Eric Lee / smarc-fsl-linux-kernel

08 Apr, 2020

1 commit

  • 76426e238   kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig ... Browse Code ยป

    Staring v4.18, Kconfig evaluates compiler capabilities, and hides CONFIG
    options your compiler does not support. This works well if you configure
    and build the kernel on the same host machine.

    It is inconvenient if you prepare the .config that is carried to a
    different build environment (typically this happens when you package
    the kernel for distros) because using a different compiler potentially
    produces different CONFIG options than the real build environment.
    So, you probably want to make as many options visible as possible.
    In other words, you need to create a super-set of CONFIG options that
    cover any build environment. If some of the CONFIG options turned out
    to be unsupported on the build machine, they are automatically disabled
    by the nature of Kconfig.

    However, it is not feasible to get a full-featured compiler for every
    arch.

    This issue was discussed here:

    https://lkml.org/lkml/2019/12/9/620

    Other than distros, savedefconfig is also a problem. Some arch sub-systems
    periodically resync defconfig files. If you use a less-capable compiler
    for savedefconfig, options that do not meet 'depends on $(cc-option,...)'
    will be forcibly disabled. So, 'make defconfig && make savedefconfig'
    may silently change the behavior.

    This commit adds a set of dummy toolchains that pretend to support any
    feature.

    Most of compiler features are tested by cc-option, which simply checks
    the exit code of $(CC). The dummy tools are shell scripts that always
    exit with 0. So, $(cc-option, ...) is evaluated as 'y'.

    There are more complicated checks such as:

    scripts/gcc-x86_{32,64}-has-stack-protector.sh
    scripts/gcc-plugin.sh
    scripts/tools-support-relr.sh

    scripts/dummy-tools/gcc passes all checks.

    From the top directory of the source tree, you can do:

    $ make CROSS_COMPILE=scripts/dummy-tools/ oldconfig

    Signed-off-by: Masahiro Yamada
    Reviewed-by: Philipp Rudo
    Tested-by: Jeremy Cline

    Masahiro Yamada