Re: [Qemu-devel] [Bug 929638] Re: qemu 1.0 unable to compile on the pandaboard ES

[Alexander Graf]

On 09.02.2012, at 20:18, Paul Brook wrote:

>>> On ARM Linux glibc provides a makecontext() that always fails ENOSYS,
>>> so our configure test thinks there is makecontext support but when we
>>> try to use it for coroutines it will fail and we abort.
>>> 
>>> I have a workaround in qemu-linaro that just forces the makecontext
>>> test to fail on ARM but I don't like that much. It would be better
>>> to either drop our requirement for makecontext (Paolo had some patches
>>> to try to do this IIRC) or to handle it failing at runtime.
>> 
>> Or make the configure test be an execution test and always disable it for
>> cross-compile?
> 
> I'd rather not.  If at all possible we should avoid runtime tests.  Even for 
> "native" systems they generally give the wrong answer as the machine you're 
> building on often isn't the one you will be running on.  If we know arm hosts 
> are broken then that's what we should test for in configure (with a comment 
> saying why).
> 
> IMO consistency between builds for the same target environment is more 
> important than opportunistically probing in a native builds.

I agree for CPU features, sure. Anything that would be influenced by your build 
system vs execution environment.
But in this case we're probing for a feature of a library we're linking 
against, so runtime checks really aren't all that bad, since you usually want 
to build against the same libc that you're executing against later on.


Alex