[Bug math/21035] longjmp() resets FPU exception mask

["joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=21035

--- Comment #7 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
The floating-point state is logically like a thread-local variable.  
Indeed, on some platforms some parts of it *are* TLS variables.

It would be wrong for siglongjmp to restore the value of a thread-local 
variable to what it was when sigsetjmp was called - the user program might 
have changed it after calling sigsetjmp, and that change must remain in 
effect.  Likewise, it would be wrong for siglongjmp to restore the 
floating-point environment to what it was when sigsetjmp was called - 
changes made by the user program must remain in effect.  You want the 
state as it was before the kernel called the signal handler, but 
siglongjmp doesn't have access to that information.

Note that POSIX explicitly says about longjmp (and the siglongjmp 
differences don't matter): "All accessible objects have values, and all 
other components of the abstract machine have state (for example, 
floating-point status flags and open files), as of the time longjmp() was 
called, except that the values of objects of automatic storage duration 
are unspecified if they meet all the following conditions".

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