From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Triplett Subject: Re: Sparse preprocessing bug with zero-arg variadic macros Date: Thu, 31 Aug 2017 14:34:44 -0700 Message-ID: <20170831213444.6yeyfcrry6utaeih@cloud> References: <20170831133400.zjeaxhf25rbdftic@treble> <20170831205433.GQ5426@ZenIV.linux.org.uk> <20170831210922.GA9227@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from relay2-d.mail.gandi.net ([217.70.183.194]:57336 "EHLO relay2-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751110AbdHaVeu (ORCPT ); Thu, 31 Aug 2017 17:34:50 -0400 Content-Disposition: inline In-Reply-To: <20170831210922.GA9227@ZenIV.linux.org.uk> Sender: linux-sparse-owner@vger.kernel.org List-Id: linux-sparse@vger.kernel.org To: Al Viro Cc: Linus Torvalds , Josh Poimboeuf , Sparse Mailing-list On Thu, Aug 31, 2017 at 10:09:22PM +0100, Al Viro wrote: > On Thu, Aug 31, 2017 at 09:54:33PM +0100, Al Viro wrote: > > What a mess... Note that for non-vararg it *is* the right interpretation > > (with #define A(x) [x] we will have A() interpreted as "empty token sequence > > as the only argument", not "no arguments given"). For vararg case we > > normally do not need to distinguish "not given" and "empty" - the only > > thing that cares is exactly the ,## kludge. There with > > #define B(x,...) [x,##__VA_ARGS__] > > B(1) and B(1,) yield [1] and [1,] resp. And for everything other than > > "just ..." we even get it right... > > > > I see what's going on there; will post a fix in a few. > > > Fix macro argument parsing for (...) case > > Nasty corner case for the sake of ,##__VA_ARGS__ perversion - for something > like #define A(x,...) [x,##__VA_ARGS] we want A(1) to expand to [1] and > A(1,) - to [1,]. In other words, "no vararg given" and "vararg empty" are > different and need to be distinguished. Unfortunately, in case when there > was nothing but vararg we got it wrong - #define A(...) ,##__VA_ARGS ended > up with A() interpreted as "one empty argument" (as it would in non-vararg > case) rather than "zero arguments". > > Signed-off-by: Al Viro > --- > diff --git a/pre-process.c b/pre-process.c > index 74414df..8800dce 100644 > --- a/pre-process.c > +++ b/pre-process.c > @@ -296,9 +296,11 @@ static int collect_arguments(struct token *start, struct token *arglist, struct > for (count = 0; count < wanted; count++) { > struct argcount *p = &arglist->next->count; > next = collect_arg(start, p->vararg, &what->pos, p->normal); > - arglist = arglist->next->next; > if (eof_token(next)) > goto Eclosing; > + if (p->vararg && wanted == 1 && eof_token(start->next)) > + break; > + arglist = arglist->next->next; > args[count].arg = start->next; > args[count].n_normal = p->normal; > args[count].n_quoted = p->quoted; This looks plausible; we should also add a test for it, though.