[Bug 1866032] Re: [UBUNTU 20.04] apt build-dep qemu can't resolve dependencies

[Steve Langasek]

These packages are only Build-Depends-Indep, meaning they are only
needed when you are building the arch: all packages from the qemu source
package.

The following command succeeds on s390x with an up-to-date focal system:

# apt build-dep --arch-only qemu

If you need to rebuild qemu-system-data, the only arch: all binary
package from the qemu source, you will want to do that rebuild on an x86
system.  Official arch: all builds for the Ubuntu archive are always
done on amd64, so Build-Depends-Indep are not guaranteed to be
satisfiable on other architectures.

** Changed in: qemu (Ubuntu)
       Status: New => Invalid

** Package changed: cross-toolchain-base (Ubuntu) => gcc-defaults-ports
(Ubuntu)

** Changed in: gcc-defaults-ports (Ubuntu)
   Importance: Undecided => Wishlist

** Changed in: gcc-defaults-ports (Ubuntu)
       Status: New => Triaged

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https://bugs.launchpad.net/bugs/1866032

Title:
  [UBUNTU 20.04] apt build-dep qemu can't resolve dependencies

Status in Ubuntu on IBM z Systems:
  Triaged
Status in gcc-defaults-ports package in Ubuntu:
  Triaged
Status in qemu package in Ubuntu:
  Invalid

Bug description:
  I was trying to re-build the QEMU package from source, but the build
  dependencies can't be resolved.

  Steps to reproduce:
  1. Install Ubuntu 20.04 System on an LPAR|z/VM guest|KVM guest from ports.ubuntu.com
  2. Uncomment all #deb-src lines in /etc/apt/sources.list
  3. Run the following commands:
     $ sudo apt update
     $ sudo apt install build-essential
     $ apt source qemu
     $ sudo apt build-dep qemu
  4. The last command produces the following error output
  ---
  $ sudo apt build-dep qemu
  Reading package lists... Done
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:

  The following packages have unmet dependencies:
   builddeps:qemu : Depends: libncursesw5-dev
                    Depends: gcc-alpha-linux-gnu but it is not installable
                    Depends: gcc-powerpc64-linux-gnu but it is not installable
  E: Unable to correct problems, you have held broken packages.

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