linux-kernel - [PATCH] Clarify error on directive in macro arguments (Re: [PATCH] jffs2: fix sparse errors: directive in argument list)

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Message-ID: <20131118020746.GX16018@ringworld.MIT.EDU>
Date:	Sun, 17 Nov 2013 21:07:46 -0500
From:	Greg Price <price@....EDU>
To:	Al Viro <viro@...IV.linux.org.uk>,
	Christopher Li <sparse@...isli.org>
Cc:	Joe Perches <joe@...ches.com>, Erico Nunes <nunes.erico@...il.com>,
	linux-sparse@...r.kernel.org, dwmw2 <dwmw2@...radead.org>,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] Clarify error on directive in macro arguments (Re: [PATCH]
 jffs2: fix sparse errors: directive in argument list)

[+linux-sparse and Chris]

On Mon, Nov 18, 2013 at 01:33:49AM +0000, Al Viro wrote:
> On Sun, Nov 17, 2013 at 02:45:05PM -0800, Joe Perches wrote:
> > Yes.  I think it's a defect in how sparse
> > treats string concatenation.
> > 
> > That style [... with printk ...] is pretty common in the kernel sources.
> 
> ... and it's perfectly fine, until somebody starts playing in nasal
> daemon country and do that in *macro* arguments.  And a nasal daemon
> country it is - it's an undefined behaviour.  See 6.10.3p11 in C99.
> And trying to define a semantics for that gets real ugly real fast.
> sparse matches gcc behaviour (I hope), but it warns about such abuses.
> It's a defect, all right - one being reported by sparse.

Perhaps the following tweak to the error message would make this
subtlety clearer?

Cheers,
Greg


From: Greg Price <price@....edu>
Date: Sun, 17 Nov 2013 17:57:41 -0800
Subject: [PATCH] Clarify error on directive in macro arguments

Preprocessor directives in the arguments of a real function
are innocuous and in some contexts common.  If a developer
doesn't realize that a "function" is implemented as a macro,
they may mistake this error for a false alarm.

See http://www.spinics.net/lists/kernel/msg1636974.html
and http://www.spinics.net/lists/kernel/msg1636976.html
for an example.

Easy enough to clarify that this is a macro, so do it.

Signed-off-by: Greg Price <price@....edu>
---
 pre-process.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pre-process.c b/pre-process.c
index d521318..db58a97 100644
--- a/pre-process.c
+++ b/pre-process.c
@@ -204,7 +204,7 @@ static struct token *collect_arg(struct token *prev, int vararg, struct position
 		if (next->pos.newline && match_op(next, '#')) {
 			if (!next->pos.noexpand) {
 				sparse_error(next->pos,
-					     "directive in argument list");
+					     "directive in macro argument list");
 				preprocessor_line(stream, p);
 				__free_token(next);	/* Free the '#' token */
 				continue;
-- 
1.8.3.2
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