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

[Kees Cook]

On Sun, Feb 11, 2018 at 1:10 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Sun, Feb 11, 2018 at 9:06 PM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> On Sun, Feb 11, 2018 at 11:53 AM, Linus Torvalds
>> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>
>>> Well, it's still not a very *big* bump. With modern distros being at
>>> 7.3, and people testing pre-releases of gcc-8, something like gcc-4.5
>>> is still pretty darn ancient.
>>
>> ... it's worth noting that our _documentation_ may claim that gcc-3.2
>> is the minimum supported version, but Arnd pointed out that a few
>> months ago that apparently nothing older than 4.1 has actually worked
>> for a longish while, and gcc-4.3 was needed on several architectures.
>>
>> So the _real_ jump in required gcc version would be from 4.1 (4.3 in
>> many cases) to 4.5, not from our documented "3.2 minimum".
>>
>> Arnd claimed that some architectures needed even newer-than-4.3, but I
>> assume that's limited to things like RISC-V that simply don't have old
>> gcc support at all.
>
> Right. Also architecture specific features may need something more recent,
> and in some cases like the 'initializer for anonymous union needs extra
> curly braces', a trivial change would make it work, but a lot of architectures
> have obviously never been built with toolchains old enough to actually
> run into those cases.
>
> Geert is the only person I know that actively uses gcc-4.1, and he actually
> sent some patches that seem to get additional architectures to build on
> that version, when they were previously on gcc-4.3+.
>
> gcc-4.3 in turn is used by default on SLES11, which is still in support,
> and I've even worked with someone who used that compiler to build
> new kernels, since that was what happened to be installed on his
> shared build server. In this case, having gcc-4.3 actively refused to
> force him to use a new compiler would have saved us some
> debugging trouble.
>
> In my tests last year, I identified gcc-4.6 as a nice minimum level, IIRC
> gcc-4.5 was unable to build some of the newer ARM targets.

For reference, the original discussion started here:
https://lkml.org/lkml/2016/12/16/174

I thread-necromancied it here:
https://lkml.org/lkml/2017/4/16/276

Modern analysis of compilers vs versions here:
https://lkml.org/lkml/2017/4/24/481

and seeming conclusion was here:
https://lkml.org/lkml/2017/4/25/66

Quoted:
>> - To keep it simple, we update the README.rst to say that a minimum
>>   gcc-4.3 is required, while recommending gcc-4.9 for all architectures
>> - Support for gcc-4.0 and earlier gets removed from linux/compiler.h,
>>   and instead we add a summary of what I found, explaining that
>>   gcc-4.1 has active users on a few architectures.
>> - We make the Makefile show a warning once during compilation for
>>   gcc earlier than 4.3.

But yes, if Linus wants 4.5 over 4.3, I would agree with Arnd: let's
take it to 4.6 instead.

-Kees

-- 
Kees Cook
Pixel Security