Re: [Jack-Devel] jackd2 bus error on openwrt

On Sun, Aug 16, 2015 at 09:40:18AM +1000, Matt Flax wrote:

Hi!

> I am revisiting running jackd2 on openwrt using another ARM
> architecture. It is compiled from git commit
> cd59d67847afb57393a1db6d39badd94a4973f6e
> 
> When jack starts I still get bus error :
> root@OpenWrt:/# jackd -v -d alsa
> jackdmp 1.9.11
> Bus error
> 
> Not sure what to do next to debug, beyond hacking console outputs
> into the command line.

You are most likely dealing with unaligned memory access here, usually
mis-aligned structs. I'm somewhat surprised that it didn't surface on
other ARM platforms before, but then again, there are many variations of
"ARM".

Further reading:

   https://www.kernel.org/doc/Documentation/arm/mem_alignment

specifically:

   echo 1 > /proc/sys/debug/alignment

and then check the syslog.

If this confirms that it's unaligned access, you know what to look for.

A good and comprehensive read:

   http://www.catb.org/esr/structure-packing/

Maybe "pahole" in the tools section can be of further help, but let's
not jump to conclusions.

I've only skimmed the following link, but it also seems like a good
introduction to memory alignment:

   https://lwn.net/Articles/259732/

In other words: set aside half a day for hunting this down.

Last not least: ARM behaviour may be different depending on the compiler
flags. I vaguely recall different CPU targets behaving differently. I
assume you used the correct flags that match your platform, endianess
etc.



Cheers

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