The fib.exp testcase works on RHEL6, but is broken on RHEL7 and f20, since print_ubacktrace{,_brief}() doesn't return expected output there. It looks like the user-level root cause is simply presence of the .return probe:

 7.0 S x86_64 # cat test.c 
void f3(void){}
void f2(void){f3();}
void f1(void){f2();}
void f0(void){f1();}


int main() {
        f0();
        return 0;
}
 7.0 S x86_64 # gcc -g test.c 
 7.0 S x86_64 # stap -e 'probe process.function("f3") {print_ubacktrace_brief(); printf("\n")} probe process.function("f3").return {log("hey")}' -c './a.out'
f3+0x4
0x7fffffffe000

hey
 7.0 S x86_64 # stap -e 'probe process.function("f3") {print_ubacktrace_brief(); printf("\n")}' -c './a.out'
f3+0x4
f2+0x9
f1+0x9
f0+0x9
main+0x9
0x7fc7930beaf5

WARNING: Missing unwind data for module, rerun with 'stap -d /usr/lib64/libc-2.17.so'
 7.0 S x86_64 #