disassemble on Linux x64

Hi,

I try to disassemble a simple program on x64 Linux using GDB.

The test program is like:


> main()
> {
>   getuid();
> }
>

"disassemble main" shows that getuid() corresponds to "callq *addr*". But
when I try to "disassemble getuid" or "disassemble *addr*", GDB says it is
not a vaild function address.

Why, while it is ok on x86 Linux? Is callq a new instruction added by
x86-64? What is the difference to the call instruction?

Another question: do I need to use a 32-bit GDB to debug 32-bit program?

Thanks,

Shen