Do not write the defconfig_list symbol to .config

Mirrors the following change to the C tools, now in linux-next:

commit c21a6e352766005d42c1ccae32b31e0438903eb9
Author: Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Sat Feb 17 03:38:32 2018 +0900

    kconfig: set SYMBOL_AUTO to the symbol marked with defconfig_list

    The 'defconfig_list' is a weird attribute.  If the '.config' is
    missing, conf_read_simple() iterates over all visible defaults,
    then it uses the first one for which fopen() succeeds.

    config DEFCONFIG_LIST
            string
            depends on !UML
            option defconfig_list
            default "/lib/modules/$UNAME_RELEASE/.config"
            default "/etc/kernel-config"
            default "/boot/config-$UNAME_RELEASE"
            default "$ARCH_DEFCONFIG"
            default "arch/$ARCH/defconfig"

    However, like other symbols, the first visible default is always
    written out to the .config file.  This might be different from what
    has been actually used.

    For example, on my machine, the third one "/boot/config-$UNAME_RELEASE"
    is opened, like follows:

      $ rm .config
      $ make oldconfig 2>/dev/null
      scripts/kconfig/conf  --oldconfig Kconfig
      #
      # using defaults found in /boot/config-4.4.0-112-generic
      #
      *
      * Restart config...
      *
      *
      * IRQ subsystem
      *
      Expose irq internals in debugfs (GENERIC_IRQ_DEBUGFS) [N/y/?] (NEW)

    However, the resulted .config file contains the first one since it is
    visible:

      $ grep CONFIG_DEFCONFIG_LIST .config
      CONFIG_DEFCONFIG_LIST="/lib/modules/$UNAME_RELEASE/.config"

    In order to stop confusing people, prevent this CONFIG option from
    being written to the .config file.

    Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/kconfiglib.py b/kconfiglib.py
index afd480e..0788ef7 100644
--- a/kconfiglib.py
+++ b/kconfiglib.py
@@ -2790,8 +2790,12 @@ class Symbol(object):
                         self._write_to_conf = True
                         break
 
-        # Corresponds to SYMBOL_AUTO in the C implementation
-        if self.env_var is not None:
+        # env_var corresponds to SYMBOL_AUTO in the C implementation, and is
+        # also set on the defconfig_list symbol there. Test for the
+        # defconfig_list symbol explicitly instead here, to avoid a nonsensical
+        # env_var setting and the defconfig_list being printed incorrectly.
+        # This code is pretty cold anyway.
+        if self.env_var is not None or self is self.kconfig.defconfig_list:
             self._write_to_conf = False
 
         self._cached_str_val = val