Re: [RFC PATCH 0/7] Kconfig: add new special property shell= to test compiler options in Kconfig

[Masahiro Yamada <yamada.masahiro@socionext.com>]

Hi Linus,

2018-02-09 2:19 GMT+09:00 Linus Torvalds <torvalds@linux-foundation.org>:
> On Thu, Feb 8, 2018 at 8:19 AM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> This was prompted by the email from Linus today's morning.
>
> Thanks.
>
>> I implmented this in a rush today, so there are still many TODOs,
>> but I put it here to start discussion.
>>
>> I think it is working, but as you notice, it is tedious to repeat something
>> like follows:
>>
>> config CC_HAS_STACKPROTECTOR
>>         bool
>>         option shell="$CC -Werror -fstack-protector -c -x c /dev/null"
>
> Yeah.
>
> I do think we want to have the "shell" thing as a generic escape for
> other things too, but *realistically*, the primary target for this is
> compiler flags, and I think we should target that specifically with a
> shorthand.
>
> Doing some statistics, and looking for
>
>     flag = $(call xyz ...)
>
> patterns in our makefiles (ignoring single uses), it really is
> cc-option that dominates:
>
>       2  name-fix
>       2  try-run
>       3  __cc-option
>       3  grep-libs
>       3  strip-libs
>       4  flags
>       4  get-executable
>       4  ld-option
>       4  logo-cfiles
>       5  as-option
>       5  cc-cross-prefix
>       6  cc-ldoption
>       6  cc-supports
>       7  cc-option-yn
>       7  tune
>       9  cc-ifversion
>      30  as-instr
>      48  cc-disable-warning
>     239  cc-option
>
> so I think that's the one that we want to special-case.
>
> If we then have a _usable_ - but perhaps not wonderful "shell" escape
> to do any random thing (including scripts etc), that will take care of
> the rest, but cc-option is so common that I think it's worth making a
> special Kconfig syntax for them. For all I know, the others aren't
> even worth Kconfig options at all.
>
>> I was thinking of something like follows:
>>
>> config CC_STACKPROTECTOR
>>           bool
>>           option shell="$(CC_OPTION -fstack-protector)"
>
> I think we should go even further, and just make it be
>
> config CC_STACKPROTECTOR
>           bool
>           option cc_option="-fstack-protector"
>
> and actually have the Kconfig language itself have this special-cased.
>
> And obviously that "option cc_option" would be *implemented* as just
> "option shell", with just some stupid string substitution. So it
> really would be purely a shorthand for readability.
>
> What do you think?


OK, I will try this way.



> And btw, the patches look nice. What I like in particular is that they
> don't even seem to add a lot of lines: the new shell option code is
> almost balanced out by the Kconfig script simplifications. And maybe
> it's just that I read C a lot better than I read GNU Makefile magic,
> but I think it's more understandable too.


I am glad you like it.  :)



-- 
Best Regards
Masahiro Yamada