[PATCH v4] sparse: add support for _Static_assert

[PATCH v4] sparse: add support for _Static_assert

[Lance Richardson]

This patch introduces support for the C11 _Static_assert() construct.

Per the N1539 draft standard, the syntax changes for this construct
include:

    declaration:
        <declaration-specifiers> <init-declarator-list>[opt] ;
        <static_assert-declaration>

    struct-declaration:
        <specifier-qualifier-list> <struct-declarator-list>[opt] ;
        <static_assert-declaration>

    static_assert-declaration:
        _Static_assert ( <constant-expression> , <string-literal> ) ;

Signed-off-by: Lance Richardson <lrichard@redhat.com>
---
v4: Addressed feedback, simplified and restructured to better model
    description in draft standard.

v3:
    - Removed bogus test case introduced in v2 (static assertion on sizeof
      a structure within the definition of the structure).

v2: 
    - Added additional test cases.
    - Added additional validation for parameters to _Static_assert().
    - Reworked implementation to avoid impacting struct/union definition
      handling ( the v1 implementation, which treated _Static_assert()
      as an NS_TYPEDEF term, had the unfortunate side-effect of
      leaving an unnamed field with unknown size attached to structure
      definitions when a static assert was inside a structure definition).

 parse.c                    | 65 +++++++++++++++++++++++++++++++++++++++++-----
 validation/static_assert.c | 57 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+), 7 deletions(-)
 create mode 100644 validation/static_assert.c

diff --git a/parse.c b/parse.c
index b52c6ab..f1b96cc 100644
--- a/parse.c
+++ b/parse.c
@@ -73,6 +73,7 @@ static struct token *parse_context_statement(struct token *token, struct stateme
 static struct token *parse_range_statement(struct token *token, struct statement *stmt);
 static struct token *parse_asm_statement(struct token *token, struct statement *stmt);
 static struct token *toplevel_asm_declaration(struct token *token, struct symbol_list **list);
+static struct token *parse_static_assert(struct token *token, struct symbol_list **unused);
 
 typedef struct token *attr_t(struct token *, struct symbol *,
 			     struct decl_state *);
@@ -308,6 +309,10 @@ static struct symbol_op asm_op = {
 	.toplevel = toplevel_asm_declaration,
 };
 
+static struct symbol_op static_assert_op = {
+	.toplevel = parse_static_assert,
+};
+
 static struct symbol_op packed_op = {
 	.attribute = attribute_packed,
 };
@@ -437,6 +442,9 @@ static struct init_keyword {
 	{ "__restrict",	NS_TYPEDEF, .op = &restrict_op},
 	{ "__restrict__",	NS_TYPEDEF, .op = &restrict_op},
 
+	/* Static assertion */
+	{ "_Static_assert", NS_KEYWORD, .op = &static_assert_op },
+
 	/* Storage class */
 	{ "auto",	NS_TYPEDEF, .op = &auto_op },
 	{ "register",	NS_TYPEDEF, .op = &register_op },
@@ -1864,13 +1872,21 @@ static struct token *declaration_list(struct token *token, struct symbol_list **
 static struct token *struct_declaration_list(struct token *token, struct symbol_list **list)
 {
 	while (!match_op(token, '}')) {
-		if (!match_op(token, ';'))
-			token = declaration_list(token, list);
-		if (!match_op(token, ';')) {
-			sparse_error(token->pos, "expected ; at end of declaration");
-			break;
+		struct symbol *keyword = NULL;
+
+		if (token_type(token) == TOKEN_IDENT)
+			keyword = lookup_keyword(token->ident, NS_KEYWORD);
+		if (keyword && keyword->op == &static_assert_op)
+			token = parse_static_assert(token, NULL);
+		else {
+			if (!match_op(token, ';'))
+				token = declaration_list(token, list);
+			if (!match_op(token, ';')) {
+				sparse_error(token->pos, "expected ; at end of declaration");
+				break;
+			}
+			token = token->next;
 		}
-		token = token->next;
 	}
 	return token;
 }
@@ -2012,6 +2028,36 @@ static struct token *parse_asm_declarator(struct token *token, struct decl_state
 	return token;
 }
 
