Howto: Cross architecture execution

Justin Cormack edited this page Apr 2, 2014 · 1 revision

Rump kernels can easily be cross compiled for a different architecture, just adjust CC to the appropriate compiler.

You can also however execute the resulting kernels on a non-native architecture using qemu. This is useful for testing purposes, either if you do not have access to a machine with the architecture you want to test, or if it is less convenient, for example if it is slow.

While it is possible to run dynamically linked executables with qemu, it is a bit fiddly as you need to tell it where to find the libraries. Therefore it is much easier to use statically linked executables.

The qemu-user setup for executing cross architecture executables is available on Linux, and is a work in progress for FreeBSD. It is not yet available on NetBSD (that would be a fun project). The instructions below are for Linux.

Unfortunately glibc does not do static linking very well, so I have used Musl libc which is well suited for static linking. This means you need a Musl cross toolchain. I used Musl-cross. It needs to be a gcc toolchain as clang is not yet supported on most of the NetBSD architectures. There are binary downloads of Musl-cross available

Note that for the next few days you need to use a NetBSD head tree with but as this will shortly be fixed I will not give the instructions for this.

Install qemu-user. This should be packaged up for your Linux distro, eg for Ubuntu or Debian you need to do apt-get install qemu binfmt-support qemu-user-static.

Add the path to your cross compiler (which should be under /opt/cross/musl/ for the precompiled binaries) to your path and do the following:

export CC=powerpc-linux-musl-gcc # or whichever architecture you want
export LDFLAGS=-static
./ -V mkpic=no fullbuild

At this point if you check the executables and libraries built should all be cross compiled. If you run the buildrump test suite some tests may fail however. In particular the networking tests currently use shared memory locking which may not be emulated correctly.

To use gdb on a cross architecture, use qemu-mips -g 4567 ./executable and then in gdb you can select target remote

Known working architectures:

  • powerpc

Architectures with issues to debug, at least with some qemu versions

  • arm, armeb intermittent hanging in the networking test, probably locking related, intermittent segfaults
  • mips, mipsel are hanging on VFS test with actual file system
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