On Tue, Apr 13, 2021 at 10:08:32PM +0200, Fabio M. De Francesco wrote:
> On Tuesday, April 13, 2021 9:48:44 PM CEST Matthew Wilcox wrote:
> > On Tue, Apr 13, 2021 at 09:45:03PM +0200, Fabio M. De Francesco wrote:
> > > 1) The driver doesn't call that function from anywhere else than the
> > > macro. 2) You have explained that the macro add its symbol to a slot
> > > in an array that would shift all the subsequent elements down if that
> > > macro is not used exactly in the line where it is.
> > > 3) Dan Carpenter said that that array is full of null functions (or
> > > empty slots?).
> > >
> > > Unless that function is called anonymously dereferencing its address
> > > from the position it occupies in the array, I'm not able to see what
> > > else means can any caller use.
> > >
> > > I know I have much less experience than you with C: what can go wrong?
> >
> > Here's where the driver calls that function:
> >
> > $ git grep wlancmds drivers/staging/rtl8723bs/
> > drivers/staging/rtl8723bs/core/rtw_cmd.c:static struct cmd_hdl wlancmds[]
> > = { drivers/staging/rtl8723bs/core/rtw_cmd.c: if
> > (pcmd->cmdcode < ARRAY_SIZE(wlancmds)) {
> > drivers/staging/rtl8723bs/core/rtw_cmd.c: cmd_hdl
> > = wlancmds[pcmd->cmdcode].h2cfuns;
> >
> OK, I had imagined an anonymous call from its location in the array (as I
> wrote in the last phrase of my message). However, I thought that it could
> have been an improbable possibility, not a real one.
>
> Linux uses a lot of interesting ideas that newcomers like me should learn.
> Things here are trickier than they appear at first sight.
One trick would be to build the Smatch cross function database.
https://www.spinics.net/lists/smatch/msg00568.html
Then you could do:
$ ~/path/to/smatch_data/db/smdb.py led_blink_hdl
file | caller | function | type | parameter | key | value |
drivers/staging/rtl8723bs/core/rtw_cmd.c | rtw_cmd_thread | rtw_cmd_thread ptr cmd_hdl | INTERNAL | -1 | | uchar(*)(struct adapter*, uchar*)
drivers/staging/rtl8188eu/core/rtw_cmd.c | rtw_cmd_thread | rtw_cmd_thread ptr cmd_hdl | INTERNAL | -1 | | uchar(*)(struct adapter*, uchar*)
drivers/staging/rtl8188eu/core/rtw_cmd.c | rtw_cmd_thread | rtw_cmd_thread ptr cmd_hdl | BUF_SIZE | 1 | pbuf | 1,4,6,8,12,14,16,19-20,23-24,48,740,884,892,900,960
Which says that led_blink_hdl() is called as a function pointer called
"cmd_hdl" from rtw_cmd_thread().
Hm... It says it can be called from either rtw_cmd_thread() function
(the rtl8723bs or rtl8188eu version) which is not ideal. But also
basically harmless so whatever...
regards,
dan carpenter
