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

[Paul Eggert <eggert@cs.ucla.edu>]

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.

Part of the issue here (in case this isn't clear) is that we might want 
to have a Gnulib version (or even just a copy) of cstack_* to help port 
GNU apps to other platforms. On these other platforms, mmap might not be 
the right way to make a stack executable (or might not be needed). I 
imagine that it'd be better to have this implementation detail done by 
the cstack_* implementation, than to have each nested-function-using app 
port this detail by hand.

> The cstack_t is basically another heap object and I think it should be
> handled as such.

I hope that "handled as such" doesn't mean "the user must always 
manually free it". That is, even if the cstack_t object is on the heap, 
surely it'd be more convenient for cstack_* users if the object's 
storage is automatically reclaimed when a thread exits and the object is 
no longer needed.