Re: [PATCH] libgcc: Avoid -Wbuiltin-declaration-mismatch warnings in emutls.c

[Richard Biener <rguenther@suse.de>]

On Wed, 6 Dec 2023, Jakub Jelinek wrote:

> Hi!
> 
> When libgcc is being built in --disable-tls configuration or on
> a target without native TLS support, one gets annoying warnings:
> ../../../../libgcc/emutls.c:61:7: warning: conflicting types for built-in function ?__emutls_get_address?; expected ?void *(void *)? [-Wbuiltin-declaration-mismatch]
>    61 | void *__emutls_get_address (struct __emutls_object *);
>       |       ^~~~~~~~~~~~~~~~~~~~
> ../../../../libgcc/emutls.c:63:6: warning: conflicting types for built-in function ?__emutls_register_common?; expected ?void(void *, unsigned int,  unsigned int,  void *)? [-Wbuiltin-declaration-mismatch]
>    63 | void __emutls_register_common (struct __emutls_object *, word, word, void *);
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~
> ../../../../libgcc/emutls.c:140:1: warning: conflicting types for built-in function ?__emutls_get_address?; expected ?void *(void *)? [-Wbuiltin-declaration-mismatch]
>   140 | __emutls_get_address (struct __emutls_object *obj)
>       | ^~~~~~~~~~~~~~~~~~~~
> ../../../../libgcc/emutls.c:204:1: warning: conflicting types for built-in function ?__emutls_register_common?; expected ?void(void *, unsigned int,  unsigned int,  void *)? [-Wbuiltin-declaration-mismatch]
>   204 | __emutls_register_common (struct __emutls_object *obj,
>       | ^~~~~~~~~~~~~~~~~~~~~~~~
> The thing is that in that case __emutls_get_address and
> __emutls_register_common are builtins, and are declared with void *
> arguments rather than struct __emutls_object *.
> Now, struct __emutls_object is a type private to libgcc/emutls.c and the
> middle-end creates on demand when calling the builtins a similar structure
> (with small differences, like not having the union in there).
> 
> We have a precedent for this e.g. for fprintf or strftime builtins where
> the builtins are created with magic fileptr_type_node or const_tm_ptr_type_node
> types and then match it with user definition of pointers to some structure,
> but I think for this case users should never define these functions
> themselves nor call them and having special types for them in the compiler
> would mean extra compile time spent during compiler initialization and more
> GC data, so I think it is better to keep the compiler as is.
> 
> On the library side, there is an option to just follow what the
> compiler is doing and do
>  EMUTLS_ATTR void
> -__emutls_register_common (struct __emutls_object *obj,
> +__emutls_register_common (void *xobj,
>                            word size, word align, void *templ)
>  {
> +  struct __emutls_object *obj = (struct __emutls_object *) xobj;
> but that will make e.g. libabigail complain about ABI change in libgcc.
> 
> So, the patch just turns the warning off.
> 
> Tested on x86_64-linux with --disable-tls, ok for trunk?

Works for me.

Richard.

> 2023-12-06  Thomas Schwinge  <thomas@codesourcery.com>
> 	    Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR libgcc/109289
> 	* emutls.c: Add GCC diagnostic ignored "-Wbuiltin-declaration-mismatch"
> 	pragma.
> 
> --- libgcc/emutls.c.jj	2023-01-16 11:52:16.780723793 +0100
> +++ libgcc/emutls.c	2023-12-06 10:49:46.438060090 +0100
> @@ -57,6 +57,14 @@ struct __emutls_array
>  #  define EMUTLS_ATTR
>  #endif
>  
> +/* __emutls_get_address and __emutls_register_common are registered as
> +   builtins, but the compiler struct __emutls_object doesn't have
> +   a union in there and is only created when actually needed for
> +   the calls to the builtins, so the builtins are created with void *
> +   arguments rather than struct __emutls_object *.  Avoid
> +   -Wbuiltin-declaration-mismatch warnings.  */
> +#pragma GCC diagnostic ignored "-Wbuiltin-declaration-mismatch"
> +
>  EMUTLS_ATTR
>  void *__emutls_get_address (struct __emutls_object *);
>  EMUTLS_ATTR
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
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