Re: nested functions [was Re: valgrind]

["Koning, Paul" <Paul.Koning%dell.com@localhost>]

> On Mar 22, 2022, at 2:23 PM, Mouse <mouse%Rodents-Montreal.ORG@localhost> wrote:
> 
> 
> [EXTERNAL EMAIL] 
> 
>>> I found an interesting article about why they're bad...
>>> https://urldefense.com/v3/__https://thephd.dev/lambdas-nested-functions-block-expressions-oh-my__;!!LpKI!1zB1gatUTEiM-j9CQ_6N-NWd4jS8UvW5iTSMRgW1tEyW_mK0mG2pU48LnUwJJBvA$ [thephd[.]dev]
>> That's a good argument for why GCC's implementation of nested functions is b$
> 
> What security blunder is that?  Based on your next line, I'm going to
> assume it's "implementing them via stack trampolines".  (I would have
> to go to a work machine to tell, because thephd.dev has apparently
> drunk the "it's good to ram HTTPS down everyone's throat" koolaid.
> Even the stack trampoline mechanism, I would say, is not a security
> blunder per se; I see it as a security issue only in that it
> exacerbates the effects of certain other security issues.  Also don't
> forget that early gcc arose in a very different environment from
> today's.)

Yes, I did mean executable stacks.  True, the world was different
once, though executable stacks are also problematic on some older
architectures for entirely different reasons.  For example, you can't
necessarily use them on PDP-11s.

>> I don't believe ALGOL implementations needed executable stacks to implement $
> 
> Neither would gcc...IF it can set the ABI.  There really was very
> little choice for gcc when it started.  It had to be ABI-compatible
> with existing procedure calling sequences.  It also had to be
> compatible with existing longjmps. That eliminates pretty close to
> everything _but_ stack trampolines.

True.  Do general ABIs like the VAX one have this issue or is it 
specific to just some of the ABIs?

> Other ways of doing nested functions is one of the things I want to
> experiment with.

I know the classic answer in ALGOL is "displays", which go all the
way back to the first ALGOL compilers, but I don't have the details
in my head.

	paul