Date:   Tue, 20 Feb 2018 00:57:13 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Ulf Magnusson <ulfalizer@...il.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/23] kconfig: add function support and implement 'shell' function

2018-02-18 1:16 GMT+09:00 Ulf Magnusson <ulfalizer@...il.com>:
> On Sat, Feb 17, 2018 at 03:38:35AM +0900, Masahiro Yamada wrote:
>> This commit adds a new concept 'function' to Kconfig.  A function call
>> resembles a variable reference with arguments, and looks like this:
>>
>>   $(function arg1, arg2, arg3, ...)
>>
>> (Actually, this syntax was inspired by Makefile.)
>>
>> Real examples will look like this:
>>
>>   $(shell true)
>>   $(cc-option -fstackprotector)
>>
>> This commit adds the basic infrastructure to add, delete, evaluate
>> functions.
>>
>> Also, add the first built-in function $(shell ...).  This evaluates
>> to 'y' if the given command exits with 0, 'n' otherwise.
>>
>> I am also planning to support user-defined functions (a.k.a 'macro')
>> for cases where hard-coding is not preferred.
>>
>> If you want to try this feature, the hello-world code is someting below.
>>
>> Example code:
>>
>>   config CC_IS_GCC
>>           bool
>>           default $(shell $CC --version | grep -q gcc)
>>
>>   config CC_IS_CLANG
>>           bool
>>           default $(shell $CC --version | grep -q clang)
>>
>>   config CC_HAS_OZ
>>           bool
>>           default $(shell $CC -Werror -Oz -c -x c /dev/null -o /dev/null)
>>
>> Result:
>>
>>   $ make -s alldefconfig && tail -n 3 .config
>>   CONFIG_CC_IS_GCC=y
>>   # CONFIG_CC_IS_CLANG is not set
>>   # CONFIG_CC_HAS_OZ is not set
>>
>>   $ make CC=clang -s alldefconfig && tail -n 3 .config
>>   # CONFIG_CC_IS_GCC is not set
>>   CONFIG_CC_IS_CLANG=y
>>   CONFIG_CC_HAS_OZ=y
>>
>> A function call can appear anywhere a symbol reference can appear.
>> So, the following code is possible.
>>
>> Example code:
>>
>>   config CC_NAME
>>           string
>>           default "gcc" if $(shell $CC --version | grep -q gcc)
>>           default "clang" if $(shell $CC --version | grep -q clang)
>>           default "unknown compiler"
>>
>> Result:
>>
>>   $ make -s alldefconfig && tail -n 1 .config
>>   CONFIG_CC_NAME="gcc"
>>
>>   $ make CC=clang -s alldefconfig && tail -n 1 .config
>>   CONFIG_CC_NAME="clang"
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> ---
>>
>> Reminder for myself:
>> Update Documentation/kbuild/kconfig-language.txt
>>
>>
>>  scripts/kconfig/function.c  | 149 ++++++++++++++++++++++++++++++++++++++++++++
>>  scripts/kconfig/lkc_proto.h |   5 ++
>>  scripts/kconfig/util.c      |  46 +++++++++++---
>>  scripts/kconfig/zconf.l     |  38 ++++++++++-
>>  scripts/kconfig/zconf.y     |   9 +++
>>  5 files changed, 238 insertions(+), 9 deletions(-)
>>  create mode 100644 scripts/kconfig/function.c
>>
>> diff --git a/scripts/kconfig/function.c b/scripts/kconfig/function.c
>> new file mode 100644
>> index 0000000..60e59be
>> --- /dev/null
>> +++ b/scripts/kconfig/function.c
>> @@ -0,0 +1,149 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +//
>> +// Copyright (C) 2018 Masahiro Yamada <yamada.masahiro@...ionext.com>
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +
>> +#include "list.h"
>> +
>> +#define FUNCTION_MAX_ARGS            10
>> +
>> +static LIST_HEAD(function_list);
>> +
>> +struct function {
>> +     const char *name;
>> +     char *(*func)(int argc, char *argv[]);
>> +     struct list_head node;
>> +};
>> +
>> +static struct function *func_lookup(const char *name)
>> +{
>> +     struct function *f;
>> +
>> +     list_for_each_entry(f, &function_list, node) {
>> +             if (!strcmp(name, f->name))
>> +                     return f;
>> +     }
>> +
>> +     return NULL;
>> +}
>> +
>> +static void func_add(const char *name, char *(*func)(int argc, char *argv[]))
>> +{
>> +     struct function *f;
>> +
>> +     f = func_lookup(name);
>> +     if (f) {
>> +             fprintf(stderr, "%s: function already exists. ignored.\n", name);
>> +             return;
>> +     }
>> +
>> +     f = xmalloc(sizeof(*f));
>> +     f->name = name;
>> +     f->func = func;
>> +
>> +     list_add_tail(&f->node, &function_list);
>> +}
>> +
>> +static void func_del(struct function *f)
>> +{
>> +     list_del(&f->node);
>> +     free(f);
>> +}
>> +
>> +static char *func_call(int argc, char *argv[])
>> +{
>> +     struct function *f;
>> +
