zsh glitch

zsh glitch

[Lane Erickson]

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http://stackoverflow.com/questions/33639879/strange-zsh-segfault-glitch-with-function-definitions

Re: zsh glitch

[Mikael Magnusson]

On Tue, Nov 10, 2015 at 10:36 PM, Lane Erickson <lerickson@liveramp.com> wrote:
> http://stackoverflow.com/questions/33639879/strange-zsh-segfault-glitch-with-function-definitions

Please post the actual question to the mailing list. In 20 years when
someone reads this in the archive, stackoverflow might not exist
anymore ;).

> Does anyone know why this behavior exists in zsh, or what zsh is trying to do that causes a segfault?
>
> ➜  ~  (echo "hi"(); echo "hi"; echo "hi")
> [1]    65962 segmentation fault  ( echo "hi" () { ... }; echo "hi"; )
>
> ➜  ~  (ls(); ls; ls)
> [1]    66073 segmentation fault  ( ls -G () { ... }; ls -G; )

If it segfaults here, it's either because you're running an old
version or the compiler miscompiled, or the zsh code disagrees with
the compiler about what can be optimized out. What should happen is
the following:

% (ls(); ls; ls)
ls:1: maximum nested function level reached

What you've done is define a function that looks like this
ls() {
  ls
}
and then you call it, which causes an infinite recursion. This usually
does not end well in any language.

-- 
Mikael Magnusson

Re: zsh glitch

[Peter Stephenson]

On Tue, 10 Nov 2015 22:43:20 +0100
Mikael Magnusson <mikachu@gmail.com> wrote:
> If it segfaults here, it's either because you're running an old
> version or the compiler miscompiled, or the zsh code disagrees with
> the compiler about what can be optimized out. What should happen is
> the following:
> 
> % (ls(); ls; ls)
> ls:1: maximum nested function level reached

It's basically luck whether you hit the maximum recursion depth before
you run out of stack (and hence crash) or not.  There's no easy way for
the shell to tell when this is going to happen, so it's very system
dependent.

The only better way out I can see is for someone with a wider knowledge
of the sort of systems they're compiling zsh for to attempt a more
appropriate configuration with --enable-max-function-depth=MAX.
The default is 1000; a nice round number that works in a lot of places
is about the best we can do generally.  For general purpose Linux
distributions I suspect that statement continues to apply.

pws

Re: zsh glitch

[Christian Neukirchen]

Mikael Magnusson <mikachu@gmail.com> writes:

> What you've done is define a function that looks like this
> ls() {
>   ls
> }
> and then you call it, which causes an infinite recursion. This usually
> does not end well in any language.

Time to add tail-recursion to zsh!

-- 
Christian Neukirchen  <chneukirchen@gmail.com>  http://chneukirchen.org