Learning new ways to procrastinate^W, so there is what i've learned about gdb so far:
si - step by instruction
layout asm - show instructions
layout regs - show registers
display/3i $pc - show 3 next instructions after each step
p $r13, p $rax - print register values
p/t $r13 - print as binary value
i reg - print all registers
x/i 0x40200d - instruction at address
x/d 0x40200d - decimal value at address
x/i $pc - current instruction at PC
p $rsi, x/d $ - evaluate address in rsi, then print a value under an address
p $eflags - print processor flags (see notes for register names) ($ps is an alias for $eflags)
set $r13 = 123 - set register value
set $sp += 4 - increase stack pointer value by 4.
set disassembly-flavor intel - switch asm syntax to Intel