[v6] attribs: Implement -Wno-attributes=vendor::attr [PR101940]

  On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:
> On 11/6/21 14:28, Marek Polacek wrote:
> > On Sat, Nov 06, 2021 at 02:32:26AM +0100, Bernhard Reutner-Fischer wrote:
> > > On 6 November 2021 01:21:43 CET, Marek Polacek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> > > 
> > > > 
> > > > Thanks, so like this?  I'm including an incremental diff so that it's
> > > > clear what changed:
> > > > 
> > > > diff --git a/gcc/attribs.c b/gcc/attribs.c
> > > > index d5fba7f4bbb..addfe6f6c80 100644
> > > > --- a/gcc/attribs.c
> > > > +++ b/gcc/attribs.c
> > > > @@ -237,7 +237,7 @@ check_attribute_tables (void)
> > > >     the end of parsing of all TUs. */
> > > > static vec<attribute_spec *> ignored_attributes_table;
> > > > 
> > > > -/* Parse arguments ARGS of -Wno-attributes=.
> > > > +/* Parse arguments V of -Wno-attributes=.
> > > >     Currently we accept:
> > > >       vendor::attr
> > > >       vendor::
> > > > @@ -252,12 +252,15 @@ handle_ignored_attributes_option (vec<char *> *v)
> > > > 
> > > >    for (auto opt : v)
> > > >      {
> > > > +      /* We're going to be modifying the string.  */
> > > > +      opt = xstrdup (opt);
> > > >        char *q = strstr (opt, "::");
> > > >        /* We don't accept '::attr'.  */
> > > >        if (q == nullptr || q == opt)
> > > > 	{
> > > > 	  error ("wrong argument to ignored attributes");
> > > > 	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> > > > +	  free (opt);
> > > > 	  continue;
> > > > 	}
> > > 
> > > Only xstrdup here, after the strstr check?
> > > Should maybe strdup the rest here, not full opt..
> > 
> > No, I want q to point into the copy of the string, since I'm about
> > to modify it.  And I'd prefer a single call to xstrdup rather than
> > two.
> 
> It occurs to me that instead of calling xstrdup at all, since you're already
> passing the strings to get_identifier you could use
> get_identifier_with_length instead, and then refer to IDENTIFIER_POINTER of
> the result.

Ah, clever.  I didn't think it would work because I didn't expect that
get_identifier_with_length works when it gets a string that isn't
nul-terminated but it does.  So how about the following?

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
It is desirable for -Wattributes to warn about e.g.

[[deprecate]] void g(); // typo, should warn

However, -Wattributes also warns about vendor-specific attributes
(that's because lookup_scoped_attribute_spec -> find_attribute_namespace
finds nothing), which, with -Werror, causes grief.  We don't want the
-Wattributes warning for

[[company::attr]] void f();

GCC warns because it doesn't know the "company" namespace; it only knows
the "gnu" and "omp" namespaces.  We could entirely disable warning about
attributes in unknown scopes but then the compiler would also miss typos
like

  [[company::attrx]] void f();

or

  [[gmu::warn_used_result]] int write();

so that is not a viable solution.  A workaround is to use a #pragma:

  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wattributes"
  [[company::attr]] void f() {}
  #pragma GCC diagnostic pop

but that's a mouthful and awkward to use and could also hide typos.  In
fact, any macro-based solution doesn't seem like a way forward.

This patch implements -Wno-attributes=, which takes these arguments:

company::attr
company::

This option should go well with using @file: the user could have a file
containing
-Wno-attributes=vendor::attr1,vendor::attr2
and then invoke gcc with '@attrs' or similar.

I've also added a new pragma which has the same effect:

The pragma along with the new option should help with various static
analysis tools.

	PR c++/101940

gcc/ChangeLog:

	* attribs.c (struct scoped_attributes): Add a bool member.
	(lookup_scoped_attribute_spec): Forward declare.
	(register_scoped_attributes): New bool parameter, defaulted to
	false.  Use it.
	(handle_ignored_attributes_option): New function.
	(free_attr_data): New function.
	(init_attributes): Call handle_ignored_attributes_option.
	(attr_namespace_ignored_p): New function.
	(decl_attributes): Check attr_namespace_ignored_p before
	warning.
	* attribs.h (free_attr_data): Declare.
	(register_scoped_attributes): Adjust declaration.
	(handle_ignored_attributes_option): Declare.
	* common.opt (Wattributes=): New option with a variable.
	* doc/extend.texi: Document #pragma GCC diagnostic ignored_attributes.
	* doc/invoke.texi: Document -Wno-attributes=.
	* opts.c (common_handle_option) <case OPT_Wattributes_>: Handle.
	* plugin.h (register_scoped_attributes): Adjust declaration.
	* toplev.c (compile_file): Call free_attr_data.

gcc/c-family/ChangeLog:

	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
	ignored_attributes.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-1.c: New test.
	* c-c++-common/Wno-attributes-2.c: New test.
---
 gcc/attribs.c                                 | 123 +++++++++++++++++-
 gcc/attribs.h                                 |   5 +-
 gcc/c-family/c-pragma.c                       |  37 +++++-
 gcc/common.opt                                |   9 +-
 gcc/doc/extend.texi                           |  19 +++
 gcc/doc/invoke.texi                           |  20 +++
 gcc/opts.c                                    |  20 +++
 gcc/plugin.h                                  |   4 +-
 gcc/testsuite/c-c++-common/Wno-attributes-1.c |  55 ++++++++
 gcc/testsuite/c-c++-common/Wno-attributes-2.c |  56 ++++++++
 gcc/toplev.c                                  |   2 +
 11 files changed, 341 insertions(+), 9 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-1.c
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-2.c


