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From:   Ulf Magnusson <ulfalizer@gmail.com>
Date:   Thu, 29 Mar 2018 19:38:15 +0200
Message-ID: <CAFkk2KSRSVm-E-b_=FrQT=vakQDepuX=YYPDFrbN46UscY7soQ@mail.gmail.com>
Subject: Re: [PATCH v2 04/21] kconfig: reference environments directly and
 remove 'option env=' syntax
To:     Masahiro Yamada <yamada.masahiro@socionext.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>,
        Ingo Molnar <mingo@redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Thu, Mar 29, 2018 at 4:56 AM, Ulf Magnusson <ulfalizer@gmail.com> wrote:
> On Thu, Mar 29, 2018 at 4:19 AM, Ulf Magnusson <ulfalizer@gmail.com> wrote:
>> I've been kinda busy lately, so that's why I disappeared.
>>
>> I'll try to go over this patchset in more detail over the weekend.
>>
>> On Tue, Mar 27, 2018 at 7:29 AM, Masahiro Yamada
>> <yamada.masahiro@socionext.com> wrote:
>>> To get an environment value, Kconfig needs to define a symbol using
>>> "option env=" syntax.  It is tedious to add a config entry for each
>>> environment given that we need more environments such as 'CC', 'AS',
>>> 'srctree' etc. to evaluate the compiler capability in Kconfig.
>>>
>>> Adding '$' to symbols is weird.  Kconfig can reference symbols directly
>>> like this:
>>>
>>>   config FOO
>>>           string
>>>           default BAR
>>>
>>> So, I want to use the following syntax to get environment 'BAR' from
>>> the system:
>>>
>>>   config FOO
>>>           string
>>>           default $BAR
>>>
>>> Looking at the code, the symbols prefixed with 'S' are expanded by:
>>>  - conf_expand_value()
>>>    This is used to expand 'arch/$ARCH/defconfig' and 'defconfig_list'
>>>  - expand_string_value()
>>>    This is used to expand strings in 'source' and 'mainmenu'
>>>
>>> All of them are fixed values independent of user configuration.  So,
>>> this kind of syntax should be moved to simply take the environment.
>>>
>>> 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 be given from the environment.
>>>
>>> ARCH_DEFCONFIG is a normal symbol, so it should be simply referenced
>>> by 'default ARCH_DEFCONFIG'.
>>>
>>> The environments are expanding in the lexer; when '$' is encountered,
>>> it is expanded, and resulted strings are pushed back to the input
>>> stream.  This makes the implementation simpler.
>>>
>>> For example, the following code works.
>>>
>>> [Example code]
>>>
>>>   config TOOLCHAIN_LIST
>>>           string
>>>           default "My tools: CC=$CC, AS=$AS, CPP=$CPP"
>>>
>>> [Result]
>>>
>>>   $ make -s alldefconfig && tail -n 1 .config
>>>   CONFIG_TOOLCHAIN_LIST="My tools: CC=gcc, AS=as, CPP=gcc -E"
>>>
>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>>> ---
>>>
>>> I tested all 'make *config' for arch architectures.
>>> I confirmed this commit still produced the same result
>>> (by my kconfig test tool).
>>>
>>>
>>> Changes in v2:
>>>   - Move the string expansion to the lexer phase.
