Re: [PATCH 3/3] Misc: Add <sys/cstack.h> and the cstack_* family of functions

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 25/05/2021 09:23, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> On 25/05/2021 04:40, Florian Weimer wrote:
>>> * Paul Eggert:
>>>
>>>> On 5/24/21 12:11 PM, Adhemerval Zanella via Libc-alpha wrote:
>>>>
>>>>> If this is really a requirement, I think the best options would be to add
>>>>> an extra flag to opt-in.
>>>>
>>>> Opt-in works for me. Although the GNU apps I help maintain typically
>>>> don't have nested functions, nested functions are a longstanding GNU C 
>>>> feature and are a good thing to have when you need them.
>>>
>>> Since the requirement for non-executable stacks does not encapsulate
>>> well, I'd rather make this automatic if you think executable stack
>>> support is required.  (The code allocating the stack might not know
>>> about the trampolines.)
>>
>> Although honoring PT_GNU_STACK seems the most straightforward I still
>> think we should make it a opt-in, executable stacks has strong security
>> implications and I think it is better the caller knows it is enabling.
> 
> The caller may not know whether signal handlers need executable stacks,
> though.  That's what I meant with the lack of encapsulation.

Yes I understood it, that's why I state is the most straightforward. 
However this is a newer API, we don't really need to keep compatibility
to old binaries as the drive here. We can move away from bad API decisions.