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

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.

Linus

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