@@ -363,35 +363,47 @@ parameter_declaration_list:
;
parameter_declaration:
- decl_specifier_seq abstract_declarator
+ decl_specifier_seq abstract_declarator_opt
{ $$ = $2 ? $2 : $1; }
;
+abstract_declarator_opt:
+ /* empty */ { $$ = NULL; }
+ | abstract_declarator
+ ;
+
abstract_declarator:
- ptr_operator abstract_declarator
+ ptr_operator
+ | ptr_operator abstract_declarator
{ $$ = $2 ? $2 : $1; }
| direct_abstract_declarator
{ $$ = $1; dont_want_type_specifier = false; }
;
direct_abstract_declarator:
- /* empty */ { $$ = NULL; }
- | IDENT
+ IDENT
{ /* For version 2 checksums, we don't want to remember
private parameter names. */
remove_node($1);
$$ = $1;
}
- | direct_abstract_declarator '(' parameter_declaration_clause ')'
+ | direct_abstract_declarator open_paren parameter_declaration_clause ')'
{ $$ = $4; }
- | direct_abstract_declarator '(' error ')'
+ | direct_abstract_declarator open_paren error ')'
{ $$ = $4; }
| direct_abstract_declarator BRACKET_PHRASE
{ $$ = $2; }
- | '(' abstract_declarator ')'
+ | open_paren parameter_declaration_clause ')'
{ $$ = $3; }
- | '(' error ')'
+ | open_paren abstract_declarator ')'
{ $$ = $3; }
+ | open_paren error ')'
+ { $$ = $3; }
+ | BRACKET_PHRASE
+ ;
+
+open_paren:
+ '(' { $$ = $1; dont_want_type_specifier = false; }
;
function_definition:
The genksyms parser has ambiguities in its grammar, which are currently suppressed by a workaround in scripts/genksyms/Makefile. Building genksyms with W=1 generates the following warnings: YACC scripts/genksyms/parse.tab.[ch] scripts/genksyms/parse.y: warning: 3 shift/reduce conflicts [-Wconflicts-sr] scripts/genksyms/parse.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples The ambiguity arises when decl_specifier_seq is followed by '(' because the following two interpretations are possible: - decl_specifier_seq direct_abstract_declarator '(' parameter_declaration_clause ')' - decl_specifier_seq '(' abstract_declarator ')' This issue occurs because the current parser allows an empty string to be reduced to direct_abstract_declarator, which is incorrect. K&R [1] explains the correct grammar: <parameter-declaration> ::= {<declaration-specifier>}+ <declarator> | {<declaration-specifier>}+ <abstract-declarator> | {<declaration-specifier>}+ <abstract-declarator> ::= <pointer> | <pointer> <direct-abstract-declarator> | <direct-abstract-declarator> <direct-abstract-declarator> ::= ( <abstract-declarator> ) | {<direct-abstract-declarator>}? [ {<constant-expression>}? ] | {<direct-abstract-declarator>}? ( {<parameter-type-list>}? ) We need to consider the difference between the following two examples: [Example 1] ( <abstract-declarator> ) can become <direct-abstract-declarator> void my_func(int (foo)); ... is equivalent to: void my_func(int foo); [Example 2] ( <parameter-type-list> ) can become <direct-abstract-declarator> typedef int foo; void my_func(int (foo)); ... is equivalent to: void my_func(int (*callback)(int)); Please note that the function declaration is identical in both examples, but the preceding typedef creates the distinction. I introduced a new term, open_paren, to enable the type lookup immediately after the '(' token. Without this, we cannot distinguish between [Example 1] and [Example 2]. With this commit, all conflicts are resolved. [1]: https://cs.wmich.edu/~gupta/teaching/cs4850/sumII06/The%20syntax%20of%20C%20in%20Backus-Naur%20form.htm Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> --- scripts/genksyms/parse.y | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-)