On Sun, 13 Oct 2024 11:55:46 +0200 Christian Franke wrote: > Takashi Yano via Cygwin wrote: > > Hi Brian, > > > > On Tue, 8 Oct 2024 10:37:14 -0600 > > Brian Inglis wrote: > >> On 2024-10-08 10:14, Brian Inglis via Cygwin wrote: > >>> On 2024-10-08 05:20, Takashi Yano via Cygwin wrote: > >>>> 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? > >>> AIUI x87 FP handling is outdated and mainly unused on current systems, as > >>> current systems do more and use more than the legacy x87 instructions and > >>> stack. > >>> > >>> See https://en.cppreference.com/w/c/numeric/fenv and related docs for more > >>> modern approaches. > >>> > >>> You would have to look into the AMD/Intel/IEEE docs for lower level > >>> details. > >> This is basically what ISTR: > >> > >> https://beta.boost.org/doc/libs/1_82_0/libs/context/doc/html/context/rationale/x86_and_floating_point_env.html > >> > >> where legacy x87 and MMX registers are not used or preserved on > >> x86_64/amd64, as > >> SSE... instructions and XMM registers are used. > > Thanks for the advice. I read throuh the web pages and related documents > > and made a patch which uses fxsave/fxrstor and xsave/xrstror to > > cygwin-patc...@cygwin.com mailing list. > > https://cygwin.com/pipermail/cygwin-patches/2024q4/012804.html > > The patch fixes the testcases from my original post on a CPU with XSAFE > support and also if usage of FXSAVE if forced by this hack: > > movl \$1,%eax > cpuid > - andl \$0x04000000,%ecx # xsave available? > + andl \$0x00000000,%ecx # xsave available? > jnz 1f
Thanks for testing! -- Takashi Yano <takashi.y...@nifty.ne.jp> -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
