[Aboriginal] Merry christmas, I have found two bugs

[Rob Landley]

On 12/26/2012 04:23:06 PM, Bjørn Forsman wrote:
> On 26 December 2012 22:36, Rob Landley <rob at landley.net> wrote:
> > On 12/26/2012 02:55:04 PM, Bjørn Forsman wrote:
> [...]
> >> And now I think I've found two bugs. Bug 1 is
> >> a segmentation fault during system image boot:
> >>
> >> $ cd build/system-image-avmv5l
> >> $ ./run-emulator.sh
> >> [...]
> >> Freeing init memory: 96K
> >> Segmentation fault
> >> 8139cp 0000:00:0c.0 eth0: link up, 100Mbps, full-duplex, lpa 0x05E1
> >> Not using distcc.
> >> Type exit when done.
> >> (armv5l:1) /home #
> >>
> >> Not sure what exactly is segfaulting, but segfault == bug to me.  
> And
> >> it only happens with ./run-emulator.sh, not ./dev-environment.sh.
> >
> > There are somewhat different code paths in the init.sh shell script  
> so it's
> > probably something only running in the first case. I need to  
> rebuild the
> > armv5l target to test this, that'll take a few minutes...

Still grinding away on this. It's... weird.

If I run_emulator.sh with KERNEL_EXTRA=init=/bin/bash and then exec  
/sbin/init.sh it does _not_ segfault. It doesn't do so with  
init=/bin/bash or init=/bin/ash. But it _does_ do so when  
init=/sbin/init.sh when that starts with #!/bin/bash or #!/bin/ash.

So it only happens when the script is run as the first process. Not  
just as PID 1, as the _first_process_. If you exec a shell that execs  
the script, it doesn't segfault.

So the same thing happening with two different shells, but only from a  
very specific execution environment. Is there some asynchronous kernel  
thread that happens to damage whatever's running at the time it  
completes? Add a sleep 1" before the if CPU block... no difference.

Back up, confirm whether ash or bash IS running, add an ls -l  
/proc/self/exe and it says... toybox.  Sigh.  Make that ls -l  
/proc/1/exe (ask about the _shell_ not the ls process) and it says...  
/bin/bash. And when I switch the #! line to ash it... isn't segfaulting?

Hang on, according to "hg diff" the initial version wasn't #!/bin/ash  
it was #!/bin/sh which points to _bash_. So I switched it from bash to  
bash, which is an invalid test. So it's NOT a bug affecting both shells  
(and thus probably some libc thing with setsid or who knows what), it's  
a BASH BUG.

Given how old the version of bash I'm using is, and that I've already  
had to fix deep obscure bugs in it before (the backstory behind  
http://landley.net/hg/aboriginal/rev/de8e06350227 is long and epic and  
described in my blog over a course of weeks), I think the correct fix  
is #!/bin/ash (and eventually #!/bin/toysh).

Rob
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