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Initial x87 control word is different from native linux #3912

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luoqi-git opened this Issue Mar 13, 2019 · 1 comment

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luoqi-git commented Mar 13, 2019

Please fill out the below information:

  • Your Windows build number: (Type ver at a Windows Command Prompt)
    Microsoft Windows [Version 10.0.17134.523]

  • What you're doing and what's happening: (Copy&paste the full set of specific command-line steps necessary to reproduce the behavior, and their output. Include screen shots if that helps demonstrate the problem.)
    The default/initial x87 control word is different from that of a native linux system, specifically the precision control field. This affects for example all long double variants of math library functions which use x87 FPU and not SSE.

% cat t.c
#include <stdio.h>
#include <xmmintrin.h>

static unsigned short _mm_getfcw()
{
	unsigned short word;
	asm volatile("fstcw %0" : "=m" (*(&word)));
	return word;
}

int main()
{
	printf("%x %x\n", _mm_getfcw(), _mm_getcsr());
}
% cc -o t t.c
centos% ./t
37f 1f80
wsl% ./t
27f 1f80
  • What's wrong / what should be happening instead:
    The initial x87 control word is expected to be 0x37f.

  • Strace of the failing command, if applicable: (If some_command is failing, then run strace -o some_command.strace -f some_command some_args, and link the contents of some_command.strace in a gist here).
    N/A

  • For WSL launch issues, please collect detailed logs.
    N/A

See our contributing instructions for assistance.

@therealkenc

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therealkenc commented Mar 13, 2019

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