find the file:line of the current ruby thread that crashed

find-line-no.py

m_pos = int(gdb.parse_and_eval("ruby_current_thread->cfp->pc - ruby_current_thread->cfp->iseq->iseq_encoded"))
if m_pos > 0:
  m_pos -= 1

size = int(gdb.parse_and_eval("ruby_current_thread->cfp->iseq->line_info_size"))
if size == 0:
  res = 0
elif size == 1:
  res = int(gdb.parse_and_eval("ruby_current_thread->cfp->iseq->line_info_table[0].line_no"))
else:
  ix = 1
  while ix < size:
    pos = int(gdb.parse_and_eval("ruby_current_thread->cfp->iseq->line_info_table[{}].position".format(ix)))
    if pos == m_pos:
      break
    elif pos > m_pos:
      ix -= 1
      break
    ix += 1
  if ix == size:
    ix -= 1
  res = int(gdb.parse_and_eval("ruby_current_thread->cfp->iseq->line_info_table[{}].line_no".format(ix)))

path = gdb.parse_and_eval("RSTRING_PTR(ruby_current_thread->cfp->iseq->location.path)").string()
gdb.write("{}:{}\n".format(path, res))

Usage:

(gdb) bt 5
#0  0x00007f5adab06035 in raise () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007f5adab0979b in abort () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x00007f5adc0c7f4c in rb_bug (fmt=0x7f5adc0f863c "Segmentation fault at %p") at error.c:346
#3  0x00007f5adbfe88d3 in sigsegv (sig=<optimized out>, info=0x7f5ade111bf0, ctx=<optimized out>) at signal.c:824
#4  <signal handler called>
(More stack frames follow...)
(gdb) source find-line-no.py
/super/secret/file.rb:50
(gdb)