[PATCH] unwinder: Add debugging output to the Dwarf2 unwinder

Add debugging printks to the unwinder to allow easier debugging
when something goes wrong with it.

This can be controlled with the new unwinder_debug=N option
Most output is given by N=1

AK: Added documentation of unwinder_debug=

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

Documentation/kernel-parameters.txt

@@ -1735,6 +1735,9 @@ and is between 256 and 4096 characters. It is defined in the file
 	norandmaps	Don't use address space randomization
 			Equivalent to echo 0 > /proc/sys/kernel/randomize_va_space
 
+ 	unwind_debug=N 	N > 0 will enable dwarf2 unwinder debugging
+			This is useful to get more information why
+			you got a "dwarf2 unwinder stuck"
 
 ______________________________________________________________________
 

kernel/unwind.c

@@ -137,6 +137,17 @@ struct unwind_state {
 
 static const struct cfa badCFA = { ARRAY_SIZE(reg_info), 1 };
 
+static unsigned unwind_debug;
+static int __init unwind_debug_setup(char *s)
+{
+	unwind_debug = simple_strtoul(s, NULL, 0);
+	return 1;
+}
+__setup("unwind_debug=", unwind_debug_setup);
+#define dprintk(lvl, fmt, args...) \
+	((void)(lvl > unwind_debug \
+	 || printk(KERN_DEBUG "unwind: " fmt "\n", ##args)))
+
 static struct unwind_table *find_table(unsigned long pc)
 {
 	struct unwind_table *table;
@@ -281,6 +292,7 @@ static void __init setup_unwind_table(struct unwind_table *table,
 
 	hdrSize = 4 + sizeof(unsigned long) + sizeof(unsigned int)
 	        + 2 * n * sizeof(unsigned long);
+	dprintk(2, "Binary lookup table size for %s: %lu bytes", table->name, hdrSize);
 	header = alloc(hdrSize);
 	if (!header)
 		return;
@@ -500,13 +512,17 @@ static unsigned long read_pointer(const u8 **pLoc,
 		const unsigned long *pul;
 	} ptr;
 
-	if (ptrType < 0 || ptrType == DW_EH_PE_omit)
+	if (ptrType < 0 || ptrType == DW_EH_PE_omit) {
+		dprintk(1, "Invalid pointer encoding %02X (%p,%p).", ptrType, *pLoc, end);
 		return 0;
+	}
 	ptr.p8 = *pLoc;
 	switch(ptrType & DW_EH_PE_FORM) {
 	case DW_EH_PE_data2:
-		if (end < (const void *)(ptr.p16u + 1))
+		if (end < (const void *)(ptr.p16u + 1)) {
+			dprintk(1, "Data16 overrun (%p,%p).", ptr.p8, end);
 			return 0;
+		}
 		if(ptrType & DW_EH_PE_signed)
 			value = get_unaligned(ptr.p16s++);
 		else
@@ -514,8 +530,10 @@ static unsigned long read_pointer(const u8 **pLoc,
 		break;
 	case DW_EH_PE_data4:
 #ifdef CONFIG_64BIT
-		if (end < (const void *)(ptr.p32u + 1))
+		if (end < (const void *)(ptr.p32u + 1)) {
+			dprintk(1, "Data32 overrun (%p,%p).", ptr.p8, end);
 			return 0;
+		}
 		if(ptrType & DW_EH_PE_signed)
 			value = get_unaligned(ptr.p32s++);
 		else
@@ -527,8 +545,10 @@ static unsigned long read_pointer(const u8 **pLoc,
 		BUILD_BUG_ON(sizeof(u32) != sizeof(value));
 #endif
 	case DW_EH_PE_native:
-		if (end < (const void *)(ptr.pul + 1))
+		if (end < (const void *)(ptr.pul + 1)) {
+			dprintk(1, "DataUL overrun (%p,%p).", ptr.p8, end);
 			return 0;
+		}
 		value = get_unaligned(ptr.pul++);
 		break;
 	case DW_EH_PE_leb128:
@@ -536,10 +556,14 @@ static unsigned long read_pointer(const u8 **pLoc,
 		value = ptrType & DW_EH_PE_signed
 		        ? get_sleb128(&ptr.p8, end)
 		        : get_uleb128(&ptr.p8, end);
-		if ((const void *)ptr.p8 > end)
+		if ((const void *)ptr.p8 > end) {
+			dprintk(1, "DataLEB overrun (%p,%p).", ptr.p8, end);
 			return 0;
+		}
 		break;
 	default:
+		dprintk(2, "Cannot decode pointer type %02X (%p,%p).",
+		        ptrType, ptr.p8, end);
 		return 0;
 	}
 	switch(ptrType & DW_EH_PE_ADJUST) {
@@ -549,11 +573,16 @@ static unsigned long read_pointer(const u8 **pLoc,
 		value += (unsigned long)*pLoc;
 		break;
 	default:
+		dprintk(2, "Cannot adjust pointer type %02X (%p,%p).",
+		        ptrType, *pLoc, end);
 		return 0;
 	}
 	if ((ptrType & DW_EH_PE_indirect)
-	    && probe_kernel_address((unsigned long *)value, value))
+	    && probe_kernel_address((unsigned long *)value, value)) {
+		dprintk(1, "Cannot read indirect value %lx (%p,%p).",
+		        value, *pLoc, end);
 		return 0;
+	}
 	*pLoc = ptr.p8;
 
