Thread cancellation (and certain other implementation-internal things such as set*id() and timers) are implemented in userspace on Linux by stealing a couple of the realtime signals for internal use by the implementation, leaving them unavailable to applications. Unfortunately, this bites qemu application-level emulation when the application being run uses thread cancellation or other features that need such signals. The signal handler is unable to be set (because sigaction on the host rejects the signal numbers) and attempts to send the signals result in it being received not by the emulated application code, but by the libc/libpthread code on which qemu is running; this in turn seems to cause qemu to crash.
The best solution I can think of is for qemu to steal one of the realtime signals for its own use, and multiplex signal numbers outside the range SIGRTMIN..SIGRTMAX, as well as the stolen signal itself, on top of this stolen signal. This would both allow cancellation to work, and would allow applications the full range of realtime signals when the guest has more signals than the host (e.g. MIPS running on x86 host).
Patch for the issue is available here:
https:/