Re: [RFC PATCH 4/7] kconfig: support new special property shell=

[Ulf Magnusson <ulfalizer@gmail.com>]

On Sun, Feb 11, 2018 at 6:56 PM, Kees Cook <keescook@chromium.org> wrote:
>> 3. Whether to implement CC_STACKPROTECTOR_AUTO in Kconfig or the Makefiles
>>
>> I'd just go with whatever is simplest here. I don't find the Kconfig version
>> too bad, but I'm already very familiar with Kconfig, so it's harder for me to
>> tell how it looks to other people.
>>
>> I'd add some comments to explain the idea in the final version.
>>
>> @Kees:
>> I was assuming that the Makefiles would error out with a message if none of the
>> CC_STACKPROTECTOR_* variables are set, in addition to the Kconfig warning.
>
> That doesn't happy either before nor after _AUTO. The default value
> before was _NONE, and the default value after is _AUTO, which will use
> whatever is available.

I was thinking in the case where you explicitly select one of
CC_STACKPROTECTOR_{STRONG,REGULAR} and it isn't available. With the
new WANT_* version, that will cause none of
CC_STACKPROTECTOR_{STRONG,REGULAR,NONE} to be set, and in that case
you'd error out to match the old behavior (if I understand it
correctly).

CHOSEN_CC_STACKPROTECTOR_AVAILABLE would just be a helper symbol to
detect that case. It's not like it's a huge deal to detect it on the
Makefile end either, but turns it pretty nice and readable, IMO, with
more of the logic in a single location.

>>         # User request
>>         WANT_CC_STACKPROTECTOR_AUTO
>>         WANT_CC_STACKPROTECTOR_STRONG
>>         WANT_CC_STACKPROTECTOR_REGULAR
>>         WANT_CC_STACKPROTECTOR_NONE
>>
>>         # The actual "output" to the Makefiles
>>         CC_STACKPROTECTOR_STRONG
>>         CC_STACKPROTECTOR_REGULAR
>>         CC_STACKPROTECTOR_NONE
>
> This should be fine too (though by this point, I think Kconfig would
> already know the specific option, so it could just pass it with a
> single output (CC_OPT_STACKPROTECTOR below?)

Ah, yeah, that'd be simpler if all that's needed is the compiler flag.

Cheers,
Ulf