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Re: Problems with dwarf-getmacros test

Do you have the whole call stack of that failed __libdw_read_offset
call? Which source line in tests/dwarf-getmacros.c prints the "(null)"?

Actually I just managed to catch a backtrace by inserting an infinite
loop at the point where it would normally return -1. It turns out the
address we are looking for is not in the IDX_debug_info section, but in
the IDX_debug_macro section (which by itself isn't all that surprising,
but if that is a rule, how can this code ever work??).

The likely solution of the mystery is this piece of code in __libdw_in_section:

if (unlikely (addr < data->d_buf)
      || unlikely (data->d_size - (addr - data->d_buf) < size))
      __libdw_seterrno (DWARF_E_INVALID_OFFSET);
      return false;

If addr < data->d_buf we fail immediately. That's what's happening to me sometimes. However, if addr > data->d_buf, then it's likely much bigger, as the allocations of the different sections are unrelated. data->d_size is always 159 in this test case. Therefore, data->d_size - (addr - data->d_buf) will produce something negative, which then gets compared to a size_t, forcing it to overflow. size is 4, so this case never gets detected.


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