Messages in this thread |  | | Date | Tue, 27 Nov 2001 19:03:18 +0000 | From | Nathan Myers <> | Subject | Re: [BUG] Bad #define, nonportable C, missing {} |
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vda wrote in http://marc.theaimsgroup.com/?l=linux-kernel&m=100687040003540&w=2: > On Monday 26 November 2001 18:28, Alan Cox wrote: > > > > MODINC(x,y) (x = (x % y) + 1) > > > > > > drivers/message/i2o/i2o_config.c:#define MODINC(x,y) (x = x++ % y) > > > > > > Alan, can you clarify what this macro is doing? > > > What about making it less confusing? > > > > Nothing to do with me 8). I didnt write that bit of the i2o code. I agree > > its both confusing and buggy. Send a fix ? > > This is a test to be sure my replacement is equivalent: > -------------------- > #include <stdio.h> > #define MODINC(x,y) (x = x++ % y) > #define MODULO_INC(x,y) ((x) = ((x)%(y))+1) > ...
If they really are equivalent, you have certainly found a bug.
Examining the code in i2o_config.c, it is expected that the q_in argument ranges from 0 to I2O_EVT_Q_LEN-1, but the result of MODINC can never be 0, and may equal I2O_EVT_Q_LEN, overindexing the array member event_q and clobbering all the remaining members (including q_in).
The correct fix appears to be
#define MODULO_INC(x,y) ((x) = ((x)+1)%(y))
Nathan Myers ncm at cantrip dot org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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