Further Debugging in arm-elf-gdb

Here are a few quick words on using GDB, with particular reference to ARM files.

Inspect Registers

To have a look at a particular register, use the command print $[register_name]
For example,

print $r0
print $r1
print $pc

print can be abbreviated to p

p $r0
p $r1
p $pc

Change Register Values

Use the command print $[register_name] = [value]
For example,

print $r0 = 10
print $r1 = 0x20
print $pc = _start

Again, the abbreviation p can be used in place of print

Formatting Output

Format can be specified by using /[symbol] after the print command. Possible symbols are:

a for address
x for hexadecimal
d for signed decimal
u for unsigned decimal
o for octal
t for binary ('two')
c for character
f for floating point

For example

print/a $pcprint/x $r0p/c $r1p/t $cpsr 

(Use the last command to check the NZCV and interrupt flags)