[PATCH] fully support linker generated .eh_frame_hdr section

[PATCH] fully support linker generated .eh_frame_hdr section

[Jan Beulich]

Now that binutils' ld is able to properly populate .eh_frame_hdr in the
Linux kernel case, here's a patch to add some functionality to the Dwarf2
unwinder to actually be able to make use of this (applies on firstfloor
tree with the previously sent patch to add debug output, but not on plain
2.6.19).

Signed-off-by: Jan Beulich <jbeulich@novell.com>

Index: 2.6.19-ff-unwind-debug-msg/kernel/unwind.c
===================================================================
--- 2.6.19-ff-unwind-debug-msg.orig/kernel/unwind.c	2006-12-04 17:11:14.000000000 +0100
+++ 2.6.19-ff-unwind-debug-msg/kernel/unwind.c	2006-12-04 17:11:45.000000000 +0100
@@ -164,7 +164,9 @@ static struct unwind_table *find_table(u
 
 static unsigned long read_pointer(const u8 **pLoc,
                                   const void *end,
-                                  signed ptrType);
+                                  signed ptrType,
+                                  unsigned long text_base,
+                                  unsigned long data_base);
 
 static void init_unwind_table(struct unwind_table *table,
                               const char *name,
@@ -189,10 +191,13 @@ static void init_unwind_table(struct unw
 	/* See if the linker provided table looks valid. */
 	if (header_size <= 4
 	    || header_start[0] != 1
-	    || (void *)read_pointer(&ptr, end, header_start[1]) != table_start
-	    || header_start[2] == DW_EH_PE_omit
-	    || read_pointer(&ptr, end, header_start[2]) <= 0
-	    || header_start[3] == DW_EH_PE_omit)
+	    || (void *)read_pointer(&ptr, end, header_start[1], 0, 0)
+	       != table_start
+	    || !read_pointer(&ptr, end, header_start[2], 0, 0)
+	    || !read_pointer(&ptr, end, header_start[3], 0,
+	                     (unsigned long)header_start)
+	    || !read_pointer(&ptr, end, header_start[3], 0,
+	                     (unsigned long)header_start))
 		header_start = NULL;
 	table->hdrsz = header_size;
 	smp_wmb();
@@ -282,7 +287,7 @@ static void __init setup_unwind_table(st
 		ptr = (const u8 *)(fde + 2);
 		if (!read_pointer(&ptr,
 		                  (const u8 *)(fde + 1) + *fde,
-		                  ptrType))
+		                  ptrType, 0, 0))
 			return;
 		++n;
 	}
@@ -317,7 +322,7 @@ static void __init setup_unwind_table(st
 		ptr = (const u8 *)(fde + 2);
 		header->table[n].start = read_pointer(&ptr,
 		                                      (const u8 *)(fde + 1) + *fde,
-		                                      fde_pointer_type(cie));
+		                                      fde_pointer_type(cie), 0, 0);
 		header->table[n].fde = (unsigned long)fde;
 		++n;
 	}
@@ -500,7 +505,9 @@ static const u32 *cie_for_fde(const u32 
 
 static unsigned long read_pointer(const u8 **pLoc,
                                   const void *end,
-                                  signed ptrType)
+                                  signed ptrType,
+                                  unsigned long text_base,
+                                  unsigned long data_base)
 {
 	unsigned long value = 0;
 	union {
@@ -572,6 +579,22 @@ static unsigned long read_pointer(const 
 	case DW_EH_PE_pcrel:
 		value += (unsigned long)*pLoc;
 		break;
+	case DW_EH_PE_textrel:
+		if (likely(text_base)) {
+			value += text_base;
+			break;
+		}
+		dprintk(2, "Text-relative encoding %02X (%p,%p), but zero text base.",
+		        ptrType, *pLoc, end);
+		return 0;
+	case DW_EH_PE_datarel:
+		if (likely(data_base)) {
+			value += data_base;
+			break;
+		}
+		dprintk(2, "Data-relative encoding %02X (%p,%p), but zero data base.",
+		        ptrType, *pLoc, end);
+		return 0;
 	default:
 		dprintk(2, "Cannot adjust pointer type %02X (%p,%p).",
 		        ptrType, *pLoc, end);
@@ -625,7 +648,8 @@ static signed fde_pointer_type(const u32
 			case 'P': {
 					signed ptrType = *ptr++;
 
-					if (!read_pointer(&ptr, end, ptrType) || ptr > end)
+					if (!read_pointer(&ptr, end, ptrType, 0, 0)
+					    || ptr > end)
 						return -1;
 				}
 				break;
@@ -685,7 +709,8 @@ static int processCFI(const u8 *start,
 			case DW_CFA_nop:
 				break;
 			case DW_CFA_set_loc:
-				if ((state->loc = read_pointer(&ptr.p8, end, ptrType)) == 0)
+				state->loc = read_pointer(&ptr.p8, end, ptrType, 0, 0);
+				if (state->loc == 0)
 					result = 0;
 				break;
 			case DW_CFA_advance_loc1:
@@ -854,9 +879,9 @@ int unwind(struct unwind_frame_info *fra
 			ptr = hdr + 4;
 			end = hdr + table->hdrsz;
 			if (tableSize
-			    && read_pointer(&ptr, end, hdr[1])
+			    && read_pointer(&ptr, end, hdr[1], 0, 0)
 			       == (unsigned long)table->address
-			    && (i = read_pointer(&ptr, end, hdr[2])) > 0
+			    && (i = read_pointer(&ptr, end, hdr[2], 0, 0)) > 0
 			    && i == (end - ptr) / (2 * tableSize)
 			    && !((end - ptr) % (2 * tableSize))) {
 				do {
@@ -864,7 +889,8 @@ int unwind(struct unwind_frame_info *fra
 