>> +     f = func_lookup(argv[0]);
>> +     if (!f) {
>> +             fprintf(stderr, "%s: function not found\n", argv[0]);
>> +             return NULL;
>> +     }
>> +
>> +     return f->func(argc, argv);
>> +}
>> +
>> +static char *func_eval(const char *func)
>> +{
>> +     char *expanded, *saveptr, *str, *token, *res;
>> +     const char *delim;
>> +     int argc = 0;
>> +     char *argv[FUNCTION_MAX_ARGS];
>> +
>> +     expanded = expand_string_value(func);
>> +
>> +     str = expanded;
>> +     delim = " ";
>> +
>> +     while ((token = strtok_r(str, delim, &saveptr))) {
>> +             argv[argc++] = token;
>> +             str = NULL;
>> +             delim = ",";
>> +     }
>> +
>> +     res = func_call(argc, argv);
>> +
>> +     free(expanded);
>> +
>> +     return res ?: xstrdup("");
>> +}
>> +
>> +char *func_eval_n(const char *func, size_t n)
>> +{
>> +     char *tmp, *res;
>> +
>> +     tmp = xmalloc(n + 1);
>> +     memcpy(tmp, func, n);
>> +     *(tmp + n) = '\0';
>> +
>> +     res = func_eval(tmp);
>> +
>> +     free(tmp);
>> +
>> +     return res;
>> +}
>> +
>> +/* built-in functions */
>> +static char *do_shell(int argc, char *argv[])
>> +{
>> +     static const char *pre = "(";
>> +     static const char *post = ") >/dev/null 2>&1";
>> +     char *cmd;
>> +     int ret;
>> +
>> +     if (argc != 2)
>> +             return NULL;
>> +
>> +     /*
>> +      * Surround the command with ( ) in case it is piped commands.
>> +      * Also, redirect stdout and stderr to /dev/null.
>> +      */
>> +     cmd = xmalloc(strlen(pre) + strlen(argv[1]) + strlen(post) + 1);
>> +     strcpy(cmd, pre);
>> +     strcat(cmd, argv[1]);
>> +     strcat(cmd, post);
>> +
>> +     ret = system(cmd);
>> +
>> +     free(cmd);
>> +
>> +     return xstrdup(ret == 0 ? "y" : "n");
>> +}
>> +
>> +void func_init(void)
>> +{
>> +     /* register built-in functions */
>> +     func_add("shell", do_shell);
>> +}
>> +
>> +void func_exit(void)
>> +{
>> +     struct function *f, *tmp;
>> +
>> +     /* unregister all functions */
>> +     list_for_each_entry_safe(f, tmp, &function_list, node)
>> +             func_del(f);
>> +}
>> diff --git a/scripts/kconfig/lkc_proto.h b/scripts/kconfig/lkc_proto.h
>> index 9884adc..09a4f53 100644
>> --- a/scripts/kconfig/lkc_proto.h
>> +++ b/scripts/kconfig/lkc_proto.h
>> @@ -48,5 +48,10 @@ const char * sym_get_string_value(struct symbol *sym);
>>
>>  const char * prop_get_type_name(enum prop_type type);
>>
>> +/* function.c */
>> +char *func_eval_n(const char *func, size_t n);
>> +void func_init(void);
>> +void func_exit(void);
>> +
>>  /* expr.c */
>>  void expr_print(struct expr *e, void (*fn)(void *, struct symbol *, const char *), void *data, int prevtoken);
>> diff --git a/scripts/kconfig/util.c b/scripts/kconfig/util.c
>> index dddf85b..ed89fb9 100644
>> --- a/scripts/kconfig/util.c
>> +++ b/scripts/kconfig/util.c
>> @@ -93,9 +93,10 @@ static char *env_expand_n(const char *name, size_t n)
>>  }
>>
>>  /*
>> - * Expand environments embedded in the string given in argument. Environments
>> - * to be expanded shall be prefixed by a '$'. Unknown environment expands to
>> - * the empty string.
>> + * Expand environments and functions embedded in the string given in argument.
>> + * Environments to be expanded shall be prefixed by a '$'. Functions to be
>> + * evaluated shall be surrounded by $(). Unknown environment/function expands
>> + * to the empty string.
>>   */
>>  char *expand_string_value(const char *in)
>>  {
>> @@ -113,11 +114,40 @@ char *expand_string_value(const char *in)
>>       while ((p = strchr(in, '$'))) {
>>               char *new;
>>
>> -             q = p + 1;
>> -             while (isalnum(*q) || *q == '_')
>> -                     q++;
>> -
>> -             new = env_expand_n(p + 1, q - p - 1);
>> +             /*
>> +              * If the next character is '(', it is a function.
>> +              * Otherwise, environment.
>> +              */
>> +             if (*(p + 1) == '(') {
>> +                     int nest = 0;
>> +
>> +                     q = p + 2;
>> +                     while (1) {
>> +                             if (*q == '\0') {
>> +                                     fprintf(stderr,
>> +                                             "unterminated function: %s\n",
>> +                                             p);
>> +                                     new = xstrdup("");
