[Bug 275322] Improper handling of mxcsr register during debug (gdb/lldb)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275322

Mark Johnston <markj@FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |markj@FreeBSD.org

--- Comment #7 from Mark Johnston <markj@FreeBSD.org> ---
When I run this on a Ryzen 7950X3D running main, I get:

ra=7.01209994486364354e-310 reatt=10000000000 ra * reatt-> result =0 savemxcsr
00001f80 mxcsr_set 00009fc0 showmxcsr 00009fc0 mxcsr 00009fc0

when I have a breakpoint on the "mulsd" instruction:

ra=7.01209994486364354e-310 reatt=10000000000 ra * reatt-> result =0 savemxcsr
00001f80 mxcsr_set 00009fc0 showmxcsr 00009fc0 mxcsr 00009fc0

while stopped at "mulsd":

(gdb) info register mxcsr
mxcsr          0x1f80              [ IM DM ZM OM UM PM ]
(gdb) c
Continuing.
ra=7.01209994486364354e-310 reatt=10000000000 ra * reatt-> result
=7.01209994486364403e-300 savemxcsr 00001f80 mxcsr_set 00009fc0 showmxcsr
00009fc0 mxcsr 00001fa2

So I believe the problem is reproducible here. In particular, the output of the
test program varies depending on whether I print the value of mxcsr from gdb or
not.

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