base-commit: 206c08ce28a3c70afa4ecf9274611295d6369218
  

On 11/8/21 20:41, Marek Polacek wrote:
> On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:
>> On 11/6/21 14:28, Marek Polacek wrote:
>>> On Sat, Nov 06, 2021 at 02:32:26AM +0100, Bernhard Reutner-Fischer wrote:
>>>> On 6 November 2021 01:21:43 CET, Marek Polacek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>>>>
>>>>>
>>>>> Thanks, so like this?  I'm including an incremental diff so that it's
>>>>> clear what changed:
>>>>>
>>>>> diff --git a/gcc/attribs.c b/gcc/attribs.c
>>>>> index d5fba7f4bbb..addfe6f6c80 100644
>>>>> --- a/gcc/attribs.c
>>>>> +++ b/gcc/attribs.c
>>>>> @@ -237,7 +237,7 @@ check_attribute_tables (void)
>>>>>      the end of parsing of all TUs. */
>>>>> static vec<attribute_spec *> ignored_attributes_table;
>>>>>
>>>>> -/* Parse arguments ARGS of -Wno-attributes=.
>>>>> +/* Parse arguments V of -Wno-attributes=.
>>>>>      Currently we accept:
>>>>>        vendor::attr
>>>>>        vendor::
>>>>> @@ -252,12 +252,15 @@ handle_ignored_attributes_option (vec<char *> *v)
>>>>>
>>>>>     for (auto opt : v)
>>>>>       {
>>>>> +      /* We're going to be modifying the string.  */
>>>>> +      opt = xstrdup (opt);
>>>>>         char *q = strstr (opt, "::");
>>>>>         /* We don't accept '::attr'.  */
>>>>>         if (q == nullptr || q == opt)
>>>>> 	{
>>>>> 	  error ("wrong argument to ignored attributes");
>>>>> 	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
>>>>> +	  free (opt);
>>>>> 	  continue;
>>>>> 	}
>>>>
>>>> Only xstrdup here, after the strstr check?
>>>> Should maybe strdup the rest here, not full opt..
>>>
>>> No, I want q to point into the copy of the string, since I'm about
>>> to modify it.  And I'd prefer a single call to xstrdup rather than
>>> two.
>>
>> It occurs to me that instead of calling xstrdup at all, since you're already
>> passing the strings to get_identifier you could use
>> get_identifier_with_length instead, and then refer to IDENTIFIER_POINTER of
>> the result.
> 
> Ah, clever.  I didn't think it would work because I didn't expect that
> get_identifier_with_length works when it gets a string that isn't
> nul-terminated but it does.  So how about the following?
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> -- >8 --
> It is desirable for -Wattributes to warn about e.g.
> 
> [[deprecate]] void g(); // typo, should warn
> 
> However, -Wattributes also warns about vendor-specific attributes
> (that's because lookup_scoped_attribute_spec -> find_attribute_namespace
> finds nothing), which, with -Werror, causes grief.  We don't want the
> -Wattributes warning for
> 
> [[company::attr]] void f();
> 
> GCC warns because it doesn't know the "company" namespace; it only knows
> the "gnu" and "omp" namespaces.  We could entirely disable warning about
> attributes in unknown scopes but then the compiler would also miss typos
> like
> 
>    [[company::attrx]] void f();
> 
> or
> 
>    [[gmu::warn_used_result]] int write();
> 
> so that is not a viable solution.  A workaround is to use a #pragma:
> 
>    #pragma GCC diagnostic push
>    #pragma GCC diagnostic ignored "-Wattributes"
>    [[company::attr]] void f() {}
>    #pragma GCC diagnostic pop
> 
> but that's a mouthful and awkward to use and could also hide typos.  In
> fact, any macro-based solution doesn't seem like a way forward.
> 
> This patch implements -Wno-attributes=, which takes these arguments:
> 
> company::attr
> company::
> 
> This option should go well with using @file: the user could have a file
> containing
> -Wno-attributes=vendor::attr1,vendor::attr2
> and then invoke gcc with '@attrs' or similar.
> 
> I've also added a new pragma which has the same effect:
> 
> The pragma along with the new option should help with various static
> analysis tools.
> 
> 	PR c++/101940
> 
> gcc/ChangeLog:
> 
> 	* attribs.c (struct scoped_attributes): Add a bool member.
> 	(lookup_scoped_attribute_spec): Forward declare.
> 	(register_scoped_attributes): New bool parameter, defaulted to
> 	false.  Use it.
> 	(handle_ignored_attributes_option): New function.
> 	(free_attr_data): New function.
> 	(init_attributes): Call handle_ignored_attributes_option.
> 	(attr_namespace_ignored_p): New function.
> 	(decl_attributes): Check attr_namespace_ignored_p before
> 	warning.
> 	* attribs.h (free_attr_data): Declare.
> 	(register_scoped_attributes): Adjust declaration.
> 	(handle_ignored_attributes_option): Declare.
> 	* common.opt (Wattributes=): New option with a variable.
> 	* doc/extend.texi: Document #pragma GCC diagnostic ignored_attributes.
> 	* doc/invoke.texi: Document -Wno-attributes=.
> 	* opts.c (common_handle_option) <case OPT_Wattributes_>: Handle.
> 	* plugin.h (register_scoped_attributes): Adjust declaration.
> 	* toplev.c (compile_file): Call free_attr_data.
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
> 	ignored_attributes.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* c-c++-common/Wno-attributes-1.c: New test.
> 	* c-c++-common/Wno-attributes-2.c: New test.
> ---
>   gcc/attribs.c                                 | 123 +++++++++++++++++-
>   gcc/attribs.h                                 |   5 +-
>   gcc/c-family/c-pragma.c                       |  37 +++++-
>   gcc/common.opt                                |   9 +-
>   gcc/doc/extend.texi                           |  19 +++
>   gcc/doc/invoke.texi                           |  20 +++
>   gcc/opts.c                                    |  20 +++
>   gcc/plugin.h                                  |   4 +-
>   gcc/testsuite/c-c++-common/Wno-attributes-1.c |  55 ++++++++
>   gcc/testsuite/c-c++-common/Wno-attributes-2.c |  56 ++++++++
>   gcc/toplev.c                                  |   2 +
>   11 files changed, 341 insertions(+), 9 deletions(-)
>   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-1.c
>   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-2.c
> 
> diff --git a/gcc/attribs.c b/gcc/attribs.c
> index 83fafc98b7d..23d92ca9474 100644
> --- a/gcc/attribs.c
> +++ b/gcc/attribs.c
> @@ -87,6 +87,8 @@ struct scoped_attributes
>     const char *ns;
>     vec<attribute_spec> attributes;
>     hash_table<attribute_hasher> *attribute_hash;
> +  /* True if we should not warn about unknown attributes in this NS.  */
> +  bool ignored_p;
>   };
>   
>   /* The table of scope attributes.  */
> @@ -95,6 +97,8 @@ static vec<scoped_attributes> attributes_table;
>   static scoped_attributes* find_attribute_namespace (const char*);
>   static void register_scoped_attribute (const struct attribute_spec *,
>   				       scoped_attributes *);
> +static const struct attribute_spec *lookup_scoped_attribute_spec (const_tree,
> +								  const_tree);
>   
>   static bool attributes_initialized = false;
>   
> @@ -121,12 +125,14 @@ extract_attribute_substring (struct substring *str)
>   
>   /* Insert an array of attributes ATTRIBUTES into a namespace.  This
>      array must be NULL terminated.  NS is the name of attribute
> -   namespace.  The function returns the namespace into which the
> -   attributes have been registered.  */
> +   namespace.  IGNORED_P is true iff all unknown attributes in this
> +   namespace should be ignored for the purposes of -Wattributes.  The
> +   function returns the namespace into which the attributes have been
> +   registered.  */
>   
>   scoped_attributes *
>   register_scoped_attributes (const struct attribute_spec *attributes,
> -			    const char *ns)
> +			    const char *ns, bool ignored_p /*=false*/)
>   {
>     scoped_attributes *result = NULL;
>   
> @@ -144,9 +150,12 @@ register_scoped_attributes (const struct attribute_spec *attributes,
>         memset (&sa, 0, sizeof (sa));
>         sa.ns = ns;
>         sa.attributes.create (64);
> +      sa.ignored_p = ignored_p;
>         result = attributes_table.safe_push (sa);
>         result->attribute_hash = new hash_table<attribute_hasher> (200);
>       }
> +  else
> +    result->ignored_p |= ignored_p;
>   
>     /* Really add the attributes to their namespace now.  */
>     for (unsigned i = 0; attributes[i].name != NULL; ++i)
> @@ -224,6 +233,95 @@ check_attribute_tables (void)
>   				 attribute_tables[j][l].name));
>   }
>   
> +/* Used to stash pointers to allocated memory so that we can free them at
> +   the end of parsing of all TUs. */
> +static vec<attribute_spec *> ignored_attributes_table;
> +
> +/* Parse arguments V of -Wno-attributes=.
> +   Currently we accept:
> +     vendor::attr
> +     vendor::
> +   This functions also registers the parsed attributes so that we don't
> +   warn that we don't recognize them.  */
> +
> +void
> +handle_ignored_attributes_option (vec<char *> *v)
> +{
> +  if (v == nullptr)
> +    return;
> +
> +  for (auto opt : v)
> +    {
> +      char *cln = strstr (opt, "::");
> +      /* We don't accept '::attr'.  */
> +      if (cln == nullptr || cln == opt)
> +	{
> +	  error ("wrong argument to ignored attributes");
> +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> +	  continue;
> +	}
> +      char *vendor_start = opt;
> +      ptrdiff_t vendor_len = cln - opt;
> +      char *attr_start = cln + 2;
> +      /* This could really use rawmemchr :(.  */
> +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
> +      /* Verify that they look valid.  */
> +      auto valid_p = [](const char *const s, ptrdiff_t len) {
> +	for (int i = 0; i < len; ++i)
> +	  if (!ISALNUM (*s) && *s != '_')
> +	    return false;
> +	return true;
> +      };
> +      if (!valid_p (vendor_start, vendor_len)
> +	  || !valid_p (attr_start, attr_len))
> +	{
> +	  error ("wrong argument to ignored attributes");
> +	  continue;
> +	}
> +      /* Turn "__attr__" into "attr" so that we have a canonical form of
> +	 attribute names.  Likewise for vendor.  */
> +      auto strip = [](char *&s, ptrdiff_t &l) {
> +	if (l > 4 && s[0] == '_' && s[1] == '_'
> +	    && s[l - 1] == '_' && s[l - 2] == '_')
> +	  {
> +	    s += 2;
> +	    l -= 4;
> +	  }
> +      };
> +      strip (attr_start, attr_len);
> +      strip (vendor_start, vendor_len);
> +      /* We perform all this hijinks so that we don't have to copy OPT.  */
> +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
> +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
> +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
> +	 register it twice would lead to a crash.  */
> +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
> +	continue;

