Wireshark · Wireshark-dev: Re: [Wireshark-dev] Lint of packet-tcp.c

["Maynard, Chris" <Christopher.Maynard@xxxxxxxxx>]

Yes, I think you’re right.  I was too focused on msp itself.  If ipfd_head is not NULL then I don’t see any way for msp to be NULL either.  Sorry, false alarm.

 

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From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Sébastien Tandel
Sent: Friday, August 15, 2008 9:47 AM
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] Lint of packet-tcp.c

 

 

On Fri, Aug 15, 2008 at 2:30 AM, Jaap Keuter <jaap.keuter@xxxxxxxxx> wrote:

Hi Chris,

Thanks for taking a look. I looked at your new log also, and still wonder how
lint get these 'Possible use of null pointer' results. Use of msp is guarded by
ipfd_head, so this should never cause a problem. I wonder what lint sees as path
to get in trouble.

 

desegment_tcp (... struct tcp_analysis *tcp)

{

  *msp = NULL;

  *ipfd_head = NULL;

 

  if (tcpd) {

    msp = se_tree_lookup();

  }

  if (msp) {

    ...

    ipfd_head = fragment_add();

    ...

  }

  ...

  if (ipfd_head) {

    ...

    tcpinfo->seq = msp->seq

  }

}

 

it is already not a so simple inspection path to check that if ipfd_head != NULL, it implies that msp != NULL ...  even for a human! :-p

I don't think it costs a lot to have something like the following for the last "if" of the excerpt :

 

if (msp && ipfd_head) {

  ...

  tcpinfo->seq = msp->seq;

  ...

}

 

and it should let lint happy ... and humans too héhé ;)

 

 

Furthermore, gcc already eliminates useless checks for NULL pointers ;)

 

 -fdelete-null-pointer-checks

           Use global dataflow analysis to identify and eliminate useless

           checks for null pointers.  The compiler assumes that dereferencing

           a null pointer would have halted the program.  If a pointer is

           checked after it has already been dereferenced, it cannot be null.

 

           In some environments, this assumption is not true, and programs can

           safely dereference null pointers.  Use

           -fno-delete-null-pointer-checks to disable this optimization for

           programs which depend on that behavior.

 

           Enabled at levels -O2, -O3, -Os.

 

Regards,

Sebastien

 

 

Thanx,
Jaap

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