patch-2.1.44 linux/arch/mips/kernel/branch.c

• Lines: 197
• Date: Thu Jun 26 12:33:37 1997
• Orig file: v2.1.43/linux/arch/mips/kernel/branch.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.43/linux/arch/mips/kernel/branch.c linux/arch/mips/kernel/branch.c
@@ -0,0 +1,196 @@
+/*
+ * Branch and jump emulation.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1996, 1997 by Ralf Baechle
+ */
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+#include <asm/branch.h>
+#include <asm/inst.h>
+#include <asm/ptrace.h>
+#include <asm/uaccess.h>
+
+/*
+ * Compute the return address and do emulate branch and instruction
+ * simulation, if required.
+ */
+int __compute_return_epc(struct pt_regs *regs)
+{
+	unsigned int *addr, bit, fcr31;
+	long epc;
+	union mips_instruction insn;
+
+	epc = regs->cp0_epc;
+	if (epc & 3) {
+		printk("%s: unaligned epc - sending SIGBUS.\n", current->comm);
+		force_sig(SIGBUS, current);
+		return -EFAULT;
+	}
+
+	/*
+	 * Read the instruction
+	 */
+	addr = (unsigned int *) (unsigned long) epc;
+	if (__get_user(insn.word, addr)) {
+		force_sig(SIGSEGV, current);
+		return -EFAULT;
+	}
+
+	regs->regs[0] = 0;
+	switch (insn.i_format.opcode) {
+	/*
+	 * jr and jalr are in r_format format.
+	 */
+	case spec_op:
+		switch (insn.r_format.func) {
+		case jalr_op:
+			regs->regs[insn.r_format.rd] = epc + 8;
+			/* Fall through */
+		case jr_op:
+			regs->cp0_epc = regs->regs[insn.r_format.rs];
+			break;
+		}
+		break;
+
+	/*
+	 * This group contains:
+	 * bltz_op, bgez_op, bltzl_op, bgezl_op,
+	 * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
+	 */
+	case bcond_op:
+		switch (insn.i_format.rt) {
+	 	case bltz_op:
+		case bltzl_op:
+			if (regs->regs[insn.i_format.rs] < 0)
+				epc = epc + 4 + (insn.i_format.simmediate << 2);
+			else
+				epc += 8;
+			regs->cp0_epc = epc;
+			break;
+
+		case bgez_op:
+		case bgezl_op:
+			if (regs->regs[insn.i_format.rs] >= 0)
+				epc = epc + 4 + (insn.i_format.simmediate << 2);
+			else
+				epc += 8;
+			regs->cp0_epc = epc;
+			break;
+
+		case bltzal_op:
+		case bltzall_op:
+			regs->regs[31] = epc + 8;
+			if (regs->regs[insn.i_format.rs] < 0)
+				epc = epc + 4 + (insn.i_format.simmediate << 2);
+			else
+				epc += 8;
+			regs->cp0_epc = epc;
+			break;
+
+		case bgezal_op:
+		case bgezall_op:
+			regs->regs[31] = epc + 8;
+			if (regs->regs[insn.i_format.rs] >= 0)
+				epc = epc + 4 + (insn.i_format.simmediate << 2);
+			else
+				epc += 8;
+			regs->cp0_epc = epc;
+			break;
+		}
+		break;
+
+	/*
+	 * These are unconditional and in j_format.
+	 */
+	case jal_op:
+		regs->regs[31] = regs->cp0_epc + 8;
+	case j_op:
+		epc += 4;
+		epc >>= 28;
+		epc <<= 28;
+		epc |= (insn.j_format.target << 2);
+		regs->cp0_epc = epc;
+		break;
+
+	/*
+	 * These are conditional and in i_format.
+	 */
+	case beq_op:
+	case beql_op:
+		if (regs->regs[insn.i_format.rs] ==
+		    regs->regs[insn.i_format.rt])
+			epc = epc + 4 + (insn.i_format.simmediate << 2);
+		else
+			epc += 8;
+		regs->cp0_epc = epc;
+		break;
+
+	case bne_op:
+	case bnel_op:
+		if (regs->regs[insn.i_format.rs] !=
+		    regs->regs[insn.i_format.rt])
+			epc = epc + 4 + (insn.i_format.simmediate << 2);
+		else
+			epc += 8;
+		regs->cp0_epc = epc;
+		break;
+
+	case blez_op: /* not really i_format */
+	case blezl_op:
+		/* rt field assumed to be zero */
+		if (regs->regs[insn.i_format.rs] <= 0)
+			epc = epc + 4 + (insn.i_format.simmediate << 2);
+		else
+			epc += 8;
+		regs->cp0_epc = epc;
+		break;
+
+	case bgtz_op:
+	case bgtzl_op:
+		/* rt field assumed to be zero */
+		if (regs->regs[insn.i_format.rs] > 0)
+			epc = epc + 4 + (insn.i_format.simmediate << 2);
+		else
+			epc += 8;
+		regs->cp0_epc = epc;
+		break;
+
+	/*
+	 * And now the FPA/cp1 branch instructions.
+	 *
+	 * FIXME: This will silently fail for MIPS IV cop1 branches with
+	 *        the cc field != 0.
+	 */
+	case cop1_op:
+		asm ("cfc1\t%0,$31":"=r" (fcr31));
+		bit = (insn.i_format.rt >> 2);
+		bit += bit ? 24 : 23;
+		switch (insn.i_format.rt) {
+		case 0:	/* bc1f */
+		case 2:	/* bc1fl */
+			if (~fcr31 & (1 << bit))
+				epc = epc + 4 + (insn.i_format.simmediate << 2);
+			else
+				epc += 8;
+			regs->cp0_epc = epc;
+			break;
+
+		case 1:	/* bc1t */
+		case 3:	/* bc1tl */
+			if (fcr31 & (1 << bit))
+				epc = epc + 4 + (insn.i_format.simmediate << 2);
+			else
+				epc += 8;
+			regs->cp0_epc = epc;
+			break;
+		}
+		break;
+	}
+
+	return 0;
+}