>>>   - Split environment helpers to env.c
>>>
>>>  Documentation/kbuild/kconfig-language.txt |  8 ---
>>>  Kconfig                                   |  4 --
>>>  Makefile                                  |  3 +-
>>>  arch/sh/Kconfig                           |  4 +-
>>>  arch/sparc/Kconfig                        |  4 +-
>>>  arch/tile/Kconfig                         |  2 +-
>>>  arch/um/Kconfig.common                    |  4 --
>>>  arch/x86/Kconfig                          |  4 +-
>>>  arch/x86/um/Kconfig                       |  4 +-
>>>  init/Kconfig                              | 10 +---
>>>  scripts/kconfig/confdata.c                | 31 +---------
>>>  scripts/kconfig/env.c                     | 95 +++++++++++++++++++++++++++++++
>>>  scripts/kconfig/kconf_id.c                |  1 -
>>>  scripts/kconfig/lkc.h                     |  8 +--
>>>  scripts/kconfig/menu.c                    |  3 -
>>>  scripts/kconfig/symbol.c                  | 56 ------------------
>>>  scripts/kconfig/util.c                    | 75 ++++++++----------------
>>>  scripts/kconfig/zconf.l                   | 20 ++++++-
>>>  scripts/kconfig/zconf.y                   |  2 +-
>>>  19 files changed, 158 insertions(+), 180 deletions(-)
>>>  create mode 100644 scripts/kconfig/env.c
>>>
>>> diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
>>> index f5b9493..0e966e8 100644
>>> --- a/Documentation/kbuild/kconfig-language.txt
>>> +++ b/Documentation/kbuild/kconfig-language.txt
>>> @@ -198,14 +198,6 @@ applicable everywhere (see syntax).
>>>      enables the third modular state for all config symbols.
>>>      At most one symbol may have the "modules" option set.
>>>
>>> -  - "env"=<value>
>>> -    This imports the environment variable into Kconfig. It behaves like
>>> -    a default, except that the value comes from the environment, this
>>> -    also means that the behaviour when mixing it with normal defaults is
>>> -    undefined at this point. The symbol is currently not exported back
>>> -    to the build environment (if this is desired, it can be done via
>>> -    another symbol).
>>> -
>>>    - "allnoconfig_y"
>>>      This declares the symbol as one that should have the value y when
>>>      using "allnoconfig". Used for symbols that hide other symbols.
>>> diff --git a/Kconfig b/Kconfig
>>> index 8c4c1cb..e6ece5b 100644
>>> --- a/Kconfig
>>> +++ b/Kconfig
>>> @@ -5,8 +5,4 @@
>>>  #
>>>  mainmenu "Linux/$ARCH $KERNELVERSION Kernel Configuration"
>>>
>>> -config SRCARCH
>>> -       string
>>> -       option env="SRCARCH"
>>> -
>>>  source "arch/$SRCARCH/Kconfig"
>>> diff --git a/Makefile b/Makefile
>>> index 5c395ed..4ae1486 100644
>>> --- a/Makefile
>>> +++ b/Makefile
>>> @@ -284,7 +284,8 @@ include scripts/Kbuild.include
>>>  # Read KERNELRELEASE from include/config/kernel.release (if it exists)
>>>  KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
>>>  KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
>>> -export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
>>> +UNAME_RELEASE := $(shell uname --release)
>>> +export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION UNAME_RELEASE
>>>
>>>  # SUBARCH tells the usermode build what the underlying arch is.  That is set
>>>  # first, and if a usermode build is happening, the "ARCH=um" on the command
>>> diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
>>> index 97fe293..14f3ef1 100644
>>> --- a/arch/sh/Kconfig
>>> +++ b/arch/sh/Kconfig
>>> @@ -57,7 +57,7 @@ config SUPERH
>>>           <http://www.linux-sh.org/>.
