From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Julia Lawall <julia.lawall@inria.fr>,
outreachy-kernel@googlegroups.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [Outreachy kernel] [PATCH] :staging: rtl8723bs: Remove useless led_blink_hdl()
Date: Wed, 14 Apr 2021 08:33:48 +0200 [thread overview]
Message-ID: <2418632.vfNx7fMs9o@linux.local> (raw)
In-Reply-To: <20210414052150.GO6021@kadam>
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.
Regards,
Fabio
next prev parent reply other threads:[~2021-04-14 6:33 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 15:59 [Outreachy kernel] [PATCH] :staging: rtl8723bs: Remove useless led_blink_hdl() Fabio M. De Francesco
2021-04-13 16:04 ` Julia Lawall
2021-04-13 16:19 ` Fabio M. De Francesco
2021-04-13 16:27 ` Julia Lawall
2021-04-13 16:47 ` Fabio M. De Francesco
2021-04-13 18:20 ` Dan Carpenter
2021-04-13 18:30 ` Fabio M. De Francesco
2021-04-13 18:57 ` Julia Lawall
2021-04-13 19:16 ` Fabio M. De Francesco
2021-04-13 19:25 ` Julia Lawall
2021-04-13 19:45 ` Fabio M. De Francesco
2021-04-13 19:48 ` Matthew Wilcox
2021-04-13 20:08 ` Fabio M. De Francesco
2021-04-14 5:21 ` Dan Carpenter
2021-04-14 6:33 ` Fabio M. De Francesco [this message]
2021-04-14 7:00 ` Dan Carpenter
2021-04-14 7:59 ` Fabio M. De Francesco
2021-04-14 8:06 ` Dan Carpenter
2021-04-14 7:40 ` Fabio Aiuto
2021-04-14 7:47 ` Dan Carpenter
2021-04-13 16:06 ` Greg Kroah-Hartman
-- strict thread matches above, loose matches on Subject: below --
2021-04-14 11:52 [Outreachy kernel] [PATCH] staging: " Fabio M. De Francesco
2021-04-14 12:00 ` Fabio Aiuto
2021-04-14 12:18 ` Greg Kroah-Hartman
2021-04-14 13:27 ` Fabio M. De Francesco
2021-04-14 13:24 ` Dan Carpenter
2021-04-14 15:36 ` Fabio M. De Francesco
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