3 files changed, 54 insertions, 4 deletions

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index d8e9b3d1c23c..0df513b7a9f8 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -36,6 +36,7 @@ const char *kallsyms_lookup(unsigned long addr,
 
 /* Look up a kernel symbol and return it in a text buffer. */
 extern int sprint_symbol(char *buffer, unsigned long address);
+extern int sprint_backtrace(char *buffer, unsigned long address);
 
 /* Look up a kernel symbol and print it to the kernel messages. */
 extern void __print_symbol(const char *fmt, unsigned long address);
@@ -79,6 +80,12 @@ static inline int sprint_symbol(char *buffer, unsigned long addr)
         return 0;
 }
 
+static inline int sprint_backtrace(char *buffer, unsigned long addr)
+{
+        *buffer = '\0';
+        return 0;
+}
+
 static inline int lookup_symbol_name(unsigned long addr, char *symname)
 {
         return -ERANGE;
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6f6d091b5757..59e879929b17 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)
 {
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d3023df8477f..d9e01fc3168e 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -574,7 +574,9 @@ char *symbol_string(char *buf, char *end, void *ptr,
         unsigned long value = (unsigned long) ptr;
 #ifdef CONFIG_KALLSYMS
         char sym[KSYM_SYMBOL_LEN];
-        if (ext != 'f' && ext != 's')
+        if (ext == 'B')
+                sprint_backtrace(sym, value);
+        else if (ext != 'f' && ext != 's')
                 sprint_symbol(sym, value);
         else
                 kallsyms_lookup(value, NULL, NULL, NULL, sym);
@@ -949,6 +951,7 @@ int kptr_restrict = 1;
  * - 'f' For simple symbolic function names without offset
  * - 'S' For symbolic direct pointers with offset
  * - 's' For symbolic direct pointers without offset
+ * - 'B' For backtraced symbolic direct pointers with offset
  * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref]
  * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201]
  * - 'M' For a 6-byte MAC address, it prints the address in the
@@ -1008,6 +1011,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
                 /* Fallthrough */
         case 'S':
         case 's':
+        case 'B':
                 return symbol_string(buf, end, ptr, spec, *fmt);
         case 'R':
         case 'r':
@@ -1279,6 +1283,7 @@ qualifier:
  * %ps output the name of a text symbol without offset
  * %pF output the name of a function pointer with its offset
  * %pf output the name of a function pointer without its offset
+ * %pB output the name of a backtrace symbol with its offset
  * %pR output the address range in a struct resource with decoded flags
  * %pr output the address range in a struct resource with raw flags
  * %pM output a 6-byte MAC address with colons