>>>
>>>  config SUPERH32
>>> -       def_bool ARCH = "sh"
>>> +       def_bool "$ARCH" = "sh"
>>>         select HAVE_KPROBES
>>>         select HAVE_KRETPROBES
>>>         select HAVE_IOREMAP_PROT if MMU && !X2TLB
>>> @@ -76,7 +76,7 @@ config SUPERH32
>>>         select HAVE_CC_STACKPROTECTOR
>>>
>>>  config SUPERH64
>>> -       def_bool ARCH = "sh64"
>>> +       def_bool "$ARCH" = "sh64"
>>>         select HAVE_EXIT_THREAD
>>>         select KALLSYMS
>>>
>>> diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
>>> index 8767e45..86b852e 100644
>>> --- a/arch/sparc/Kconfig
>>> +++ b/arch/sparc/Kconfig
>>> @@ -1,6 +1,6 @@
>>>  config 64BIT
>>> -       bool "64-bit kernel" if ARCH = "sparc"
>>> -       default ARCH = "sparc64"
>>> +       bool "64-bit kernel" if "$ARCH" = "sparc"
>>> +       default "$ARCH" = "sparc64"
>>>         help
>>>           SPARC is a family of RISC microprocessors designed and marketed by
>>>           Sun Microsystems, incorporated.  They are very widely found in Sun
>>> diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
>>> index ef9d403..acc2182 100644
>>> --- a/arch/tile/Kconfig
>>> +++ b/arch/tile/Kconfig
>>> @@ -119,7 +119,7 @@ config HVC_TILE
>>>  # Building with ARCH=tilegx (or ARCH=tile) implies using the
>>>  # 64-bit TILE-Gx toolchain, so force CONFIG_TILEGX on.
>>>  config TILEGX
>>> -       def_bool ARCH != "tilepro"
>>> +       def_bool "$ARCH" != "tilepro"
>>>         select ARCH_SUPPORTS_ATOMIC_RMW
>>>         select GENERIC_IRQ_LEGACY_ALLOC_HWIRQ
>>>         select HAVE_ARCH_JUMP_LABEL
>>> diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
>>> index c68add8..07f84c8 100644
>>> --- a/arch/um/Kconfig.common
>>> +++ b/arch/um/Kconfig.common
>>> @@ -54,10 +54,6 @@ config HZ
>>>         int
>>>         default 100
>>>
>>> -config SUBARCH
>>> -       string
>>> -       option env="SUBARCH"
>>> -
>>>  config NR_CPUS
>>>         int
>>>         range 1 1
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 0fa71a7..986fb0a 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -1,8 +1,8 @@
>>>  # SPDX-License-Identifier: GPL-2.0
>>>  # Select 32 or 64 bit
>>>  config 64BIT
>>> -       bool "64-bit kernel" if ARCH = "x86"
>>> -       default ARCH != "i386"
>>> +       bool "64-bit kernel" if "$ARCH" = "x86"
>>> +       default "$ARCH" != "i386"
>>>         ---help---
>>>           Say yes to build a 64-bit kernel - formerly known as x86_64
>>>           Say no to build a 32-bit kernel - formerly known as i386
>>> diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
>>> index 13ed827..d355413 100644
>>> --- a/arch/x86/um/Kconfig
>>> +++ b/arch/x86/um/Kconfig
>>> @@ -16,8 +16,8 @@ config UML_X86
>>>         select GENERIC_FIND_FIRST_BIT
>>>
>>>  config 64BIT
>>> -       bool "64-bit kernel" if SUBARCH = "x86"
>>> -       default SUBARCH != "i386"
>>> +       bool "64-bit kernel" if $SUBARCH = "x86"
>>> +       default $SUBARCH != "i386"
>>>
>>>  config X86_32
>>>         def_bool !64BIT
>>> diff --git a/init/Kconfig b/init/Kconfig
>>> index df18492..b4814e6 100644
>>> --- a/init/Kconfig
>>> +++ b/init/Kconfig
>>> @@ -1,11 +1,3 @@
>>> -config ARCH
>>> -       string
>>> -       option env="ARCH"
>>> -
>>> -config KERNELVERSION
>>> -       string
>>> -       option env="KERNELVERSION"
>>> -
>>>  config DEFCONFIG_LIST
>>>         string
>>>         depends on !UML
>>> @@ -13,7 +5,7 @@ config DEFCONFIG_LIST
>>>         default "/lib/modules/$UNAME_RELEASE/.config"
>>>         default "/etc/kernel-config"
>>>         default "/boot/config-$UNAME_RELEASE"
>>> -       default "$ARCH_DEFCONFIG"