 	return value;
@@ -702,8 +731,10 @@ static int processCFI(const u8 *start,
 					state->label = NULL;
 					return 1;
 				}
-				if (state->stackDepth >= MAX_STACK_DEPTH)
+				if (state->stackDepth >= MAX_STACK_DEPTH) {
+					dprintk(1, "State stack overflow (%p,%p).", ptr.p8, end);
 					return 0;
+				}
 				state->stack[state->stackDepth++] = ptr.p8;
 				break;
 			case DW_CFA_restore_state:
@@ -718,8 +749,10 @@ static int processCFI(const u8 *start,
 					result = processCFI(start, end, 0, ptrType, state);
 					state->loc = loc;
 					state->label = label;
-				} else
+				} else {
+					dprintk(1, "State stack underflow (%p,%p).", ptr.p8, end);
 					return 0;
+				}
 				break;
 			case DW_CFA_def_cfa:
 				state->cfa.reg = get_uleb128(&ptr.p8, end);
@@ -751,6 +784,7 @@ static int processCFI(const u8 *start,
 				break;
 			case DW_CFA_GNU_window_save:
 			default:
+				dprintk(1, "Unrecognized CFI op %02X (%p,%p).", ptr.p8[-1], ptr.p8 - 1, end);
 				result = 0;
 				break;
 			}
@@ -766,12 +800,17 @@ static int processCFI(const u8 *start,
 			set_rule(*ptr.p8++ & 0x3f, Nowhere, 0, state);
 			break;
 		}
-		if (ptr.p8 > end)
+		if (ptr.p8 > end) {
+			dprintk(1, "Data overrun (%p,%p).", ptr.p8, end);
 			result = 0;
+		}
 		if (result && targetLoc != 0 && targetLoc < state->loc)
 			return 1;
 	}
 
+	if (result && ptr.p8 < end)
+		dprintk(1, "Data underrun (%p,%p).", ptr.p8, end);
+
 	return result
 	   && ptr.p8 == end
 	   && (targetLoc == 0
@@ -843,6 +882,8 @@ int unwind(struct unwind_frame_info *frame)
 					                           hdr[3]);
 			}
 		}
+		if(hdr && !fde)
+			dprintk(3, "Binary lookup for %lx failed.", pc);
 
