reproducible: fix DATE/TIME macros in toolchain-wrapper

The use of the __DATE__ and __TIME__ macros are one of the most common
sources of non-reproducible binaries. In order to fix that, gcc 7 supports
the SOURCE_DATE_EPOCH variable:

https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=e3e8c48c4a494d9da741c1c8ea6c4c0b7c4ff934

This patch take advantage of toolchain-wrapper to provide support of
SOURCE_DATE_EPOCH to older gcc versions.

Function get_source_date_epoch() come directly from gcc git.

This work was sponsored by `BA Robotic Systems'.

[Peter: use sizeof for character array sizes, make function static,
	extend commit message, add upstream gcc commit]
Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

toolchain/toolchain-wrapper.c

@@ -22,12 +22,15 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <time.h>
 
 #ifdef BR_CCACHE
 static char ccache_path[PATH_MAX];
 #endif
 static char path[PATH_MAX];
 static char sysroot[PATH_MAX];
+static char source_time[sizeof("-D__TIME__=\"HH:MM:SS\"")];
+static char source_date[sizeof("-D__DATE__=\"MMM DD YYYY\"")];
 
 /**
  * GCC errors out with certain combinations of arguments (examples are
@@ -39,8 +42,11 @@ static char sysroot[PATH_MAX];
  * 	-mfloat-abi=
  * 	-march=
  * 	-mcpu=
+ * 	-D__TIME__=
+ * 	-D__DATE__=
+ * 	-Wno-builtin-macro-redefined
  */
-#define EXCLUSIVE_ARGS	3
+#define EXCLUSIVE_ARGS	6
 
 static char *predef_args[] = {
 #ifdef BR_CCACHE
@@ -157,6 +163,47 @@ static void check_unsafe_path(const char *arg,
 	}
 }
 
+/* Read SOURCE_DATE_EPOCH from environment to have a deterministic
+ * timestamp to replace embedded current dates to get reproducible
+ * results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.
+ */
+static time_t get_source_date_epoch()
+{
+	char *source_date_epoch;
+	long long epoch;
+	char *endptr;
+
+	source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+	if (!source_date_epoch)
+		return (time_t) -1;
+
+	errno = 0;
+	epoch = strtoll(source_date_epoch, &endptr, 10);
+	if ((errno == ERANGE && (epoch == LLONG_MAX || epoch == LLONG_MIN))
+			|| (errno != 0 && epoch == 0)) {
+		fprintf(stderr, "environment variable $SOURCE_DATE_EPOCH: "
+				"strtoll: %s\n", strerror(errno));
+		exit(2);
+	}
+	if (endptr == source_date_epoch) {
+		fprintf(stderr, "environment variable $SOURCE_DATE_EPOCH: "
+				"no digits were found: %s\n", endptr);
+		exit(2);
+	}
+	if (*endptr != '\0') {
+		fprintf(stderr, "environment variable $SOURCE_DATE_EPOCH: "
+				"trailing garbage: %s\n", endptr);
+		exit(2);
+	}
+	if (epoch < 0) {
+		fprintf(stderr, "environment variable $SOURCE_DATE_EPOCH: "
+				"value must be nonnegative: %lld \n", epoch);
+		exit(2);
+	}
+
+	return (time_t) epoch;
+}
+
 int main(int argc, char **argv)
 {
 	char **args, **cur, **exec_args;
@@ -167,6 +214,7 @@ int main(int argc, char **argv)
 	char *paranoid_wrapper;
 	int paranoid;
 	int ret, i, count = 0, debug;
+	time_t source_date_epoch;
 
 	/* Calculate the relative paths */
 	basename = strrchr(progpath, '/');
@@ -272,6 +320,28 @@ int main(int argc, char **argv)
 	}
 #endif /* ARCH || CPU */
 
+	source_date_epoch = get_source_date_epoch();
+	if (source_date_epoch != -1) {
+		struct tm *tm = localtime(&source_date_epoch);
+		if (!tm) {
+			perror("__FILE__: localtime");
+			return 3;
+		}
+		ret = strftime(source_time, sizeof(source_time), "-D__TIME__=\"%T\"", tm);
+		if (!ret) {
+			perror("__FILE__: overflow");
+			return 3;
+		}
+		*cur++ = source_time;
+		ret = strftime(source_date, sizeof(source_date), "-D__DATE__=\"%b %e %Y\"", tm);
+		if (!ret) {
+			perror("__FILE__: overflow");
+			return 3;
+		}
+		*cur++ = source_date;
+		*cur++ = "-Wno-builtin-macro-redefined";
+	}
+
 	paranoid_wrapper = getenv("BR_COMPILER_PARANOID_UNSAFE_PATH");
 	if (paranoid_wrapper && strlen(paranoid_wrapper) > 0)
 		paranoid = 1;