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.
Ulf