Hmm, this looks like it isn't handling the case of previously ignoring 
vendor::; it seems we'll look for vendor::<empty string> instead, not 
find it, and register again.

> +      /* In the "vendor::" case, we should ignore *any* attribute coming
> +	 from this attribute namespace.  */
> +      const char *vendor = IDENTIFIER_POINTER (vendor_id);
> +      const char *attr = attr_len == 0 ? nullptr : IDENTIFIER_POINTER (attr_id);
> +      /* Create a table with extra attributes which we will register.
> +	 We can't free it here, so squirrel away the pointers.  */
> +      attribute_spec *table = new attribute_spec[2];
> +      ignored_attributes_table.safe_push (table);
> +      table[0] = { attr, 0, 0, false, false, false, false, nullptr, nullptr };
> +      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr,
> +		   nullptr };
> +      register_scoped_attributes (table, vendor, !attr);
> +    }
> +}
> +
> +/* Free data we might have allocated when adding extra attributes.  */
> +
> +void
> +free_attr_data ()
> +{
> +  for (auto x : ignored_attributes_table)
> +    delete[] x;
> +  ignored_attributes_table.release ();
> +}
> +
>   /* Initialize attribute tables, and make some sanity checks if checking is
>      enabled.  */
>   
> @@ -252,6 +350,9 @@ init_attributes (void)
>       /* Put all the GNU attributes into the "gnu" namespace.  */
>       register_scoped_attributes (attribute_tables[i], "gnu");
>   
> +  vec<char *> *ignored = (vec<char *> *) flag_ignored_attributes;
> +  handle_ignored_attributes_option (ignored);
> +
>     invoke_plugin_callbacks (PLUGIN_ATTRIBUTES, NULL);
>     attributes_initialized = true;
>   }
> @@ -456,6 +557,19 @@ diag_attr_exclusions (tree last_decl, tree node, tree attrname,
>     return found;
>   }
>   
> +/* Return true iff we should not complain about unknown attributes
> +   coming from the attribute namespace NS.  This is the case for
> +   the -Wno-attributes=ns:: command-line option.  */
> +
> +static bool
> +attr_namespace_ignored_p (tree ns)
> +{
> +  if (ns == NULL_TREE)
> +    return false;
> +  scoped_attributes *r = find_attribute_namespace (IDENTIFIER_POINTER (ns));
> +  return r && r->ignored_p;
> +}
> +
>   /* Process the attributes listed in ATTRIBUTES and install them in *NODE,
>      which is either a DECL (including a TYPE_DECL) or a TYPE.  If a DECL,
>      it should be modified in place; if a TYPE, a copy should be created
> @@ -556,7 +670,8 @@ decl_attributes (tree *node, tree attributes, int flags,
>   
>         if (spec == NULL)
>   	{
> -	  if (!(flags & (int) ATTR_FLAG_BUILT_IN))
> +	  if (!(flags & (int) ATTR_FLAG_BUILT_IN)
> +	      && !attr_namespace_ignored_p (ns))
>   	    {
>   	      if (ns == NULL_TREE || !cxx11_attr_p)
>   		warning (OPT_Wattributes, "%qE attribute directive ignored",
> diff --git a/gcc/attribs.h b/gcc/attribs.h
> index 138c509bce1..96a527f67a9 100644
> --- a/gcc/attribs.h
> +++ b/gcc/attribs.h
> @@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
>   #define GCC_ATTRIBS_H
>   
>   extern const struct attribute_spec *lookup_attribute_spec (const_tree);
> +extern void free_attr_data ();
>   extern void init_attributes (void);
>   
>   /* Process the attributes listed in ATTRIBUTES and install them in *NODE,
> @@ -40,12 +41,14 @@ extern void apply_tm_attr (tree, tree);
>   extern tree make_attribute (const char *, const char *, tree);
>   
>   extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
> -							     const char *);
> +							     const char *,
> +							     bool = false);
>   
>   extern char *sorted_attr_string (tree);
>   extern bool common_function_versions (tree, tree);
>   extern tree make_dispatcher_decl (const tree);
>   extern bool is_function_default_version (const tree);
> +extern void handle_ignored_attributes_option (vec<char *> *);
>   
>   /* Return a type like TTYPE except that its TYPE_ATTRIBUTES
>      is ATTRIBUTE.
> diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
> index a9be8df0384..a299ceff6a2 100644
> --- a/gcc/c-family/c-pragma.c
> +++ b/gcc/c-family/c-pragma.c
> @@ -764,7 +764,7 @@ handle_pragma_diagnostic(cpp_reader *ARG_UNUSED(dummy))
>     if (token != CPP_NAME)
>       {
>         warning_at (loc, OPT_Wpragmas,
> -		  "missing [error|warning|ignored|push|pop]"
> +		  "missing [error|warning|ignored|push|pop|ignored_attributes]"
>   		  " after %<#pragma GCC diagnostic%>");
>         return;
>       }
> @@ -787,10 +787,43 @@ handle_pragma_diagnostic(cpp_reader *ARG_UNUSED(dummy))
>         diagnostic_pop_diagnostics (global_dc, input_location);
>         return;
>       }
> +  else if (strcmp (kind_string, "ignored_attributes") == 0)
> +    {
> +      token = pragma_lex (&x, &loc);
> +      if (token != CPP_STRING)
> +	{
> +	  warning_at (loc, OPT_Wpragmas,
> +		      "missing attribute name after %<#pragma GCC diagnostic "
> +		      "ignored_attributes%>");
> +	  return;
> +	}
> +      char *args = xstrdup (TREE_STRING_POINTER (x));
> +      const size_t l = strlen (args);
> +      if (l == 0)
> +	{
> +	  warning_at (loc, OPT_Wpragmas, "missing argument to %<#pragma GCC "
> +		      "diagnostic ignored_attributes%>");
> +	  free (args);
> +	  return;
> +	}
> +      else if (args[l - 1] == ',')
> +	{
> +	  warning_at (loc, OPT_Wpragmas, "trailing %<,%> in arguments for "
> +		      "%<#pragma GCC diagnostic ignored_attributes%>");
> +	  free (args);
> +	  return;
> +	}
> +      auto_vec<char *> v;
> +      for (char *p = strtok (args, ","); p; p = strtok (NULL, ","))
> +	v.safe_push (p);
> +      handle_ignored_attributes_option (&v);
> +      free (args);
> +      return;
> +    }
>     else
>       {
>         warning_at (loc, OPT_Wpragmas,
> -		  "expected [error|warning|ignored|push|pop]"
> +		  "expected [error|warning|ignored|push|pop|ignored_attributes]"
>   		  " after %<#pragma GCC diagnostic%>");
>         return;
>       }
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 1a5b9bfcca9..de9b848eda5 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -83,7 +83,7 @@ int flag_gen_aux_info = 0
>   Variable
>   int flag_shlib
>   
> -; These two are really VEC(char_p,heap) *.
> +; These three are really VEC(char_p,heap) *.
>   
>   Variable
>   void *flag_instrument_functions_exclude_functions
> @@ -91,6 +91,9 @@ void *flag_instrument_functions_exclude_functions
>   Variable
>   void *flag_instrument_functions_exclude_files
>   
> +Variable
> +void *flag_ignored_attributes
> +
>   ; Generic structs (e.g. templates not explicitly specialized)
>   ; may not have a compilation unit associated with them, and so
>   ; may need to be treated differently from ordinary structs.
> @@ -549,6 +552,10 @@ Wattributes
>   Common Var(warn_attributes) Init(1) Warning
>   Warn about inappropriate attribute usage.
>   
> +Wattributes=
> +Common Joined
> +Do not warn about specified attributes.
> +
>   Wattribute-alias
>   Common Alias(Wattribute_alias=, 1, 0) Warning
>   Warn about type safety and similar errors and mismatches in declarations with alias attributes.
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index eee4c6737bb..6e6c580e329 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -23767,6 +23767,25 @@ restored.
>     foo(d);                       /* depends on command-line options */
>   @end smallexample
>   
> +@item #pragma GCC diagnostic ignored_attributes
> +
> +Similarly to @option{-Wno-attributes=}, this pragma allows users to suppress
> +warnings about unknown scoped attributes (in C++11 and C2X).  For example,
> +@code{#pragma GCC diagnostic ignored_attributes "vendor::attr"} disables
> +warning about the following declaration:
> +
> +@smallexample
> +[[vendor::attr]] void f();
> +@end smallexample
> +
> +whereas @code{#pragma GCC diagnostic ignored_attributes "vendor::"} prevents
> +warning about both of these declarations:
> +
> +@smallexample
