Re: [PATCH v2 07/21] kconfig: add function support and implement 'shell' function

From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Ulf Magnusson <ulfalizer@gmail.com>
Cc: Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Sam Ravnborg <sam@ravnborg.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Luis R . Rodriguez" <mcgrof@kernel.org>,
	Nicolas Pitre <nico@linaro.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 07/21] kconfig: add function support and implement 'shell' function
Date: Fri, 13 Apr 2018 14:37:22 +0900	[thread overview]
Message-ID: <CAK7LNAQg7KvXe_of+emcti_e--xtzpdxmbQkwV_r2hRGTh1p3w@mail.gmail.com> (raw)
In-Reply-To: <CAFkk2KQn2TQ8iRqNQADN2WgYGchMaZ-pA7dyT_qmPb1Ed5pS2Q@mail.gmail.com>

2018-04-01 13:19 GMT+09:00 Ulf Magnusson <ulfalizer@gmail.com>:
> On Tue, Mar 27, 2018 at 7:29 AM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> This commit adds a new concept 'function' to do more text processing
>> in Kconfig.
>>
>> A function call looks like this:
>>
>>   $(function arg1, arg2, arg3, ...)
>>
>> (Actually, this syntax was inspired by make.)
>>
>> Real examples will look like this:
>>
>>   $(shell echo hello world)
>>   $(cc-option -fstackprotector)
>>
>> This commit adds the basic infrastructure to add, delete, evaluate
>> functions, and also the first built-in function $(shell ...).  This
>> accepts a single command to execute.  It returns the standard output
>> from it.
>>
>> [Example code]
>>
>>   config HELLO
>>           string
>>           default "$(shell echo hello world)"
>>
>>   config Y
>>           def_bool $(shell echo y)
>>
>> [Result]
>>
>>   $ make -s alldefconfig && tail -n 2 .config
>>   CONFIG_HELLO="hello world"
>>   CONFIG_Y=y
>>
>> Caveat:
>> Like environments, functions are expanded in the lexer.  You cannot
>> pass symbols to function arguments.  This is a limitation to simplify
>> the implementation.  I want to avoid the dynamic function evaluation,
>> which would introduce much more complexity.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> ---
>>
>> Reminder for myself:
>> Update Documentation/kbuild/kconfig-language.txt
>>
>>
>> Changes in v2:
>>   - Use 'shell' for getting stdout from the comment.
>>     It was 'shell-stdout' in the previous version.
>>   - Symplify the implementation since the expansion has been moved to
>>     lexer.
>>
>>  scripts/kconfig/function.c  | 170 ++++++++++++++++++++++++++++++++++++++++++++
>>  scripts/kconfig/lkc_proto.h |   5 ++
>>  scripts/kconfig/util.c      |  46 +++++++++---
>>  scripts/kconfig/zconf.y     |   9 +++
>>  4 files changed, 222 insertions(+), 8 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..913685f
>> --- /dev/null
>> +++ b/scripts/kconfig/function.c
>> @@ -0,0 +1,170 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +//
>> +// Copyright (C) 2018 Masahiro Yamada <yamada.masahiro@socionext.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 {
>> +       char *name;
>> +       char *(*func)(struct function *f, 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)(struct function *f, 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 = xstrdup(name);
>> +       f->func = func;
>> +
>> +       list_add_tail(&f->node, &function_list);
>> +}
>> +
>> +static void func_del(struct function *f)
>> +{
>> +       list_del(&f->node);
>> +       free(f->name);
>> +       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(f, 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;
>
> Would be nice to error out if the array is overstepped.

In V3, I made this a feature.

>> +               str = NULL;
>> +               delim = ",";
>> +       }
>> +
>> +       res = func_call(argc, argv);
>> +
>> +       free(expanded);
>> +
>> +       return res ?: xstrdup("");
>> +}
>
> Since only 'macro' will take multiple parameters, I wonder if it might
> be better to implement the argument parsing there, and simply pass the
> string (minus the function name) as-is to functions.

I may add more built-in functions in the future.
For example, I want to add 'if' function, which takes two or three arguments.

> You would then be able to have ',' in shell commands, which might be
> required -- think gcc -Wl,option and the like.

I fixed 'shell' function in v3.

>> +
>> +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(struct function *f, int argc, char *argv[])
>> +{
>> +       static const char *pre = "(";
>> +       static const char *post = ") 2>/dev/null";
>
> Arrays seem neater, since the pointers aren't needed.
>
>> +       FILE *p;
>> +       char buf[256];
>> +       char *cmd;
>> +       int ret;
>
> Could get rid of 'ret' and just do
>
>     if (pclose(p) == -1)
>         perror(cmd);

Done.

>> +
>> +       if (argc != 2)
>> +               return NULL;
>> +
>> +       /*
>> +        * Surround the command with ( ) in case it is piped commands.
>> +        * Also, redirect stderr to /dev/null.
>> +        */
>> +       cmd = xmalloc(strlen(pre) + strlen(argv[1]) + strlen(post) + 1);
>> +       strcpy(cmd, pre);
>> +       strcat(cmd, argv[1]);
>> +       strcat(cmd, post);
>> +
>> +       p = popen(cmd, "r");
>> +       if (!p) {
>> +               perror(cmd);
>> +               goto free;
>> +       }
>> +       if (fgets(buf, sizeof(buf), p)) {
>> +               size_t len = strlen(buf);
>> +
>> +               if (buf[len - 1] == '\n')
>> +                       buf[len - 1] = '\0';
>> +       } else {
>> +               buf[0] = '\0';
>> +       }
>> +
>> +       ret = pclose(p);
>> +       if (ret == -1)
>> +               perror(cmd);
>> +
>> +free:
>> +       free(cmd);
>> +
>> +       return xstrdup(buf);
>> +}
>> +
>> +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 3d27c49..218b051 100644
>> --- a/scripts/kconfig/util.c
>> +++ b/scripts/kconfig/util.c
>> @@ -13,9 +13,10 @@
>>  #include "lkc.h"
>>
>>  /*
>> - * 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 $(). Unknown environment/function expands
>> + * to the empty string.
>>   */
>>  char *expand_string_value(const char *in)
>>  {
>> @@ -33,11 +34,40 @@ char *expand_string_value(const char *in)
>>         while ((p = strchr(in, '$'))) {
>>                 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++;
>> +                       }
>
> A loop like this might work too:
>
>     q = p + 1;
>     do {
>         if (*q == '\0') {
>             *error*
>             val = ...
>             goto error;
>         }
>
>         if (*q == '(')
>             nest++;
>         if (*q == ')')
>             nest--;
>         q++;
>     } while (nest > 0);
>
>     val = func_eval_n(...)
> error:
>
>> +               } 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.y b/scripts/kconfig/zconf.y
>> index d8120c7..feaea18 100644
>> --- a/scripts/kconfig/zconf.y
>> +++ b/scripts/kconfig/zconf.y
>> @@ -520,11 +520,19 @@ 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)
>> @@ -765,4 +773,5 @@ void zconfdump(FILE *out)
>>  #include "confdata.c"
>>  #include "expr.c"
>>  #include "symbol.c"
>> +#include "function.c"
>>  #include "menu.c"
>> --
>> 2.7.4
>>
>
> Cheers,
> Ulf
> --
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-- 
Best Regards
Masahiro Yamada