+
+static struct token *parse_static_assert(struct token *token, struct symbol_list **unused)
+{
+	struct expression *expr1 = NULL, *expr2 = NULL;
+	int val;
+
+	token = expect(token->next, '(', "after _Static_assert");
+	token = constant_expression(token, &expr1);
+	token = expect(token, ',', "after first argument of _Static_assert");
+	token = parse_expression(token, &expr2);
+	token = expect(token, ')', "after second argument of _Static_assert");
+
+        token = expect(token, ';', "after _Static_assert()");
+
+	if (!expr1 || !expr2)
+		return token;
+
+	val = const_expression_value(expr1);
+
+	if (expr2->type != EXPR_STRING)
+		sparse_error(expr2->pos, "bad string literal");
+	else if (expr1 && (expr1->type == EXPR_VALUE)) {
+		if (!val)
+			sparse_error(expr1->pos, "static assertion failed: %s",
+				     show_string(expr2->string));
+	}
+
+	return token;
+}
+
 /* Make a statement out of an expression */
 static struct statement *make_statement(struct expression *expr)
 {
@@ -2378,6 +2424,7 @@ static struct token * statement_list(struct token *token, struct statement_list
 		token = label_statement(token->next);
 	for (;;) {
 		struct statement * stmt;
+		struct symbol *keyword;
 		if (eof_token(token))
 			break;
 		if (match_op(token, '}'))
@@ -2389,6 +2436,10 @@ static struct token * statement_list(struct token *token, struct statement_list
 			}
 			stmt = alloc_statement(token->pos, STMT_DECLARATION);
 			token = external_declaration(token, &stmt->declaration);
+		} else if (token_type(token) == TOKEN_IDENT &&
+			   (keyword = lookup_keyword(token->ident, NS_KEYWORD)) &&
+			   keyword->op == &static_assert_op) {
+			token = parse_static_assert(token, NULL);
 		} else {
 			seen_statement = Wdeclarationafterstatement;
 			token = statement(token, &stmt);
@@ -2726,7 +2777,7 @@ struct token *external_declaration(struct token *token, struct symbol_list **lis
 	unsigned long mod;
 	int is_typedef;
 
-	/* Top-level inline asm? */
+	/* Top-level inline asm or static assertion? */
 	if (token_type(token) == TOKEN_IDENT) {
 		struct symbol *s = lookup_keyword(token->ident, NS_KEYWORD);
 		if (s && s->op->toplevel)
diff --git a/validation/static_assert.c b/validation/static_assert.c
new file mode 100644
index 0000000..a1ef68f
--- /dev/null
+++ b/validation/static_assert.c
@@ -0,0 +1,57 @@
+_Static_assert(1, "global ok");
+
+struct foo {
+	_Static_assert(1, "struct ok");
+};
+
+void bar(void)
+{
+	_Static_assert(1, " func ok");
+}
+
+_Static_assert(0, "expected assertion failure");
+
+static int f;
+_Static_assert(f, "non-constant expression");
+
+static int *p;
+_Static_assert(p, "non-integer expression");
+
+_Static_assert(0.1, "float expression");
+        
+_Static_assert(!0 == 1, "non-trivial expression");
+        
+static char array[4];
+_Static_assert(sizeof(array) == 4, "sizeof expression");
+        
+static const char non_literal_string[] = "non literal string";
+_Static_assert(0, non_literal_string);
+
+_Static_assert(1 / 0, "invalid expression: should not show up?");
+
+struct s {
+	char arr[16];
+	_Static_assert(1, "inside struct");
+};
+
+union u {
+	char c;
+	int  i;
+	_Static_assert(1, "inside union");
+};
+
+_Static_assert(sizeof(struct s) == 16, "sizeof assertion");
+
+/*
+ * check-name: static assertion
+ *
+ * check-error-start
+static_assert.c:12:16: error: static assertion failed: "expected assertion failure"
+static_assert.c:15:16: error: bad constant expression
+static_assert.c:18:16: error: bad constant expression
+static_assert.c:20:16: error: bad constant expression
+static_assert.c:28:19: error: bad string literal
+static_assert.c:30:18: error: bad constant expression
+ * check-error-end
+ */
+
-- 
2.9.3

Re: [PATCH v4] sparse: add support for _Static_assert

[Luc Van Oostenryck]

On Wed, May 03, 2017 at 12:55:18PM -0400, Lance Richardson wrote:
> This patch introduces support for the C11 _Static_assert() construct.

