What is a "bus error"?

[Grant Edwards]

In article <mailman.1012579203.9499.python-list at python.org>, Steven Majewski wrote:

>> | 	However, some of these programs now give a "bus error" message -
>> | what does this mean?
>>
>> it means python got a SIGBUS signal from the kernel, ie it crashed.
>> SIGBUS commonly results from attempting to access unaligned memory.
> 
> ... or chasing a nil pointer or useing something that's not a pointer
> as a pointer.

On many systems (e.g. Linux/Intel) that's a different signal.
On Linux/Intel SIGSEGV is used to indicate you've tried to
access memory which you're not allowed to access (e.g.
de-referencing a null pointer).

In my experience SIGBUS has always been an alignment error.
I've seen it on SPARCs running both SunOS and Linux.  I don't
think I've ever seena SIGBUS on Intel hardware.

It's not uncommon for SW developed on Intel hardware to have
SIGBUS faults when it's run on SPARC, ARM, or other hardware
with alignment requirements.  I remember finding such a bug in
the Linux ppp daemon when I tried to run it on a SPARC system.

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