On Wed, Oct 11, 2017 at 06:02:47PM +0530, Shreeya Patel wrote:
> On Tue, 2017-10-10 at 11:06 +1100, Tobin C. Harding wrote:
> > On Tue, Oct 10, 2017 at 02:48:58AM +0530, Shreeya Patel wrote:
> > >
> > > Remove NULL pointer dereference as it results in undefined
> > > behaviour, and will usually lead to a runtime error.
> > The diff does not show any pointer dereference so it is hard to
> > understand what you are trying to do
> > with this patch.
> >
> > >
> > > Signed-off-by: Shreeya Patel <shreeya.patel23498@xxxxxxxxx>
> > > ---
> > > drivers/staging/rtlwifi/base.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/rtlwifi/base.c
> > > b/drivers/staging/rtlwifi/base.c
> > > index b88b0e8..5bb8f98 100644
> > > --- a/drivers/staging/rtlwifi/base.c
> > > +++ b/drivers/staging/rtlwifi/base.c
> > > @@ -781,7 +781,7 @@ static void _rtl_txrate_selectmode(struct
> > > ieee80211_hw *hw,
> > >
> > > struct rtl_priv *rtlpriv = rtl_priv(hw);
> > > struct rtl_mac *mac = rtl_mac(rtl_priv(hw));
> > > - struct rtl_sta_info *sta_entry = NULL;
> > > + struct rtl_sta_info *sta_entry;
> > Now the pointer just has garbage in it instead of the testable value
> > of NULL. If you are concerned
> > with the dereference perhaps you could add a NULL check, again it's
> > hard to say without seeing the
> > code.
>
> Hello,
>
> Thanks for making me understand.
>
> Here is the code after declaration and initialization of sta_entry.
> Will it be good to add a NULL check in this case?
>
> struct rtl_sta_info *sta_entry = NULL;
> u8 ratr_index = SET_RATE_ID(RATR_INX_WIRELESS_MC);
>
> if (sta) {
> sta_entry = (struct rtl_sta_info *)sta->drv_priv;
> ratr_index = sta_entry->ratr_index;
> }
Later in this function the macro SET_RATE_ID() is called, it relies on sta_entry being NULL if it
was not explicitly set.
Here is the macro;
#define SET_RATE_ID(rate_id) \
((rtlpriv->cfg->spec_ver & RTL_SPEC_NEW_RATEID) ? \
rtl_mrate_idx_to_arfr_id(hw, rate_id, \
(sta_entry ? sta_entry->wireless_mode : \
WIRELESS_MODE_G)) : \
rate_id)
> If we are making a pointer point to NULL then what if any other
> variable is already pointing to NULL for some other purpose.
> Instead, removing initialization will be good right?
A pointer does not _point_ to NULL as such. A NULL pointer has a value of all zero bytes. Have you
read (and completed all the exercises) in KnR
https://en.wikipedia.org/wiki/The_C_Programming_Language
It is, in my opinion, one of the best tech books ever written. If you have any holes in your C
knowledge, this is the place to start.
Good luck,
Tobin.
_______________________________________________
devel mailing list
devel@xxxxxxxxxxxxxxxxxxxxxx
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
