Hi Peter,

Thanks for digging into this.  I've created a ticket at
https://github.com/ros/ros_comm/issues/184 to track this.

Tully


On Sun, Mar 3, 2013 at 2:59 AM, Austin Hendrix <legotown@aol.com> wrote:

> Awesome! I've been running into the same thing over the past few days, but
> I haven't had time to look into it extensively.
>
> I'll keep my eyes peeled for a patch. Have you made any measurements of
> how it affects performance on arm and x86?
>
> -Austin
>
> On Mar 3, 2013, at 2:23 AM, Peter Rudolph <semael23@gmail.com> wrote:
>
> > He guys!
> > I tried to solved and it seems solved! First i will explain the problem
> itself: while de-/serializing unaligned pointercasts are done. normally
> this is not a problem! but since newer versions of arm-gcc use float
> support with options -mfloat-abi=hard/softfp, there are many possibilities
> to hit this alignment fault, because NEON instructions must be aligned!
> This is a very big problem... compiling ROS with -Wcast-align shows the
> potential lines! Solving this by setting "-mno-unaligned-access" as
> compiler-flag does NOT work! Every prebuilt-compiler i used seemed to
> ignore this switch.
> >
> > example from www, demonstrates the error (compile it w/o any
> optimization(-O0), else compiler will re-align the pointercast, but this
> won't work for ROS, since everything is built w/ optimization(-O2)):
> >
> > #include <stdio.h>
> >
> > int main(int argc, char* argv[])
> > {
> >    char __attribute__ ((aligned(32))) buffer[8] = { 0 };
> >    float* fval_p;
> >
> >    fval_p = (float*)&buffer[1];
> >    *fval_p = 0.1234;
> >
> >    printf("\nfloat at &buf[1] is %f\n", *fval_p);
> >
> >    return 0;
> > }
> >
> > Build my own example from this, to check what works correctly and
> serious...
> >
> > Only possibility was to hack the correct lines in roscpp_serialization.
> I only changed the lines from pointercasts to simple memcpy's and now
> everything seems to work fine! No alignment faults, no bus errors, no
> kernel exceptions! Tried a lightweight openni version, my own robot stack,
> and gmapping! navigation stack will follow!
> >
> > Due to having no time now, patchfile will follow, too!
> >
> > Regards,
> > sem23
> > _______________________________________________
> > ros-users mailing list
> > ros-users@code.ros.org
> > https://code.ros.org/mailman/listinfo/ros-users
>
> _______________________________________________
> ros-users mailing list
> ros-users@code.ros.org
> https://code.ros.org/mailman/listinfo/ros-users
>