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
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