When parsing a linespec without an enclosing symbol, add_sal_to_sals
(linespec.c:888) assigns "canonical->suffix = NULL;", but then, in
decode_line_full (linespec.c:2462) we have
"gdb_assert(state->canonical_names[i].suffix != NULL);"

Although the case is hard to tickle--I only found it myself with an
object file with an erroneous line table entry--GDB shouldn't crash,
and recovery is quite straight-forward.

The following patch simply assigns the symbol name as "<unknown>"
instead of NULL, allowing the debugger to make forward progress in the
face of an erroneous debug line table entry.

Sterling

gdb/ChangeLog
2013-12-17  Sterling Augustine  <saugustine@google.com>

        * linespec.c (add_sal_to_sals): Use "<unknown>" when a symbol
        isn't found.