> +[[vendor::safe]] void f();
> +[[vendor::unsafe]] void f2();
> +@end smallexample
> +
>   @end table
>   
>   GCC also offers a simple mechanism for printing messages during
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index f206cff1221..339b8d7597b 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -8707,6 +8707,26 @@ unrecognized attributes, function attributes applied to variables,
>   etc.  This does not stop errors for incorrect use of supported
>   attributes.
>   
> +Additionally, using @option{-Wno-attributes=}, it is possible to suppress
> +warnings about unknown scoped attributes (in C++11 and C2X).  For example,
> +@option{-Wno-attributes=vendor::attr} disables warning about the following
> +declaration:
> +
> +@smallexample
> +[[vendor::attr]] void f();
> +@end smallexample
> +
> +It is also possible to disable warning about all attributes in a namespace
> +using @option{-Wno-attributes=vendor::} which prevents warning about both
> +of these declarations:
> +
> +@smallexample
> +[[vendor::safe]] void f();
> +[[vendor::unsafe]] void f2();
> +@end smallexample
> +
> +Note that @option{-Wno-attributes=} does not imply @option{-Wno-attributes}.
> +
>   @item -Wno-builtin-declaration-mismatch
>   @opindex Wno-builtin-declaration-mismatch
>   @opindex Wbuiltin-declaration-mismatch
> diff --git a/gcc/opts.c b/gcc/opts.c
> index caed6255500..175b4635bb4 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -2611,6 +2611,26 @@ common_handle_option (struct gcc_options *opts,
>         /* Currently handled in a prescan.  */
>         break;
>   
> +    case OPT_Wattributes_:
> +      if (lang_mask == CL_DRIVER)
> +	break;
> +
> +      if (value)
> +	{
> +	  error_at (loc, "arguments ignored for %<-Wattributes=%>; use "
> +		    "%<-Wno-attributes=%> instead");
> +	  break;
> +	}
> +      else if (arg[strlen (arg) - 1] == ',')
> +	{
> +	  error_at (loc, "trailing %<,%> in arguments for "
> +		    "%<-Wno-attributes=%>");
> +	  break;
> +	}
> +
> +      add_comma_separated_to_vector (&opts->x_flag_ignored_attributes, arg);
> +      break;
> +
>       case OPT_Werror:
>         dc->warning_as_error_requested = value;
>         break;
> diff --git a/gcc/plugin.h b/gcc/plugin.h
> index 1640e253ca5..5556763d1bf 100644
> --- a/gcc/plugin.h
> +++ b/gcc/plugin.h
> @@ -197,7 +197,9 @@ invoke_plugin_callbacks (int event ATTRIBUTE_UNUSED,
>   /* In attribs.c.  */
>   
>   extern void register_attribute (const struct attribute_spec *attr);
> +/* The default argument for the third parameter is given in attribs.h.  */
>   extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
> -							     const char *);
> +							     const char *,
> +							     bool);
>   
>   #endif /* PLUGIN_H */
> diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-1.c b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
> new file mode 100644
> index 00000000000..aac1a69fd85
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
> @@ -0,0 +1,55 @@
> +/* PR c++/101940 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "-std=c++11" { target c++ } } */
> +/* { dg-additional-options "-Wno-attributes=company::,yoyodyne::attr" } */
> +/* { dg-additional-options "-Wno-attributes=c1::attr,c1::attr,c1::__attr__" } */
> +/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
> +/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
> +/* { dg-additional-options "-Wno-attributes=x::" } */
> +/* { dg-additional-options "-Wno-attributes=yoyodyne::attr_new" } */
> +/* { dg-additional-options "-Wno-attributes=c4::__attr__" } */
> +/* { dg-additional-options "-Wno-attributes=c5::attr" } */
> +/* { dg-additional-options "-Wno-attributes=__c6__::attr" } */
> +
> +[[company::attr]] void f1();
> +[[company::attr2]] void f2();
> +
> +[[yoyodyne::attr]] void f3();
> +[[yoyodyne::__attr__]] void f3__();
> +[[yoyodyne::attrx]] void f4(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attrx__]] void f4__(); /* { dg-warning "ignored" } */
> +
> +[[c1::attr]] void f5();
> +
> +[[c2::attr]] void f6();
> +[[c2::attrx]] void f7();
> +[[c2::__attr__]] void f6__();
> +[[c2::__attrx__]] void f7__();
> +
> +[[c3::attr]] void f8();
> +[[c3::attrx]] void f9();
> +
> +[[x::x]] void f10();
> +
> +[[yoyodyne::attr_new]] void f11();
> +[[yoyodyne::__attr_new__]] void f11__();
> +[[yoyodyne::attr_mew]] void f12(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attr_mew__]] void f12__(); /* { dg-warning "ignored" } */
> +
> +[[c4::attr]] void f13();
> +[[c4::__attr__]] void f13__();
> +[[c4::attrx]] void f14(); /* { dg-warning "ignored" } */
> +
> +[[c5::attr]] void f15();
> +[[c5::__attr__]] void f15__();
> +[[__c5__::attr]] void __f15();
> +[[__c5__::__attr__]] void __f15__();
> +[[c5::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +[[__c5__::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +
> +[[c6::attr]] void f16();
> +[[c6::__attr__]] void f16__();
> +[[__c6__::attr]] void __f16();
> +[[__c6__::__attr__]] void __f16__();
> +[[c6::attrx]] void f16x(); /* { dg-warning "ignored" } */
> +[[__c6__::attrx]] void f16x(); /* { dg-warning "ignored" } */
> diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-2.c b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
> new file mode 100644
> index 00000000000..4307c74b048
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
> @@ -0,0 +1,56 @@
> +/* PR c++/101940 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "-std=c++11" { target c++ } } */
> +
> +#pragma GCC diagnostic ignored_attributes "company::,yoyodyne::attr"
> +#pragma GCC diagnostic ignored_attributes "c1::attr,c1::attr,c1::__attr__"
> +#pragma GCC diagnostic ignored_attributes "c2::,c2::attr"
> +#pragma GCC diagnostic ignored_attributes "c3::attr,c3::"
> +#pragma GCC diagnostic ignored_attributes "x::"
> +#pragma GCC diagnostic ignored_attributes "yoyodyne::attr_new"
> +#pragma GCC diagnostic ignored_attributes "c4::__attr__"
> +#pragma GCC diagnostic ignored_attributes "c5::attr"
> +#pragma GCC diagnostic ignored_attributes "__c6__::attr"
> +
> +[[company::attr]] void f1();
> +[[company::attr2]] void f2();
> +
> +[[yoyodyne::attr]] void f3();
> +[[yoyodyne::__attr__]] void f3__();
> +[[yoyodyne::attrx]] void f4(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attrx__]] void f4__(); /* { dg-warning "ignored" } */
> +
> +[[c1::attr]] void f5();
> +
> +[[c2::attr]] void f6();
> +[[c2::attrx]] void f7();
> +[[c2::__attr__]] void f6__();
> +[[c2::__attrx__]] void f7__();
> +
> +[[c3::attr]] void f8();
> +[[c3::attrx]] void f9();
> +
> +[[x::x]] void f10();
> +
> +[[yoyodyne::attr_new]] void f11();
> +[[yoyodyne::__attr_new__]] void f11__();
> +[[yoyodyne::attr_mew]] void f12(); /* { dg-warning "ignored" } */
> +[[yoyodyne::__attr_mew__]] void f12__(); /* { dg-warning "ignored" } */
> +
> +[[c4::attr]] void f13();
> +[[c4::__attr__]] void f13__();
> +[[c4::attrx]] void f14(); /* { dg-warning "ignored" } */
> +
> +[[c5::attr]] void f15();
> +[[c5::__attr__]] void f15__();
> +[[__c5__::attr]] void __f15();
> +[[__c5__::__attr__]] void __f15__();
> +[[c5::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +[[__c5__::attrx]] void f15x(); /* { dg-warning "ignored" } */
> +
> +[[c6::attr]] void f16();
> +[[c6::__attr__]] void f16__();
> +[[__c6__::attr]] void __f16();
> +[[__c6__::__attr__]] void __f16__();
> +[[c6::attrx]] void f16x(); /* { dg-warning "ignored" } */
> +[[__c6__::attrx]] void f16x(); /* { dg-warning "ignored" } */
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index e91f083f8ff..99276bde87d 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -457,6 +457,8 @@ compile_file (void)
>     if (flag_dump_locations)
>       dump_location_info (stderr);
>   
> +  free_attr_data ();
> +
>     /* Compilation is now finished except for writing
>        what's left of the symbol table output.  */
>   
> 
> base-commit: 206c08ce28a3c70afa4ecf9274611295d6369218
>
  

