vsprintf: Add extension %pSR - print_symbol replacement

print_symbol takes a long and converts it to a function
name and offset.  %pS does something similar, but doesn't
translate the address via __builtin_extract_return_addr.
%pSR does the translation.

This will enable replacing multiple calls like
	printk(...);
	printk_symbol(addr);
	printk("\n");
with a single non-interleavable in dmesg
	printk("... %pSR\n", (void *)addr);

Update documentation too.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/printk-formats.txt

@@ -17,6 +17,8 @@ Symbols/Function Pointers:
 	%pF	versatile_init+0x0/0x110
 	%pf	versatile_init
 	%pS	versatile_init+0x0/0x110
+	%pSR	versatile_init+0x9/0x110
+		(with __builtin_extract_return_addr() translation)
 	%ps	versatile_init
 	%pB	prev_fn_of_versatile_init+0x88/0x88
 

lib/vsprintf.c

@@ -534,14 +534,21 @@ char *string(char *buf, char *end, const char *s, struct printf_spec spec)
 
 static noinline_for_stack
 char *symbol_string(char *buf, char *end, void *ptr,
-		    struct printf_spec spec, char ext)
+		    struct printf_spec spec, const char *fmt)
 {
-	unsigned long value = (unsigned long) ptr;
+	unsigned long value;
 #ifdef CONFIG_KALLSYMS
 	char sym[KSYM_SYMBOL_LEN];
-	if (ext == 'B')
+#endif
+
+	if (fmt[1] == 'R')
+		ptr = __builtin_extract_return_addr(ptr);
+	value = (unsigned long)ptr;
+
+#ifdef CONFIG_KALLSYMS
+	if (*fmt == 'B')
 		sprint_backtrace(sym, value);
-	else if (ext != 'f' && ext != 's')
+	else if (*fmt != 'f' && *fmt != 's')
 		sprint_symbol(sym, value);
 	else
 		sprint_symbol_no_offset(sym, value);
@@ -987,6 +994,7 @@ int kptr_restrict __read_mostly;
  * - 'f' For simple symbolic function names without offset
  * - 'S' For symbolic direct pointers with offset
  * - 's' For symbolic direct pointers without offset
+ * - '[FfSs]R' as above with __builtin_extract_return_addr() translation
  * - '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]
@@ -1060,7 +1068,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	case 'S':
 	case 's':
 	case 'B':
-		return symbol_string(buf, end, ptr, spec, *fmt);
+		return symbol_string(buf, end, ptr, spec, fmt);
 	case 'R':
 	case 'r':
 		return resource_string(buf, end, ptr, spec, fmt);