AssemblyLanguage code is not portable across different [CPU] architectures, of which there are many: Intel [x86], [MIPS], and the Motorola m68000 series, to name but a few. Early versions of [Unix] were written in assembler, and when BellLabs got new machines, they re-wrote their operating system for the new MachineCode, until they finally re-wrote most of it in [C] in 1973. 

  

 AssemblyLanguage code is difficult to understand and maintain. It is usually easier to start from scratch than to debug faulty code. 

  

  

 Here is an example. First, the [C] code: 

  int main(void) { 

  int i; 

 __movl__, __jmp__, __addl__, etc are mnemonics for individual [CPU] instruction OpCodes. __%esp__, ___%ebp__ etc are mnemonics for registers. For example, __%esp__ is the [Stack] Pointer - it points to the top of the current process's [Stack]. The first __movl__ copies the value in __%esp__ into __%ebp__, then the __subl__ subtracts 24 off __%esp__, so that the [Stack] has grown by 24 bytes. The next __movl__ copies the value 5 into [Stack], 4 bytes below its end. This address is where the variable __i__ is being stored, so all accesses to __i__ in the [C] code become references to this memory location in MachineCode. We can also witness an optimization here: instead of doing i*3, it does i+(i+i). That's the __addl__ and __leal__ instructions. Below that, it puts some pointers (to __printf__'s arguments) on the stack and calls __printf__, which pulls its arguments from the stack. 

  

 As you can see, explaining what AssemblyLanguage code is doing line-by-line is tediously boring. This is how programmers used to write code, and it is a common fact that AssemblyLanguage programmers get paid more per line of code than those who hack away in higher level languages. 

  

  

  

 Another sample piece of [AssemblyLanguage] code for [Linux] can be found in the [HelloWorld] page. 

  

 ---- 

 CategoryProgrammingLanguages