The combination ARM6/FreeBSD is not supported.
Valgrind fully supports FreeBSD i386 and amd64. You can find information on the ports here FreeBSD stable port and here FreeBSD development port.
At a guess, Valgrind support for ARM won't be implemented until and if ARM becomes a Tier 1 platform or until someone steps forward to do the porting.
See also the Valgrind team's statement on porting:
Maintaining each port takes a lot of effort, more so than for most other programs. Valgrind is fragile due to the low-level nature of what it does. Also, each platform port has CPU-specific code, OS-specific code and platform-specific code, and testing all the combinations is difficult.
Update:
On FreeBSD you can use the very powerful dtrace tool for performance monitoring and debugging. It does have a steep learning curve, though.
My favorite debugging tool is still placing printf() in strategic locations. Say you suspect your program crashes in a large block of code. Place a printf in the middle, recompile and re-run. If you see the output, the error came after the printf. If you don't it was before the printf. You have now halved the size of the block containing the error. Now add another printf in the middle of the remaining suspicious code and repeat. This technique is called bisection. You can also use it to monitor the value of a variable.
I would suggest to wrap the debugging printf in a macro ([1], [2]), so you can leave them in the code but you can disable them for a release build.
