From 9b796691eb794e9f5279886e917c028a09f8a728 Mon Sep 17 00:00:00 2001
From: info@mobile-stream.com
Date: Wed, 6 Mar 2019 16:28:48 +0300
Subject: wctomb, wcrtomb: guard slow/trap path with MB_LEN_MAX

This allows the compiler to optimize out the slow/trap path at all
for the typical correct code:

char buf[MB_LEN_MAX];
r = wctomb(buf, c);

The change tries to keep the "unknown object size" case handling in
wcrtomb() as is even if it seems redundant and not helping (we copy
__buf to possibly undersized __s in any case) and inconsistent with
wctomb() (where we let the original library method itself overwrite
the possibly undersized __s).
---
 include/wchar.h | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

(limited to 'include/wchar.h')

diff --git a/include/wchar.h b/include/wchar.h
index 09ffa97..c5d0e5d 100644
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -111,15 +111,14 @@ _FORTIFY_FN(mbstowcs) size_t mbstowcs(wchar_t *__ws, const char *__s, size_t __w
 
 _FORTIFY_FN(wcrtomb) size_t wcrtomb(char *__s, wchar_t __w, mbstate_t *__st)
 {
-	char __buf[MB_LEN_MAX];
-	size_t __b = __builtin_object_size(__s, 0);
-	size_t __r;
+	if (__s && MB_LEN_MAX > __builtin_object_size(__s, 2)) {
+		char __buf[MB_LEN_MAX];
+		size_t __r;
 
-	if (__s) {
 		__r = __orig_wcrtomb(__buf, __w, __st);
 		if (__r == (size_t)-1)
 			return __r;
-		if (__r > __b)
+		if (__r > __builtin_object_size(__s, 0))
 			__builtin_trap();
 		__builtin_memcpy(__s, __buf, __r);
 		return __r;
@@ -218,7 +217,7 @@ _FORTIFY_FN(wctomb) int wctomb(char *__s, wchar_t __w)
 {
 	size_t __b = __builtin_object_size(__s, 0);
 
-	if (__s && MB_CUR_MAX > __b)
+	if (__s && MB_LEN_MAX > __b && MB_CUR_MAX > __b)
 		__builtin_trap();
 	return __orig_wctomb(__s, __w);
 }
-- 
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