8 files changed, 95 insertions, 26 deletions

diff --git a/arch/sh/include/asm/bug.h b/arch/sh/include/asm/bug.h
index c01718040166..b7d9822fd6c2 100644
--- a/arch/sh/include/asm/bug.h
+++ b/arch/sh/include/asm/bug.h
@@ -1,6 +1,7 @@
 #ifndef __ASM_SH_BUG_H
 #define __ASM_SH_BUG_H
 
+#define TRAPA_UNWINDER_BUG_OPCODE 0xc33b /* trapa #0x3b */
 #define TRAPA_BUG_OPCODE        0xc33e  /* trapa #0x3e */
 
 #ifdef CONFIG_GENERIC_BUG
@@ -72,6 +73,30 @@ do {							\
         unlikely(__ret_warn_on);                                \
 })
 
+#define UNWINDER_BUG()                                          \
+do {                                                    \
+        __asm__ __volatile__ (                          \
+                "1:\t.short %O0\n"                      \
+                _EMIT_BUG_ENTRY         \
+                 :                                      \
+                 : "n" (TRAPA_UNWINDER_BUG_OPCODE),     \
+                   "i" (__FILE__),                      \
+                   "i" (__LINE__), "i" (0),             \
+                   "i" (sizeof(struct bug_entry)));     \
+} while (0)
+
+#define UNWINDER_BUG_ON(x) ({                                   \
+        int __ret_unwinder_on = !!(x);                          \
+        if (__builtin_constant_p(__ret_unwinder_on)) {          \
+                if (__ret_unwinder_on)                          \
+                        UNWINDER_BUG();                         \
+        } else {                                                \
+                if (unlikely(__ret_unwinder_on))                \
+                        UNWINDER_BUG();                         \
+        }                                                       \
+        unlikely(__ret_unwinder_on);                            \
+})
+
 #endif /* CONFIG_GENERIC_BUG */
 
 #include <asm-generic/bug.h>
diff --git a/arch/sh/include/asm/system.h b/arch/sh/include/asm/system.h
index ab79e1f4fbe0..f9e2ceb94d9b 100644
--- a/arch/sh/include/asm/system.h
+++ b/arch/sh/include/asm/system.h
@@ -181,6 +181,11 @@ BUILD_TRAP_HANDLER(breakpoint);
 BUILD_TRAP_HANDLER(singlestep);
 BUILD_TRAP_HANDLER(fpu_error);
 BUILD_TRAP_HANDLER(fpu_state_restore);
+BUILD_TRAP_HANDLER(unwinder);
+
+#ifdef CONFIG_BUG
+extern void handle_BUG(struct pt_regs *);
+#endif
 
 #define arch_align_stack(x) (x)
 
diff --git a/arch/sh/include/asm/unwinder.h b/arch/sh/include/asm/unwinder.h
index 3dc551453e28..1e65c07b3e18 100644
--- a/arch/sh/include/asm/unwinder.h
+++ b/arch/sh/include/asm/unwinder.h
@@ -22,4 +22,10 @@ extern void stack_reader_dump(struct task_struct *, struct pt_regs *,
                               unsigned long *, const struct stacktrace_ops *,
                               void *);
 
+/*
+ * Used by fault handling code to signal to the unwinder code that it
+ * should switch to a different unwinder.
+ */
+extern int unwinder_faulted;
+
 #endif /* _LINUX_UNWINDER_H */
diff --git a/arch/sh/kernel/debugtraps.S b/arch/sh/kernel/debugtraps.S
index 591741383ee6..cb00e4a82d4d 100644
--- a/arch/sh/kernel/debugtraps.S
+++ b/arch/sh/kernel/debugtraps.S
@@ -21,6 +21,10 @@
 #define sh_bios_handler                 debug_trap_handler
 #endif
 
+#if !defined(CONFIG_DWARF_UNWINDER)
+#define unwinder_trap_handler           debug_trap_handler
+#endif
+
         .data
 
