[ros-users] ros on armhf (beagleboard, pandaboard, raspberryPi, gumstix) error/alignment fault/kernel exception - possibly solved

[Peter Rudolph]

Hello again!

Posted my patch-file as comment on ticket. I saw that there is already a
patch-file which is declared as not multi-arch safe. So plz test it!
Used compiler defined macros ( gcc -dM -E - <<<'' ) __ARMEL__ and
__VFP_FP__ to ensure, that its only done on arm mcu with float-abi softfp
or hard enabled!

hopefully it helps!

Peter

2013/3/3 Tully Foote <tfoote at osrfoundation.org>

> 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 at 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 at 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
>> > _______________________________________________
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>> > https://code.ros.org/mailman/listinfo/ros-users
>>
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