>>> +       default ARCH_DEFCONFIG
>>>         default "arch/$ARCH/defconfig"
>>>
>>>  config CONSTRUCTORS
>>> diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
>>> index df26c7b..98c2014 100644
>>> --- a/scripts/kconfig/confdata.c
>>> +++ b/scripts/kconfig/confdata.c
>>> @@ -81,39 +81,13 @@ const char *conf_get_autoconfig_name(void)
>>>         return name ? name : "include/config/auto.conf";
>>>  }
>>>
>>> -static char *conf_expand_value(const char *in)
>>> -{
>>> -       struct symbol *sym;
>>> -       const char *src;
>>> -       static char res_value[SYMBOL_MAXLENGTH];
>>> -       char *dst, name[SYMBOL_MAXLENGTH];
>>> -
>>> -       res_value[0] = 0;
>>> -       dst = name;
>>> -       while ((src = strchr(in, '$'))) {
>>> -               strncat(res_value, in, src - in);
>>> -               src++;
>>> -               dst = name;
>>> -               while (isalnum(*src) || *src == '_')
>>> -                       *dst++ = *src++;
>>> -               *dst = 0;
>>> -               sym = sym_lookup(name, 0);
>>> -               sym_calc_value(sym);
>>> -               strcat(res_value, sym_get_string_value(sym));
>>> -               in = src;
>>> -       }
>>> -       strcat(res_value, in);
>>> -
>>> -       return res_value;
>>> -}
>>> -
>>>  char *conf_get_default_confname(void)
>>>  {
>>>         struct stat buf;
>>>         static char fullname[PATH_MAX+1];
>>>         char *env, *name;
>>>
>>> -       name = conf_expand_value(conf_defname);
>>> +       name = expand_string_value(conf_defname);
>>>         env = getenv(SRCTREE);
>>>         if (env) {
>>>                 sprintf(fullname, "%s/%s", env, name);
>>> @@ -274,7 +248,8 @@ int conf_read_simple(const char *name, int def)
>>>                         if (expr_calc_value(prop->visible.expr) == no ||
>>>                             prop->expr->type != E_SYMBOL)
>>>                                 continue;
>>> -                       name = conf_expand_value(prop->expr->left.sym->name);
>>> +                       sym_calc_value(prop->expr->left.sym);
>>> +                       name = sym_get_string_value(prop->expr->left.sym);
>>>                         in = zconf_fopen(name);
>>>                         if (in) {
>>>                                 conf_message(_("using defaults found in %s"),
>>> diff --git a/scripts/kconfig/env.c b/scripts/kconfig/env.c
>>> new file mode 100644
>>> index 0000000..9702f5c
>>> --- /dev/null
>>> +++ b/scripts/kconfig/env.c
>>> @@ -0,0 +1,95 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +//
>>> +// Copyright (C) 2018 Masahiro Yamada <yamada.masahiro@socionext.com>
>>> +
>>> +static LIST_HEAD(env_list);
>>> +
>>> +struct env {
>>> +       char *name;
>>> +       char *value;
>>> +       struct list_head node;
>>> +};
>>> +
>>> +static struct env *env_list_lookup(const char *name)
>>> +{
>>> +       struct env *e;
>>> +
>>> +       list_for_each_entry(e, &env_list, node) {
>>> +               if (!strcmp(name, e->name))
>>> +                       return e;
>>> +       }
>>> +
>>> +       return NULL;
>>> +}
>>> +
>>> +static void env_list_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_list_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;
>>> +
>>> +       e = env_list_lookup(name);
>>> +       if (e)
>>> +               return xstrdup(e->value);
>>> +
>>> +       value = getenv(name);
>>> +       if (!value) {
>>> +               fprintf(stderr, "environment variable \"%s\" undefined\n", name);
>>> +               value = "";
>>> +       }
>>> +
>>> +       /*
>>> +        * we need to remember all referenced environments.
