include timegm fallback

crypto/Makefile.am

@@ -73,6 +73,12 @@ if !HAVE_INET_PTON
 libcompat_la_SOURCES += compat/inet_pton.c
 endif
 
+if !HAVE_TIMEGM
+if !HAVE__MKGMTIME
+libcompat_la_SOURCES += compat/timegm.c
+endif
+endif
+
 if !HAVE_REALLOCARRAY
 libcompat_la_SOURCES += compat/reallocarray.c
 endif

crypto/compat/timegm.c

@@ -0,0 +1,71 @@
+/*
+ * timegm shims based on example code from in the glibc timegm manpage.
+ *
+ * These should be replaced with lockless versions that do not require
+ * modifying global state.
+ */
+
+#include <time.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#ifdef _WIN32
+#include <windows.h>
+time_t
+timegm(struct tm *tm)
+{
+	time_t ret;
+	char *tz, *buf;
+	static volatile HANDLE mtx = NULL;
+
+	if (!mtx) {
+		HANDLE p = CreateMutex(NULL, FALSE, NULL);
+		if (InterlockedCompareExchangePointer(
+		    (void **)&mtx, (void *)p, NULL))
+			CloseHandle(p);
+	}
+	WaitForSingleObject(mtx, INFINITE);
+	tz = getenv("TZ");
+	if (tz) {
+		if (asprintf(&buf, "TZ=%s", tz) == -1)
+			buf = NULL;
+	}
+	putenv("TZ=UTC");
+	tzset();
+	ret = mktime(tm);
+	if (buf) {
+		putenv(buf);
+		free(buf);
+	} else
+		putenv("TZ=");
+	tzset();
+	ReleaseMutex(mtx);
+	return ret;
+}
+#else
+#include <pthread.h>
+time_t
+timegm(struct tm *tm)
+{
+	time_t ret;
+	char *tz;
+	static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
+
+	pthread_mutex_lock(&mtx);
+	tz = getenv("TZ");
+	if (tz)
+		tz = strdup(tz);
+	setenv("TZ", "", 1);
+	tzset();
+	ret = mktime(tm);
+	if (tz) {
+		setenv("TZ", tz, 1);
+		free(tz);
+	} else
+		unsetenv("TZ");
+	tzset();
+	pthread_mutex_unlock(&mtx);
+	return ret;
+}
+#endif