On Wed, Apr 14, 2021 at 08:33:48AM +0200, Fabio M. De Francesco wrote:
> On Wednesday, April 14, 2021 7:21:50 AM CEST Dan Carpenter wrote:
> > 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
> >
> Nice tool, thanks. I'll surely use it when it is needed to find out which
> callers use a function pointer.
>
> However I cannot see how it can help in this context. That function *does*
> something, even if I cannot understand why someone needs a function to test
> the initialization of a pointer. Furthermore it is actually called by
> rtw_cmd_thread() (as you found out by using smatch) that expect one of the
> two possible values that led_blink_hdl() returns.
>
> That said, what trick could I use for the purpose of getting rid of that
> function? At this point I'm not sure it could be made.
If you look at how this is called:
drivers/staging/rtl8723bs/core/rtw_cmd.c
449 memcpy(pcmdbuf, pcmd->parmbuf, pcmd->cmdsz);
450
451 if (pcmd->cmdcode < ARRAY_SIZE(wlancmds)) {
452 cmd_hdl = wlancmds[pcmd->cmdcode].h2cfuns;
453
454 if (cmd_hdl) {
455 ret = cmd_hdl(pcmd->padapter, pcmdbuf);
^^^^^^^
456 pcmd->res = ret;
457 }
458
459 pcmdpriv->cmd_seq++;
460 } else {
461 pcmd->res = H2C_PARAMETERS_ERROR;
462 }
463
464 cmd_hdl = NULL;
The led_blink_hdl() function returns success if "pcmdbuf" is non-NULL
and fail if it's NULL. "pcmdbuf" is never supposed to be NULL. (The
"supposed" caveat is because there may be a race in rtw_sdio_if1_init()
which briefly allows a NULL "pcmdbuf", but that is an unrelated bug).
Anyway, there is no point to the led_blink_hdl() function. Likely
they intended it to do something but never got around to implementing
it. Just delete it.
regards,
dan carpenter