On Tue, 9 Nov 2021 00:12:10 -0500
Jason Merrill <jason@redhat.com> wrote:

> On 11/8/21 20:41, Marek Polacek wrote:
> > On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:  

> > +  for (auto opt : v)
> > +    {
> > +      char *cln = strstr (opt, "::");
> > +      /* We don't accept '::attr'.  */
> > +      if (cln == nullptr || cln == opt)
> > +	{
> > +	  error ("wrong argument to ignored attributes");
> > +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> > +	  continue;
> > +	}
> > +      char *vendor_start = opt;
> > +      ptrdiff_t vendor_len = cln - opt;
> > +      char *attr_start = cln + 2;
> > +      /* This could really use rawmemchr :(.  */
> > +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
> > +      /* Verify that they look valid.  */
> > +      auto valid_p = [](const char *const s, ptrdiff_t len) {
> > +	for (int i = 0; i < len; ++i)
> > +	  if (!ISALNUM (*s) && *s != '_')
> > +	    return false;
> > +	return true;
> > +      };
> > +      if (!valid_p (vendor_start, vendor_len)
> > +	  || !valid_p (attr_start, attr_len))
> > +	{
> > +	  error ("wrong argument to ignored attributes");
> > +	  continue;
> > +	}
> > +      /* Turn "__attr__" into "attr" so that we have a canonical form of
> > +	 attribute names.  Likewise for vendor.  */
> > +      auto strip = [](char *&s, ptrdiff_t &l) {
> > +	if (l > 4 && s[0] == '_' && s[1] == '_'
> > +	    && s[l - 1] == '_' && s[l - 2] == '_')
> > +	  {
> > +	    s += 2;
> > +	    l -= 4;
> > +	  }
> > +      };
> > +      strip (attr_start, attr_len);
> > +      strip (vendor_start, vendor_len);
> > +      /* We perform all this hijinks so that we don't have to copy OPT.  */
> > +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
> > +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
> > +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
> > +	 register it twice would lead to a crash.  */
> > +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
> > +	continue;  
> 
> Hmm, this looks like it isn't handling the case of previously ignoring 
> vendor::; it seems we'll look for vendor::<empty string> instead, not 
> find it, and register again.

I don't know if there are __attrib with 2 leading underscores but no
trailing that we accept and should normalize?

And it is surprising that we do not have a simple normalize_attr_name().
There must be existing spots where we would normalize attribute names?
extract_attribute_substring does about the same but with a struct substring(?).
Maybe that's just to avoid a normal string hash.

