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Date:   Wed, 14 Apr 2021 10:47:07 +0300
From:   Dan Carpenter <dan.carpenter@oracle.com>
To:     Fabio Aiuto <fabioaiuto83@gmail.com>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        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()
Message-ID: <20210414074707.GC6048@kadam>
References: <20210413155908.8691-1-fmdefrancesco@gmail.com>
 <7008359.Jy8utYDuns@linux.local>
 <20210413194844.GR2531743@casper.infradead.org>
 <3505455.GpAHCVcAZI@linux.local>
 <20210414052150.GO6021@kadam>
 <20210414074035.GA1880@agape.jhs>
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On Wed, Apr 14, 2021 at 09:40:36AM +0200, Fabio Aiuto wrote:
> 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@agape:~/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
> 

It takes a few hours to build the DB.  The instructions are in the
email.

	~/path/to/smatch/smatch_scripts/build_kernel_data.sh

regards,
dan carpenter