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    SubjectRe: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig
    Hello,

    On Sun, Feb 18, 2018 at 11:13 PM, Sam Ravnborg <sam@ravnborg.org> wrote:
    > Hi Masahiro.
    >
    > On Sat, Feb 17, 2018 at 03:38:28AM +0900, Masahiro Yamada wrote:
    >> I brushed up the implementation in this version.
    >>
    >> In the previous RFC, CC_HAS_ was described by using 'option shell=',
    >> like this:
    >>
    >> config CC_HAS_STACKPROTECTOR
    >> bool
    >> option shell="$CC -Werror -fstack-protector -c -x c /dev/null"
    >>
    >> After I thought a bit more, the following syntax is more grammatical,
    >> and flexible.
    >>
    >> config CC_HAS_STACKPROTECTOR
    >> bool
    >> default $(shell $CC -Werror -fstack-protector -c -x c /dev/null)
    >
    > Looks good - but maybe we should go one step further.
    >
    > So we in the syntax explicit handles:
    > - shell commands
    > - other commands, defined as strings
    > - environment variables
    > - config variables
    >
    > Each case is explicit - so the reader is not confused what is used when.
    >
    > $(shell foo) - output of the shell command foo. Uses $SHELL as the shell.
    > May include optional paramters.
    > foo may be a config variable referenced using ${} or a config variable prefixed with $
    > Example:
    >
    > config BUILD_DIR
    > string
    > default $(shell cd ${objtree}; pwd)
    >
    > $(call bar) - output of the bar command that may take optional parameters.
    > bar may be a text string, a config variable or an environment variable
    > The definition of bar may reference the parameters using $(1), $(2)
    > In this context a config variable needs to be prefixed with $
    >
    > Example:
    >
    > config reverse
    > string
    > default $(2) $(1)
    >
    > config NEW_ORDER
    > string
    > $(call $reverse, A, B) # Will assign REVERSE the value "B A"
    >
    >
    > Example2:
    >
    > config CC_OPTION
    > string
    > default $(shell ${srctree}/scripts/cc-option ${CC} $(1) $(2))
    >
    > config CC_OPTIMIZE
    > string
    > $(call $CC_OPTION, -Oz, -Os)
    >
    >
    > ${FOO} - environment variable
    >
    > The above is inspired by how make implement similar functionality.
    >
    > I'm not happy that we in one context can reference CONFIG variables
    > directly, but inside the $(call ...) and $(shell ...) needs the $ prefix.
    > But I could not come up with something un-ambigious where this could be avoided.

    I think we should be careful about allowing references to config
    symbols. It mixes up the parsing and evaluation phases, since $() is
    expanded during parsing (which I consider a feature and think is
    needed to retain sanity).

    Patch 06/23 removes the last existing instance of symbol references in
    strings by getting rid of 'option env'. That's an improvement to me.
    We shouldn't add it back.

    >
    > The above proposal include the functionality of the macro stuff proposed in this patch-set.
    > But with a simpler syntax and we keep all the other kconfig logic (depends on etc) - so
    > users will not be limited in their creativity.
    >
    >> Current limitations:
    >>
    >> Dependency on outside scripts.
    >> Inter-option dependency:
    >> Functions are evaluated statically:
    >
    > Same limitations exists with the syntax suggested above.
    >
    > Sam

    Cheers,
    Ulf

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