[PATCH v2] attribs: Fix wrong error with -Wno-attribute=A::b [PR103649]

[Marek Polacek]

On Thu, Dec 16, 2021 at 11:53:46PM +0100, Jakub Jelinek wrote:
> On Thu, Dec 16, 2021 at 05:35:55PM -0500, Marek Polacek wrote:
> > My patch to implement -Wno-attribute=A::b caused a bogus error when
> > parsing
> > 
> >   [[foo::bar(1, 2)]];
> > 
> > when -Wno-attributes=foo::bar was specified on the command line, because
> > when we create a fake foo::bar attribute and insert it into our attribute
> > table, it is created with max_length == 0 which doesn't allow any args.
> > That is wrong -- we know nothing about the attribute, so we shouldn't
> > require any specific number of arguments.
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > 	PR c/103649
> > 
> > gcc/ChangeLog:
> > 
> > 	* attribs.c (handle_ignored_attributes_option): Create the fake
> > 	attribute with max_length == -1.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* c-c++-common/Wno-attributes-6.c: New test.
> 
> I'm afraid this still changes behavior.  0, -1 range attribute arguments
> are parsed normally, while unknown attributes have the balanced token
> sequence skipped.
> E.g. the omp::{directive,sequence} attribute arguments are much more complex
> than what the normal parsing can handle.
> Can you make max -2 instead and special case it in the C and C++ FE
> attribute handling and in a testcase try something that is a balanced token
> sequence but not really valid when parsed as ordinary attributes' arguments?

Ah I see what you mean now.  Fixed here, thanks.

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

-- >8 --
My patch to implement -Wno-attribute=A::b caused a bogus error when
parsing

  [[foo::bar(1, 2)]];

when -Wno-attributes=foo::bar was specified on the command line, because
when we create a fake foo::bar attribute and insert it into our attribute
table, it is created with max_length == 0 which doesn't allow any args.
That is wrong -- we know nothing about the attribute, so we shouldn't
require any specific number of arguments.  And since unknown attributes
can be rather complex (see for example omp::{directive,sequence}), we
must skip parsing their arguments.  To that end, I'm using max_length
with value -2.

	PR c/103649

gcc/ChangeLog:

	* attribs.c (handle_ignored_attributes_option): Create the fake
	attribute with max_length == -2.
	* tree-core.h (struct attribute_spec): Document that max_length
	can be -2.

gcc/c/ChangeLog:

	* c-parser.c (c_parser_std_attribute): Skip parsing of the attribute
	arguments when max_length == -2.

gcc/cp/ChangeLog:

	* parser.c (cp_parser_std_attribute): Skip parsing of the attribute
	arguments when max_length == -2.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-6.c: New test.
---
 gcc/attribs.c                                 |  2 +-
 gcc/c/c-parser.c                              |  4 +++-
 gcc/cp/parser.c                               |  4 +++-
 gcc/testsuite/c-c++-common/Wno-attributes-6.c | 14 ++++++++++++++
 gcc/tree-core.h                               |  4 +++-
 5 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-6.c

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 29703e75fba..6af7f93e61c 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -304,7 +304,7 @@ handle_ignored_attributes_option (vec<char *> *v)
 	 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[0] = { attr, 0, -2, false, false, false, false, nullptr, nullptr };
       table[1] = { nullptr, 0, 0, false, false, false, false, nullptr,
 		   nullptr };
       register_scoped_attributes (table, IDENTIFIER_POINTER (vendor_id), !attr);
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index d7e5f051ac0..c9068bdbb8a 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -4943,7 +4943,9 @@ c_parser_std_attribute (c_parser *parser, bool for_tm)
 	parens.skip_until_found_close (parser);
 	return error_mark_node;
       }
-    if (as)
+    /* When MAX_LENGTH is -2, this is a fake attribute created to
+       handle -Wno-attributes, and we must skip parsing the arguments.  */
+    if (as && as->max_length != -2)
       {
 	bool takes_identifier
 	  = (ns != NULL_TREE
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 44eed7ea638..763d74eaf6c 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -28979,7 +28979,9 @@ cp_parser_std_attribute (cp_parser *parser, tree attr_ns)
       /* A GNU attribute that takes an identifier in parameter.  */
       attr_flag = id_attr;
 
-    if (as == NULL)
+    /* When MAX_LENGTH is -2, this is a fake attribute created to
+       handle -Wno-attributes, and we must skip parsing the arguments.  */
+    if (as == NULL || as->max_length == -2)
       {
 	if ((flag_openmp || flag_openmp_simd) && attr_ns == omp_identifier)
 	  {
diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-6.c b/gcc/testsuite/c-c++-common/Wno-attributes-6.c
new file mode 100644
index 00000000000..0b2dd5aa290
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-6.c
@@ -0,0 +1,14 @@
+/* PR c/103649 */
+/* { dg-do compile { target { c || c++11 } } } */
+/* { dg-additional-options "-Wno-attributes=foo::bar" } */
+/* { dg-additional-options "-Wno-attributes=baz::" } */
+/* { dg-additional-options "-Wno-attributes=womp::womp" } */
+/* { dg-additional-options "-Wno-attributes=qux::foo" } */
+
+[[foo::bar(1, 2)]]; /* { dg-warning "attribute ignored" } */
+[[baz::bar(1, 2)]]; /* { dg-warning "attribute ignored" } */
+[[foo::bar(1, 2)]] void f1();
+[[baz::bar(1, 2)]] void f2();
+[[qux::foo({t})]] void f3(); 
+[[womp::womp (another::directive (threadprivate (t)))]] void f4();
+[[womp::womp (another::directive (threadprivate (t)))]]; /* { dg-warning "attribute ignored" } */
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 91ae5237d7e..9b37a065d18 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -2077,7 +2077,9 @@ struct attribute_spec {
   /* The minimum length of the list of arguments of the attribute.  */
   int min_length;
   /* The maximum length of the list of arguments of the attribute
-     (-1 for no maximum).  */
+     (-1 for no maximum).  It can also be -2 for fake attributes
+     created for the sake of -Wno-attributes; in that case, we
+     should skip the balanced token sequence when parsing the attribute.  */
   int max_length;
   /* Whether this attribute requires a DECL.  If it does, it will be passed
      from types of DECLs, function return types and array element types to

base-commit: 840a22e0fee9e7369a2eb1c9e3c70dcae24a20e4
-- 
2.33.1