[PATCH] Add some sysfs files to debug unaligned accesses

[Atsushi Nemoto <anemo@mba.ocn.ne.jp>]

Currently a number of unaligned instructions is counted but not used.
Add /sys/kernel/mips/unaligned_instructions file to show the value.

And add /sys/kernel/mips/unaligned_action to control behavior upon an
unaligned access.  Possible actions are:

quiet: silently fixup the unaligned access.
signal: send SIGBUS.
show: dump registers, process name, etc. and fixup.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
---
 arch/mips/kernel/setup.c     |   14 ++++++++
 arch/mips/kernel/unaligned.c |   70 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 4975da0..af88f27 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -574,3 +574,17 @@ __setup("nodsp", dsp_disable);
 
 unsigned long kernelsp[NR_CPUS];
 unsigned long fw_arg0, fw_arg1, fw_arg2, fw_arg3;
+
+static struct attribute *mips_attrs[] = {
+       NULL
+};
+static struct attribute_group mips_attr_group = {
+       .name = "mips",
+       .attrs = mips_attrs,
+};
+
+static int __init sysfs_mips(void)
+{
+       return sysfs_create_group(&kernel_subsys.kset.kobj, &mips_attr_group);
+}
+arch_initcall(sysfs_mips);
diff --git a/arch/mips/kernel/unaligned.c b/arch/mips/kernel/unaligned.c
index 24b7b05..3f08ab9 100644
--- a/arch/mips/kernel/unaligned.c
+++ b/arch/mips/kernel/unaligned.c
@@ -88,9 +88,14 @@
 #define STR(x)  __STR(x)
 #define __STR(x)  #x
 
-#ifdef CONFIG_PROC_FS
-unsigned long unaligned_instructions;
+#ifdef CONFIG_SYSFS
+static unsigned long unaligned_instructions;
+static int unaligned_action;
+static const char *unaligned_actions[] = {"quiet", "signal", "show"};
+#else
+#define unaligned_action 0
 #endif
+extern void show_registers(struct pt_regs *regs);
 
 static inline int emulate_load_store_insn(struct pt_regs *regs,
        void __user *addr, unsigned int __user *pc,
@@ -460,7 +465,7 @@ static inline int emulate_load_store_ins
                goto sigill;
        }
 
-#ifdef CONFIG_PROC_FS
+#ifdef CONFIG_SYSFS
        unaligned_instructions++;
 #endif
 
@@ -517,6 +522,10 @@ asmlinkage void do_ade(struct pt_regs *r
        pc = (unsigned int __user *) exception_epc(regs);
        if (user_mode(regs) && (current->thread.mflags & MF_FIXADE) == 0)
                goto sigbus;
+       if (unaligned_action == 1)
+               goto sigbus;
+       else if (unaligned_action == 2)
+               show_registers(regs);
 
        /*
         * Do branch emulation only if we didn't forward the exception.
@@ -547,3 +556,58 @@ sigbus:
         * XXX On return from the signal handler we should advance the epc
         */
 }
+
+#ifdef CONFIG_SYSFS
+static ssize_t unaligned_instructions_show(struct subsystem *subsys, char *buf)
+{
+       return sprintf(buf, "%lu\n", unaligned_instructions);
+}
+
+static ssize_t unaligned_action_show(struct subsystem *subsys, char *buf)
+{
+       int i;
+       char *s = buf;
+
+       for (i = 0; i < ARRAY_SIZE(unaligned_actions); i++) {
+               if (i == unaligned_action)
+                       s += sprintf(s, "[%s] ", unaligned_actions[i]);
+               else
+                       s += sprintf(s, "%s ", unaligned_actions[i]);
+       }
+       s += sprintf(s, "\n");
+       return s - buf;
+}
+
+static ssize_t unaligned_action_store(struct subsystem *subsys,
+                                     const char *buf, size_t count)
+{
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(unaligned_actions); i++) {
+               if (!strncmp(buf, unaligned_actions[i],
+                            min(count, strlen(unaligned_actions[i])))) {
+                       unaligned_action = i;
+                       return count;
+               }
+       }
+       return -EINVAL;
+}
+
+#define __ATTR_RW(_name) __ATTR(_name, 0644, _name##_show, _name##_store)
+static struct subsys_attribute unaligned_attrs[] = {
+       __ATTR_RO(unaligned_instructions),
+       __ATTR_RW(unaligned_action),
+};
+
+static int __init sysfs_unaligned(void)
+{
+       int i;
+
+       for (i = 0; i < ARRAY_SIZE(unaligned_attrs); i++)
+               sysfs_add_file_to_group(&kernel_subsys.kset.kobj,
+                                       &unaligned_attrs[i].attr,
+                                       "mips");
+       return 0;
+}
+__initcall(sysfs_unaligned);
+#endif