# Debugging with GDB

### (1)

``b'` cannot be used because these format letters are also used with the `x` command, where ``b'` stands for "byte"; see section Examining memory.

### (2)

This is a way of removing one word from the stack, on machines where stacks grow downward in memory (most machines, nowadays). This assumes that the innermost stack frame is selected; setting `$sp` is not allowed when other stack frames are selected. To pop entire frames off the stack, regardless of machine architecture, use `return`; see section Returning from a function.

### (3)

If you choose a port number that conflicts with another service, `gdbserver` prints an error message and exits.

### (4)

In ``gdb-4.16/gdb/refcard.ps'` of the version 4.16 release.

### (5)

If you have a more recent version of GDB than 4.16, look at the ``README'` file in the sources; we may have improved the installation procedures since publishing this manual.