assemblyx86mnemonics

Assembly JLE jmp instruction example


How do you use the jump family of instructions?

This is what they've got:

JL label
"It" jumps if it is less than or if it is not larger than or equal to.

My question is what is it in this sentence? Say I have a variable in ebx and I want to jump to label there: if ebx is <= 10.

Specifically I'm interested in using the x86 jump family of instructions


Solution

  • The jump itself checks the flags in the EFL register. These are usually set with TEST or CMP(or as a side effect of many other instructions).

    CMP ebx,10
    JLE there
    

    See also: The art of assembly language on CMP

    As a sidenote: You should get the Intel reference manuals. In particular the two part "IntelĀ® 64 and IA-32 Architectures Software Developer's Manual Volume 2: Instruction Set Reference" which describes all x86 instructions.