[Qemu-devel] [Bug 883136] Re: qemu on ARM hosts aborts on startup because makecontext() always fails

[Peter Maydell]

Michael Hope pointed out that glibc defines a macro __stub_makecontext
when the makecontext() implementation is a stub, so we can just add this
to the qemu configure test to make it automatically fall back to the
pthreads version as required.

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https://bugs.launchpad.net/bugs/883136

Title:
  qemu on ARM hosts aborts on startup because makecontext() always fails

Status in QEMU:
  New
Status in Linaro QEMU:
  In Progress

Bug description:
  qemu has recently grown a coroutines implementation. There are two
  versions, one using the makecontext/setcontext/swapcontext functions
  from ucontext.h, and one falling back to implementing coroutines as
  separate glib threads. configure chooses the former if the platform
  has a makecontext().

  Unfortunately ARM eglibc provides a makecontext() which always fails
  ENOSYS, which means the configure check passes but when qemu starts it
  abort()s.

  The best fix for this is probably going to involve making the
  coroutine implementation runtime-selectable.

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