 ENTRY(debug_trap_table)
@@ -35,7 +39,7 @@ ENTRY(debug_trap_table)
         .long debug_trap_handler        /* 0x38 */
         .long debug_trap_handler        /* 0x39 */
         .long debug_trap_handler        /* 0x3a */
-        .long debug_trap_handler        /* 0x3b */
+        .long unwinder_trap_handler     /* 0x3b */
         .long breakpoint_trap_handler   /* 0x3c */
         .long singlestep_trap_handler   /* 0x3d */
         .long bug_trap_handler          /* 0x3e */
diff --git a/arch/sh/kernel/dwarf.c b/arch/sh/kernel/dwarf.c
index d271d04adccd..606ece37eb42 100644
--- a/arch/sh/kernel/dwarf.c
+++ b/arch/sh/kernel/dwarf.c
@@ -69,7 +69,7 @@ static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
                  * Let's just bomb hard here, we have no way to
                  * gracefully recover.
                  */
-                BUG();
+                UNWINDER_BUG();
         }
 
         reg->number = reg_num;
@@ -232,7 +232,7 @@ static int dwarf_read_encoded_value(char *addr, unsigned long *val,
                 break;
         default:
                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
-                BUG();
+                UNWINDER_BUG();
         }
 
         if ((encoding & 0x07) == 0x00)
@@ -247,7 +247,7 @@ static int dwarf_read_encoded_value(char *addr, unsigned long *val,
                 break;
         default:
                 pr_debug("encoding=0x%x\n", encoding);
-                BUG();
+                UNWINDER_BUG();
         }
 
         return count;
@@ -519,6 +519,7 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
                         break;
                 default:
                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
+                        UNWINDER_BUG();
                         break;
                 }
         }
@@ -535,8 +536,8 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
  *      on the callstack. Each of the lower (older) stack frames are
  *      linked via the "prev" member.
  */
-struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
-                                       struct dwarf_frame *prev)
+struct dwarf_frame * dwarf_unwind_stack(unsigned long pc,
+                                        struct dwarf_frame *prev)
 {
         struct dwarf_frame *frame;
         struct dwarf_cie *cie;
@@ -558,7 +559,7 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
         frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
         if (!frame) {
                 printk(KERN_ERR "Unable to allocate a dwarf frame\n");
-                BUG();
+                UNWINDER_BUG();
         }
 
         INIT_LIST_HEAD(&frame->reg_list);
@@ -605,7 +606,8 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
         case DWARF_FRAME_CFA_REG_OFFSET:
                 if (prev) {
                         reg = dwarf_frame_reg(prev, frame->cfa_register);
-                        BUG_ON(!reg);
+                        UNWINDER_BUG_ON(!reg);
+                        UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 
                         addr = prev->cfa + reg->addr;
                         frame->cfa = __raw_readl(addr);
@@ -624,12 +626,13 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
                 frame->cfa += frame->cfa_offset;
                 break;
         default:
-                BUG();
+                UNWINDER_BUG();
         }
 
         /* If we haven't seen the return address reg, we're screwed. */
         reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
-        BUG_ON(!reg);
+        UNWINDER_BUG_ON(!reg);
+        UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 
         addr = frame->cfa + reg->addr;
         frame->return_addr = __raw_readl(addr);
@@ -664,7 +667,7 @@ static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
         cie->cie_pointer = (unsigned long)entry;
 
         cie->version = *(char *)p++;
-        BUG_ON(cie->version != 1);
+        UNWINDER_BUG_ON(cie->version != 1);
 
         cie->augmentation = p;
         p += strlen(cie->augmentation) + 1;
@@ -694,7 +697,7 @@ static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
                 count = dwarf_read_uleb128(p, &length);
                 p += count;
 
-                BUG_ON((unsigned char *)p > end);
+                UNWINDER_BUG_ON((unsigned char *)p > end);
 
                 cie->initial_instructions = p + length;
                 cie->augmentation++;
@@ -722,16 +725,16 @@ static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
                          * routine in the CIE
                          * augmentation.
                          */
-                        BUG();
+                        UNWINDER_BUG();
                 } else if (*cie->augmentation == 'S') {
-                        BUG();
+                        UNWINDER_BUG();
                 } else {
                         /*
                          * Unknown augmentation. Assume
                          * 'z' augmentation.
                          */
                         p = cie->initial_instructions;
-                        BUG_ON(!p);
+                        UNWINDER_BUG_ON(!p);
                         break;
                 }
         }
@@ -805,9 +808,11 @@ static int dwarf_parse_fde(void *entry, u32 entry_type,
         return 0;
 }
 
