kconfig: reference environment variables directly and remove 'option env='

To get access to environment variables, Kconfig needs to define a
symbol using "option env=" syntax.  It is tedious to add a symbol entry
for each environment variable given that we need to define much more
such as 'CC', 'AS', 'srctree' etc. to evaluate the compiler capability
in Kconfig.

Adding '$' for symbol references is grammatically inconsistent.
Looking at the code, the symbols prefixed with 'S' are expanded by:
 - conf_expand_value()
   This is used to expand 'arch/$ARCH/defconfig' and 'defconfig_list'
 - sym_expand_string_value()
   This is used to expand strings in 'source' and 'mainmenu'

All of them are fixed values independent of user configuration.  So,
they can be changed into the direct expansion instead of symbols.

This change makes the code much cleaner.  The bounce symbols 'SRCARCH',
'ARCH', 'SUBARCH', 'KERNELVERSION' are gone.

sym_init() hard-coding 'UNAME_RELEASE' is also gone.  'UNAME_RELEASE'
should be replaced with an environment variable.

ARCH_DEFCONFIG is a normal symbol, so it should be simply referenced
without '$' prefix.

The new syntax is addicted by Make.  The variable reference needs
parentheses, like $(FOO), but you can omit them for single-letter
variables, like $F.  Yet, in Makefiles, people tend to use the
parenthetical form for consistency / clarification.

At this moment, only the environment variable is supported, but I will
extend the concept of 'variable' later on.

The variables are expanded in the lexer so we can simplify the token
handling on the parser side.

For example, the following code works.

[Example code]

  config MY_TOOLCHAIN_LIST
          string
          default "My tools: CC=$(CC), AS=$(AS), CPP=$(CPP)"

[Result]

  $ make -s alldefconfig && tail -n 1 .config
  CONFIG_MY_TOOLCHAIN_LIST="My tools: CC=gcc, AS=as, CPP=gcc -E"

