MIPS: Enable HAVE_ARCH_TRACEHOOK.

This enables /proc/<pid>/syscall and the ptrace PTRACE_GETREGSET and
PTRACE_SETREGSET operations.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -8,6 +8,7 @@ config MIPS
 	select HAVE_PERF_EVENTS
 	select PERF_USE_VMALLOC
 	select HAVE_ARCH_KGDB
+	select HAVE_ARCH_TRACEHOOK
 	select ARCH_HAVE_CUSTOM_GPIO_H
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST

arch/mips/include/asm/ptrace.h

@@ -81,7 +81,6 @@ static inline long regs_return_value(struct pt_regs *regs)
 
 #define instruction_pointer(regs) ((regs)->cp0_epc)
 #define profile_pc(regs) instruction_pointer(regs)
-#define user_stack_pointer(r) ((r)->regs[29])
 
 extern asmlinkage void syscall_trace_enter(struct pt_regs *regs);
 extern asmlinkage void syscall_trace_leave(struct pt_regs *regs);
@@ -100,4 +99,17 @@ static inline void die_if_kernel(const char *str, struct pt_regs *regs)
 	(struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1 - 32) - 1;	\
 })
 
+/* Helpers for working with the user stack pointer */
+
+static inline unsigned long user_stack_pointer(struct pt_regs *regs)
+{
+	return regs->regs[29];
+}
+
+static inline void user_stack_pointer_set(struct pt_regs *regs,
+	unsigned long val)
+{
+	regs->regs[29] = val;
+}
+
 #endif /* _ASM_PTRACE_H */

arch/mips/include/asm/syscall.h

 /*
+ * Access to user system call parameters and results
+ *
  * 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.
  *
+ * See asm-generic/syscall.h for descriptions of what we must do here.
+ *
  * Copyright (C) 2012 Ralf Baechle <ralf@linux-mips.org>
  */
 
 #ifndef __ASM_MIPS_SYSCALL_H
 #define __ASM_MIPS_SYSCALL_H
 
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+#include <asm/ptrace.h>
+
+static inline long syscall_get_nr(struct task_struct *task,
+				  struct pt_regs *regs)
+{
+	return regs->regs[2];
+}
+
+static inline unsigned long mips_get_syscall_arg(unsigned long *arg,
+	struct task_struct *task, struct pt_regs *regs, unsigned int n)
+{
+	unsigned long usp = regs->regs[29];
+
+	switch (n) {
+	case 0: case 1: case 2: case 3:
+		*arg = regs->regs[4 + n];
+
+		return 0;
+
+#ifdef CONFIG_32BIT
+	case 4: case 5: case 6: case 7:
+		return get_user(*arg, (int *)usp + 4 * n);
+#endif
+
+#ifdef CONFIG_64BIT
+	case 4: case 5: case 6: case 7:
+#ifdef CONFIG_MIPS32_O32
+		if (test_thread_flag(TIF_32BIT_REGS))
+			return get_user(*arg, (int *)usp + 4 * n);
+		else
+#endif
+			*arg = regs->regs[4 + n];
+
+		return 0;
+#endif
+
+	default:
+		BUG();
+	}
+}
+
+static inline void syscall_get_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned int i, unsigned int n,
+					 unsigned long *args)
+{
+	unsigned long arg;
+	int ret;
+
+	while (n--)
+		ret |= mips_get_syscall_arg(&arg, task, regs, i++);
+
+	/*
+	 * No way to communicate an error because this is a void function.
+	 */
+#if 0
+	return ret;
+#endif
+}
+
 extern const unsigned long sys_call_table[];
 extern const unsigned long sys32_call_table[];
 extern const unsigned long sysn32_call_table[];