FPU emulator unsafe for SMP?

2 messages, 2 authors, 2002-02-15 · open the first message on its own page

FPU emulator unsafe for SMP?

From: Jun Sun <hidden>
Date: 2002-02-15 02:56:46

I have been chasing a FPU register corruption problem on a SMP box.  The
curruption seems to be caused by FPU emulator code.  Is that code SMP safe? 
If not, what are the volunerable spots?

Just thought I'd check before I dive into it ....

BTW, I think even with the latest fpu emu patch, the classic fpu/signal
problem is still there.  I will post in a separate email later.

Jun

Re: FPU emulator unsafe for SMP?

From: Kevin D. Kissell <hidden>
Date: 2002-02-15 10:49:03

I have been chasing a FPU register corruption problem on a SMP box.  The
curruption seems to be caused by FPU emulator code.  Is that code SMP
safe?
If not, what are the volunerable spots?

Just thought I'd check before I dive into it ....
While the very first prototype was grossly SMP unsafe, the
state associated with the emulated "FPU" was migrated
into the thread context area long ago.  It is just possible,
however, that some internal emulator state persists in
a global variable somewhere, which could create problems
under SMP execution.
BTW, I think even with the latest fpu emu patch, the classic fpu/signal
problem is still there.  I will post in a separate email later.
I submitted a series of patches a year or so ago, the
last of which really should have been a comprehensive
fix to the FPU context switch and signal problems.
The last time I looked, that patch had never made it into
the OSS repository, but neither had anyone reported
any holes in it.

            Kevin K.
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