Require a C99-compliant snprintf(), and remove related workarounds.

Since our substitute snprintf now returns a C99-compliant result,
there's no need anymore to have complicated code to cope with pre-C99
behavior.  We can just make configure substitute snprintf.c if it finds
that the system snprintf() is pre-C99.  (Note: I do not believe that
there are any platforms where this test will trigger that weren't
already being rejected due to our other C99-ish feature requirements for
snprintf.  But let's add the check for paranoia's sake.)  Then, simplify
the call sites that had logic to cope with the pre-C99 definition.

I also dropped some stuff that was being paranoid about the possibility
of snprintf overrunning the given buffer.  The only reports we've ever
heard of that being a problem were for Solaris 7, which is long dead,
and we've sure not heard any reports of these assertions triggering in
a long time.  So let's drop that complexity too.

Likewise, drop some code that wasn't trusting snprintf to set errno
when it returns -1.  That would be not-per-spec, and again there's
no real reason to believe it is a live issue, especially not for
snprintfs that pass all of configure's feature checks.

Discussion: https://postgr.es/m/17245.1534289329@sss.pgh.pa.us

1 files changed, 8 insertions, 15 deletions

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index f458c0eeae8..9989d3a3517 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -9441,26 +9441,19 @@ do_serialize(char **destptr, Size *maxbytes, const char *fmt,...)
 	if (*maxbytes <= 0)
 		elog(ERROR, "not enough space to serialize GUC state");
 
-	errno = 0;
-
 	va_start(vargs, fmt);
 	n = vsnprintf(*destptr, *maxbytes, fmt, vargs);
 	va_end(vargs);
 
-	/*
-	 * Cater to portability hazards in the vsnprintf() return value just like
-	 * appendPQExpBufferVA() does.  Note that this requires an extra byte of
-	 * slack at the end of the buffer.  Since serialize_variable() ends with a
-	 * do_serialize_binary() rather than a do_serialize(), we'll always have
-	 * that slack; estimate_variable_size() need not add a byte for it.
-	 */
-	if (n < 0 || n >= *maxbytes - 1)
+	if (n < 0)
 	{
-		if (n < 0 && errno != 0 && errno != ENOMEM)
-			/* Shouldn't happen. Better show errno description. */
-			elog(ERROR, "vsnprintf failed: %m");
-		else
-			elog(ERROR, "not enough space to serialize GUC state");
+		/* Shouldn't happen. Better show errno description. */
+		elog(ERROR, "vsnprintf failed: %m");
+	}
+	if (n >= *maxbytes)
+	{
+		/* This shouldn't happen either, really. */
+		elog(ERROR, "not enough space to serialize GUC state");
 	}
 
 	/* Shift the destptr ahead of the null terminator */