NetBSD Problem Report #57684
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Date: Mon, 6 Nov 2023 16:03:20 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: fpsetround(3) fails to set SSE rounding mode
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>Number: 57684
>Category: port-i386
>Synopsis: fpsetround(3) fails to set SSE rounding mode
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: port-i386-maintainer
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Mon Nov 06 16:05:00 +0000 2023
>Originator: Taylor R Campbell
>Release: current
>Organization:
The 387BSD Foundation
>Environment:
>Description:
The i386 fpsetround function only sets the i387 rounding mode in the FP control word with fldcw:
https://nxr.netbsd.org/xref/src/lib/libc/arch/i386/gen/fpsetround.S?r=1.6
If machdep.sse is true, it needs to also set the SSE rounding mode in the MXCSR with ldmxcsr like fesetround does:
https://nxr.netbsd.org/xref/src/lib/libm/arch/i387/fenv.c?r=1.10#335
However, fpsetround can't simply call fesetround because fpsetround lives in libc while fesetround lives in libm.
>How-To-Repeat:
call fpsetround, read the mxcsr or do SSE floating-point
>Fix:
Yes, please!
Copy & paste of the i387/fenv.c approach should work.
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