[PATCH] Cygwin: fegetenv() in winsup/cygwin/fenv.cc should not disable exceptions!

Corinna Vinschen corinna-cygwin@cygwin.com
Fri Aug 3 10:39:00 GMT 2018

On Aug  3 11:27, Houder wrote:
> On 2018-08-03 09:36, Corinna Vinschen wrote:
> > Hi J.H.,
> > 
> > Pushed with tweaks.  The string in __asm__ statements works a
> Bah! Must be the heat! I did a compare (sdiff), but missed it. You
> are correct: the '\n' is required.
> > bit different and I made a slight change to the commit message.
> No problem! (you could have gone even further; your command of the
> English language is far better than mine).
> > In terms of x86_64, do we have to change the fenv stuff completely
> > to use only SSE opcodes?  Does that make sense at all?
> Ho! I have to disappoint you here! I am not an expert at all.

Thanks all the same for your detailed description.  A quick search in
glibc shows that x86_64 FP exceptions in fact work somewhat different in
that it additionally reads and writes from the SSE control register,
e.g. sysdeps/x86_64/fpu/fesetenv.c:

    __asm__ ("fnstenv %0\n"
           "stmxcsr %1" : "=m" (*&temp), "=m" (*&temp.__mxcsr));
      __asm__ ("fldenv %0\n"
           "ldmxcsr %1" : : "m" (temp), "m" (temp.__mxcsr));

If you're still interested in this stuff, feel free to create more
patches :)


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat
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