[libunwind] Circular links in the script/rs cache?

[Arun Sharma]

I'm noticing a few cases where there is a circular linked list in 
rs_lookup() (which is derived from script_lookup()).

(gdb) p (cache->buckets[1])
$2 = {next = 0x0, reg = {{where = DWARF_WHERE_SAME, val = 0}, {
      where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_SAME, 
val = 0},
    {where = DWARF_WHERE_CFAREL, val = 18446744073709551592}, {
      where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_SAME, 
val = 0},
    {where = DWARF_WHERE_CFAREL, val = 18446744073709551600}, {
      where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_SAME, 
val = 0},
    {where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_SAME, val 
= 0}, {
      where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_SAME, 
val = 0},
    {where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_SAME, val 
= 0}, {
      where = DWARF_WHERE_SAME, val = 0}, {where = DWARF_WHERE_CFAREL,
      val = 18446744073709551608}, {where = DWARF_WHERE_REG, val = 7}, {
      where = DWARF_WHERE_UNDEF, val = 32}}, ip = 15269205,
  ret_addr_column = 16, lru_chain = 0, coll_chain = 1, hint = 0}

i.e cache->buckets[1].coll_chain = 1.

So the loop never terminates. I don't have an easily reproducible test case.

What is protecting us from this case in the script cache?

        -Arun