• Masahiro Yamada's avatar
    kconfig: allow all config targets to write auto.conf if missing · 00c864f8
    Masahiro Yamada authored
    Currently, only syncconfig creates or updates include/config/auto.conf
    and some other files.  Other config targets create or update only the
    .config file.
    
    When you configure and build the kernel from a pristine source tree,
    any config target is followed by syncconfig in the build stage since
    include/config/auto.conf is missing.
    
    We are moving compiler tests from Makefile to Kconfig.  It means that
    parsing Kconfig files will be more costly since Kconfig invokes the
    compiler commands internally.  Thus, we want to avoid invoking Kconfig
    twice (one for *config to create the .config, and one for syncconfig
    to synchronize the auto.conf).  If auto.conf does not exist, we can
    generate all configuration files in the first configuration stage,
    which will save the syncconfig in the build stage.
    
    Please note this should be done only when auto.conf is missing.  If
    *config blindly did this, time stamp files under include/config/ would
    be unnecessarily touched, triggering unneeded rebuild of objects.
    
    I assume a scenario like this:
    
     1. You have a source tree that has already been built
        with CONFIG_FOO disabled
    
     2. Run "make menuconfig" to enable CONFIG_FOO
    
     3. CONFIG_FOO turns out to be unnecessary.
        Run "make menuconfig" again to disable CONFIG_FOO
    
     4. Run "make"
    
    In this case, include/config/foo.h should not be touched since there
    is no change in CONFIG_FOO.  The sync process should be delayed until
    the user really attempts to build the kernel.
    
    This commit has another motivation; I want to suppress the 'No such
    file or directory' warning from the 'include' directive.
    
    The top-level Makefile includes auto.conf with '-include' directive,
    like this:
    
      ifeq ($(dot-config),1)
      -include include/config/auto.conf
      endif
    
    This looks strange because auto.conf is mandatory when dot-config is 1.
    I guess only the reason of using '-include' is to suppress the warning
    'include/config/auto.conf: No such file or directory' when building
    from a clean tree.  However, this has a side-effect; Make considers
    the files included by '-include' are optional.  Hence, Make continues
    to build even if it fails to generate include/config/auto.conf.  I will
    change this in the next commit, but the warning message is annoying.
    (At least, kbuild test robot reports it as a regression.)
    
    With this commit, Kconfig will generate all configuration files together
    with the .config and I guess it is a solution good enough to suppress
    the warning.
    
    Note:
    GNU Make 4.2 or later does not display the warning from the 'include'
    directive if include files are successfully generated.  See GNU Make
    commit 87a5f98d248f ("[SV 102] Don't show unnecessary include file
    errors.")  However, older GNU Make versions are still widely used.
    Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    00c864f8
confdata.c 26.9 KB