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Filename : last_100_frees.stp

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#!/usr/bin/stap

global bt%[100]

probe process("/lib*/libc.so.*").function("free") {
  // we use @defined($mem) here because on 64 bit systems, the
  // wildcard search takes us through both 64 bit and 32 bit
  // libc (which doesn't have debuginfo), this means the probe
  // point resolved from the 32 bit library has no context info
  if (@defined($mem)) {
    bt[execname(),tid(),$mem,sprint_ubacktrace()]
      <<< local_clock_ns()
  }
  // Any monotonically increasing expression would do.
  // With some arbitrary expression or constant instead,
  // at worst we get the last 100ish results out of order.
}

probe end,error {
  foreach ([e,t,p,b] in bt @max+) // iterate in increasing index order
     printf("free #%d: %s[%d], pointer %p:\n%s\n\n",
            @max(bt[e,t,p,b]), e, t, p, b)
}