This is incorrect dwarf that I mistakenly generated in GCC's debug-early project.  I am generating two DW_TAG_label's for the same source label, and of of them doesn't have line information.

reynosa:/build/dearly/gcc$ cat a.c
int
main ()
{
here:
  return 0;
}

Faulty dwarf is:

 <2><4e>: Abbrev Number: 3 (DW_TAG_label)
    <4f>   DW_AT_name        : (indirect string, offset: 0x0): here     
    <53>   DW_AT_decl_file   : 1        
    <54>   DW_AT_decl_line   : 4        
 <2><55>: Abbrev Number: 4 (DW_TAG_label)
    <56>   DW_AT_name        : (indirect string, offset: 0x0): here     
    <5a>   DW_AT_decl_file   : 1        
    <5b>   DW_AT_decl_line   : 4        
    <5c>   DW_AT_low_pc      : 0x4004ca 

End result:

(gdb) b main
Breakpoint 1 at 0x4004ca: file a.c, line 5.
(gdb) r
Starting program: /home/build/dearly/gcc/a.out

Breakpoint 1, main () at a.c:5
5         return 0;
(gdb) b here
/source/binutils-gdb/gdb/linespec.c:2459: internal-error: decode_line_full: Assertion `result.nelts == 1 || canonical->pre_expanded' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)