>>> +        * They will be written out to include/config/auto.conf.cmd
>>> +        */
>>> +       env_list_add(name, value);
>>> +
>>> +       return xstrdup(value);
>>> +}
>>> +
>>> +/* works like env_expand, but 'name' does not need to be null-terminated */
>>> +char *env_expand_n(const char *name, size_t n)
>>> +{
>>> +       char *tmp, *res;
>>> +
>>> +       tmp = xmalloc(n + 1);
>>> +       memcpy(tmp, name, n);
>>> +       *(tmp + n) = '\0';
>>> +
>>> +       res = env_expand(tmp);
>>> +
>>> +       free(tmp);
>>> +
>>> +       return res;
>>> +}
>>> +
>>> +void env_write_dep(FILE *f, const char *autoconfig_name)
>>> +{
>>> +       struct env *env, *tmp;
>>> +
>>> +       list_for_each_entry_safe(env, tmp, &env_list, node) {
>>> +               fprintf(f, "ifneq \"$(%s)\" \"%s\"\n", env->name, env->value);
>>> +               fprintf(f, "%s: FORCE\n", autoconfig_name);
>>> +               fprintf(f, "endif\n");
>>> +               env_list_del(env);
>>> +       }
>>> +}
>>> diff --git a/scripts/kconfig/kconf_id.c b/scripts/kconfig/kconf_id.c
>>> index 3ea9c5f..b3e0ea0 100644
>>> --- a/scripts/kconfig/kconf_id.c
>>> +++ b/scripts/kconfig/kconf_id.c
>>> @@ -32,7 +32,6 @@ static struct kconf_id kconf_id_array[] = {
>>>         { "on",                 T_ON,                   TF_PARAM },
>>>         { "modules",            T_OPT_MODULES,          TF_OPTION },
>>>         { "defconfig_list",     T_OPT_DEFCONFIG_LIST,   TF_OPTION },
>>> -       { "env",                T_OPT_ENV,              TF_OPTION },
>>>         { "allnoconfig_y",      T_OPT_ALLNOCONFIG_Y,    TF_OPTION },
>>>  };
>>>
>>> diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
>>> index c8d9e55..03d007f 100644
>>> --- a/scripts/kconfig/lkc.h
>>> +++ b/scripts/kconfig/lkc.h
>>> @@ -58,7 +58,6 @@ enum conf_def_mode {
>>>
>>>  #define T_OPT_MODULES          1
>>>  #define T_OPT_DEFCONFIG_LIST   2
>>> -#define T_OPT_ENV              3
>>>  #define T_OPT_ALLNOCONFIG_Y    4
>>>
>>>  struct kconf_id {
>>> @@ -95,6 +94,10 @@ static inline void xfwrite(const void *str, size_t len, size_t count, FILE *out)
>>>                 fprintf(stderr, "Error in writing or end of file.\n");
>>>  }
>>>
>>> +/* env.c */
>>> +char *env_expand_n(const char *name, size_t n);
>>> +void env_write_dep(FILE *f, const char *auto_conf_name);
>>> +
>>>  /* menu.c */
>>>  void _menu_init(void);
>>>  void menu_warn(struct menu *menu, const char *fmt, ...);
>>> @@ -135,9 +138,6 @@ void str_printf(struct gstr *gs, const char *fmt, ...);
>>>  const char *str_get(struct gstr *gs);
>>>
>>>  /* symbol.c */
>>> -extern struct expr *sym_env_list;
>>> -
>>> -void sym_init(void);
>>>  void sym_clear_all_valid(void);
>>>  struct symbol *sym_choice_default(struct symbol *sym);
>>>  const char *sym_get_string_default(struct symbol *sym);
>>> diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
>>> index 5c5c137..8148305 100644
>>> --- a/scripts/kconfig/menu.c
>>> +++ b/scripts/kconfig/menu.c
>>> @@ -214,9 +214,6 @@ void menu_add_option(int token, char *arg)
>>>                         zconf_error("trying to redefine defconfig symbol");
>>>                 sym_defconfig_list->flags |= SYMBOL_AUTO;
