linux-kernel - Re: [Outreachy kernel] [PATCH] :staging: rtl8723bs: Remove useless led_blink

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Date:   Wed, 14 Apr 2021 09:40:36 +0200
From:   Fabio Aiuto <fabioaiuto83@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Julia Lawall <julia.lawall@...ia.fr>,
        outreachy-kernel@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [Outreachy kernel] [PATCH] :staging: rtl8723bs: Remove useless
 led_blink_hdl()

On Wed, Apr 14, 2021 at 08:21:50AM +0300, 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
> 

very powerful tool.

I tried this:

fabio@...pe:~/src/git/kernels/staging$ ~/src/git/smatch/smatch_data/db/smdb.py led_blink_hdl
Traceback (most recent call last):
  File "/home/fabio/src/git/smatch/smatch_data/db/smdb.py", line 725, in <module>
    print_caller_info("", func)
  File "/home/fabio/src/git/smatch/smatch_data/db/smdb.py", line 366, in print_caller_info
    ptrs = get_function_pointers(func)
  File "/home/fabio/src/git/smatch/smatch_data/db/smdb.py", line 53, in get_function_pointers
    get_function_pointers_helper(func)
  File "/home/fabio/src/git/smatch/smatch_data/db/smdb.py", line 38, in get_function_pointers_helper
    cur.execute("select distinct ptr from function_ptr where function = '%s';" %(func))
sqlite3.OperationalError: no such table: function_ptr

I run smatch version 1.71 on Debian Buster machine

what's happened?

thanks in advance,

fabio