why don't setjmp save MXCSR register and x87 control word?

[Fengkai Sun]

Hello Adhemerval,

Thank you very much for your informative reply!

I think I've figured it out: setjmp and longjmp, though look like function
call
and return, are actually not. Thus their behavior should be defined by
standard
 instead of calling conventions, is that correct?

I still have one question here:

On Thu, Mar 18, 2021 at 2:59 AM Adhemerval Zanella <
adhemerval.zanella@linaro.org> wrote:

>   Note that standards don't require longjmp to restore either control
>   word, and none of Linux, MacOS X 10.3 and earlier, NetBSD, OpenBSD,
>   or Solaris do it. However, it is historical FreeBSD behavior, and
>   bde points out that it is needed to make longjmping out of a signal
>   handler work properly, given the way FreeBSD clobbers the FPU state
>   on signal handler entry.
>
>
Does this mean that on FreeBSD, after longjmp to the saved context, the FPU
 state will be restored to what it was right after setjmp, while on other
OSs it's not?
Because the situation I think of is that, the call stack between setjmp and
longjmp
 may have operations modifying FPU state, but longjmp does not restore it
on
most OSs.


Much appreciated,
Fengkai