>>>                 break;
>>> -       case T_OPT_ENV:
>>> -               prop_add_env(arg);
>>> -               break;
>>>         case T_OPT_ALLNOCONFIG_Y:
>>>                 current_entry->sym->flags |= SYMBOL_ALLNOCONFIG_Y;
>>>                 break;
>>> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
>>> index 03143b2..7c9a88e 100644
>>> --- a/scripts/kconfig/symbol.c
>>> +++ b/scripts/kconfig/symbol.c
>>> @@ -33,33 +33,6 @@ struct symbol *sym_defconfig_list;
>>>  struct symbol *modules_sym;
>>>  tristate modules_val;
>>>
>>> -struct expr *sym_env_list;
>>> -
>>> -static void sym_add_default(struct symbol *sym, const char *def)
>>> -{
>>> -       struct property *prop = prop_alloc(P_DEFAULT, sym);
>>> -
>>> -       prop->expr = expr_alloc_symbol(sym_lookup(def, SYMBOL_CONST));
>>> -}
>>> -
>>> -void sym_init(void)
>>> -{
>>> -       struct symbol *sym;
>>> -       struct utsname uts;
>>> -       static bool inited = false;
>>> -
>>> -       if (inited)
>>> -               return;
>>> -       inited = true;
>>> -
>>> -       uname(&uts);
>>> -
>>> -       sym = sym_lookup("UNAME_RELEASE", 0);
>>> -       sym->type = S_STRING;
>>> -       sym->flags |= SYMBOL_AUTO;
>>> -       sym_add_default(sym, uts.release);
>>> -}
>>> -
>>>  enum symbol_type sym_get_type(struct symbol *sym)
>>>  {
>>>         enum symbol_type type = sym->type;
>>> @@ -1348,32 +1321,3 @@ const char *prop_get_type_name(enum prop_type type)
>>>         }
>>>         return "unknown";
>>>  }
>>> -
>>> -static void prop_add_env(const char *env)
>>> -{
>>> -       struct symbol *sym, *sym2;
>>> -       struct property *prop;
>>> -       char *p;
>>> -
>>> -       sym = current_entry->sym;
>>> -       sym->flags |= SYMBOL_AUTO;
>>> -       for_all_properties(sym, prop, P_ENV) {
>>> -               sym2 = prop_get_symbol(prop);
>>> -               if (strcmp(sym2->name, env))
>>> -                       menu_warn(current_entry, "redefining environment symbol from %s",
>>> -                                 sym2->name);
>>> -               return;
>>> -       }
>>> -
>>> -       prop = prop_alloc(P_ENV, sym);
>>> -       prop->expr = expr_alloc_symbol(sym_lookup(env, SYMBOL_CONST));
>>> -
>>> -       sym_env_list = expr_alloc_one(E_LIST, sym_env_list);
>>> -       sym_env_list->right.sym = sym;
>>> -
>>> -       p = getenv(env);
>>> -       if (p)
>>> -               sym_add_default(sym, p);
>>> -       else
>>> -               menu_warn(current_entry, "environment variable %s undefined", env);
>>> -}
>>> diff --git a/scripts/kconfig/util.c b/scripts/kconfig/util.c
>>> index 22201a4..136e497 100644
>>> --- a/scripts/kconfig/util.c
>>> +++ b/scripts/kconfig/util.c
>>> @@ -8,16 +8,18 @@
>>>  #include <stdarg.h>
>>>  #include <stdlib.h>
>>>  #include <string.h>
>>> +
>>> +#include "list.h"
>>>  #include "lkc.h"
>>>
>>>  /*
>>> - * Expand symbol's names embedded in the string given in argument. Symbols'
>>> - * name to be expanded shall be prefixed by a '$'. Unknown symbol expands to
>>> + * Expand environments embedded in the string given in argument. Environments
>>> + * to be expanded shall be prefixed by a '$'. Unknown environment expands to
>>>   * the empty string.