-static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
+static void dwarf_unwinder_dump(struct task_struct *task,
+                                struct pt_regs *regs,
                                 unsigned long *sp,
-                                const struct stacktrace_ops *ops, void *data)
+                                const struct stacktrace_ops *ops,
+                                void *data)
 {
         struct dwarf_frame *frame, *_frame;
         unsigned long return_addr;
@@ -831,7 +836,6 @@ static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
                 return_addr = frame->return_addr;
                 ops->address(data, return_addr, 1);
         }
-
 }
 
 static struct unwinder dwarf_unwinder = {
diff --git a/arch/sh/kernel/traps.c b/arch/sh/kernel/traps.c
index b3e0067db358..881b9a32b7de 100644
--- a/arch/sh/kernel/traps.c
+++ b/arch/sh/kernel/traps.c
@@ -8,7 +8,7 @@
 #include <asm/system.h>
 
 #ifdef CONFIG_BUG
-static void handle_BUG(struct pt_regs *regs)
+void handle_BUG(struct pt_regs *regs)
 {
         enum bug_trap_type tt;
         tt = report_bug(regs->pc, regs);
@@ -29,7 +29,10 @@ int is_valid_bugaddr(unsigned long addr)
         if (probe_kernel_address((insn_size_t *)addr, opcode))
                 return 0;
 
-        return opcode == TRAPA_BUG_OPCODE;
+        if (opcode == TRAPA_BUG_OPCODE || opcode == TRAPA_UNWINDER_BUG_OPCODE)
+                return 1;
+
+        return 0;
 }
 #endif
 
diff --git a/arch/sh/kernel/traps_32.c b/arch/sh/kernel/traps_32.c
index 563426487c6b..05a04b6df844 100644
--- a/arch/sh/kernel/traps_32.c
+++ b/arch/sh/kernel/traps_32.c
@@ -136,6 +136,7 @@ static void die_if_no_fixup(const char * str, struct pt_regs * regs, long err)
                         regs->pc = fixup->fixup;
                         return;
                 }
+
                 die(str, regs, err);
         }
 }
diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c
index 2b30fa28b440..b9c122abe251 100644
--- a/arch/sh/kernel/unwinder.c
+++ b/arch/sh/kernel/unwinder.c
@@ -53,8 +53,6 @@ static struct list_head unwinder_list = {
 
 static DEFINE_SPINLOCK(unwinder_lock);
 
-static atomic_t unwinder_running = ATOMIC_INIT(0);
-
 /**
  * select_unwinder - Select the best registered stack unwinder.
  *
@@ -122,6 +120,8 @@ int unwinder_register(struct unwinder *u)
         return ret;
 }
 
+int unwinder_faulted = 0;
+
 /*
  * Unwind the call stack and pass information to the stacktrace_ops
  * functions. Also handle the case where we need to switch to a new
@@ -144,19 +144,40 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs,
          * Hopefully this will give us a semi-reliable stacktrace so we
          * can diagnose why curr_unwinder->dump() faulted.
          */
-        if (atomic_inc_return(&unwinder_running) != 1) {
+        if (unwinder_faulted) {
                 spin_lock_irqsave(&unwinder_lock, flags);
 
-                if (!list_is_singular(&unwinder_list)) {
+                /* Make sure no one beat us to changing the unwinder */
+                if (unwinder_faulted && !list_is_singular(&unwinder_list)) {
                         list_del(&curr_unwinder->list);
                         curr_unwinder = select_unwinder();
+
+                        unwinder_faulted = 0;
                 }
 
                 spin_unlock_irqrestore(&unwinder_lock, flags);
-                atomic_dec(&unwinder_running);
         }
 
         curr_unwinder->dump(task, regs, sp, ops, data);
+}
+
+/*
+ * Trap handler for UWINDER_BUG() statements. We must switch to the
+ * unwinder with the next highest rating.
+ */
+BUILD_TRAP_HANDLER(unwinder)
+{
+        insn_size_t insn;
+        TRAP_HANDLER_DECL;
+
+        /* Rewind */
+        regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
+        insn = *(insn_size_t *)instruction_pointer(regs);
+
+        /* Switch unwinders when unwind_stack() is called */
+        unwinder_faulted = 1;
 
-        atomic_dec(&unwinder_running);
+#ifdef CONFIG_BUG
+        handle_BUG(regs);
+#endif
 }