Get error: invalid combination of opcodes and operands when push bl

Question

I get the message error: invalid combination of opcodes and operands from nasm when doing

push bl

This code looks perfectly valid to me so why do I get this error?

Answer 1

There's no PUSH reg8 instruction on the x86. Push the corresponding 16- or 32-bit register instead ( bx or ebx ). See page 4-265 in Intel's Software Developer's Manual Vol 2.

Alternatively you could use sub and mov to store bytes on the stack if you really need to place a series of bytes on the stack without any space in between them.