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[Qemu-devel] [Bug 1068900] Re: Thread cancellation broken in app-level e

From: Launchpad Bug Tracker
Subject: [Qemu-devel] [Bug 1068900] Re: Thread cancellation broken in app-level emulation
Date: Wed, 15 Feb 2017 04:17:23 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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  Thread cancellation broken in app-level emulation

Status in QEMU:

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

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