x86 and x64 have no problems with unaligned read/write as far as I know --
which is why this hasn't come up.  Can you open a ticket and continue this
discussion there?  It should be fairly easy to do some conditional changes
based on CPU type.

Josh

On Mon, Jul 12, 2010 at 5:38 PM, Daniel Stonier <d.stonier@gmail.com> wrote:

>
> This seems to be a bit of problem code with regards to the alignment
> issues:
>
> roscpp/src/libros/service_server_link.cpp
>
>
> *****************************************************************************************
>
> void ServiceServerLink::onResponseOkAndLength(const ConnectionPtr& conn,
> const boost::shared_array<uint8_t>& buffer, uint32_t size, bool success)
> {
> ROS_ASSERT(conn == connection_);
> ROS_ASSERT(size == 5);
>
> if (!success)
> return;
>
> uint8_t ok = buffer[0];
> uint32_t len = *((uint32_t*)(buffer.get() + 1));
>
>
> *****************************************************************************************
>
> That last line is where the signal is caught. I think the problem is, the
> arm core reads the uint32 values only at alignmed 4 byte boundaries - but
> that +1 generally shifts it off the 4 byte boundary and causes the signal.
>
> Do intel machines even have an alignment trap like this arm core does? I
> noticed my machine does not have /proc/cpu/alignment.
>
> Sorry, don't have a potential fix for it as I'm not familiar with this
> section of code yet.
>
> More to come,
> Regards,
> Daniel.
>
>
> On 12 July 2010 19:04, Daniel Stonier <d.stonier@gmail.com> wrote:
>
>>
>>
>> On 12 July 2010 17:24, René Wagner <rene.wagner@dfki.de> wrote:
>>
>>> On Fri, 2010-07-09 at 10:45 +0900, Daniel Stonier wrote:
>>> > - Patched (using the memcpy's rather than the reinterprets in the
>>> > SERIALIZER macro).
>>> > - In signal+warn mode (echo 5 > /proc/cpu/alignment)
>>> >   - (float64&int32) client gives a bus error and kernel outputs an
>>> > alignment trap message, but servers are fine
>>> > - In default mode (echo 0 > /proc/cpu/alignment)
>>> >   - (float64&int32) client and server function without hanging like
>>> before
>>> >
>>> > So...its working, but is this the right fix?
>>>
>>> You probably want to check where the unaligned memory access is
>>> happening. Can you run your float_client from within gdb? This should
>>> allow you to get a backtrace once the kernel has sent the signal (bus
>>> error) from the alignment trap.
>>>
>>> Cheers,
>>>
>>> Rene
>>>
>>> Getting some more meaningful backtraces now - catch bus errors for both
>> the float64's and the int32's in some cases, some with, some without that
>> memcopy patch above. I'll put together some results when I get back to work
>> in the morning.
>>
>>
>>
>>
>>> -
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>>> Safe and Secure Cognitive Systems             D-28359 Bremen
>>>
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>>
>>
>>
>> --
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>>
>
>
>
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