[PATCH] Create kallsyms_lookup_size_offset()

Some uses of kallsyms_lookup() do not need to find out the name of a symbol
and its module's name it belongs.  This is specially true in arch specific
code, which needs to unwind the stack to show the back trace during oops
(mips is an example).  In this specific case, we just need to retreive the
function's size and the offset of the active intruction inside it.

Adds a new entry "kallsyms_lookup_size_offset()" This new entry does
exactly the same as kallsyms_lookup() but does not require any buffers to
store any names.

It returns 0 if it fails otherwise 1.
Signed-off-by: NFranck Bui-Huu <vagabon.xyz@gmail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

include/linux/kallsyms.h

@@ -12,6 +12,10 @@
 /* Lookup the address for a symbol. Returns 0 if not found. */
 unsigned long kallsyms_lookup_name(const char *name);
 
+extern int kallsyms_lookup_size_offset(unsigned long addr,
+				  unsigned long *symbolsize,
+				  unsigned long *offset);
+
 /* Lookup an address.  modname is set to NULL if it's in the kernel. */
 const char *kallsyms_lookup(unsigned long addr,
 			    unsigned long *symbolsize,
@@ -28,6 +32,13 @@ static inline unsigned long kallsyms_lookup_name(const char *name)
 	return 0;
 }
 
+static inline int kallsyms_lookup_size_offset(unsigned long addr,
+					      unsigned long *symbolsize,
+					      unsigned long *offset)
+{
+	return 0;
+}
+
 static inline const char *kallsyms_lookup(unsigned long addr,
 					  unsigned long *symbolsize,
 					  unsigned long *offset,

kernel/kallsyms.c

@@ -69,6 +69,15 @@ static inline int is_kernel(unsigned long addr)
 	return in_gate_area_no_task(addr);
 }
 
+static int is_ksym_addr(unsigned long addr)
+{
+	if (all_var)
+		return is_kernel(addr);
+
+	return is_kernel_text(addr) || is_kernel_inittext(addr) ||
+		is_kernel_extratext(addr);
+}
+
 /* expand a compressed symbol data into the resulting uncompressed string,
    given the offset to where the symbol is in the compressed stream */
 static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
@@ -155,53 +164,40 @@ unsigned long kallsyms_lookup_name(const char *name)
 	return module_kallsyms_lookup_name(name);
 }
 
-/*
- * Lookup an address
- * - modname is set to NULL if it's in the kernel
- * - we guarantee that the returned name is valid until we reschedule even if
- *   it resides in a module
- * - we also guarantee that modname will be valid until rescheduled
- */
-const char *kallsyms_lookup(unsigned long addr,
+static unsigned long get_symbol_pos(unsigned long addr,
 				    unsigned long *symbolsize,
-			    unsigned long *offset,
-			    char **modname, char *namebuf)
+				    unsigned long *offset)
 {
+	unsigned long symbol_start = 0, symbol_end = 0;
 	unsigned long i, low, high, mid;
-	const char *msym;
 
 	/* This kernel should never had been booted. */
 	BUG_ON(!kallsyms_addresses);
 
-	namebuf[KSYM_NAME_LEN] = 0;
-	namebuf[0] = 0;
-
-	if ((all_var && is_kernel(addr)) ||
-	    (!all_var && (is_kernel_text(addr) || is_kernel_inittext(addr) ||
-				is_kernel_extratext(addr)))) {
-		unsigned long symbol_end = 0;
-
 	/* do a binary search on the sorted kallsyms_addresses array */
 	low = 0;
 	high = kallsyms_num_syms;
 
-		while (high-low > 1) {
+	while (high - low > 1) {
 		mid = (low + high) / 2;
-			if (kallsyms_addresses[mid] <= addr) low = mid;
-			else high = mid;
+		if (kallsyms_addresses[mid] <= addr)
+			low = mid;
+		else
+			high = mid;
 	}
 
-		/* search for the first aliased symbol. Aliased symbols are
-		   symbols with the same address */
-		while (low && kallsyms_addresses[low - 1] == kallsyms_addresses[low])
+	/*
+	 * search for the first aliased symbol. Aliased
+	 * symbols are symbols with the same address
+	 */
+	while (low && kallsyms_addresses[low-1] == kallsyms_addresses[low])
 		--low;
 
-		/* Grab name */
-		kallsyms_expand_symbol(get_symbol_offset(low), namebuf);
+	symbol_start = kallsyms_addresses[low];
 
 	/* Search for next non-aliased symbol */
 	for (i = low + 1; i < kallsyms_num_syms; i++) {
-			if (kallsyms_addresses[i] > kallsyms_addresses[low]) {
+		if (kallsyms_addresses[i] > symbol_start) {
 			symbol_end = kallsyms_addresses[i];
 			break;
 		}
@@ -211,13 +207,54 @@ const char *kallsyms_lookup(unsigned long addr,
 	if (!symbol_end) {
 		if (is_kernel_inittext(addr))
 			symbol_end = (unsigned long)_einittext;
+		else if (all_var)
+			symbol_end = (unsigned long)_end;
 		else
-				symbol_end = all_var ? (unsigned long)_end : (unsigned long)_etext;
+			symbol_end = (unsigned long)_etext;
 	}
 
-		*symbolsize = symbol_end - kallsyms_addresses[low];
+	*symbolsize = symbol_end - symbol_start;
+	*offset = addr - symbol_start;
+
+	return low;
+}
+
+/*
+ * Lookup an address but don't bother to find any names.
+ */
+int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
+				unsigned long *offset)
+{
+	if (is_ksym_addr(addr))
+		return !!get_symbol_pos(addr, symbolsize, offset);
+
+	return !!module_address_lookup(addr, symbolsize, offset, NULL);
+}
+
+/*
+ * Lookup an address
+ * - modname is set to NULL if it's in the kernel
+ * - we guarantee that the returned name is valid until we reschedule even if
+ *   it resides in a module
+ * - we also guarantee that modname will be valid until rescheduled
+ */
+const char *kallsyms_lookup(unsigned long addr,
+			    unsigned long *symbolsize,
+			    unsigned long *offset,
+			    char **modname, char *namebuf)
+{
+	const char *msym;
+
+	namebuf[KSYM_NAME_LEN] = 0;
+	namebuf[0] = 0;
+
+	if (is_ksym_addr(addr)) {
+		unsigned long pos;
+
+		pos = get_symbol_pos(addr, symbolsize, offset);
+		/* Grab name */
+		kallsyms_expand_symbol(get_symbol_offset(pos), namebuf);
 		*modname = NULL;
-		*offset = addr - kallsyms_addresses[low];
 		return namebuf;
 	}
 

kernel/module.c

@@ -2040,6 +2040,7 @@ const char *module_address_lookup(unsigned long addr,
 	list_for_each_entry(mod, &modules, list) {
 		if (within(addr, mod->module_init, mod->init_size)
 		    || within(addr, mod->module_core, mod->core_size)) {
+			if (modname)
 				*modname = mod->name;
 			return get_ksymbol(mod, addr, size, offset);
 		}