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From: Jeff King <>
To: "Ævar Arnfjörð Bjarmason" <>
Cc: Junio C Hamano <>,
	Derrick Stolee <>,
	Derrick Stolee via GitGitGadget <>,
Subject: Re: [PATCH] ci: update 'static-analysis' to Ubuntu 22.04
Date: Fri, 26 Aug 2022 03:48:15 -0400	[thread overview]
Message-ID: <Ywh6v8oo3nRl/> (raw)
In-Reply-To: <>

On Thu, Aug 25, 2022 at 12:47:53PM +0200, Ævar Arnfjörð Bjarmason wrote:

> What's happening here is that coccinelle can no longer properly parse
> the file after the UNUSED() macros were applied to refs.c.

Ugh. Thanks for finding this.

I'm a little disappointed in coccinelle here. I mean, I get that it
probably can't just use the output of "gcc -E"; it wants to see and
transform the code as written (and maybe even translate macros). But
if it doesn't understand the macros enough to see inside them, there are
a lot of things it is going to get confused by.

A simple example like this shows that it doesn't really see inside them:

  $ cat foo.c
  #define foo(x) bar(x)
  static void fun(int x) { foo(x); }

  $ cat foo.cocci
  expression E;
  - bar(E);
  + changed(E);

I wonder what it makes of code-generation macros like
for_each_string_list_item(). Or all of commit-slab.

Likewise, the manner in which it fails is unexpected. I could see it
getting confused about the line in question, but why would that cause it
to fail to see the of a strbuf in another function entirely?

I realize that pseudo-parsing C is an incredibly hard problem. But I
also wonder how robust the tool actually is in practice. We've had a lot
of mystery "now why didn't it catch this case" incidents over the years.
Just running the tip of master with --verbose-parsing yields quite a few
"bad" and "parse error" entries in the log. I wonder how much that

> We should probably coerce coccinelle into stopping in general if it's
> encountering "BAD:!!!!!" parse errors behind the scenes, as it clearly
> results in broken logic, but offhand (and from briefly browsing the
> manpage) I don't know a way to do that.

You could detect the BAD entries from the log and complain before
returning the exit code to make. But since there are several instances
already, I suspect it's a losing battle. We need some way to actually
_fix_ them. And in the meantime, it does seem to _mostly_ work, as it
clearly has some kind of resync logic.

> But the fix here isn't to delete unused.cocci, but to hold off on the
> UNUSEwork D() patches until we figure out how to make coccinelle jive with
> them.

Yeah, my general skepticism and disappointment above notwithstanding,
this seems like the best path forward from here. I tried a few other
tricks (like --macro-file and --iso-file), but if its parser chokes, I
don't think there's much we can do about it. Even if we wrote a patch to
coccinelle itself (and I have no interest in doing that myself), it
would take a while to become available.


  parent reply	other threads:[~2022-08-26  7:48 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-23 17:28 [PATCH] ci: update 'static-analysis' to Ubuntu 22.04 Derrick Stolee via GitGitGadget
2022-08-24 14:40 ` Johannes Schindelin
2022-08-24 19:59   ` Junio C Hamano
2022-08-24 23:43 ` Junio C Hamano
2022-08-25  0:30   ` Derrick Stolee
2022-08-25  4:43     ` Junio C Hamano
2022-08-25 10:47       ` Ævar Arnfjörð Bjarmason
2022-08-25 16:08         ` Junio C Hamano
2022-08-25 17:09           ` [PATCH 0/2] git-compat-util.h: change UNUSED(var) to UNUSED Ævar Arnfjörð Bjarmason
2022-08-25 17:09             ` [PATCH 1/2] git-compat-util.h: use "UNUSED", not "UNUSED(var)" Ævar Arnfjörð Bjarmason
2022-08-25 17:09             ` [PATCH 2/2] git-compat-util.h: use "deprecated" for UNUSED variables Ævar Arnfjörð Bjarmason
2022-08-26  7:52             ` [PATCH 0/2] git-compat-util.h: change UNUSED(var) to UNUSED Jeff King
2022-08-26  7:48         ` Jeff King [this message]
2022-08-26 16:46           ` [PATCH] ci: update 'static-analysis' to Ubuntu 22.04 Junio C Hamano
2022-08-27 12:58             ` Jeff King
2022-08-29  5:56               ` Junio C Hamano
2022-08-29 10:29             ` Ævar Arnfjörð Bjarmason
2022-08-31 15:12               ` Jeff King
2022-08-31  8:44             ` SZEDER Gábor
2022-08-31 12:13               ` Ævar Arnfjörð Bjarmason
2022-08-31 15:24                 ` Jeff King
2022-08-31 19:19                   ` Junio C Hamano
2022-08-31 18:05                 ` SZEDER Gábor
2022-08-31 19:29                   ` Ævar Arnfjörð Bjarmason
2022-08-25 14:57 ` Ævar Arnfjörð Bjarmason
2022-08-25 16:17   ` Junio C Hamano

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