1) IEEE Std 1003.1-2008, "errno" section, is explicit that

"The setting of errno after a successful call to a function is
unspecified unless the description of that function specifies that
errno shall not be modified."

However, free() in IEEE Std 1003.1-2008 does not mention its interaction
with errno, so MAY modify it after successful call
(it depends on particular free() implementation, OS-specific, etc.).

So, save errno across free() calls to make code portable and
POSIX-conformant.

2) Remove unused serrno assignment.

MFC after:      1 week

1 files changed, 16 insertions, 6 deletions

diff --git a/lib/libc/stdlib/realpath.c b/lib/libc/stdlib/realpath.c
index ffbf8ec..185dbb6 100644
--- a/lib/libc/stdlib/realpath.c
+++ b/lib/libc/stdlib/realpath.c
@@ -65,7 +65,6 @@ realpath(const char * __restrict path, char * __restrict resolved)
 		errno = ENOENT;
 		return (NULL);
 	}
-	serrno = errno;
 	if (resolved == NULL) {
 		resolved = malloc(PATH_MAX);
 		if (resolved == NULL)
@@ -83,9 +82,11 @@ realpath(const char * __restrict path, char * __restrict resolved)
 		left_len = strlcpy(left, path + 1, sizeof(left));
 	} else {
 		if (getcwd(resolved, PATH_MAX) == NULL) {
-			if (m)
+			if (m) {
+				serrno = errno;
 				free(resolved);
-			else {
+				errno = serrno;
+			} else {
 				resolved[0] = '.';
 				resolved[1] = '\0';
 			}
@@ -143,8 +144,11 @@ realpath(const char * __restrict path, char * __restrict resolved)
 			 * occurence to not implement lookahead.
 			 */
 			if (lstat(resolved, &sb) != 0) {
-				if (m)
+				if (m) {
+					serrno = errno;
 					free(resolved);
+					errno = serrno;
+				}
 				return (NULL);
 			}
 			if (!S_ISDIR(sb.st_mode)) {
@@ -184,8 +188,11 @@ realpath(const char * __restrict path, char * __restrict resolved)
 		if (lstat(resolved, &sb) != 0) {
 			if (errno != ENOENT || p != NULL)
 				errno = ENOTDIR;
-			if (m)
+			if (m) {
+				serrno = errno;
 				free(resolved);
+				errno = serrno;
+			}
 			return (NULL);
 		}
 		if (S_ISLNK(sb.st_mode)) {
@@ -197,8 +204,11 @@ realpath(const char * __restrict path, char * __restrict resolved)
 			}
 			slen = readlink(resolved, symlink, sizeof(symlink) - 1);
 			if (slen < 0) {
-				if (m)
+				if (m) {
+					serrno = errno;
 					free(resolved);
+					errno = serrno;
+				}
 				return (NULL);
 			}
 			symlink[slen] = '\0';