sh: BUG() handling through trapa vector.

Previously we haven't been doing anything with verbose BUG() reporting,
and we've been relying on the oops path for handling BUG()'s, which is
rather sub-optimal.

This switches BUG handling to use a fixed trapa vector (#0x3e) where we
construct a small bug frame post trapa instruction to get the context
right. This also makes it trivial to wire up a DIE_BUG for the atomic
die chain, which we couldn't really do before.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

2 files changed, 45 insertions, 0 deletions

diff --git a/arch/sh/kernel/process.c b/arch/sh/kernel/process.c
index f3e2631be144..7347f6afa030 100644
--- a/arch/sh/kernel/process.c
+++ b/arch/sh/kernel/process.c
@@ -498,6 +498,16 @@ asmlinkage void break_point_trap_software(unsigned long r4, unsigned long r5,
 {
         struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
 
+        /* Rewind */
         regs->pc -= 2;
+
+#ifdef CONFIG_BUG
+        if (__kernel_text_address(instruction_pointer(regs))) {
+                u16 insn = *(u16 *)instruction_pointer(regs);
+                if (insn == TRAPA_BUG_OPCODE)
+                        handle_BUG(regs);
+        }
+#endif
+
         force_sig(SIGTRAP, current);
 }
diff --git a/arch/sh/kernel/traps.c b/arch/sh/kernel/traps.c
index 3762d9dc2046..ec110157992d 100644
--- a/arch/sh/kernel/traps.c
+++ b/arch/sh/kernel/traps.c
@@ -19,6 +19,7 @@
 #include <linux/kallsyms.h>
 #include <linux/io.h>
 #include <linux/debug_locks.h>
+#include <linux/limits.h>
 #include <asm/system.h>
 #include <asm/uaccess.h>
 
@@ -129,6 +130,40 @@ static int die_if_no_fixup(const char * str, struct pt_regs * regs, long err)
         return -EFAULT;
 }
 
+#ifdef CONFIG_BUG
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+static inline void do_bug_verbose(struct pt_regs *regs)
+{
+        struct bug_frame f;
+        long len;
+
+        if (__copy_from_user(&f, (const void __user *)regs->pc,
+                             sizeof(struct bug_frame)))
+                return;
+
+        len = __strnlen_user(f.file, PATH_MAX) - 1;
+        if (unlikely(len < 0 || len >= PATH_MAX))
+                f.file = "<bad filename>";
+        len = __strnlen_user(f.func, PATH_MAX) - 1;
+        if (unlikely(len < 0 || len >= PATH_MAX))
+                f.func = "<bad function>";
+
+        printk(KERN_ALERT "kernel BUG in %s() at %s:%d!\n",
+               f.func, f.file, f.line);
+}
+#else
+static inline void do_bug_verbose(struct pt_regs *regs)
+{
+}
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+#endif /* CONFIG_BUG */
+
+void handle_BUG(struct pt_regs *regs)
+{
+        do_bug_verbose(regs);
+        die("Kernel BUG", regs, TRAPA_BUG_OPCODE & 0xff);
+}
+
 /*
  * handle an instruction that does an unaligned memory access by emulating the
  * desired behaviour