Great!
 
> diff --git a/parse.c b/parse.c
...
> index b52c6ab..f1b96cc 100644
> --- a/parse.c
> +++ b/parse.c
> @@ -1864,13 +1872,21 @@ static struct token *declaration_list(struct token *token, struct symbol_list **
>  static struct token *struct_declaration_list(struct token *token, struct symbol_list **list)
>  {
>  	while (!match_op(token, '}')) {
> -		if (!match_op(token, ';'))
> -			token = declaration_list(token, list);
> -		if (!match_op(token, ';')) {
> -			sparse_error(token->pos, "expected ; at end of declaration");
> -			break;
> +		struct symbol *keyword = NULL;
> +
> +		if (token_type(token) == TOKEN_IDENT)
> +			keyword = lookup_keyword(token->ident, NS_KEYWORD);
> +		if (keyword && keyword->op == &static_assert_op)

Is it possible to move this test in a helper? Something like
	static int match_static_assert(struct token *token)
	{
		struct symbol *keyword;
		if (token_type(token) != TOKEN_IDENT)
			return 0;
		keyword = lookup_keyword(token->ident, NS_KEYWORD);
		return keyword && keyword->op == &static_assert_op;
	}

> @@ -2389,6 +2436,10 @@ static struct token * statement_list(struct token *token, struct statement_list
>  			}
>  			stmt = alloc_statement(token->pos, STMT_DECLARATION);
>  			token = external_declaration(token, &stmt->declaration);
> +		} else if (token_type(token) == TOKEN_IDENT &&
> +			   (keyword = lookup_keyword(token->ident, NS_KEYWORD)) &&
> +			   keyword->op == &static_assert_op) {
> +			token = parse_static_assert(token, NULL);

The helper can be reused here too.

But then I saw that code like:
	extern int _Static_assert;
didn't gave a warning because '_Static_assert' is not reserved
keyword as it should. And then I wonder how this can be simplified. 

For the test cases, it would also be good to add a small test using
the assert not on the top of a block (thus not where declarations
normally are).

-- Luc

Re: [PATCH v4] sparse: add support for _Static_assert

[Luc Van Oostenryck]

On Thu, May 4, 2017 at 1:54 AM, Luc Van Oostenryck
<luc.vanoostenryck@gmail.com> wrote:
> On Wed, May 03, 2017 at 12:55:18PM -0400, Lance Richardson wrote:
>> This patch introduces support for the C11 _Static_assert() construct.
>
> Great!
>
>> diff --git a/parse.c b/parse.c
> ...
>> index b52c6ab..f1b96cc 100644
>> --- a/parse.c
>> +++ b/parse.c
>> @@ -1864,13 +1872,21 @@ static struct token *declaration_list(struct token *token, struct symbol_list **
>>  static struct token *struct_declaration_list(struct token *token, struct symbol_list **list)
>>  {
>>       while (!match_op(token, '}')) {
>> -             if (!match_op(token, ';'))
>> -                     token = declaration_list(token, list);
>> -             if (!match_op(token, ';')) {
>> -                     sparse_error(token->pos, "expected ; at end of declaration");
>> -                     break;
>> +             struct symbol *keyword = NULL;
>> +
>> +             if (token_type(token) == TOKEN_IDENT)
>> +                     keyword = lookup_keyword(token->ident, NS_KEYWORD);
>> +             if (keyword && keyword->op == &static_assert_op)
>
> Is it possible to move this test in a helper? Something like
>         static int match_static_assert(struct token *token)
>         {
>                 struct symbol *keyword;
>                 if (token_type(token) != TOKEN_IDENT)
>                         return 0;
>                 keyword = lookup_keyword(token->ident, NS_KEYWORD);
>                 return keyword && keyword->op == &static_assert_op;
>         }
>
>> @@ -2389,6 +2436,10 @@ static struct token * statement_list(struct token *token, struct statement_list
>>                       }
>>                       stmt = alloc_statement(token->pos, STMT_DECLARATION);
>>                       token = external_declaration(token, &stmt->declaration);
>> +             } else if (token_type(token) == TOKEN_IDENT &&
>> +                        (keyword = lookup_keyword(token->ident, NS_KEYWORD)) &&
>> +                        keyword->op == &static_assert_op) {
>> +                     token = parse_static_assert(token, NULL);

