problems using gprof

I’m trying to use gprof on QNX6.
with a simple test program, I see all reported times set to zero, while
the effective times should be different (the program use the CPU for at
least 10 seconds).
Using gprof on linux with the same (recompiled) test program, I see that
the report seems to be correct.

There are known problems with gprof on QNX6 or there are particular
compiling options or so to use it?

I have compiled my test program as:

gcc -pg main.c

obtaining an executable a.out; executing a.out (it last 10 seconds) I
obtain the gmon.out file, but execution gprof I obtain:

Flat profile:

Each sample counts as 0.001 seconds.
no time accumulated

% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 100000 0.00 0.00 f2
0.00 0.00 0.00 1 0.00 0.00 f1
0.00 0.00 0.00 1 0.00 0.00 f3
0.00 0.00 0.00 1 0.00 0.00 main