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.
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:You probably want to check where the unaligned memory access is
> - 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?
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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Web: http://www.informatik.uni-bremen.de/agebv/en/ReneWagner
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