 					startLoc = read_pointer(&cur,
 					                        cur + tableSize,
-					                        hdr[3]);
+					                        hdr[3], 0,
+					                        (unsigned long)hdr);
 					if (pc < startLoc)
 						i /= 2;
 					else {
@@ -875,11 +901,13 @@ int unwind(struct unwind_frame_info *fra
 				if (i == 1
 				    && (startLoc = read_pointer(&ptr,
 				                                ptr + tableSize,
-				                                hdr[3])) != 0
+				                                hdr[3], 0,
+				                                (unsigned long)hdr)) != 0
 				    && pc >= startLoc)
 					fde = (void *)read_pointer(&ptr,
 					                           ptr + tableSize,
-					                           hdr[3]);
+					                           hdr[3], 0,
+					                           (unsigned long)hdr);
 			}
 		}
 		if(hdr && !fde)
@@ -894,13 +922,13 @@ int unwind(struct unwind_frame_info *fra
 			   && (ptrType = fde_pointer_type(cie)) >= 0
 			   && read_pointer(&ptr,
 			                   (const u8 *)(fde + 1) + *fde,
-			                   ptrType) == startLoc) {
+			                   ptrType, 0, 0) == startLoc) {
 				if (!(ptrType & DW_EH_PE_indirect))
 					ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
 				endLoc = startLoc
 				         + read_pointer(&ptr,
 				                        (const u8 *)(fde + 1) + *fde,
-				                        ptrType);
+				                        ptrType, 0, 0);
 				if(pc >= endLoc)
 					fde = NULL;
 			} else
@@ -926,7 +954,7 @@ int unwind(struct unwind_frame_info *fra
 				ptr = (const u8 *)(fde + 2);
 				startLoc = read_pointer(&ptr,
 				                        (const u8 *)(fde + 1) + *fde,
-				                        ptrType);
+				                        ptrType, 0, 0);
 				if (!startLoc)
 					continue;
 				if (!(ptrType & DW_EH_PE_indirect))
@@ -934,7 +962,7 @@ int unwind(struct unwind_frame_info *fra
 				endLoc = startLoc
 				         + read_pointer(&ptr,
 				                        (const u8 *)(fde + 1) + *fde,
-				                        ptrType);
+				                        ptrType, 0, 0);
 				if (pc >= startLoc && pc < endLoc)
 					break;
 			}

Re: [PATCH] fully support linker generated .eh_frame_hdr section

[Randy Dunlap]

On Mon, 04 Dec 2006 16:23:27 +0000 Jan Beulich wrote:

> Now that binutils' ld is able to properly populate .eh_frame_hdr in the
> Linux kernel case, here's a patch to add some functionality to the Dwarf2
> unwinder to actually be able to make use of this (applies on firstfloor
> tree with the previously sent patch to add debug output, but not on plain
> 2.6.19).

Requires what version of binutils / ld?

Thanks,
---
~Randy

Re: [PATCH] fully support linker generated .eh_frame_hdr section

[Jan Beulich]

>>> Randy Dunlap <randy.dunlap@oracle.com> 04.12.06 23:58 >>>
>On Mon, 04 Dec 2006 16:23:27 +0000 Jan Beulich wrote:
>
>> Now that binutils' ld is able to properly populate .eh_frame_hdr in the
>> Linux kernel case, here's a patch to add some functionality to the Dwarf2
>> unwinder to actually be able to make use of this (applies on firstfloor
>> tree with the previously sent patch to add debug output, but not on plain
>> 2.6.19).
>
>Requires what version of binutils / ld?

mainline - the second of the required patches went in just yesterday.

Jan

Re: [PATCH] fully support linker generated .eh_frame_hdr section

[Jan Engelhardt]

>>> Now that binutils' ld is able to properly populate .eh_frame_hdr in the
>>> Linux kernel case, here's a patch to add some functionality to the Dwarf2
>>> unwinder to actually be able to make use of this (applies on firstfloor
>>> tree with the previously sent patch to add debug output, but not on plain
>>> 2.6.19).
>>
>>Requires what version of binutils / ld?
>
>mainline - the second of the required patches went in just yesterday.

Which means people using distros will have it in some 6 months, unless 
vendors give an earlier update.


	-`J'
-- 

Re: [PATCH] fully support linker generated .eh_frame_hdr section

[Jan Beulich]

>>> Jan Engelhardt <jengelh@linux01.gwdg.de> 05.12.06 20:52 >>>
>
>>>> Now that binutils' ld is able to properly populate .eh_frame_hdr in the
>>>> Linux kernel case, here's a patch to add some functionality to the Dwarf2
>>>> unwinder to actually be able to make use of this (applies on firstfloor
>>>> tree with the previously sent patch to add debug output, but not on plain
>>>> 2.6.19).
>>>
>>>Requires what version of binutils / ld?
>>
>>mainline - the second of the required patches went in just yesterday.
>
>Which means people using distros will have it in some 6 months, unless 
>vendors give an earlier update.

That's not the point here - the point is that the kernel should be ready to take
advantage of this whenever somebody tries to build with newer binutils. Also,
the patch adds a previously missing check that would result in not creating a
runtime allocated table (assuming the linker created one is usable), but failing
to read from that table during later lookups (resulting in the originally
observed long boot time due to lockdep making heavy use of this code).

Jan