>>>   */
>>>  char *expand_string_value(const char *in)
>>>  {
>>> -       const char *src;
>>> +       const char *p, *q;
>>>         char *res;
>>>         size_t reslen;
>>>
>>> @@ -25,39 +27,28 @@ char *expand_string_value(const char *in)
>>>          * Note: 'in' might come from a token that's about to be
>>>          * freed, so make sure to always allocate a new string
>>>          */
>>> -       reslen = strlen(in) + 1;
>>> -       res = xmalloc(reslen);
>>> -       res[0] = '\0';
>>> -
>>> -       while ((src = strchr(in, '$'))) {
>>> -               char *p, name[SYMBOL_MAXLENGTH];
>>> -               const char *symval = "";
>>> -               struct symbol *sym;
>>> -               size_t newlen;
>>> -
>>> -               strncat(res, in, src - in);
>>> -               src++;
>>> -
>>> -               p = name;
>>> -               while (isalnum(*src) || *src == '_')
>>> -                       *p++ = *src++;
>>> -               *p = '\0';
>>> -
>>> -               sym = sym_find(name);
>>> -               if (sym != NULL) {
>>> -                       sym_calc_value(sym);
>>> -                       symval = sym_get_string_value(sym);
>>> -               }
>>> +       res = xmalloc(1);
>>> +       *res = '\0';
>>>
>>> -               newlen = strlen(res) + strlen(symval) + strlen(src) + 1;
>>> -               if (newlen > reslen) {
>>> -                       reslen = newlen;
>>> -                       res = xrealloc(res, reslen);
>>> -               }
>>> +       while ((p = strchr(in, '$'))) {
>>> +               char *new;
>>> +
>>> +               q = p + 1;
>>> +               while (isalnum(*q) || *q == '_')
>>> +                       q++;
>>>
>>> -               strcat(res, symval);
>>> -               in = src;
>>> +               new = env_expand_n(p + 1, q - p - 1);
>>> +
>>> +               reslen = strlen(res) + (p - in) + strlen(new) + 1;
>>> +               res = xrealloc(res, reslen);
>>> +               strncat(res, in, p - in);
>>> +               strcat(res, new);
>>> +               free(new);
>>> +               in = q;
>>>         }
>>> +
>>> +       reslen = strlen(res) + strlen(in) + 1;
>>> +       res = xrealloc(res, reslen);
>>>         strcat(res, in);
>>>
>>>         return res;
>>> @@ -87,8 +78,6 @@ struct file *file_lookup(const char *name)
>>>  /* write a dependency file as used by kbuild to track dependencies */
>>>  int file_write_dep(const char *name)
>>>  {
>>> -       struct symbol *sym, *env_sym;
>>> -       struct expr *e;
>>>         struct file *file;
>>>         FILE *out;
>>>
>>> @@ -107,21 +96,7 @@ int file_write_dep(const char *name)
>>>         fprintf(out, "\n%s: \\\n"
>>>                      "\t$(deps_config)\n\n", conf_get_autoconfig_name());
>>>
>>> -       expr_list_for_each_sym(sym_env_list, e, sym) {
>>> -               struct property *prop;
>>> -               const char *value;
>>> -
>>> -               prop = sym_get_env_prop(sym);
>>> -               env_sym = prop_get_symbol(prop);
>>> -               if (!env_sym)
>>> -                       continue;
>>> -               value = getenv(env_sym->name);
>>> -               if (!value)
>>> -                       value = "";
>>> -               fprintf(out, "ifneq \"$(%s)\" \"%s\"\n", env_sym->name, value);
