* m88ds3103: Undefined division
@ 2016-02-19 10:10 Peter Rosin
2016-02-19 10:46 ` Antti Palosaari
0 siblings, 1 reply; 2+ messages in thread
From: Peter Rosin @ 2016-02-19 10:10 UTC (permalink / raw)
To: Antti Palosaari; +Cc: linux-media, Mauro Carvalho Chehab, linux-kernel
Hi!
I'm looking at this code in drivers/media/dvb-frontends/m88ds3103.c in
the m88ds3103_set_frontend() function, line 600 (give or take):
s32tmp = 0x10000 * (tuner_frequency - c->frequency);
s32tmp = DIV_ROUND_CLOSEST(s32tmp, priv->mclk_khz);
if (s32tmp < 0)
s32tmp += 0x10000;
There is code that tries to handle negative s32tmp, so I assume that
negative s32tmp is a possibility. Further, priv->mclk_khz is an unsigned
type as far as I can tell. But then we have this comment for the
DIV_ROUND_CLOSEST macro:
/*
* Divide positive or negative dividend by positive divisor and round
* to closest integer. Result is undefined for negative divisors and
* for negative dividends if the divisor variable type is unsigned.
*/
#define DIV_ROUND_CLOSEST(x, divisor)( \
I don't know how bad this is, and what the consequences of garbage are,
but from here it looks like a problem waiting to happen...
Cheers,
Peter
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: m88ds3103: Undefined division
2016-02-19 10:10 m88ds3103: Undefined division Peter Rosin
@ 2016-02-19 10:46 ` Antti Palosaari
0 siblings, 0 replies; 2+ messages in thread
From: Antti Palosaari @ 2016-02-19 10:46 UTC (permalink / raw)
To: Peter Rosin; +Cc: linux-media, Mauro Carvalho Chehab, linux-kernel
On 02/19/2016 12:10 PM, Peter Rosin wrote:
> Hi!
>
> I'm looking at this code in drivers/media/dvb-frontends/m88ds3103.c in
> the m88ds3103_set_frontend() function, line 600 (give or take):
>
> s32tmp = 0x10000 * (tuner_frequency - c->frequency);
> s32tmp = DIV_ROUND_CLOSEST(s32tmp, priv->mclk_khz);
> if (s32tmp < 0)
> s32tmp += 0x10000;
>
> There is code that tries to handle negative s32tmp, so I assume that
> negative s32tmp is a possibility. Further, priv->mclk_khz is an unsigned
> type as far as I can tell. But then we have this comment for the
> DIV_ROUND_CLOSEST macro:
>
> /*
> * Divide positive or negative dividend by positive divisor and round
> * to closest integer. Result is undefined for negative divisors and
> * for negative dividends if the divisor variable type is unsigned.
> */
> #define DIV_ROUND_CLOSEST(x, divisor)( \
>
> I don't know how bad this is, and what the consequences of garbage are,
> but from here it looks like a problem waiting to happen...
Divisor type (mclk) needs to be changed signed then somehow...
regards
Antti
--
http://palosaari.fi/
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