string-util: rework memory_erase() so that it cannot be optimized away

memory_erase() so far just called memset(), which the compiler might optimize away under certain conditions if it feels there's benefit in it. C11 knows a new memset_s() call that is like memset(), but may not be optimized away. Ideally, we'd just use that call, but glibc currently does not support it. Hence, implement our own simplistic version of it. We use a GCC pragma to turn off optimization for this call, and also use the "volatile" keyword on the pointers to ensure that gcc will use the pointers as-is. According to a variety of internet sources, either one does the trick. However, there are also reports that at least the volatile thing isn't fully correct, hence let's add some snake oil and employ both techniques. https://news.ycombinator.com/item?id=4711346
2015-11-02 23:07:20 +01:00
parent 5732a7dbb0
commit 9fe4ea21be
5 changed files with 94 additions and 10 deletions
@@ -0,0 +1,61 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2015 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "string-util.h"
+
+static void test_string_erase(void) {
+        char *x;
+
+        x = strdupa("");
+        assert_se(streq(string_erase(x), ""));
+
+        x = strdupa("1");
+        assert_se(streq(string_erase(x), "x"));
+
+        x = strdupa("12");
+        assert_se(streq(string_erase(x), "xx"));
+
+        x = strdupa("123");
+        assert_se(streq(string_erase(x), "xxx"));
+
+        x = strdupa("1234");
+        assert_se(streq(string_erase(x), "xxxx"));
+
+        x = strdupa("12345");
+        assert_se(streq(string_erase(x), "xxxxx"));
+
+        x = strdupa("123456");
+        assert_se(streq(string_erase(x), "xxxxxx"));
+
+        x = strdupa("1234567");
+        assert_se(streq(string_erase(x), "xxxxxxx"));
+
+        x = strdupa("12345678");
+        assert_se(streq(string_erase(x), "xxxxxxxx"));
+
+        x = strdupa("123456789");
+        assert_se(streq(string_erase(x), "xxxxxxxxx"));
+}
+
+int main(int argc, char *argv[]) {
+        test_string_erase();
+        return 0;
+}