>>> -               fprintf(out, "%s: FORCE\n", conf_get_autoconfig_name());
>>> -               fprintf(out, "endif\n");
>>> -       }
>>> +       env_write_dep(out, conf_get_autoconfig_name());
>>>
>>>         fprintf(out, "\n$(deps_config): ;\n");
>>>         fclose(out);
>>> diff --git a/scripts/kconfig/zconf.l b/scripts/kconfig/zconf.l
>>> index 045093d..551ca47 100644
>>> --- a/scripts/kconfig/zconf.l
>>> +++ b/scripts/kconfig/zconf.l
>>> @@ -35,6 +35,7 @@ struct buffer *current_buf;
>>>
>>>  static int last_ts, first_ts;
>>>
>>> +static void expand_string(const char *in);
>>>  static void zconf_endhelp(void);
>>>  static void zconf_endfile(void);
>>>
>>> @@ -120,6 +121,7 @@ n   [A-Za-z0-9_-]
>>>  }
>>>
>>>  <PARAM>{
>>> +       "$".*   expand_string(yytext);
>>>         "&&"    return T_AND;
>>>         "||"    return T_OR;
>>>         "("     return T_OPEN_PAREN;
>>> @@ -157,12 +159,13 @@ n [A-Za-z0-9_-]
>>>  }
>>>
>>>  <STRING>{
>>> -       [^'"\\\n]+/\n   {
>>> +       "$".*   expand_string(yytext);
>>> +       [^$'"\\\n]+/\n  {
>>>                 append_string(yytext, yyleng);
>>>                 yylval.string = text;
>>>                 return T_WORD_QUOTE;
>>>         }
>>> -       [^'"\\\n]+      {
>>> +       [^$'"\\\n]+     {
>>>                 append_string(yytext, yyleng);
>>>         }
>>>         \\.?/\n {
>>> @@ -249,6 +252,19 @@ n  [A-Za-z0-9_-]
>>>  }
>>>
>>>  %%
>>> +static void expand_string(const char *in)
>>> +{
>>> +       char *p, *q;
>>> +
>>> +       p = expand_string_value(in);
>>> +
>>> +       q = p + strlen(p);
>>> +       while (q > p)
>>> +               unput(*--q);
>>> +
>>> +       free(p);
>>> +}
>>> +
>>
>> I like the simplicity of this approach, but I suspect it might be too simple.
>>
>> For example, the following breaks with a syntax error if $ENV has any
>> double quotes in its value:
>>
>>     config FOO
>>         string "foo"
>>         default "$ENV"
>>
>> The following will only work as expected if $ENV expands to a valid
>> Kconfig symbol name. If it doesn't, random stuff will happen (most
>> likely a syntax error).
>>
>>     config FOO
>>         string "foo"
>>         default $ENV
>>
>> The reason it works if $ENV expands to a valid symbol name is that
>> undefined symbols get their name as their (string) value. If the
>> symbol happens to be defined, it will be referenced, which seems
>> confusing too.
>>
>> In general, that reinterpretation of expanded values feels a bit icky
>> to me, and as something that might add complexity to Kconfig for
>> little value. If $ENV outside of quotes absolutely must be supported,
>> I think it should be a shorthand for "$ENV" (which means "constant
>> value" in Kconfig speak).
>
> If you want something as general as the C preprocessor (which I think
> would be overkill and complexity land), then it seems kinda weird to
> limit it to certain Kconfig contexts as well: Right now you'd be able
> to output arbitrary tokens inside an expression, but you couldn't do
> something like generate a 'default X if Y'.
>
> Cheers,
> Ulf

I know you're not a fan, but if expansion was limited to within
constant values (quotes), then you'd be able to handle it all by just
expanding the text before a T_WORD_QUOTE is returned. Extremely
simple, and no gotchas. ;)

Cheers,
Ulf