There is another problem here. With a few more line of context, we have:
>> @@ -2389,6 +2436,10 @@ static struct token * statement_list(struct token *token, struct statement_list
>>                       }
>>                       stmt = alloc_statement(token->pos, STMT_DECLARATION);
>>                       token = external_declaration(token, &stmt->declaration);
>> +             } else if (token_type(token) == TOKEN_IDENT &&
>> +                        (keyword = lookup_keyword(token->ident, NS_KEYWORD)) &&
>> +                        keyword->op == &static_assert_op) {
>> +                     token = parse_static_assert(token, NULL);
>>                }
>>                add_statement(list, stmt);

but when the static assert matches 'stmt' is not initialized and still added
to the statement list (with sporadic crashes).

-- Luc

Re: [PATCH v4] sparse: add support for _Static_assert

[Lance Richardson]

> From: "Luc Van Oostenryck" <luc.vanoostenryck@gmail.com>
> To: "Lance Richardson" <lrichard@redhat.com>
> Cc: "Linux-Sparse" <linux-sparse@vger.kernel.org>
> Sent: Wednesday, 3 May, 2017 10:29:27 PM
> Subject: Re: [PATCH v4] sparse: add support for _Static_assert
> 
> On Thu, May 4, 2017 at 1:54 AM, Luc Van Oostenryck
> <luc.vanoostenryck@gmail.com> wrote:
> > On Wed, May 03, 2017 at 12:55:18PM -0400, Lance Richardson wrote:
> >> This patch introduces support for the C11 _Static_assert() construct.
> >
> > Great!
> >
> >> diff --git a/parse.c b/parse.c
> > ...
> >> index b52c6ab..f1b96cc 100644
> >> --- a/parse.c
> >> +++ b/parse.c
> >> @@ -1864,13 +1872,21 @@ static struct token *declaration_list(struct token
> >> *token, struct symbol_list **
> >>  static struct token *struct_declaration_list(struct token *token, struct
> >>  symbol_list **list)
> >>  {
> >>       while (!match_op(token, '}')) {
> >> -             if (!match_op(token, ';'))
> >> -                     token = declaration_list(token, list);
> >> -             if (!match_op(token, ';')) {
> >> -                     sparse_error(token->pos, "expected ; at end of
> >> declaration");
> >> -                     break;
> >> +             struct symbol *keyword = NULL;
> >> +
> >> +             if (token_type(token) == TOKEN_IDENT)
> >> +                     keyword = lookup_keyword(token->ident, NS_KEYWORD);
> >> +             if (keyword && keyword->op == &static_assert_op)
> >
> > Is it possible to move this test in a helper? Something like
> >         static int match_static_assert(struct token *token)
> >         {
> >                 struct symbol *keyword;
> >                 if (token_type(token) != TOKEN_IDENT)
> >                         return 0;
> >                 keyword = lookup_keyword(token->ident, NS_KEYWORD);
> >                 return keyword && keyword->op == &static_assert_op;
> >         }
> >
> >> @@ -2389,6 +2436,10 @@ static struct token * statement_list(struct token
> >> *token, struct statement_list
> >>                       }
> >>                       stmt = alloc_statement(token->pos,
> >>                       STMT_DECLARATION);
> >>                       token = external_declaration(token,
> >>                       &stmt->declaration);
> >> +             } else if (token_type(token) == TOKEN_IDENT &&
> >> +                        (keyword = lookup_keyword(token->ident,
> >> NS_KEYWORD)) &&
> >> +                        keyword->op == &static_assert_op) {
> >> +                     token = parse_static_assert(token, NULL);
> 
> There is another problem here. With a few more line of context, we have:
> >> @@ -2389,6 +2436,10 @@ static struct token * statement_list(struct token
> >> *token, struct statement_list
> >>                       }
> >>                       stmt = alloc_statement(token->pos,
> >>                       STMT_DECLARATION);
> >>                       token = external_declaration(token,
> >>                       &stmt->declaration);
> >> +             } else if (token_type(token) == TOKEN_IDENT &&
> >> +                        (keyword = lookup_keyword(token->ident,
> >> NS_KEYWORD)) &&
> >> +                        keyword->op == &static_assert_op) {
> >> +                     token = parse_static_assert(token, NULL);
> >>                }
> >>                add_statement(list, stmt);
> 
> but when the static assert matches 'stmt' is not initialized and still added
> to the statement list (with sporadic crashes).
> 

