cygwin 3.5.4-1: signal handling destroys 'long double' values
Takashi Yano
takashi.yano@nifty.ne.jp
Tue Oct 8 11:20:57 GMT 2024
On Mon, 7 Oct 2024 15:11:52 +0200
Christian Franke wrote:
> $ gcc -o sigtest -O2 sigtest.c
>
> $ ./sigtest > out.txt
> (press ^C 42x :-)
>
> $ sort out.txt | uniq -c
> 3 x = 0x1.23456789p+0, y = -nan, d = -nan
> 6 x = 0x1.23456789p+0, y = 0x1.23456789p+0, d = -nan
> 33 x = 0x1.23456789p+0, y = 0x1.23456789p+0, d = 0x0p+0
>
> The problem also occurs if compiled without -O2, but less often. No
> problem occurs if compiled with -DWORKS which suggests that only 'long
> double' is affected.
Thanks for the report. I looked into this problem and might find the
cause. It seems due to a bug of scripts/gendef. It generates signal
handler caller (sigfe.s) which stores/restores the registers.
In sigdelayed, control word is stored/restored by fnstcw/fldcw instruction,
however, fninit instruction destroys some status registers in FPU (x87).
I think we shold use fnstenv/fldenv rather than fnstcw/fldcw and fninit.
However, I'm not familiar with x87 instructions, so I may overlook
something.
Could anyone expert of x87 instructions and sigfe stuff give some
comments?
--
Takashi Yano <takashi.yano@nifty.ne.jp>
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