1 files changed, 41 insertions, 3 deletions

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index a56aa58b9cb0..079f1d39a8b8 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -342,13 +342,15 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 }
 
 /* Look up a kernel symbol and return it in a text buffer. */
-int sprint_symbol(char *buffer, unsigned long address)
+static int __sprint_symbol(char *buffer, unsigned long address,
+			   int symbol_offset)
 {
 	char *modname;
 	const char *name;
 	unsigned long offset, size;
 	int len;
 
+	address += symbol_offset;
 	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
 	if (!name)
 		return sprintf(buffer, "0x%lx", address);
@@ -357,17 +359,53 @@ int sprint_symbol(char *buffer, unsigned long address)
 		strcpy(buffer, name);
 	len = strlen(buffer);
 	buffer += len;
+	offset -= symbol_offset;
 
 	if (modname)
-		len += sprintf(buffer, "+%#lx/%#lx [%s]",
-						offset, size, modname);
+		len += sprintf(buffer, "+%#lx/%#lx [%s]", offset, size, modname);
 	else
 		len += sprintf(buffer, "+%#lx/%#lx", offset, size);
 
 	return len;
 }
+
+/**
+ * sprint_symbol - Look up a kernel symbol and return it in a text buffer
+ * @buffer: buffer to be stored
+ * @address: address to lookup
+ *
+ * This function looks up a kernel symbol with @address and stores its name,
+ * offset, size and module name to @buffer if possible. If no symbol was found,
+ * just saves its @address as is.
+ *
+ * This function returns the number of bytes stored in @buffer.
+ */
+int sprint_symbol(char *buffer, unsigned long address)
+{
+	return __sprint_symbol(buffer, address, 0);
+}
+
 EXPORT_SYMBOL_GPL(sprint_symbol);
 
+/**
+ * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
+ * @buffer: buffer to be stored
+ * @address: address to lookup
+ *
+ * This function is for stack backtrace and does the same thing as
+ * sprint_symbol() but with modified/decreased @address. If there is a
+ * tail-call to the function marked "noreturn", gcc optimized out code after
+ * the call so that the stack-saved return address could point outside of the
+ * caller. This function ensures that kallsyms will find the original caller
+ * by decreasing @address.
+ *
+ * This function returns the number of bytes stored in @buffer.
+ */
+int sprint_backtrace(char *buffer, unsigned long address)
+{
+	return __sprint_symbol(buffer, address, -1);
+}
+
 /* Look up a kernel symbol and print it to the kernel messages. */
 void __print_symbol(const char *fmt, unsigned long address)
 {