Re: validating signed/unsigned comparisons with Coccinelle, was Re: [PATCH 0/3] A couple of CI fixes regarding the built-in add --patch

From: Jeff King <peff@peff.net>
Date: Aug 30, 2022, 21:32 UTC
Message-ID: <Yw6B6OB5gJhPVn5/@coredump.intra.peff.net>
In-Reply-To: <73spp934-1q41-1123-41no-q2337954op92@tzk.qr>

On Tue, Aug 30, 2022 at 11:12:24PM +0200, Johannes Schindelin wrote:

Show 8 quoted lines

> On Tue, 30 Aug 2022, Phillip Wood wrote:
> 
> > I wonder if they would be interested in fixing the parsing bug we found
> > with Peff's UNUSED() series.
> 
> Could you point me to the relevant mail? I am sure that I can come up with
> an MCVE that will help them pinpoint the bug and fix it as quickly as they
> did with this here bug.

It's the sub-thread starting here:

  https://lore.kernel.org/git/220825.86ilmg4mil.gmgdl@evledraar.gmail.com/

I tried to put together a minimal example, which would be something like:

  $ cat foo.c
  void old_function(int);
  void new_function(int);
  
  #if defined(__GNUC__)
  #define UNUSED(var) UNUSED_##var __attribute__((unused))
  #else
  #define UNUSED(var) UNUSED_##var
  #endif
  
  void foo(int UNUSED(bar), int x)
  {
  	old_function(x);
  }

  $ cat foo.cocci
  @@
  expression E;
  @@
  -old_function(E)
  +new_function(E)

but to my frustration, it actually works! If you add --verbose-parsing to the spatch command, you can see it complaining about some of the parsing. And it produces wrong outputs in the real-world with our actual unused.cocci file. I suspect the example semantic patch might just need to be a little more complicated.

-Peff