74 lines
3.0 KiB
C
74 lines
3.0 KiB
C
/*
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* Copyright (c) 2009
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* The President and Fellows of Harvard College.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef _MIPS_CURRENT_H_
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#define _MIPS_CURRENT_H_
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/*
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* Macro for current thread, or current cpu.
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*
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* This file should only be included via <current.h> (q.v.)
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*
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* On mips we track the current thread. There's an architectural
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* issue that informs this choice: there's no easy way to find the
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* current cpu, the current thread, or even the kernel stack of the
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* current thread when entering the kernel at trap time. (On most CPUs
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* there's a canonical way to find at least the stack.)
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*
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* Therefore we do the following:
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*
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* - We misuse a kernel-settable field of a nonessential MMU register
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* to hold the CPU number.
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*
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* - On trap entry we use this number to index an array that gets us
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* both the kernel stack and curthread.
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*
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* - We tell the compiler not to use the s7 register and keep
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* curthread there.
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*
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* Note that if you want to change this scheme to use a different
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* register, or change to a different scheme, you need to touch three
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* places: here, the mips-specific kernel CFLAGS in the makefiles, and
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* the trap entry and return code.
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*/
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#ifdef __GNUC__
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register struct thread *curthread __asm("$23"); /* s7 register */
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#else
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#error "Don't know how to declare curthread in this compiler"
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#endif
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#undef __NEED_CURTHREAD
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#define __NEED_CURCPU
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/* For how we've defined it, curthread gets set first, then curcpu. */
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#define INIT_CURCPU(cpu, thread) (curthread = (thread), curcpu = (cpu))
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#endif /* _MIPS_CURRENT_H_ */
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