Hi, On Sun, 3 Oct 2021 21:42:42 +0300 Michael Tokarev <m...@tls.msk.ru> wrote: > On Sat, 2 Oct 2021 12:42:00 +0200 Helmut Grohne <hel...@subdivi.de> wrote: > > qemu cannot satisfy its cross Build-Depends, because its dependencies on > > sphinx are not satisfiable. Unfortunately, sphinx can be used in > > architecture-dependent ways, so it cannot be annotated M-A:foreign. I > > think that qemu uses sphinx in an architecture-independent way (as most > > architecture-dependent use cases import python extensions and qemu uses > > it to generate manual pages instead). As such, we can address the issue > > by annotating the relevant dependencies with :native. Please consider > > applying the attached patch. > > Please count me confused. I don't understand what you're talking about. > What does this: "unfortunately, sphinx can be used in architecture-dependent > ways" means, and why this is unfortunate?
when building packages in Debian, we talk about three different architectures: the build architecture, the host architecture and the target architecture. The latter is only interesting for building compilers and the build and host architecture are the same when doing native builds. The build architecture is the architecture the package is built on. The host architecture is the architecture the package is built for. Without any annotation, build dependencies require the host architecture package. So if you write: Build-Depends: python3-sphinx And you cross-build the package on amd64 for mipsel, then you would need to have python3-sphinx from mipsel installed. Since python3-sphinx is an Architecture:all package and since Architecture:all packages are always treated as if they were of the native architecture, you can only ever install python3-sphinx as if it were amd64 and thus you cannot satisfy your cross build dependencies. One way to solve this would be to mark the python3-sphinx package as Multi-Arch:foreign. If it were marked like that, then python3-sphinx on amd64 would be able to satisfy that dependency even though you are building for mipsel. Unfortunately, that is out of question, because the interface of the python3-sphinx package includes the sphinx Python module, which happens to depend on markupsafe via jinja2. Since markupsafe is architecture-dependent, there is no way to make python3-sphinx Multi-Arch: foreign. That would've been the easy way but we cannot do it and that's why this is unfortunate. > Maybe it's better to annotate it with :any, as we don't really care which > arch it is, as long as it works? Yes, we do care. Using our example above, if python3-sphinx was not Architecture:all and we would install the mipsel version, then it would probably not work because we cannot execute mipsel on an amd64 machine. So instead we pick the architecture it works and use :native to pick the native architecture instead. Furthermore, the :any qualifier is only allowed for packages that are marked as Multi-Arch:allowed. > Also, what does this :native annotation do within build-depends, to start > with? Is there any documentation about this? As explained above, by default, build dependencies are fulfilled by packages of the host architecture (the architecture the package is built for). By adding :native you state that you don't want this package for the host architecture but instead you want it for the build architecture, which makes perfect sence for python3-sphinx. Documentation: https://wiki.ubuntu.com/MultiarchCross Thanks! cheers, josch
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