nasmshell

commands

1. as, assemble - set to assembly mode
2. disas - set to disassembly mode
3. bits - set bits (32 or 64)
4. exit, quit - exit shell

examples

assembling

$ nasmshell
nasm> push eax
50                       push eax
nasm> push eax ; retn 4
50                       push eax
C20400                   ret 0x4
nasm> push eax ; call [eax+1ch]
50                       push eax
FF501C                   call dword [eax+0x1c]
nasm> inc ecx; loop: push eax; push ebx; jmp loop
41                       inc ecx
50                       push eax
53                       push ebx
EBFC                     jmp short 0x1
nasm> times 3 movsb
A4                       movsb
A4                       movsb
A4                       movsb

disassembling

nasm> disas
disas mode
ndisasm> 50ff501c
50                       push eax
FF501C                   call dword [eax+0x1c]
ndisasm> 4141414141414141
41                       inc ecx
41                       inc ecx
41                       inc ecx
41                       inc ecx
41                       inc ecx
41                       inc ecx
41                       inc ecx
41                       inc ecx

x86-64

ndisasm> bits 64
ndisasm> as
assemble mode
nasm> push rax
50                       push rax
nasm> push rax ; push rbx
50                       push rax
53                       push rbx
nasm> jmp pastsym; sym: db 0x11,0x01,0x11,0xff; pastsym: lea rax, [rel sym]
EB04                     jmp short 0x6
1101                     adc [rcx],eax
11FF                     adc edi,edi
488D05F5FFFFFF           lea rax,[rel 0x2]