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When unwinding using frame pointers on ARM64, the return address of the
current function may not have been pushed into the stack when a function
was interrupted, which makes perf show an incorrect call graph to the
user.

Consider the following example program:

  void leaf() {
      /* long computation */
  }

  void parent() {
      // (1)
      leaf();
      // (2)
  }

  ... could be compiled into (using gcc -fno-inline -fno-omit-frame-pointer):

  leaf:
      /* long computation */
      nop
      ret
  parent:
      // (1)
      stp     x29, x30, [sp, -16]!
      mov     x29, sp
      bl      parent
      nop
      ldp     x29, x30, [sp], 16
      // (2)
      ret

If the program is interrupted at (1), (2), or any point in "leaf:", the
call graph will skip the callers of the current function. We can unwind
using the dwarf info and check if the return addr is the same as the LR
register, and inject the missing frame into the c...