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

1 files changed, 238 insertions, 0 deletions

diff --git a/scripts/kconfig/preprocess.c b/scripts/kconfig/preprocess.c
new file mode 100644
index 000000000000..a2eb2eb02929
--- /dev/null
+++ b/scripts/kconfig/preprocess.c
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (C) 2018 Masahiro Yamada <yamada.masahiro@socionext.com>
+
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "list.h"
+
+static void __attribute__((noreturn)) pperror(const char *format, ...)
+{
+        va_list ap;
+
+        fprintf(stderr, "%s:%d: ", current_file->name, yylineno);
+        va_start(ap, format);
+        vfprintf(stderr, format, ap);
+        va_end(ap);
+        fprintf(stderr, "\n");
+
+        exit(1);
+}
+
+/*
+ * Environment variables
+ */
+static LIST_HEAD(env_list);
+
+struct env {
+        char *name;
+        char *value;
+        struct list_head node;
+};
+
+static void env_add(const char *name, const char *value)
+{
+        struct env *e;
+
+        e = xmalloc(sizeof(*e));
+        e->name = xstrdup(name);
+        e->value = xstrdup(value);
+
+        list_add_tail(&e->node, &env_list);
+}
+
+static void env_del(struct env *e)
+{
+        list_del(&e->node);
+        free(e->name);
+        free(e->value);
+        free(e);
+}
+
+/* The returned pointer must be freed when done */
+static char *env_expand(const char *name)
+{
+        struct env *e;
+        const char *value;
+
+        if (!*name)
+                return NULL;
+
+        list_for_each_entry(e, &env_list, node) {
+                if (!strcmp(name, e->name))
+                        return xstrdup(e->value);
+        }
+
+        value = getenv(name);
+        if (!value)
+                return NULL;
+
+        /*
+         * We need to remember all referenced environment variables.
+         * They will be written out to include/config/auto.conf.cmd
+         */
+        env_add(name, value);
+
+        return xstrdup(value);
+}
+
+void env_write_dep(FILE *f, const char *autoconfig_name)
+{
+        struct env *e, *tmp;
+
+        list_for_each_entry_safe(e, tmp, &env_list, node) {
+                fprintf(f, "ifneq \"$(%s)\" \"%s\"\n", e->name, e->value);
+                fprintf(f, "%s: FORCE\n", autoconfig_name);
+                fprintf(f, "endif\n");
+                env_del(e);
+        }
+}
+
+static char *eval_clause(const char *str, size_t len)
+{
+        char *tmp, *name, *res;
+
+        tmp = xstrndup(str, len);
+
+        name = expand_string(tmp);
+
+        res = env_expand(name);
+        if (res)
+                goto free;
+
+        res = xstrdup("");
+free:
+        free(name);
+        free(tmp);
+
+        return res;
+}
+
+/*
+ * Expand a string that follows '$'
+ *
+ * For example, if the input string is
+ *     ($(FOO)$($(BAR)))$(BAZ)
+ * this helper evaluates
+ *     $($(FOO)$($(BAR)))
+ * and returns a new string containing the expansion (note that the string is
+ * recursively expanded), also advancing 'str' to point to the next character
+ * after the corresponding closing parenthesis, in this case, *str will be
+ *     $(BAR)
+ */
+char *expand_dollar(const char **str)
+{
+        const char *p = *str;
+        const char *q;
+        int nest = 0;
+
+        /*
+         * In Kconfig, variable references always start with "$(".
+         * Neither single-letter variables as in $A nor curly braces as in ${CC}
+         * are supported.  '$' not followed by '(' loses its special meaning.
+         */
+        if (*p != '(') {
+                *str = p;
+                return xstrdup("$");
+        }
+
+        p++;
+        q = p;
+        while (*q) {
+                if (*q == '(') {
+                        nest++;
+                } else if (*q == ')') {
+                        if (nest-- == 0)
+                                break;
+                }
+                q++;
+        }
+
+        if (!*q)
+                pperror("unterminated reference to '%s': missing ')'", p);
+
+        /* Advance 'str' to after the expanded initial portion of the string */
+        *str = q + 1;
+
+        return eval_clause(p, q - p);
+}
+
+static char *__expand_string(const char **str, bool (*is_end)(char c))
+{
+        const char *in, *p;
+        char *expansion, *out;
+        size_t in_len, out_len;
+
+        out = xmalloc(1);
+        *out = 0;
+        out_len = 1;
+
+        p = in = *str;
+
+        while (1) {
+                if (*p == '$') {
+                        in_len = p - in;
+                        p++;
+                        expansion = expand_dollar(&p);
+                        out_len += in_len + strlen(expansion);
+                        out = xrealloc(out, out_len);
+                        strncat(out, in, in_len);
+                        strcat(out, expansion);
+                        free(expansion);
+                        in = p;
+                        continue;
+                }
+
+                if (is_end(*p))
+                        break;
+
+                p++;
+        }
+
+        in_len = p - in;
+        out_len += in_len;
+        out = xrealloc(out, out_len);
+        strncat(out, in, in_len);
+
+        /* Advance 'str' to the end character */
+        *str = p;
+
+        return out;
+}
+
+static bool is_end_of_str(char c)
+{
+        return !c;
+}
+
+/*
+ * Expand variables in the given string.  Undefined variables
+ * expand to an empty string.
+ * The returned string must be freed when done.
+ */
+char *expand_string(const char *in)
+{
+        return __expand_string(&in, is_end_of_str);
+}
+
+static bool is_end_of_token(char c)
+{
+        /* Why are '.' and '/' valid characters for symbols? */
+        return !(isalnum(c) || c == '_' || c == '-' || c == '.' || c == '/');
+}
+
+/*
+ * Expand variables in a token.  The parsing stops when a token separater
+ * (in most cases, it is a whitespace) is encountered.  'str' is updated to
+ * point to the next character.
+ *
+ * The returned string must be freed when done.
+ */
+char *expand_one_token(const char **str)
+{
+        return __expand_string(str, is_end_of_token);
+}