send-pack: report signal death of pack-objects

If our pack-objects sub-process dies of a signal, then it
likely didn't have a chance to write anything useful to
stderr. The user may be left scratching their head why the
push failed. Let's detect this situation and write something
to stderr.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

send-pack.c

@@ -72,6 +72,7 @@ static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, stru
 	struct child_process po = CHILD_PROCESS_INIT;
 	FILE *po_in;
 	int i;
+	int rc;
 
 	i = 4;
 	if (args->use_thin_pack)
@@ -125,8 +126,20 @@ static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, stru
 		po.out = -1;
 	}
 
-	if (finish_command(&po))
+	rc = finish_command(&po);
+	if (rc) {
+		/*
+		 * For a normal non-zero exit, we assume pack-objects wrote
+		 * something useful to stderr. For death by signal, though,
+		 * we should mention it to the user. The exception is SIGPIPE
+		 * (141), because that's a normal occurence if the remote end
+		 * hangs up (and we'll report that by trying to read the unpack
+		 * status).
+		 */
+		if (rc > 128 && rc != 141)
+			error("pack-objects died of signal %d", rc - 128);
 		return -1;
+	}
 	return 0;
 }