Handling aliases in debug information

[Andrew Haley]

In this program, a and b are aliases for the same variable:

int
main (int argc, char *argv[])
{
  union
  {
    int a;
    int b;
  };
  a = argc;
  return b;
}

But debugging is hard:

cuddles:~ $ g++ -v
Reading specs from /usr/local/lib/gcc/i686-pc-linux-gnu/3.4/specs
Configured with: '/local/aph/gcc/gcc/configure' '--enable-threads=posix '--enable-languages=c,c++,java : (reconfigured) 
Thread model: posix
gcc version 3.4 20030915 (experimental)
cuddles:~ $ g++ union.cc -g
cuddles:~ $ gdb ./a.out
GNU gdb 5.2.1
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu"...
(gdb) b main
Breakpoint 1 at 0x8048434: file union.cc, line 10.
(gdb) r
Starting program: /cuddles/aph/home/a.out 

Breakpoint 1, main (argc=1, argv=0xbfffdbc4) at union.cc:10
10        a = argc;
(gdb) n
11        return b;
(gdb) p a
No symbol "a" in current context.
(gdb) info locals
No locals.

Is this because

a.  g++ is not generating good debug info for anonymous unions?
b.  gdb is not interpreting g++ debug info correctly?
c.  Some other reason?

Thanks,
Andrew.