thanks,
  

On Tue, Nov 09, 2021 at 12:12:10AM -0500, Jason Merrill wrote:
> On 11/8/21 20:41, Marek Polacek wrote:
> > On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:
> > > On 11/6/21 14:28, Marek Polacek wrote:
> > > > On Sat, Nov 06, 2021 at 02:32:26AM +0100, Bernhard Reutner-Fischer wrote:
> > > > > On 6 November 2021 01:21:43 CET, Marek Polacek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> > > > > 
> > > > > > 
> > > > > > Thanks, so like this?  I'm including an incremental diff so that it's
> > > > > > clear what changed:
> > > > > > 
> > > > > > diff --git a/gcc/attribs.c b/gcc/attribs.c
> > > > > > index d5fba7f4bbb..addfe6f6c80 100644
> > > > > > --- a/gcc/attribs.c
> > > > > > +++ b/gcc/attribs.c
> > > > > > @@ -237,7 +237,7 @@ check_attribute_tables (void)
> > > > > >      the end of parsing of all TUs. */
> > > > > > static vec<attribute_spec *> ignored_attributes_table;
> > > > > > 
> > > > > > -/* Parse arguments ARGS of -Wno-attributes=.
> > > > > > +/* Parse arguments V of -Wno-attributes=.
> > > > > >      Currently we accept:
> > > > > >        vendor::attr
> > > > > >        vendor::
> > > > > > @@ -252,12 +252,15 @@ handle_ignored_attributes_option (vec<char *> *v)
> > > > > > 
> > > > > >     for (auto opt : v)
> > > > > >       {
> > > > > > +      /* We're going to be modifying the string.  */
> > > > > > +      opt = xstrdup (opt);
> > > > > >         char *q = strstr (opt, "::");
> > > > > >         /* We don't accept '::attr'.  */
> > > > > >         if (q == nullptr || q == opt)
> > > > > > 	{
> > > > > > 	  error ("wrong argument to ignored attributes");
> > > > > > 	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> > > > > > +	  free (opt);
> > > > > > 	  continue;
> > > > > > 	}
> > > > > 
> > > > > Only xstrdup here, after the strstr check?
> > > > > Should maybe strdup the rest here, not full opt..
> > > > 
> > > > No, I want q to point into the copy of the string, since I'm about
> > > > to modify it.  And I'd prefer a single call to xstrdup rather than
> > > > two.
> > > 
> > > It occurs to me that instead of calling xstrdup at all, since you're already
> > > passing the strings to get_identifier you could use
> > > get_identifier_with_length instead, and then refer to IDENTIFIER_POINTER of
> > > the result.
> > 
> > Ah, clever.  I didn't think it would work because I didn't expect that
> > get_identifier_with_length works when it gets a string that isn't
> > nul-terminated but it does.  So how about the following?
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > -- >8 --
> > It is desirable for -Wattributes to warn about e.g.
> > 
> > [[deprecate]] void g(); // typo, should warn
> > 
> > However, -Wattributes also warns about vendor-specific attributes
> > (that's because lookup_scoped_attribute_spec -> find_attribute_namespace
> > finds nothing), which, with -Werror, causes grief.  We don't want the
> > -Wattributes warning for
> > 
> > [[company::attr]] void f();
> > 
> > GCC warns because it doesn't know the "company" namespace; it only knows
> > the "gnu" and "omp" namespaces.  We could entirely disable warning about
> > attributes in unknown scopes but then the compiler would also miss typos
> > like
> > 
> >    [[company::attrx]] void f();
> > 
> > or
> > 
> >    [[gmu::warn_used_result]] int write();
> > 
> > so that is not a viable solution.  A workaround is to use a #pragma:
> > 
> >    #pragma GCC diagnostic push
> >    #pragma GCC diagnostic ignored "-Wattributes"
> >    [[company::attr]] void f() {}
> >    #pragma GCC diagnostic pop
> > 
> > but that's a mouthful and awkward to use and could also hide typos.  In
> > fact, any macro-based solution doesn't seem like a way forward.
> > 
> > This patch implements -Wno-attributes=, which takes these arguments:
> > 
> > company::attr
> > company::
> > 
> > This option should go well with using @file: the user could have a file
> > containing
> > -Wno-attributes=vendor::attr1,vendor::attr2
> > and then invoke gcc with '@attrs' or similar.
> > 
> > I've also added a new pragma which has the same effect:
> > 
> > The pragma along with the new option should help with various static
> > analysis tools.
> > 
> > 	PR c++/101940
> > 
> > gcc/ChangeLog:
> > 
> > 	* attribs.c (struct scoped_attributes): Add a bool member.
> > 	(lookup_scoped_attribute_spec): Forward declare.
> > 	(register_scoped_attributes): New bool parameter, defaulted to
> > 	false.  Use it.
> > 	(handle_ignored_attributes_option): New function.
> > 	(free_attr_data): New function.
> > 	(init_attributes): Call handle_ignored_attributes_option.
> > 	(attr_namespace_ignored_p): New function.
> > 	(decl_attributes): Check attr_namespace_ignored_p before
> > 	warning.
> > 	* attribs.h (free_attr_data): Declare.
> > 	(register_scoped_attributes): Adjust declaration.
> > 	(handle_ignored_attributes_option): Declare.
> > 	* common.opt (Wattributes=): New option with a variable.
> > 	* doc/extend.texi: Document #pragma GCC diagnostic ignored_attributes.
> > 	* doc/invoke.texi: Document -Wno-attributes=.
> > 	* opts.c (common_handle_option) <case OPT_Wattributes_>: Handle.
> > 	* plugin.h (register_scoped_attributes): Adjust declaration.
> > 	* toplev.c (compile_file): Call free_attr_data.
> > 
> > gcc/c-family/ChangeLog:
> > 
> > 	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
> > 	ignored_attributes.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* c-c++-common/Wno-attributes-1.c: New test.
> > 	* c-c++-common/Wno-attributes-2.c: New test.
> > ---
> >   gcc/attribs.c                                 | 123 +++++++++++++++++-
> >   gcc/attribs.h                                 |   5 +-
> >   gcc/c-family/c-pragma.c                       |  37 +++++-
> >   gcc/common.opt                                |   9 +-
> >   gcc/doc/extend.texi                           |  19 +++
