sh: unwinder: Introduce UNWINDER_BUG() and UNWINDER_BUG_ON()

We can't assume that if we execute the unwinder code and the unwinder
was already running that it has faulted. Clearly two kernel threads can
invoke the unwinder at the same time and may be running simultaneously.

The previous approach used BUG() and BUG_ON() in the unwinder code to
detect whether the unwinder was incapable of unwinding the stack, and
that the next available unwinder should be used instead. A better
approach is to explicitly invoke a trap handler to switch unwinders when
the current unwinder cannot continue.

Signed-off-by: Matt Fleming <matt@console-pimps.org>

1 files changed, 21 insertions, 17 deletions

diff --git a/arch/sh/kernel/dwarf.c b/arch/sh/kernel/dwarf.c
index d271d04..606ece3 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 = {