[PATCH 2alt/2] work around unreliable gmtime errors on AIX

[Jeff King <peff@peff.net>]

AIX's gmtime will happily overflow the tm_year field. Let's
catch this error before handing the value to gmtime.

Signed-off-by: Jeff King <peff@peff.net>
---
This is an alternative to loosening the test in t4212.

It's really not _that_ ugly.  The "LL" here may not be portable, though.
32-bit systems can't represent this timestamp at all (so they're safe),
but I don't know what would be the best way to conditionally compile
here.

 compat/gmtime.c  | 10 ++++++++++
 config.mak.uname |  1 +
 2 files changed, 11 insertions(+)

diff --git a/compat/gmtime.c b/compat/gmtime.c
index 75a5835..f95ba50 100644
--- a/compat/gmtime.c
+++ b/compat/gmtime.c
@@ -12,6 +12,16 @@ struct tm *git_gmtime_r(const time_t *timep, struct tm *result)
 {
 	struct tm *ret;
 
+	/*
+	 * Some systems, like AIX, will happily overflow the tm_year field.
+	 * So let's recognize obviously out-of-bound data before it hits gmtime
+	 * and just mark it as an error. This date is ~316 million years in the
+	 * future, which is far enough that nobody should care, but close
+	 * enough for the year to fit into a 32-bit tm_year.
+	 */
+	if (*timep > 9999999999999999LL)
+		return NULL;
+
 	ret = gmtime_r(timep, result);
 
 	/*
diff --git a/config.mak.uname b/config.mak.uname
index 0e22ac0..c1110ad 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -236,6 +236,7 @@ ifeq ($(uname_S),AIX)
 		INLINE = ''
 	endif
 	GIT_TEST_CMP = cmp
+	GMTIME_UNRELIABLE_ERRORS = UnfortunatelyYes
 endif
 ifeq ($(uname_S),GNU)
 	# GNU/Hurd
-- 
1.9.1.656.ge8a0637