Add GNU-compatible strerror_r.

We already had the POSIX strerror_r, but some third-party code defines
_GNU_SOURCE and expects to get the GNU strerror_r instead.

This exposed a bug in the libc internal logging functions where unlike
their standard brethren they wouldn't return the number of bytes they'd
have liked to have written.

Bug: 16243479
Change-Id: I1745752ccbdc569646d34f5071f6df2be066d5f4

tests/string_posix_strerror_r_test.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#undef _GNU_SOURCE
+
+// Old versions of glibc (like our current host prebuilt sysroot one) have
+// headers that don't work if you #undef _GNU_SOURCE, which makes it
+// impossible to build this test.
+#include <features.h>
+
+#if !defined(__GLIBC__)
+#include <string.h>
+
+#include <errno.h>
+#include <gtest/gtest.h>
+
+TEST(string, posix_strerror_r) {
+  char buf[256];
+
+  // Valid.
+  ASSERT_EQ(0, strerror_r(0, buf, sizeof(buf)));
+  ASSERT_STREQ("Success", buf);
+  ASSERT_EQ(0, strerror_r(1, buf, sizeof(buf)));
+  ASSERT_STREQ("Operation not permitted", buf);
+
+  // Invalid.
+  ASSERT_EQ(0, strerror_r(-1, buf, sizeof(buf)));
+  ASSERT_STREQ("Unknown error -1", buf);
+  ASSERT_EQ(0, strerror_r(1234, buf, sizeof(buf)));
+  ASSERT_STREQ("Unknown error 1234", buf);
+
+  // Buffer too small.
+  errno = 0;
+  memset(buf, 0, sizeof(buf));
+  ASSERT_EQ(-1, strerror_r(4567, buf, 2));
+  ASSERT_STREQ("U", buf);
+  // The POSIX strerror_r sets errno to ERANGE (the GNU one doesn't).
+  ASSERT_EQ(ERANGE, errno);
+}
+#else
+# if __GLIBC_PREREQ(2, 15)
+#  error this test should work now
+# endif
+#endif