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, 15 insertions, 2 deletions

diff --git a/scripts/kconfig/zconf.l b/scripts/kconfig/zconf.l
index 9a147977dc3f..dd08f7a38ccd 100644
--- a/scripts/kconfig/zconf.l
+++ b/scripts/kconfig/zconf.l
@@ -1,12 +1,13 @@
 %option nostdinit noyywrap never-interactive full ecs
 %option 8bit nodefault yylineno
-%x COMMAND HELP STRING PARAM
+%x COMMAND HELP STRING PARAM ASSIGN_VAL
 %{
 /*
  * Copyright (C) 2002 Roman Zippel <zippel@linux-m68k.org>
  * Released under the terms of the GNU GPL v2.0.
  */
 
+#include <assert.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -111,8 +112,10 @@ n	[A-Za-z0-9_-]
 		}
 		alloc_string(yytext, yyleng);
 		yylval.string = text;
-		return T_WORD;
+		return T_VARIABLE;
 	}
+	"="	{ BEGIN(ASSIGN_VAL); return T_ASSIGN; }
+	[[:blank:]]+
 	.	warn_ignored_character(*yytext);
 	\n	{
 		BEGIN(INITIAL);
@@ -120,6 +123,16 @@ n	[A-Za-z0-9_-]
 	}
 }
 
+<ASSIGN_VAL>{
+	[^[:blank:]\n]+.*	{
+		alloc_string(yytext, yyleng);
+		yylval.string = text;
+		return T_ASSIGN_VAL;
+	}
+	\n	{ BEGIN(INITIAL); return T_EOL; }
+	.
+}
+
 <PARAM>{
 	"&&"	return T_AND;
 	"||"	return T_OR;