> >   gcc/doc/invoke.texi                           |  20 +++
> >   gcc/opts.c                                    |  20 +++
> >   gcc/plugin.h                                  |   4 +-
> >   gcc/testsuite/c-c++-common/Wno-attributes-1.c |  55 ++++++++
> >   gcc/testsuite/c-c++-common/Wno-attributes-2.c |  56 ++++++++
> >   gcc/toplev.c                                  |   2 +
> >   11 files changed, 341 insertions(+), 9 deletions(-)
> >   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-1.c
> >   create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-2.c
> > 
> > diff --git a/gcc/attribs.c b/gcc/attribs.c
> > index 83fafc98b7d..23d92ca9474 100644
> > --- a/gcc/attribs.c
> > +++ b/gcc/attribs.c
> > @@ -87,6 +87,8 @@ struct scoped_attributes
> >     const char *ns;
> >     vec<attribute_spec> attributes;
> >     hash_table<attribute_hasher> *attribute_hash;
> > +  /* True if we should not warn about unknown attributes in this NS.  */
> > +  bool ignored_p;
> >   };
> >   /* The table of scope attributes.  */
> > @@ -95,6 +97,8 @@ static vec<scoped_attributes> attributes_table;
> >   static scoped_attributes* find_attribute_namespace (const char*);
> >   static void register_scoped_attribute (const struct attribute_spec *,
> >   				       scoped_attributes *);
> > +static const struct attribute_spec *lookup_scoped_attribute_spec (const_tree,
> > +								  const_tree);
> >   static bool attributes_initialized = false;
> > @@ -121,12 +125,14 @@ extract_attribute_substring (struct substring *str)
> >   /* Insert an array of attributes ATTRIBUTES into a namespace.  This
> >      array must be NULL terminated.  NS is the name of attribute
> > -   namespace.  The function returns the namespace into which the
> > -   attributes have been registered.  */
> > +   namespace.  IGNORED_P is true iff all unknown attributes in this
> > +   namespace should be ignored for the purposes of -Wattributes.  The
> > +   function returns the namespace into which the attributes have been
> > +   registered.  */
> >   scoped_attributes *
> >   register_scoped_attributes (const struct attribute_spec *attributes,
> > -			    const char *ns)
> > +			    const char *ns, bool ignored_p /*=false*/)
> >   {
> >     scoped_attributes *result = NULL;
> > @@ -144,9 +150,12 @@ register_scoped_attributes (const struct attribute_spec *attributes,
> >         memset (&sa, 0, sizeof (sa));
> >         sa.ns = ns;
> >         sa.attributes.create (64);
> > +      sa.ignored_p = ignored_p;
> >         result = attributes_table.safe_push (sa);
> >         result->attribute_hash = new hash_table<attribute_hasher> (200);
> >       }
> > +  else
> > +    result->ignored_p |= ignored_p;
> >     /* Really add the attributes to their namespace now.  */
> >     for (unsigned i = 0; attributes[i].name != NULL; ++i)
> > @@ -224,6 +233,95 @@ check_attribute_tables (void)
> >   				 attribute_tables[j][l].name));
> >   }
> > +/* Used to stash pointers to allocated memory so that we can free them at
> > +   the end of parsing of all TUs. */
> > +static vec<attribute_spec *> ignored_attributes_table;
> > +
> > +/* Parse arguments V of -Wno-attributes=.
> > +   Currently we accept:
> > +     vendor::attr
> > +     vendor::
> > +   This functions also registers the parsed attributes so that we don't
> > +   warn that we don't recognize them.  */
> > +
> > +void
> > +handle_ignored_attributes_option (vec<char *> *v)
> > +{
> > +  if (v == nullptr)
> > +    return;
> > +
> > +  for (auto opt : v)
> > +    {
> > +      char *cln = strstr (opt, "::");
> > +      /* We don't accept '::attr'.  */
> > +      if (cln == nullptr || cln == opt)
> > +	{
> > +	  error ("wrong argument to ignored attributes");
> > +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> > +	  continue;
> > +	}
> > +      char *vendor_start = opt;
> > +      ptrdiff_t vendor_len = cln - opt;
> > +      char *attr_start = cln + 2;
> > +      /* This could really use rawmemchr :(.  */
> > +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
> > +      /* Verify that they look valid.  */
> > +      auto valid_p = [](const char *const s, ptrdiff_t len) {
> > +	for (int i = 0; i < len; ++i)
> > +	  if (!ISALNUM (*s) && *s != '_')
> > +	    return false;
> > +	return true;
> > +      };
> > +      if (!valid_p (vendor_start, vendor_len)
> > +	  || !valid_p (attr_start, attr_len))
> > +	{
> > +	  error ("wrong argument to ignored attributes");
> > +	  continue;
> > +	}
> > +      /* Turn "__attr__" into "attr" so that we have a canonical form of
> > +	 attribute names.  Likewise for vendor.  */
> > +      auto strip = [](char *&s, ptrdiff_t &l) {
> > +	if (l > 4 && s[0] == '_' && s[1] == '_'
> > +	    && s[l - 1] == '_' && s[l - 2] == '_')
> > +	  {
> > +	    s += 2;
> > +	    l -= 4;
> > +	  }
> > +      };
> > +      strip (attr_start, attr_len);
> > +      strip (vendor_start, vendor_len);
> > +      /* We perform all this hijinks so that we don't have to copy OPT.  */
> > +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
> > +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
> > +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
> > +	 register it twice would lead to a crash.  */
> > +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
> > +	continue;
> 
> Hmm, this looks like it isn't handling the case of previously ignoring
> vendor::; it seems we'll look for vendor::<empty string> instead, not find
> it, and register again.

Yes, for -Wno-attributes=vendor::,vendor:: we call register_scoped_attributes
twice, but I think that's OK: register_scoped_attributes will see that 
find_attribute_namespace finds the namespace and returns without creating a new  
one.

I think the current code handles -Wno-attributes=vendor::a,vendor:: well so
I'm not sure if I should change it.