>> +                                     break;
>> +                             } else if (*q == '(') {
>> +                                     nest++;
>> +                             } else if (*q == ')') {
>> +                                     if (nest-- == 0) {
>> +                                             new = func_eval_n(p + 2,
>> +                                                               q - p - 2);
>> +                                             q++;
>> +                                             break;
>> +                                     }
>> +                             }
>> +                             q++;
>> +                     }
>> +             } else {
>> +                     q = p + 1;
>> +                     while (isalnum(*q) || *q == '_')
>> +                             q++;
>> +
>> +                     new = env_expand_n(p + 1, q - p - 1);
>> +             }
>>
>>               reslen = strlen(res) + (p - in) + strlen(new) + 1;
>>               res = xrealloc(res, reslen);
>> diff --git a/scripts/kconfig/zconf.l b/scripts/kconfig/zconf.l
>> index 0d89ea6..f433ab0 100644
>> --- a/scripts/kconfig/zconf.l
>> +++ b/scripts/kconfig/zconf.l
>> @@ -1,7 +1,7 @@
>>  %option nostdinit noyywrap never-interactive full ecs
>>  %option 8bit nodefault perf-report perf-report
>>  %option noinput
>> -%x COMMAND HELP STRING PARAM
>> +%x COMMAND HELP STRING PARAM FUNCTION
>>  %{
>>  /*
>>   * Copyright (C) 2002 Roman Zippel <zippel@...ux-m68k.org>
>> @@ -25,6 +25,7 @@ static struct {
>>
>>  static char *text;
>>  static int text_size, text_asize;
>> +static int function_nest;
>>
>>  struct buffer {
>>       struct buffer *parent;
>> @@ -138,6 +139,12 @@ n        [$A-Za-z0-9_-]
>>               new_string();
>>               BEGIN(STRING);
>>       }
>> +     "$("    {
>> +             new_string();
>> +             append_string(yytext, yyleng);
>> +             function_nest = 0;
>> +             BEGIN(FUNCTION);
>> +     }
>>       \n      BEGIN(INITIAL); current_file->lineno++; return T_EOL;
>>       ({n}|[/.])+     {
>>               const struct kconf_id *id = kconf_id_lookup(yytext, yyleng);
>> @@ -196,6 +203,35 @@ n        [$A-Za-z0-9_-]
>>       }
>>  }
>>
>> +<FUNCTION>{
>> +     [^()\n]* {
>> +             append_string(yytext, yyleng);
>> +     }
>> +     "(" {
>> +             append_string(yytext, yyleng);
>> +             function_nest++;
>> +     }
>> +     ")" {
>> +             append_string(yytext, yyleng);
>> +             if (function_nest-- == 0) {
>> +                     BEGIN(PARAM);
>> +                     yylval.string = text;
>> +                     return T_WORD;
>
> T_WORD_QUOTE (which would turn into a constant symbol in most contexts)
> would be better here, IMO. That would turn $(foo) into just an alias for
> "$(foo)".
>
> See below.
>
>> +             }
>> +     }
>> +     \n {
>> +             fprintf(stderr,
>> +                     "%s:%d:warning: multi-line function not supported\n",
>> +                     zconf_curname(), zconf_lineno());
>> +             current_file->lineno++;
>> +             BEGIN(INITIAL);
>> +             return T_EOL;
>> +     }
>> +     <<EOF>> {
>> +             BEGIN(INITIAL);
>> +     }
>> +}
>> +
>>  <HELP>{
>>       [ \t]+  {
>>               ts = 0;
>> diff --git a/scripts/kconfig/zconf.y b/scripts/kconfig/zconf.y
>> index 784083d..d9977de 100644
>> --- a/scripts/kconfig/zconf.y
>> +++ b/scripts/kconfig/zconf.y
>> @@ -534,11 +534,19 @@ void conf_parse(const char *name)
>>
>>       zconf_initscan(name);
>>
>> +     func_init();
>>       _menu_init();
>>
>>       if (getenv("ZCONF_DEBUG"))
>>               yydebug = 1;
>>       yyparse();
>> +
>> +     /*
>> +      * Currently, functions are evaluated only when Kconfig files are
>> +      * parsed. We can free functions here.
>> +      */
>> +     func_exit();
>> +
>>       if (yynerrs)
>>               exit(1);
>>       if (!modules_sym)
>> @@ -778,4 +786,5 @@ void zconfdump(FILE *out)
>>  #include "confdata.c"
>>  #include "expr.c"
>>  #include "symbol.c"
>> +#include "function.c"
>>  #include "menu.c"
>> --
>> 2.7.4
>>
>
> Here's a simplification idea I'm throwing out there:
>
> What about only allowing $ENV and $() within quotes, and just having
> them always do simple text substitution (so that they'd indirectly
> always generate T_WORD_QUOTE tokens)?


