disassemble on Linux x64

[jj shen]

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