Thanks,
Marek
  

On Tue, Nov 09, 2021 at 08:09:10AM +0100, Bernhard Reutner-Fischer wrote:
> On Tue, 9 Nov 2021 00:12:10 -0500
> Jason Merrill <jason@redhat.com> wrote:
> 
> > On 11/8/21 20:41, Marek Polacek wrote:
> > > On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:  
> 
> > > +  for (auto opt : v)
> > > +    {
> > > +      char *cln = strstr (opt, "::");
> > > +      /* We don't accept '::attr'.  */
> > > +      if (cln == nullptr || cln == opt)
> > > +	{
> > > +	  error ("wrong argument to ignored attributes");
> > > +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
> > > +	  continue;
> > > +	}
> > > +      char *vendor_start = opt;
> > > +      ptrdiff_t vendor_len = cln - opt;
> > > +      char *attr_start = cln + 2;
> > > +      /* This could really use rawmemchr :(.  */
> > > +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
> > > +      /* Verify that they look valid.  */
> > > +      auto valid_p = [](const char *const s, ptrdiff_t len) {
> > > +	for (int i = 0; i < len; ++i)
> > > +	  if (!ISALNUM (*s) && *s != '_')
> > > +	    return false;
> > > +	return true;
> > > +      };
> > > +      if (!valid_p (vendor_start, vendor_len)
> > > +	  || !valid_p (attr_start, attr_len))
> > > +	{
> > > +	  error ("wrong argument to ignored attributes");
> > > +	  continue;
> > > +	}
> > > +      /* Turn "__attr__" into "attr" so that we have a canonical form of
> > > +	 attribute names.  Likewise for vendor.  */
> > > +      auto strip = [](char *&s, ptrdiff_t &l) {
> > > +	if (l > 4 && s[0] == '_' && s[1] == '_'
> > > +	    && s[l - 1] == '_' && s[l - 2] == '_')
> > > +	  {
> > > +	    s += 2;
> > > +	    l -= 4;
> > > +	  }
> > > +      };
> > > +      strip (attr_start, attr_len);
> > > +      strip (vendor_start, vendor_len);
> > > +      /* We perform all this hijinks so that we don't have to copy OPT.  */
> > > +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
> > > +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
> > > +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
> > > +	 register it twice would lead to a crash.  */
> > > +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
> > > +	continue;  
> > 
> > Hmm, this looks like it isn't handling the case of previously ignoring 
> > vendor::; it seems we'll look for vendor::<empty string> instead, not 
> > find it, and register again.
> 
> I don't know if there are __attrib with 2 leading underscores but no
> trailing that we accept and should normalize?
> 
> And it is surprising that we do not have a simple normalize_attr_name().
> There must be existing spots where we would normalize attribute names?
> extract_attribute_substring does about the same but with a struct substring(?).
> Maybe that's just to avoid a normal string hash.

We have canonicalize_attr_name which I based my code on.

Marek
  

On 11/9/21 10:55, Marek Polacek wrote:
> On Tue, Nov 09, 2021 at 08:09:10AM +0100, Bernhard Reutner-Fischer wrote:
>> On Tue, 9 Nov 2021 00:12:10 -0500
>> Jason Merrill <jason@redhat.com> wrote:
>>
>>> On 11/8/21 20:41, Marek Polacek wrote:
>>>> On Sat, Nov 06, 2021 at 03:29:57PM -0400, Jason Merrill wrote:
>>
>>>> +  for (auto opt : v)
>>>> +    {
>>>> +      char *cln = strstr (opt, "::");
>>>> +      /* We don't accept '::attr'.  */
>>>> +      if (cln == nullptr || cln == opt)
>>>> +	{
>>>> +	  error ("wrong argument to ignored attributes");
>>>> +	  inform (input_location, "valid format is %<ns::attr%> or %<ns::%>");
>>>> +	  continue;
>>>> +	}
>>>> +      char *vendor_start = opt;
>>>> +      ptrdiff_t vendor_len = cln - opt;
>>>> +      char *attr_start = cln + 2;
>>>> +      /* This could really use rawmemchr :(.  */
>>>> +      ptrdiff_t attr_len = strchr (attr_start, '\0') - attr_start;
>>>> +      /* Verify that they look valid.  */
>>>> +      auto valid_p = [](const char *const s, ptrdiff_t len) {
>>>> +	for (int i = 0; i < len; ++i)
>>>> +	  if (!ISALNUM (*s) && *s != '_')
>>>> +	    return false;
>>>> +	return true;
>>>> +      };
>>>> +      if (!valid_p (vendor_start, vendor_len)
>>>> +	  || !valid_p (attr_start, attr_len))
>>>> +	{
>>>> +	  error ("wrong argument to ignored attributes");
>>>> +	  continue;
>>>> +	}
>>>> +      /* Turn "__attr__" into "attr" so that we have a canonical form of
>>>> +	 attribute names.  Likewise for vendor.  */
>>>> +      auto strip = [](char *&s, ptrdiff_t &l) {
>>>> +	if (l > 4 && s[0] == '_' && s[1] == '_'
>>>> +	    && s[l - 1] == '_' && s[l - 2] == '_')
>>>> +	  {
>>>> +	    s += 2;
>>>> +	    l -= 4;
>>>> +	  }
>>>> +      };
>>>> +      strip (attr_start, attr_len);
>>>> +      strip (vendor_start, vendor_len);
>>>> +      /* We perform all this hijinks so that we don't have to copy OPT.  */
>>>> +      tree vendor_id = get_identifier_with_length (vendor_start, vendor_len);
>>>> +      tree attr_id = get_identifier_with_length (attr_start, attr_len);
>>>> +      /* If we've already seen this vendor::attr, ignore it.  Attempting to
>>>> +	 register it twice would lead to a crash.  */
>>>> +      if (lookup_scoped_attribute_spec (vendor_id, attr_id))
>>>> +	continue;
>>>
>>> Hmm, this looks like it isn't handling the case of previously ignoring
>>> vendor::; it seems we'll look for vendor::<empty string> instead, not
>>> find it, and register again.

> Yes, for -Wno-attributes=vendor::,vendor:: we call register_scoped_attributes
> twice, but I think that's OK: register_scoped_attributes will see that 
> find_attribute_namespace finds the namespace and returns without creating a new  
> one.
> 
> I think the current code handles -Wno-attributes=vendor::a,vendor:: well so
> I'm not sure if I should change it.

Makes sense.  But we should be able to avoid calling 
lookup_scoped_attribute_spec, and even get_identifier_with_length 
(attr...), if attr_len is 0.

>> I don't know if there are __attrib with 2 leading underscores but no
>> trailing that we accept and should normalize?
>>
>> And it is surprising that we do not have a simple normalize_attr_name().
>> There must be existing spots where we would normalize attribute names?
>> extract_attribute_substring does about the same but with a struct substring(?).
>> Maybe that's just to avoid a normal string hash.
> 
> We have canonicalize_attr_name which I based my code on.

We could factor out of that function an overload equivalent to your 
strip lambda?

Jason