I ended up with a new state <FUNCTION>,
but the real problem is the lexer is too ugly.

So, maybe, the solution is not to make it into a string,
but to re-write the lexer.


<STRING> and <FUNCTION> are almost the same in the sense
that whitespaces do not split tokens.

The difference is the characters to start/end with.

  ' ... '
  " ... "
  ( ... )

If we encounter with the 3 special characters,  ' , '', (,
then we enter into <STRING> state,
then it ends with ', ", ), respectively.
(but we need to take care of nesting, escaping)

Double-surrounding like  "$(cc-option -Oz)"
looks ugly to me.





> Pros:
>
>  - Zero new syntax outside of strings (until the macro stuff).
>
>  - Makes the behavior and limitations of the syntax obvious: You can't
>    have $(foo) expand to a full expression, only to (possibly part of) a
>    value. This is a good limitation, IMO, and it's already there.
>
>  - Super simple and straightforward Kconfig implementation. All the new
>    magic would happen in expand_string_value().
>
> Neutral:
>
>  - Just as general where it matters. Take something like
>
>      default "$(foo)"
>
>    If $(foo) happens to expand to "y", then that will do its usual thing
>    for a bool/tristate symbol. Same for string symbols, etc. It'd just
>    be a thin preprocessing step on constant symbol values.
>
>  - The only loss in generality would be that you can no longer have
>    a function expand to the name of non-constant symbol. For example,
>    take the following:
>
>         default $(foo)
>
>    If $(foo) expands to MY_SYMBOL, then that would work as
>
>         default MY_SYMBOL


Probably, this is a "do not do this".


If the symbol is 'int' type,
and  $MY_NUMBER is expanded to 1,
it is our intention.





>   (I.e., it would default to the value of the symbol MY_SYMBOL.)
>
>   With the quotes, it would instead work as
>
>      default "MY_SYMBOL"
>
>   IMO, the second version is less confusing, and deliberately using the
>   first version seems like a bad idea (there's likely to be cleaner ways
>   to do the indirection in plain Kconfig).
>
>   This is also why I think T_WORD_QUOTE is better in the code above. It
>   would make $(foo) work more like a shorthand for "$(foo)".
>
>
> Cons:
>
>  - Bit more typing to add the quotes
>
>  - Maybe it isn't widely known that "n", "m", "y" work just like n, m, y
>    for bool and tristate symbols (the latter automatically get converted
>    to the former), though you see them quite a lot in Kconfig files.

Not only bool/tristate, but also int/hex.
"1" is equivalent to 1.


Kconfig is screwed up in handling of literals.


>    ("n", "foo bar", etc., are all just constant symbols. Kconfig keeps
>    track of them separately from non-constant symbols. The constant
>    symbols "n", "m", and "y" are predefined.)
>
>    If we go with obligatory quotes, I volunteer to explain things in
>    kconfig-language.txt at least, to make it clear why you'd see quotes
>    in bool/tristate symbols using $(shell). I suspect it wouldn't be
>    that tricky to figure out anyway.


I think the right thing to do is
to fix the code instead of advertising it.






> What do you think?
>
> Cheers,
> Ulf
> --
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-- 
Best Regards
Masahiro Yamada

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