kconfig: support user-defined function and recursively expanded variable

Now, we got a basic ability to test compiler capability in Kconfig.

config CC_HAS_STACKPROTECTOR
        def_bool $(shell,($(CC) -Werror -fstack-protector -E -x c /dev/null -o /dev/null 2>/dev/null) && echo y || echo n)

This works, but it is ugly to repeat this long boilerplate.

We want to describe like this:

config CC_HAS_STACKPROTECTOR
        bool
        default $(cc-option,-fstack-protector)

It is straight-forward to add a new function, but I do not like to
hard-code specialized functions like that.  Hence, here is another
feature, user-defined function.  This works as a textual shorthand
with parameterization.

A user-defined function is defined by using the = operator, and can
be referenced in the same way as built-in functions.  A user-defined
function in Make is referenced like $(call my-func,arg1,arg2), but I
omitted the 'call' to make the syntax shorter.

The definition of a user-defined function contains $(1), $(2), etc.
in its body to reference the parameters.  It is grammatically valid
to pass more or fewer arguments when calling it.  We already exploit
this feature in our makefiles; scripts/Kbuild.include defines cc-option
which takes two arguments at most, but most of the callers pass only
one argument.

By the way, a variable is supported as a subset of this feature since
a variable is "a user-defined function with zero argument".  In this
context, I mean "variable" as recursively expanded variable.  I will
add a different flavored variable in the next commit.

The code above can be written as follows:

[Example Code]

  success = $(shell,($(1)) >/dev/null 2>&1 && echo y || echo n)
  cc-option = $(success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null)

  config CC_HAS_STACKPROTECTOR
          def_bool $(cc-option,-fstack-protector)

[Result]
  $ make -s alldefconfig && tail -n 1 .config
  CONFIG_CC_HAS_STACKPROTECTOR=y

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/scripts/kconfig/zconf.y b/scripts/kconfig/zconf.y
index 8a82aaf27581..e15e8c7063e0 100644
--- a/scripts/kconfig/zconf.y
+++ b/scripts/kconfig/zconf.y
@@ -77,6 +77,9 @@ static struct menu *current_menu, *current_entry;
 %token T_CLOSE_PAREN
 %token T_OPEN_PAREN
 %token T_EOL
+%token <string> T_VARIABLE
+%token T_ASSIGN
+%token <string> T_ASSIGN_VAL
 
 %left T_OR
 %left T_AND
@@ -92,7 +95,7 @@ static struct menu *current_menu, *current_entry;
 %type <id> end
 %type <id> option_name
 %type <menu> if_entry menu_entry choice_entry
-%type <string> symbol_option_arg word_opt
+%type <string> symbol_option_arg word_opt assign_val
 
 %destructor {
 	fprintf(stderr, "%s:%d: missing end statement for this entry\n",
@@ -143,6 +146,7 @@ common_stmt:
 	| config_stmt
 	| menuconfig_stmt
 	| source_stmt
+	| assignment_stmt
 ;
 
 option_error:
@@ -511,6 +515,15 @@ symbol:	  nonconst_symbol
 word_opt: /* empty */			{ $$ = NULL; }
 	| T_WORD
 
+/* assignment statement */
+
+assignment_stmt:  T_VARIABLE T_ASSIGN assign_val T_EOL	{ variable_add($1, $3); free($1); free($3); }
+
+assign_val:
+	/* empty */		{ $$ = xstrdup(""); };
+	| T_ASSIGN_VAL
+;
+
 %%
 
 void conf_parse(const char *name)
@@ -525,6 +538,10 @@ void conf_parse(const char *name)
 	if (getenv("ZCONF_DEBUG"))
 		yydebug = 1;
 	yyparse();
+
+	/* Variables are expanded in the parse phase. We can free them here. */
+	variable_all_del();
+
 	if (yynerrs)
 		exit(1);
 	if (!modules_sym)