Wireshark-dev: Re: [Wireshark-dev] New GCC, new option required?
From: Bill Meier <[email protected]>
Date: Wed, 13 Jul 2011 22:51:04 -0400
On 7/13/2011 7:38 PM, Guy Harris wrote:
Haven't you (and maybe others) been fixing the same issues already,
as  a result of Coverity warnings about the same thing?

And how many of those are

static void
dissect_whatever(...)
{

		...

	proto_tree_add_item(tree, hf_foo, tvb, offset, len_foo, encoding);
	offset += len_foo;
	proto_tree_add_item(tree, hf_bar, tvb, offset, len_bar, encoding);
	offset += len_bar;
}

and how many of those ultimately represent dissectors that should be
converted to use ptvcursors, in which case the "offset +=" stuff will
disappear into the ptvcursor code and not get whined about by dataflow
analyzers?
I'd have to go back and look but I guess that some of the "Coverity 
[unused]" defects for the dissectors were related to the pattern as 
shown above:
{
    ...
    offset += ...;
}



However, ISTR that many more were related to the following pattern:
{
	...
	foo = proto_tree_add_item(...);
	offset += ...;
	foo = proto_tree_add_item(...);
	...
}

Others were real bugs (such doing 'foo=proto_item_add_subtree()' and then failing to use the returned value in following 'proto_tree_add_item()' calls.
At some point I stopped fixing "Coverity [unused]" even though ISTR that 
were (at least a few) more "unused" defects yet to be fixed.
Some time later I started working on the GCC 4.6 "set-but-unused" warnings.

I now see (after doing a little research) that it appears that the "unused" defects found by Coverity were only a subset of the "unused-but-set" cases found by GCC 4.6.
I don't know what the pattern is for things not found by Coverity but I 
do note that many cases like the following weren't found by Coverity:
{
    ...
    int foo;
    ...
    foo = ...;
    ...
}


In any case: Since much of the "Coverity [unused"" dissector cases have already been fixed, much of the remaining (non-generated) dissector "set-but-not-used" cases seem to be for stuff not found by "Coverity [unused]".
(See SVN #37716 for many examples of this type of fix).