linux-kernel - Re: Possible code defects: macros and precedence

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Date:   Tue, 20 Sep 2016 11:03:44 -0700
From:   Joe Perches <joe@...ches.com>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     Dan Carpenter <error27@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: Possible code defects: macros and precedence

On Tue, 2016-09-20 at 10:07 -0700, Joe Perches wrote:
> On Tue, 2016-09-20 at 15:14 +0200, Julia Lawall wrote:
> > The semantic patch below finds a binary operator in a macro and a binary
> > operator in the use of the macro, and checks if the priority of the
> > operator in the macro is higher (lower number) than the priority of the
> > operator in the use.  If this is the case, it adds parentheses in the use,
> > which is not what one wants, but serves to show where the problem is

> Thanks, this works on the trivial example I suggested
> without an #include
> 
> I've tried it on trivial files with --recursive-includes
> and it seems to work there too.

I tried it on drivers/net with --recursive-includes and got
just 1 hit on an old and probably relatively untested driver.

No hardware, can't test.  It may be correct now.  Who knows...
---
diff --urN a/drivers/net/ethernet/smsc/smc911x.h b/drivers/net/ethernet/smsc/smc911x.h
--- a/drivers/net/ethernet/smsc/smc911x.h
+++ b/drivers/net/ethernet/smsc/smc911x.h
@@ -700,8 +700,8 @@ static const struct chip_id chip_ids[] =
  * capabilities.  Please use those and not the in/out primitives.
  */
 /* FIFO read/write macros */
-#define SMC_PUSH_DATA(lp, p, l)	SMC_outsl( lp, TX_DATA_FIFO, p, (l) >> 2 )
-#define SMC_PULL_DATA(lp, p, l)	SMC_insl ( lp, RX_DATA_FIFO, p, (l) >> 2 )
+#define SMC_PUSH_DATA(lp, p, l)	SMC_outsl( lp, TX_DATA_FIFO, p, ((l) >> 2) )
+#define SMC_PULL_DATA(lp, p, l)	SMC_insl ( lp, RX_DATA_FIFO, p, ((l) >> 2) )
 #define SMC_SET_TX_FIFO(lp, x) 	SMC_outl( x, lp, TX_DATA_FIFO )
 #define SMC_GET_RX_FIFO(lp)	SMC_inl( lp, RX_DATA_FIFO )