[Toybox] [PATCH 2] Fix segfault in config2help

[Rob Landley]

On 09/21/2017 12:52 AM, Patrick Oppenlander wrote:
> For some reason config2help started segfaulting on me.

Yeah, the openembedded maintainer recently hit this too:

http://lists.openembedded.org/pipermail/openembedded-devel/2017-September/114879.html

But only on a system with all the package upgrades applied, installing
straight from DVD ditn't reproduce it. I've een very slowly debugging it
under a qemu instance (which takes like 15 seconds to pull up "vi" on a
file, for some reason arch linux's gui is REALLY slow under qemu).

Either gcc or the libc (or ld, or...) got upgraded recently and started
Doing A Thing.

His workaround was to turn "usage: ls --color" into "usage: --color"
(which means it bypasses that entry entirely)...

> I haven't had time to completely track down the reason for this, but it
> seems that under some conditions sym->help is left dangling after memory
> is free'd by:
> 
>         // Append trailing lines.
>         while (tfrom) dlist_add(&anchor, dlist_zap(&tfrom));
> 
> Either way, testing sym->enabled appears to fix the problem.

That's a workaround, not a fix. And it means we'd need to rebuild
generated/help.h every time .config changes (which right now we don't).

Lemme look at your other patch more closely, that's probably the start
of the right fix...

Thanks,

Rob