Re: [PATCH] tap: Avoid bogus missingReturn cppcheck warning in tap_l2_max_len()

[Stefano Brivio <sbrivio@redhat.com>]

On Sat, 17 May 2025 20:29:20 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, May 16, 2025 at 06:26:23PM +0200, Stefano Brivio wrote:
> > On Fri, 16 May 2025 17:25:21 +1000
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > On Thu, May 15, 2025 at 06:05:01PM +0200, Stefano Brivio wrote:  
> > > > Cppcheck 2.14.2 on Alpine Linux (musl) says that:
> > > > 
> > > > tap.c:111:19: error: Found an exit path from function with non-void return type that has missing return statement [missingReturn]
> > > >  switch (c->mode) {
> > > >                   ^
> > > > 
> > > > This exit path is not reachable because we ASSERT(0) after the switch,
> > > > but for some reason cppcheck doesn't see this with musl headers. Hide
> > > > the warning with a redundant return statement.
> > > > 
> > > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>    
> > > 
> > > Hm.  Alternatively you could change this to call abort_with_msg()
> > > directly.  That's marked as ((noreturn)) so with any luck cppcheck
> > > will then be able to figure out what's going on.  Although, I'm
> > > slightly surprised it can't do so already: I thought I put the
> > > ((noreturn)) in there to avoid warnings exactly like this.  
> > 
> > So, I checked, and abort_with_msg(""); works. ASSERT() ultimately
> > expands to abort_with_msg(), but for some reason cppcheck together with
> > Clang can't "follow" that, I suppose it's something related to the
> > pre-processor.
> > 
> > But in any case, abort_with_msg("") doesn't look as descriptive and
> > as obviously redundant as a return statement with a comment, so I don't
> > quite see the benefit changing it (also considering that I need to test
> > other versions, which takes time).  
> 
> Well, kind of the whole point of abort_with_msg() is that you can give
> it a meaningful message, which might change the picture.

Right, but I was struggling with making it meaningful: "dodged cppcheck
warning, you'll never see this"? I much prefer a return with a comment.

> It would
> also be trivial to write an unreachable() wrapper around that.

Ah, that would be nice, yes. I would consider writing one after 2-3
more cases like this.

-- 
Stefano