From owner-cvs-all  Tue Apr 24 14: 6:57 2001
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From: John Baldwin <jhb@FreeBSD.org>
Date: Tue, 24 Apr 2001 14:06:53 -0700 (PDT)
To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: cvs commit: src/sys/alpha/alpha exception.s genassym.c interrupt.c
         machdep.c trap.c src/sys/alpha/include proc.h
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jhb         2001/04/24 14:06:53 PDT

  Modified files:
    sys/alpha/alpha      exception.s genassym.c interrupt.c 
                         machdep.c trap.c 
    sys/alpha/include    proc.h 
  Log:
  Add a new field 'md_kernnest' to the alpha machine dependent process
  structure.  This field keeps track of how many levels deep we are nested
  into the kernel.  The nesting level is bumped at the start of a trap,
  interrupt, syscall, or exception and is decremented on return.  This is
  used to detect the case when the kernel is returning back to a kernel
  context in exception_return().  If we are returning to the kernel we need
  to update the globaldata pointer register saved in the stack frame in case
  we have switched CPU's between taking the initial interrupt that saved the
  frame and returning.  If we don't do this fixup it is possible for a CPU to
  use the wrong per-cpu data.  On UP systems this is not a problem, so the
  code is conditional on SMP.
  
  A count was used instead of simply checking the process status register in
  the frame during exception_return() since there are critical sections at
  the very start and end of a trap, exception, or interrupt from userland in
  which we could trash the t7 register being used in userland.  The counter
  is incremented after adn before these critical sections respectively so
  that we will not overwrite the saved t7 register if we are interrupted
  during one of these critical sections.
  
  Revision  Changes    Path
  1.10      +32 -15    src/sys/alpha/alpha/exception.s
  1.29      +4 -1      src/sys/alpha/alpha/genassym.c
  1.48      +11 -1     src/sys/alpha/alpha/interrupt.c
  1.125     +4 -1      src/sys/alpha/alpha/machdep.c
  1.57      +23 -3     src/sys/alpha/alpha/trap.c
  1.10      +2 -1      src/sys/alpha/include/proc.h


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