Initial Spring 2016 commit.

kern/arch/mips/include/current.h

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2009
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _MIPS_CURRENT_H_
+#define _MIPS_CURRENT_H_
+
+
+/*
+ * Macro for current thread, or current cpu.
+ *
+ * This file should only be included via <current.h> (q.v.)
+ *
+ * On mips we track the current thread. There's an architectural
+ * issue that informs this choice: there's no easy way to find the
+ * current cpu, the current thread, or even the kernel stack of the
+ * current thread when entering the kernel at trap time. (On most CPUs
+ * there's a canonical way to find at least the stack.)
+ *
+ * Therefore we do the following:
+ *
+ * - We misuse a kernel-settable field of a nonessential MMU register
+ *   to hold the CPU number.
+ *
+ * - On trap entry we use this number to index an array that gets us
+ *   both the kernel stack and curthread.
+ *
+ * - We tell the compiler not to use the s7 register and keep
+ *   curthread there.
+ *
+ * Note that if you want to change this scheme to use a different
+ * register, or change to a different scheme, you need to touch three
+ * places: here, the mips-specific kernel CFLAGS in the makefiles, and
+ * the trap entry and return code.
+ */
+
+#ifdef __GNUC__
+register struct thread *curthread __asm("$23");	/* s7 register */
+#else
+#error "Don't know how to declare curthread in this compiler"
+#endif
+#undef __NEED_CURTHREAD
+#define __NEED_CURCPU
+
+/* For how we've defined it, curthread gets set first, then curcpu. */
+#define INIT_CURCPU(cpu, thread) (curthread = (thread), curcpu = (cpu))
+
+#endif /* _MIPS_CURRENT_H_ */