local repository with a package. For example, let’s say it’s a simple hello world.
default.nix:
{ pkgs ? import <nixpkgs> { } }:
{
myhello = pkgs.callPackage ./pkgs/myhello { };
}
However, I can't build it the same way:
# nix-build -A pkgs.pkgsCross.aarch64-multiplatform.myhello
error: attribute 'pkgs' in selection path 'pkgs.pkgsCross.aarch64-multiplatform.myhello' not found
I can change pkgs.callPackage in default.nix to pkgs.pkgsCross.aarch64-multiplatform.callPackage. Then the package builds:
# nix-build -A myhello
this derivation will be built:
/nix/store/3mbcklrdg4dc90qg47fvakv6zv9gwqm2-myhello-1.0-aarch64-unknown-linux-gnu.drv
...
How can I properly test cross-compilation without adding the repository via a channel or flake?
I’d like to test building for different platforms without modifying nix files, as if the package were part of nixpkgs.
| 09:06:44 |
 K900 | You can do something like nix-build --expr "(import <nixpkgs> {}).pkgsCross.aarch64-multiplatform.callPackage ./pkgs/myhello {}" | 09:06:47 |
| Maxim Moseychuk | Thank you very much!
But what is the difference between a local file and nixpkgs? How does nix know that a package with a prefix should be cross-compiled? I looked in the nixpkgs repository, but I didn't understand how pkgsCross works, since the packages are declared in one place. Apparently, it's not just the package name, but something generated automatically. | 09:14:43 |
| K900 | pkgsCross is basically another instance of nixpkgs | 09:15:32 |
| K900 | Created with the right configuration to be cross-compiled | 09:15:44 |
| K900 | The difference between a local file and nixpkgs is that pkgsCross knows nothing about your local file | 09:16:08 |
| K900 | And neither does nixpkgs for that matter | 09:16:14 |
| K900 | Nix itself knows absolutely nothing about any of it | 09:17:22 |
| K900 | Nixpkgs is just one big attrset that it pulls from without understanding its structure in any real way | 09:17:41 |
| Maxim Moseychuk | If pkgsCross is another instance of nixpkgs, I tried passing it as an explicit parameter, and it worked.
# nix-build --arg pkgs "(import <nixpkgs> {}).pkgsCross.aarch64-multiplatform" -A myhello
| 09:33:26 |
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| 1 Jan 2025 |
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| 2 Jan 2025 |
 rhelmot | alright chat I think we are almost out of dogshit edge cases before I can resume reviews on the rustc stuff | 09:09:31 |
| rhelmot | this last case comes from being on freebsd and compiling... get ready for it... | 09:09:45 |
| rhelmot | pkgsCross.aarch64-multiplatform.pkgsLLVM.buildPackages.rustc | 09:09:59 |
| K900 | One day we'll get to Qt6 cross | 09:10:15 |
| K900 | And then to KF6 | 09:10:17 |
| K900 | And then we'll have to figure out corrosion on cross | 09:10:23 |
| K900 | And I am not looking forward to that day | 09:10:28 |
| rhelmot | the problem for the thing I posted seems to be related to clang being multi-target now. we tell rustc configureFlags that --set=target.aarch64-unknown-linux-gnu.linker=/nix/store/6bjs7ai2ai14fdx6kvrfgdfhc16a19md-aarch64-unknown-linux-gnu-clang-wrapper-19.1.6/bin/aarch64-unknown-linux-gnu-clang which is correct but it doesn't pass any flags indicating what linker to use, so it just uses un-prefixed ld which is NOT multi-target and so the compile fails | 09:13:52 |
| rhelmot | ld is gnu binutils here | 09:14:44 |
| rhelmot | is this even a legal configuration? | 09:14:52 |
| rhelmot | I can't remember why I set up the freebsd stdenv to be clang + gnu binutils but it's been working until now... | 09:16:15 |
| 3 Jan 2025 |
|  elikoga changed their display name from elikoga (@38c3 📞488{0,1,9}) to elikoga. | 10:28:12 |
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