Linux emulation

SOURCE

DOCUMENTATION

Documentation is provided in the doc directory:

	doc/linuxemu.txt
	doc/todo.txt

INSTALLATION

	tar xzf linuxemu3.tgz
	cd linuxemu3
	mk
	mk install

BOOTSTRAP

You need a Linux rootfilesystem packed in a tarball. Go! Get some Linux rootfs:

RUNNING

Use the provided "linux" script to chroot into your Linux rootfs. The "linux" script is neccesary because for Linux programs to run, shared libraries from your rootfs have to appear at /lib and /usr/lib, while configuration files are expected to be in /etc. The script will build a private namespace and bind the Linux rootfs over the Plan 9 root. the original Plan 9 namespace is mounted at /9.

	linux -r ./mroot /bin/bash -i

If the -r option is omitted, the Linux rootfs defaults to /sys/lib/linux. you may put your Linux rootfs there or add a bind to your $home/lib/profile.

In the Linux rootfs, /etc/resolv.conf should be changed to match your network nameserver. In addition, /etc/apt/sources.list should be updated to a working Debian mirror. (Sarge packages can still be accessed at deb http://archive.debian.org/debian-archive/debian sarge main)

EXAMPLES

DEBUGGING

If linuxemu crashes, use acid to figure out whats going on:

	mk acid
	acid -l linuxemu.acid <pid>

Then you can issue the following commands:

	ustk()				dump a (userspace) stacktrace for the current thread
	umem(Current())			dump the memory mappings
	ufds(Current())			dump the filedescriptor table
	utrace(Current())		dump the internal tracebuffer (enabled by -d option)

Use xasm()/xcasm() for disassembly for Linux code.

You can also enable full trace logging:

	linux -r ./mroot -dd /bin/bash -i >[2]/tmp/linuxemu.log

This slows linuxemu down. In case of race conditions, it often happens that the bug disapears when doing full trace logging!

NPTL

If you get one of these errors:

	cannot set up thread-local storage: cannot set up LDT for thread-local storage

This is glibc/libpthread complaining! The problem is the following: glibc on i386 decided at some point to use the extra segment registers GS and FS as an indirection pointer for thread local storage. The operating system kernel therfore must have a mechanism to let userspace change descriptor table entries and swap them in/out on context switch.

To make it work here are several options:

1) Recompile and link the program with a pre NPTL version of glibc.

2) On some distributions, a non-tls version of libc/libpthread is available. in the -linuxemu fsroot, the NPTL version is in /lib/tls, the older version is in /lib. By renaming /lib/tls to /lib/_tls_disabled_ the loader will use the non-tls version.

3) Cinap made a kernel patch that adds support for per process descriptors to Plan 9: