10 files changed, 252 insertions, 105 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/dwarf.h b/arch/sh/include/asm/dwarf.h
index 2fbe8720411e..c367ed3373c5 100644
--- a/arch/sh/include/asm/dwarf.h
+++ b/arch/sh/include/asm/dwarf.h
@@ -265,10 +265,7 @@ struct dwarf_frame {
 
         unsigned long pc;
 
-        struct dwarf_reg *regs;
-        unsigned int num_regs;  /* how many regs are allocated? */
-
-        unsigned int depth;     /* what level are we in the callstack? */
+        struct list_head reg_list;
 
         unsigned long cfa;
 
@@ -292,20 +289,15 @@ struct dwarf_frame {
  *      @flags: Describes how to calculate the value of this register
  */
 struct dwarf_reg {
+        struct list_head link;
+
+        unsigned int number;
+
         unsigned long addr;
         unsigned long flags;
 #define DWARF_REG_OFFSET        (1 << 0)
-};
-
-/**
- *      dwarf_stack - a DWARF stack contains a collection of DWARF frames
- *      @depth: the number of frames in the stack
- *      @level: an array of DWARF frames, indexed by stack level
- *
- */
-struct dwarf_stack {
-        unsigned int depth;
-        struct dwarf_frame **level;
+#define DWARF_VAL_OFFSET        (1 << 1)
+#define DWARF_UNDEFINED         (1 << 2)
 };
 
 /*
@@ -372,13 +364,14 @@ static inline unsigned int DW_CFA_operand(unsigned long insn)
 
 extern struct dwarf_frame *dwarf_unwind_stack(unsigned long,
                                               struct dwarf_frame *);
-#endif /* __ASSEMBLY__ */
+#endif /* !__ASSEMBLY__ */
 
 #define CFI_STARTPROC   .cfi_startproc
 #define CFI_ENDPROC     .cfi_endproc
 #define CFI_DEF_CFA     .cfi_def_cfa
 #define CFI_REGISTER    .cfi_register
 #define CFI_REL_OFFSET  .cfi_rel_offset
+#define CFI_UNDEFINED   .cfi_undefined
 
 #else
 
@@ -392,6 +385,7 @@ extern struct dwarf_frame *dwarf_unwind_stack(unsigned long,
 #define CFI_DEF_CFA     CFI_IGNORE
 #define CFI_REGISTER    CFI_IGNORE
 #define CFI_REL_OFFSET  CFI_IGNORE
+#define CFI_UNDEFINED   CFI_IGNORE
 
 #ifndef __ASSEMBLY__
 static inline void dwarf_unwinder_init(void)
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/cpu/sh3/entry.S b/arch/sh/kernel/cpu/sh3/entry.S
index 67ad6467c694..f89ec87e3fc3 100644
--- a/arch/sh/kernel/cpu/sh3/entry.S
+++ b/arch/sh/kernel/cpu/sh3/entry.S
@@ -508,6 +508,8 @@ ENTRY(handle_interrupt)
         bsr     save_regs       ! needs original pr value in k3
          mov    #-1, k2         ! default vector kept in k2
 
+        setup_frame_reg
+
         ! Setup return address and jump to do_IRQ
         mov.l   4f, r9          ! fetch return address
         lds     r9, pr          ! put return address in pr
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 d0652153f576..577302f31e6a 100644
--- a/arch/sh/kernel/dwarf.c
+++ b/arch/sh/kernel/dwarf.c
@@ -11,12 +11,14 @@
  *
  * TODO:
  *      - DWARF64 doesn't work.
+ *      - Registers with DWARF_VAL_OFFSET rules aren't handled properly.
  */
 
 /* #define DEBUG */
 #include <linux/kernel.h>
 #include <linux/io.h>
 #include <linux/list.h>
+#include <linux/mempool.h>
 #include <linux/mm.h>
 #include <asm/dwarf.h>
 #include <asm/unwinder.h>
@@ -25,6 +27,17 @@
 #include <asm/dwarf.h>
 #include <asm/stacktrace.h>
 
+/* Reserve enough memory for two stack frames */
+#define DWARF_FRAME_MIN_REQ     2
+/* ... with 4 registers per frame. */
+#define DWARF_REG_MIN_REQ       (DWARF_FRAME_MIN_REQ * 4)
+
+static struct kmem_cache *dwarf_frame_cachep;
+static mempool_t *dwarf_frame_pool;
+
+static struct kmem_cache *dwarf_reg_cachep;
+static mempool_t *dwarf_reg_pool;
+
 static LIST_HEAD(dwarf_cie_list);
 static DEFINE_SPINLOCK(dwarf_cie_lock);
 
@@ -33,47 +46,70 @@ static DEFINE_SPINLOCK(dwarf_fde_lock);
 
 static struct dwarf_cie *cached_cie;
 
-/*
- * Figure out whether we need to allocate some dwarf registers. If dwarf
- * registers have already been allocated then we may need to realloc
- * them. "reg" is a register number that we need to be able to access
- * after this call.
+/**
+ *      dwarf_frame_alloc_reg - allocate memory for a DWARF register
+ *      @frame: the DWARF frame whose list of registers we insert on
+ *      @reg_num: the register number
+ *
+ *      Allocate space for, and initialise, a dwarf reg from
+ *      dwarf_reg_pool and insert it onto the (unsorted) linked-list of
+ *      dwarf registers for @frame.
  *
- * Register numbers start at zero, therefore we need to allocate space
- * for "reg" + 1 registers.
+ *      Return the initialised DWARF reg.
  */
-static void dwarf_frame_alloc_regs(struct dwarf_frame *frame,
-                                   unsigned int reg)
+static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
+                                               unsigned int reg_num)
 {
-        struct dwarf_reg *regs;
-        unsigned int num_regs = reg + 1;
-        size_t new_size;
-        size_t old_size;
+        struct dwarf_reg *reg;
 
-        new_size = num_regs * sizeof(*regs);
-        old_size = frame->num_regs * sizeof(*regs);
-
-        /* Fast path: don't allocate any regs if we've already got enough. */
-        if (frame->num_regs >= num_regs)
-                return;
-
-        regs = kzalloc(new_size, GFP_ATOMIC);
-        if (!regs) {
-                printk(KERN_WARNING "Unable to allocate DWARF registers\n");
+        reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
+        if (!reg) {
+                printk(KERN_WARNING "Unable to allocate a DWARF register\n");
                 /*
                  * Let's just bomb hard here, we have no way to
                  * gracefully recover.
                  */
-                BUG();
+                UNWINDER_BUG();
+        }
+
+        reg->number = reg_num;
+        reg->addr = 0;
+        reg->flags = 0;
+
+        list_add(&reg->link, &frame->reg_list);
+
+        return reg;
+}
+
+static void dwarf_frame_free_regs(struct dwarf_frame *frame)
+{
+        struct dwarf_reg *reg, *n;
+
+        list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
+                list_del(&reg->link);
+                mempool_free(reg, dwarf_reg_pool);
         }
+}
+
+/**
+ *      dwarf_frame_reg - return a DWARF register
+ *      @frame: the DWARF frame to search in for @reg_num
+ *      @reg_num: the register number to search for
+ *
+ *      Lookup and return the dwarf reg @reg_num for this frame. Return
+ *      NULL if @reg_num is an register invalid number.
+ */
+static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
+                                         unsigned int reg_num)
+{
+        struct dwarf_reg *reg;
 
-        if (frame->regs) {
-                memcpy(regs, frame->regs, old_size);
-                kfree(frame->regs);
+        list_for_each_entry(reg, &frame->reg_list, link) {
+                if (reg->number == reg_num)
+                        return reg;
         }
 
-        frame->regs = regs;
-        frame->num_regs = num_regs;
+        return NULL;
 }
 
 /**
@@ -196,7 +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)
@@ -211,7 +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;
@@ -347,6 +383,7 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
         unsigned char insn;
         unsigned char *current_insn;
         unsigned int count, delta, reg, expr_len, offset;
+        struct dwarf_reg *regp;
 
         current_insn = insn_start;
 
@@ -369,9 +406,9 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
                         count = dwarf_read_uleb128(current_insn, &offset);
                         current_insn += count;
                         offset *= cie->data_alignment_factor;
-                        dwarf_frame_alloc_regs(frame, reg);
-                        frame->regs[reg].addr = offset;
-                        frame->regs[reg].flags |= DWARF_REG_OFFSET;
+                        regp = dwarf_frame_alloc_reg(frame, reg);
+                        regp->addr = offset;
+                        regp->flags |= DWARF_REG_OFFSET;
                         continue;
                         /* NOTREACHED */
                 case DW_CFA_restore:
@@ -415,6 +452,8 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
                 case DW_CFA_undefined:
                         count = dwarf_read_uleb128(current_insn, &reg);
                         current_insn += count;
+                        regp = dwarf_frame_alloc_reg(frame, reg);
+                        regp->flags |= DWARF_UNDEFINED;
                         break;
                 case DW_CFA_def_cfa:
                         count = dwarf_read_uleb128(current_insn,
@@ -453,17 +492,18 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
                         count = dwarf_read_leb128(current_insn, &offset);
                         current_insn += count;
                         offset *= cie->data_alignment_factor;
-                        dwarf_frame_alloc_regs(frame, reg);
-                        frame->regs[reg].flags |= DWARF_REG_OFFSET;
-                        frame->regs[reg].addr = offset;
+                        regp = dwarf_frame_alloc_reg(frame, reg);
+                        regp->flags |= DWARF_REG_OFFSET;
+                        regp->addr = offset;
                         break;
                 case DW_CFA_val_offset:
                         count = dwarf_read_uleb128(current_insn, &reg);
                         current_insn += count;
                         count = dwarf_read_leb128(current_insn, &offset);
                         offset *= cie->data_alignment_factor;
-                        frame->regs[reg].flags |= DWARF_REG_OFFSET;
-                        frame->regs[reg].addr = offset;
+                        regp = dwarf_frame_alloc_reg(frame, reg);
+                        regp->flags |= DWARF_VAL_OFFSET;
+                        regp->addr = offset;
                         break;
                 case DW_CFA_GNU_args_size:
                         count = dwarf_read_uleb128(current_insn, &offset);
@@ -474,12 +514,14 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
                         current_insn += count;
                         count = dwarf_read_uleb128(current_insn, &offset);
                         offset *= cie->data_alignment_factor;
-                        dwarf_frame_alloc_regs(frame, reg);
-                        frame->regs[reg].flags |= DWARF_REG_OFFSET;
-                        frame->regs[reg].addr = -offset;
+
+                        regp = dwarf_frame_alloc_reg(frame, reg);
+                        regp->flags |= DWARF_REG_OFFSET;
+                        regp->addr = -offset;
                         break;
                 default:
                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
+                        UNWINDER_BUG();
                         break;
                 }
         }
@@ -496,14 +538,14 @@ 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;
         struct dwarf_fde *fde;
+        struct dwarf_reg *reg;
         unsigned long addr;
-        int i, offset;
 
         /*
          * If this is the first invocation of this recursive function we
@@ -516,11 +558,16 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
         if (!pc && !prev)
                 pc = (unsigned long)current_text_addr();
 
-        frame = kzalloc(sizeof(*frame), GFP_ATOMIC);
-        if (!frame)
-                return NULL;
+        frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
+        if (!frame) {
+                printk(KERN_ERR "Unable to allocate a dwarf frame\n");
+                UNWINDER_BUG();
+        }
 
+        INIT_LIST_HEAD(&frame->reg_list);
+        frame->flags = 0;
         frame->prev = prev;
+        frame->return_addr = 0;
 
         fde = dwarf_lookup_fde(pc);
         if (!fde) {
@@ -540,7 +587,7 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
                  *      case above, which sucks because we could print a
                  *      warning here.
                  */
-                return NULL;
+                goto bail;
         }
 
         cie = dwarf_lookup_cie(fde->cie_pointer);
@@ -560,10 +607,11 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
         switch (frame->flags) {
         case DWARF_FRAME_CFA_REG_OFFSET:
                 if (prev) {
-                        BUG_ON(!prev->regs[frame->cfa_register].flags);
+                        reg = dwarf_frame_reg(prev, frame->cfa_register);
+                        UNWINDER_BUG_ON(!reg);
+                        UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 
-                        addr = prev->cfa;
-                        addr += prev->regs[frame->cfa_register].addr;
+                        addr = prev->cfa + reg->addr;
                         frame->cfa = __raw_readl(addr);
 
                 } else {
@@ -580,27 +628,30 @@ 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. */
-        BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
+        reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
 
-        for (i = 0; i <= frame->num_regs; i++) {
-                struct dwarf_reg *reg = &frame->regs[i];
+        /*
+         * If we haven't seen the return address register or the return
+         * address column is undefined then we must assume that this is
+         * the end of the callstack.
+         */
+        if (!reg || reg->flags == DWARF_UNDEFINED)
+                goto bail;
 
-                if (!reg->flags)
-                        continue;
+        UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 
-                offset = reg->addr;
-                offset += frame->cfa;
-        }
-
-        addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
+        addr = frame->cfa + reg->addr;
         frame->return_addr = __raw_readl(addr);
 
-        frame->next = dwarf_unwind_stack(frame->return_addr, frame);
         return frame;
+
+bail:
+        dwarf_frame_free_regs(frame);
+        mempool_free(frame, dwarf_frame_pool);
+        return NULL;
 }
 
 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
@@ -625,7 +676,7 @@ 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;
@@ -655,7 +706,7 @@ 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++;
@@ -683,16 +734,16 @@ 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;
                 }
         }
@@ -709,7 +760,8 @@ static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 }
 
 static int dwarf_parse_fde(void *entry, u32 entry_type,
-                           void *start, unsigned long len)
+                           void *start, unsigned long len,
+                           unsigned char *end)
 {
         struct dwarf_fde *fde;
         struct dwarf_cie *cie;
@@ -756,7 +808,7 @@ static int dwarf_parse_fde(void *entry, u32 entry_type,
 
         /* Call frame instructions. */
         fde->instructions = p;
-        fde->end = start + len;
+        fde->end = end;
 
         /* Add to list. */
         spin_lock_irqsave(&dwarf_fde_lock, flags);
@@ -766,17 +818,33 @@ 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;
+        struct dwarf_frame *frame, *_frame;
+        unsigned long return_addr;
 
-        frame = dwarf_unwind_stack(0, NULL);
+        _frame = NULL;
+        return_addr = 0;
 
-        while (frame && frame->return_addr) {
-                ops->address(data, frame->return_addr, 1);
-                frame = frame->next;
+        while (1) {
+                frame = dwarf_unwind_stack(return_addr, _frame);
+
+                if (_frame) {
+                        dwarf_frame_free_regs(_frame);
+                        mempool_free(_frame, dwarf_frame_pool);
+                }
+
+                _frame = frame;
+
+                if (!frame || !frame->return_addr)
+                        break;
+
+                return_addr = frame->return_addr;
+                ops->address(data, return_addr, 1);
         }
 }
 
@@ -801,6 +869,9 @@ static void dwarf_unwinder_cleanup(void)
 
         list_for_each_entry(fde, &dwarf_fde_list, link)
                 kfree(fde);
+
+        kmem_cache_destroy(dwarf_reg_cachep);
+        kmem_cache_destroy(dwarf_frame_cachep);
 }
 
 /**
@@ -827,6 +898,21 @@ static int __init dwarf_unwinder_init(void)
         f_entries = 0;
         entry = &__start_eh_frame;
 
+        dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
+                        sizeof(struct dwarf_frame), 0, SLAB_PANIC, NULL);
+        dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
+                        sizeof(struct dwarf_reg), 0, SLAB_PANIC, NULL);
+
+        dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
+                                          mempool_alloc_slab,
+                                          mempool_free_slab,
+                                          dwarf_frame_cachep);
+
+        dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
+                                         mempool_alloc_slab,
+                                         mempool_free_slab,
+                                         dwarf_reg_cachep);
+
         while ((char *)entry < __stop_eh_frame) {
                 p = entry;
 
@@ -856,7 +942,7 @@ static int __init dwarf_unwinder_init(void)
                         else
                                 c_entries++;
                 } else {
-                        err = dwarf_parse_fde(entry, entry_type, p, len);
+                        err = dwarf_parse_fde(entry, entry_type, p, len, end);
                         if (err < 0)
                                 goto out;
                         else
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 5f56ff3f55e0..e83861d9739c 100644
--- a/arch/sh/kernel/unwinder.c
+++ b/arch/sh/kernel/unwinder.c
@@ -54,8 +54,6 @@ 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.
  *
@@ -123,6 +121,8 @@ 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
@@ -145,20 +145,41 @@ 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
 }
 EXPORT_SYMBOL_GPL(unwind_stack);