 		if (fde != NULL) {
 			cie = cie_for_fde(fde, table);
@@ -864,6 +905,8 @@ int unwind(struct unwind_frame_info *frame)
 					fde = NULL;
 			} else
 				fde = NULL;
+			if(!fde)
+				dprintk(1, "Binary lookup result for %lx discarded.", pc);
 		}
 		if (fde == NULL) {
 			for (fde = table->address, tableSize = table->size;
@@ -895,6 +938,8 @@ int unwind(struct unwind_frame_info *frame)
 				if (pc >= startLoc && pc < endLoc)
 					break;
 			}
+			if(!fde)
+				dprintk(3, "Linear lookup for %lx failed.", pc);
 		}
 	}
 	if (cie != NULL) {
@@ -928,6 +973,8 @@ int unwind(struct unwind_frame_info *frame)
 			if (ptr >= end || *ptr)
 				cie = NULL;
 		}
+		if(!cie)
+			dprintk(1, "CIE unusable (%p,%p).", ptr, end);
 		++ptr;
 	}
 	if (cie != NULL) {
@@ -938,9 +985,11 @@ int unwind(struct unwind_frame_info *frame)
 		if (state.codeAlign == 0 || state.dataAlign == 0 || ptr >= end)
 			cie = NULL;
 		else if (UNW_PC(frame) % state.codeAlign
-		         || UNW_SP(frame) % sleb128abs(state.dataAlign))
+		         || UNW_SP(frame) % sleb128abs(state.dataAlign)) {
+			dprintk(1, "Input pointer(s) misaligned (%lx,%lx).",
+			        UNW_PC(frame), UNW_SP(frame));
 			return -EPERM;
-		else {
+		} else {
 			retAddrReg = state.version <= 1 ? *ptr++ : get_uleb128(&ptr, end);
 			/* skip augmentation */
 			if (((const char *)(cie + 2))[1] == 'z') {
@@ -954,6 +1003,8 @@ int unwind(struct unwind_frame_info *frame)
 			   || reg_info[retAddrReg].width != sizeof(unsigned long))
 				cie = NULL;
 		}
+		if(!cie)
+			dprintk(1, "CIE validation failed (%p,%p).", ptr, end);
 	}
 	if (cie != NULL) {
 		state.cieStart = ptr;
@@ -967,6 +1018,8 @@ int unwind(struct unwind_frame_info *frame)
 			if ((ptr += augSize) > end)
 				fde = NULL;
 		}
+		if(!fde)
+			dprintk(1, "FDE validation failed (%p,%p).", ptr, end);
 	}
 	if (cie == NULL || fde == NULL) {
 #ifdef CONFIG_FRAME_POINTER
@@ -1025,8 +1078,10 @@ int unwind(struct unwind_frame_info *frame)
 	   || state.cfa.reg >= ARRAY_SIZE(reg_info)
 	   || reg_info[state.cfa.reg].width != sizeof(unsigned long)
 	   || FRAME_REG(state.cfa.reg, unsigned long) % sizeof(unsigned long)
-	   || state.cfa.offs % sizeof(unsigned long))
+	   || state.cfa.offs % sizeof(unsigned long)) {
+		dprintk(1, "Unusable unwind info (%p,%p).", ptr, end);
 		return -EIO;
+	}
 	/* update frame */
 #ifndef CONFIG_AS_CFI_SIGNAL_FRAME
 	if(frame->call_frame
@@ -1051,6 +1106,8 @@ int unwind(struct unwind_frame_info *frame)
 		if (REG_INVALID(i)) {
 			if (state.regs[i].where == Nowhere)
 				continue;
+			dprintk(1, "Cannot restore register %u (%d).",
+			        i, state.regs[i].where);
 			return -EIO;
 		}
 		switch(state.regs[i].where) {
@@ -1059,8 +1116,11 @@ int unwind(struct unwind_frame_info *frame)
 		case Register:
 			if (state.regs[i].value >= ARRAY_SIZE(reg_info)
 			   || REG_INVALID(state.regs[i].value)
-			   || reg_info[i].width > reg_info[state.regs[i].value].width)
+			   || reg_info[i].width > reg_info[state.regs[i].value].width) {
+				dprintk(1, "Cannot restore register %u from register %lu.",
+				        i, state.regs[i].value);
 				return -EIO;
+			}
 			switch(reg_info[state.regs[i].value].width) {
 #define CASE(n) \
 			case sizeof(u##n): \
@@ -1070,6 +1130,9 @@ int unwind(struct unwind_frame_info *frame)
 			CASES;
 #undef CASE
 			default:
+				dprintk(1, "Unsupported register size %u (%lu).",
+				        reg_info[state.regs[i].value].width,
+				        state.regs[i].value);
 				return -EIO;
 			}
 			break;
@@ -1094,12 +1157,17 @@ int unwind(struct unwind_frame_info *frame)
 			CASES;
 #undef CASE
 			default:
+				dprintk(1, "Unsupported register size %u (%u).",
+				        reg_info[i].width, i);
 				return -EIO;
 			}
 			break;
 		case Value:
-			if (reg_info[i].width != sizeof(unsigned long))
+			if (reg_info[i].width != sizeof(unsigned long)) {
+				dprintk(1, "Unsupported value size %u (%u).",
+				        reg_info[i].width, i);
 				return -EIO;
+			}
 			FRAME_REG(i, unsigned long) = cfa + state.regs[i].value
 			                                    * state.dataAlign;
 			break;
@@ -1111,8 +1179,11 @@ int unwind(struct unwind_frame_info *frame)
 				    % sizeof(unsigned long)
 				    || addr < startLoc
 				    || addr + sizeof(unsigned long) < addr
-				    || addr + sizeof(unsigned long) > endLoc)
+				    || addr + sizeof(unsigned long) > endLoc) {
+					dprintk(1, "Bad memory location %lx (%lx).",
+					        addr, state.regs[i].value);
 					return -EIO;
+				}
 				switch(reg_info[i].width) {
 #define CASE(n)     case sizeof(u##n): \
 					probe_kernel_address((u##n *)addr, FRAME_REG(i, u##n)); \
@@ -1120,6 +1191,8 @@ int unwind(struct unwind_frame_info *frame)
 				CASES;
 #undef CASE
 				default:
+					dprintk(1, "Unsupported memory size %u (%u).",
+					        reg_info[i].width, i);
 					return -EIO;
 				}
 			}
@@ -1128,9 +1201,15 @@ int unwind(struct unwind_frame_info *frame)
 	}
 
 	if (UNW_PC(frame) % state.codeAlign
-	    || UNW_SP(frame) % sleb128abs(state.dataAlign)
-	    || (pc == UNW_PC(frame) && sp == UNW_SP(frame)))
+	    || UNW_SP(frame) % sleb128abs(state.dataAlign)) {
+		dprintk(1, "Output pointer(s) misaligned (%lx,%lx).",
+		        UNW_PC(frame), UNW_SP(frame));
 		return -EIO;
+	}
+	if (pc == UNW_PC(frame) && sp == UNW_SP(frame)) {
+		dprintk(1, "No progress (%lx,%lx).", pc, sp);
+		return -EIO;
+	}
 
 	return 0;
 #undef CASES