Re: [Cocci] Using a macro for variable attributes

[Jaskaran Singh <jaskaransingh7654321@gmail.com>]

On Tue, 2020-04-28 at 20:17 +0200, Paul Chaignon wrote:
> Thanks for the quick answer!
> 
> On Tue, Apr 28, 2020 at 07:44:15PM +0200, Julia Lawall wrote:
> > 
> > On Tue, 28 Apr 2020, Paul Chaignon wrote:
> > 
> > > Hi all,
> > > 
> > > I am working on a small semantic patch to annotate specific
> > > variables in
> > > our codebase with __attribute__((aligned(8))). The following
> > > program works
> > > fine.
> > > 
> > >   @r@
> > >   expression e1, e2;
> > >   identifier x;
> > >   @@
> > >   (
> > >     struct \(icmphdr\|icmp6hdr\) x
> > >   + __attribute__((aligned(8)))
> > >     ;
> > >   |
> > >     struct \(icmphdr\|icmp6hdr\) x
> > >   + __attribute__((aligned(8)))
> > >     = ...;
> > >   )
> > >     ... when exists
> > >     ctx_load_bytes(e1, e2, &x, ...)
> > > 
> > > However, when I replace __attribute__((aligned(8))) with our
> > > internal
> > > macro __align_stack_8, it fails with the following error:
> > > 
> > >   plus: parse error:
> > >     File "/home/paul/cilium/contrib/coccinelle/aligned.cocci",
> > > line 7, column 2, charpos = 77
> > >     around = '__align_stack_8',
> > >     whole content = + __align_stack_8
> > > 
> > > I've tried adding '#define __align_stack_8' in a file passed with
> > > --macro-file, without success. Is this a known limitation for
> > > macros or
> > > am I missing something?
> > 
> > Try adding the "metavariable" declaration:
> > 
> > attribute name __align_stack_8;
> 
> Awesome, that worked. And I think I understand: undeclared
> identifiers are by
> default considered symbols, leading to the parse error.
> 
> Unfortunately, my semantic patch now leads to the following changes:
> 
>   -	struct icmphdr icmphdr __align_stack_8;
>   +	struct icmphdr icmphdr __align_stack_8 __align_stack_8;
> 

Hi Paul,

Just FYI if you want to avoid the double attribute problem there,
disable the optional_attributes isomorphism for the rule where you add
the __align_stack_8 attribute. Example:

@disable optional_attributes@
attribute name __align_stack_8;
@@

 int foo
+	__align_stack_8
	= 2;

With this, any attributes that you don't specify in your SmPL won't be
matched in source code either.

> I would normally add a first case to my conjunction to match on
> already-present attributes, but Coccinelle can't match on attributes
> yet.

Granted, attribute matching on Coccinelle's master branch is far from
perfect, but I think it should work for declarations/assignments.
Hopefully I can get these patches out soon :)

Cheers,
Jaskaran.

> Any workaround?
> 
> Paul
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