Oof, I recall noticing that but apparently forgot to do anything about it.

Thanks for the quick feedback, will incorporate in v5. 

> -- Luc
> 

Re: [PATCH v4] sparse: add support for _Static_assert

[Luc Van Oostenryck]

On Thu, May 04, 2017 at 09:53:50AM -0400, Lance Richardson wrote:
> Thanks for the quick feedback, will incorporate in v5. 

I also saw a small issue, possibly related to the problem with
the mixup between 'declaration-list' and 'struct-declarator-list'
that you noticed. In the following code, the static assert is not
recognized:
	void foo(void)
	{
		int i = 0;
		for (_Static_assert(1, "ok"); 1; )
			;
		for (_Static_assert(0, "ko"); 1; )
			;
	}

It should because (since C99) the first part of the for-statement
is just a 'declaration', which include the static assert.
Not that it's very important, though.

Probably, it's best to leave it as is for the moment and just
add a new test case, annotated with 'check-known-to-fail'.

-- Luc

Re: [PATCH v4] sparse: add support for _Static_assert

[Lance Richardson]

> From: "Luc Van Oostenryck" <luc.vanoostenryck@gmail.com>
> To: "Lance Richardson" <lrichard@redhat.com>
> Cc: "Linux-Sparse" <linux-sparse@vger.kernel.org>
> Sent: Thursday, 4 May, 2017 10:58:35 AM
> Subject: Re: [PATCH v4] sparse: add support for _Static_assert
> 
> On Thu, May 04, 2017 at 09:53:50AM -0400, Lance Richardson wrote:
> > Thanks for the quick feedback, will incorporate in v5.
> 
> I also saw a small issue, possibly related to the problem with
> the mixup between 'declaration-list' and 'struct-declarator-list'
> that you noticed. In the following code, the static assert is not
> recognized:
> 	void foo(void)
> 	{
> 		int i = 0;
> 		for (_Static_assert(1, "ok"); 1; )
> 			;
> 		for (_Static_assert(0, "ko"); 1; )
> 			;
> 	}
> 
> It should because (since C99) the first part of the for-statement
> is just a 'declaration', which include the static assert.
> Not that it's very important, though.
> 
> Probably, it's best to leave it as is for the moment and just
> add a new test case, annotated with 'check-known-to-fail'.
> 
> -- Luc
> 

Hi Luc,

I'm not sure it should be accepted; the standard doc says:

    "The declaration part of a for statement shall only declare
     identifiers for objects having storage class auto or register."
 
But _Static_assert() doesn't declare an identifier.

gcc accepts this syntax, although clang does not.  I did find this discussion:

    https://reviews.llvm.org/D9113

Which points to a working group discussion that made it sound as
though _Static_assert() should not be accepted in for-loop declarations:

    www.open-std.org/JTC1/SC22/WG14/13677

As you say, probably best to leave this for now.

