support u(ret)probes
new sample script: scripts/uprobes-malloc.kp

sample script:

trace "uprobes:/lib/libc.so.6:0x000773c0" function (e) {
        printf("%20s\tentry:\t%s", execname(), e.tostring())
}

trace "uprobes:/lib/libc.so.6:0x000773c0%return" function (e) {
        printf("%20s\texit:\t%s", execname(), e.tostring())
}