Hello, I think I finally understand why the problem only occurs with grafts if a dependency uses copy-build-system. It is actually somewhat complicated.
When a package is lowered into a derivation by 'package->derivation' in guix/packages.scm, a list of potentially applicable grafts is created by the 'bag-grafts' procedure. This works by first traversing the bag for native packages (where bag-build-inputs and bag-target-inputs are followed recursively; and also bag-host-inputs if not cross building) and building the native derivations of the grafted versions of the packages which have a replacement (such as glibc at the time of writing). Building the grafted package (in the 'input-graft' procedure) is done again with 'package->derivation', which eventually calls 'graft-derivation' in guix/grafts.scm, which in turn calls 'non-self-references', where the ungrafted package is actually built (ignoring the store monad indirection), not just its derivation. In the case of cross builds, the bag is also traversed for the target dependencies, where the bag-host-inputs are followed recursively. Analogously, this causes the ungrafted packages and their ungrafted replacement to be cross built to compute the grafted derivations. As dan found out, the 'lower' procedure in guix/build-system/copy.scm incorrectly puts standard-packages into the host inputs. They contain the glibc-final package in gnu/packages/commencement.scm (which inherits the replacement of glibc). Because copy-build-system puts them into bag-host-inputs, the package replacement of the glibc-final package is then cross built without grafts when calculating its grafted derivation, which it does not support. Note that the glibc-final package and its package replacement are distinct from the glibc package and its replacement in gnu/packages/base.scm. I confirmed this by running --8<---------------cut here---------------start------------->8--- ,use (guix) (with-store store (run-with-store store (package->cross-derivation (package-replacement (@@ (gnu packages commencement) glibc-final)) "i686-linux-gnu" #:graft? #f))) --8<---------------cut here---------------end--------------->8--- in the REPL, which returns the same incorrect glibc derivation that is attempted to be built as a dependency when running `guix build alsa-lib --target=i686-linux-gnu`. It is actually possible to compute the graft derivations only when needed by a store reference (which does not change the derivation of the grafted package). Then, this problem does not occur even without the fix for the copy-build-system, as the invalid derivations are never actually built. With substitutes or after running GC, this may even prevent building a package with replacement when the requested package output which (transitively) depends on it has no (transitive) store reference to it. I made a patch for that here: https://issues.guix.gnu.org/70895 Regarding the changes to the copy-build-system: Ludovic Courtès <l...@gnu.org> writes: > But still, there seem to be some expectation that ‘copy-build-system’ > can support cross-compilation for real, so maybe we should add a > ‘copy-cross-build’ procedure in addition to the patch above. In guix/build-system/copy.scm, it is described as an extension of gnu-build-system and the manual says "It adds much of the gnu-build-system packages to the set of inputs. Because of this, the copy-build-system does not require all the boilerplate code often needed for the trivial-build-system." Therefore, I think it makes sense to add the copy-cross-build procedure so that copy-build-system actually behaves like gnu-build-system. Cheers, David
