Public bug reported:
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).
** Affects: qemu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1068900
Title:
Thread cancellation broken in app-level emulation
Status in QEMU:
New
Bug description:
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).
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