[Bug c++/79008] missing detail in -Wbuiltin-declaration-mismatch

egallager at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Fri Nov 24 12:34:00 GMT 2017


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79008

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|2017-08-22 00:00:00         |2017-11-24
     Ever confirmed|0                           |1

--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #2)
> I think what I had in mind was incompatible attribute specifications rather
> than missing ones but my description sounds a little confused. 
> -Wbuiltin-declaration-mismatch also doesn't diagnose incompatible attributes
> (maybe it should).
> 
> One example of an incompatibility is the following declaration:
> 
>   int __attribute__ ((pure)) abs (int);
> 
> where abs() the built-in is actually declared const.  GCC doesn't currently
> diagnose this except with my patch for bug 81544 (yet to be reviewed).
> 
> Another, slightly different, example is declaring a standard library
> function with the wrong attributes, like this one:
> 
> void* __attribute__ ((malloc, alloc_size (1))) realloc (void*, size_t);
> 
> This is wrong on two counts: first, realloc cannot be declared with
> attribute malloc because it need not return a unique pointer.  Second,
> alloc_size specifies the wrong argument (this is bug 78667).
> 
> Since many built-in functions are decorated with multiple attributes it
> seems that rather than pointing out these kinds of issues one attribute at a
> time (either when there are more than one or as the user adjusts their
> declaration) it would be simpler and more user-friendly to include in the
> diagnostic all the attributes the built-in is decorated with.  Hence the
> suggestion to introduce a a new flag (and perhaps also a conversion
> specifier) to the pretty printer to have it (optionally) print the whole
> attribute list, or parts of it.
> 
> E.g.,
> 
>   warning ("%#qD conflicts with built-in declaration %#qD", user_decl,
> builtin_in_decl);
> 
> might print
> 
>   warning: ‘int abs(int) __attribute__ ((pure))’ conflicts with built-in
> declaration ‘int abs(int) __attribute__ ((const))’

Confirmed.


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