   Lance

Re: [PATCH v4] sparse: add support for _Static_assert

[Luc Van Oostenryck]

On Thu, May 4, 2017 at 5:46 PM, Lance Richardson <lrichard@redhat.com> wrote:
>> From: "Luc Van Oostenryck" <luc.vanoostenryck@gmail.com>
>> To: "Lance Richardson" <lrichard@redhat.com>
>> Cc: "Linux-Sparse" <linux-sparse@vger.kernel.org>
>> Sent: Thursday, 4 May, 2017 10:58:35 AM
>> Subject: Re: [PATCH v4] sparse: add support for _Static_assert
>>
>> On Thu, May 04, 2017 at 09:53:50AM -0400, Lance Richardson wrote:
>> > Thanks for the quick feedback, will incorporate in v5.
>>
>> I also saw a small issue, possibly related to the problem with
>> the mixup between 'declaration-list' and 'struct-declarator-list'
>> that you noticed. In the following code, the static assert is not
>> recognized:
>>       void foo(void)
>>       {
>>               int i = 0;
>>               for (_Static_assert(1, "ok"); 1; )
>>                       ;
>>               for (_Static_assert(0, "ko"); 1; )
>>                       ;
>>       }
>>
>> It should because (since C99) the first part of the for-statement
>> is just a 'declaration', which include the static assert.
>> Not that it's very important, though.
>>
>> Probably, it's best to leave it as is for the moment and just
>> add a new test case, annotated with 'check-known-to-fail'.
>>
>> -- Luc
>>
>
> Hi Luc,
>
> I'm not sure it should be accepted; the standard doc says:
>
>     "The declaration part of a for statement shall only declare
>      identifiers for objects having storage class auto or register."
>
> But _Static_assert() doesn't declare an identifier.

Indeed.

> gcc accepts this syntax, although clang does not.  I did find this discussion:
>
>     https://reviews.llvm.org/D9113
>
> Which points to a working group discussion that made it sound as
> though _Static_assert() should not be accepted in for-loop declarations:

It makes a lot of sense to not accept it.

>     www.open-std.org/JTC1/SC22/WG14/13677
>
> As you say, probably best to leave this for now.

Yes, even more so now.
Thanks for the info.

-- Luc

Re: [PATCH v4] sparse: add support for _Static_assert

[Christopher Li]

On Wed, May 3, 2017 at 12:55 PM, Lance Richardson <lrichard@redhat.com> wrote:
> +               } else if (token_type(token) == TOKEN_IDENT &&
> +                          (keyword = lookup_keyword(token->ident, NS_KEYWORD)) &&
> +                          keyword->op == &static_assert_op) {

I think you should add _Static_assert into header file "ident-list.h"
then you can simplify this test as:

else if (token_type(token) == TOKEN_IDENT &&
            token->ident == &_Static_assert_ident)

We don't need to go through a keyword look up then test
the keyword->op == &static_assert_op.

Chris

Re: [PATCH v4] sparse: add support for _Static_assert

[Lance Richardson]

> From: "Christopher Li" <sparse@chrisli.org>
> To: "Lance Richardson" <lrichard@redhat.com>
> Cc: "Linux-Sparse" <linux-sparse@vger.kernel.org>
> Sent: Wednesday, 3 May, 2017 11:03:22 PM
> Subject: Re: [PATCH v4] sparse: add support for _Static_assert
> 
> On Wed, May 3, 2017 at 12:55 PM, Lance Richardson <lrichard@redhat.com>
> wrote:
> > +               } else if (token_type(token) == TOKEN_IDENT &&
> > +                          (keyword = lookup_keyword(token->ident,
> > NS_KEYWORD)) &&
> > +                          keyword->op == &static_assert_op) {
> 
> I think you should add _Static_assert into header file "ident-list.h"
> then you can simplify this test as:
> 
> else if (token_type(token) == TOKEN_IDENT &&
>             token->ident == &_Static_assert_ident)
> 
> We don't need to go through a keyword look up then test
> the keyword->op == &static_assert_op.
> 
> Chris
> 

Makes sense, thanks for the suggestion. This should also address Luc's
comment about "extern int _Static_assert;" being accepted in the v4 version.

Will fold into v5.

Thanks,

   Lance