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used_math not cleared for new processes?

To: "" <>
Subject: used_math not cleared for new processes?
From: Zhang Fuxin <>
Date: Sat, 2 Feb 2002 14:20:6 +0800
   I find that current->used_math isn't cleared when we start a new process.Is 
intended? I mean 'start_thread' in do_exec but not 'copy_thread' in do_fork when
speaking 'start a new process'. We can/should? keep used_math for the 
latter,but for
the former?

   It leads to a failure in libm-test(the fpu control register doesn't equal to 
I think the reason is that init_fpu fail to be called with used_math set.
  BTW: besides this failure,i see a lot of more related to extra "Invalid 
operation" exception.
   exp(NaN) == NaN: Exception "Invalid operation" set
   fmax (0, NaN) == 0: Exception "Invalid operation" set
  My cpu is IDT RC64474,which is basically a r4600.

  I think the cause probably is mips's special SNaN and QNaN handling.

  Could somebody explain?

            Zhang Fuxin

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