gdb can not find debug info on Centos

问题

I am trying to figure out a very strange issue. I have CentOS 6.5 system with gdb:

GNU gdb (GDB) Red Hat Enterprise Linux (7.2-75.el6)

and gcc:

gcc (GCC) 4.8.2 20131212 (Red Hat 4.8.2-8)

I have this file:

#include<stdio.h>
int main()
{
    printf("OK!");
    return 0;
}

which I compile with:

gcc -o a a.c -g -O0

The file seems to be fine:

$ file a
a: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped

But when I try to debug it, this happens:

$ gdb a
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-75.el6)
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from a...done.
(gdb) b main
Breakpoint 1 at 0x4004e4
(gdb) r 
Starting program: a 

Breakpoint 1, 0x00000000004004e4 in main ()
(gdb) l
1   /* Run time dynamic linker.
2      Copyright (C) 1995-2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
3      This file is part of the GNU C Library.
4   
5      The GNU C Library is free software; you can redistribute it and/or
6      modify it under the terms of the GNU Lesser General Public
7      License as published by the Free Software Foundation; either
8      version 2.1 of the License, or (at your option) any later version.
9   
10     The GNU C Library is distributed in the hope that it will be useful,
(gdb) l main
No line number known for main.

I.e., gdb refuses to see any debug information. Anybody has an idea what could be a problem here?