[SOLVED] In x86_64 Linux NASM, is it possible to have multiple opcodes on one line?

In x86_64 Linux NASM, is it possible to have multiple opcodes on one line?

In C, you are able to have multiple things on one line, like this:

int a; int b = 1; a = b;

Could you do this in assembly?

I tried searching for this on many websites and asked for help on some discord servers, but no luck.

Solution

Multiple opcodes sure, if you're writing the machine code by hand. db 0xff, 0xc0, 0xff, 0xc9 are the opcode + ModRM bytes that encode inc eax / dec ecx.

Multiple asm source instructions, no. Unlike the GNU assembler, there's no statement-separator character other than newline.

In GAS you can write inc eax; dec ecx if you want. The x86 GAS comment character is #, the statement separator is ; - it's a very different assembler from NASM.

@ecm points out one trick, though: you can define a NASM macro that puts each arg on a separate line, and use it like this:

foo   inc eax, {mov ebx, eax}, push rax

See the manual for the macro directives for iterating over macro parameters for a macro that takes an arbitrary number of them:

%macro foo 1-*      ; require 1 or more params
  %rep  %0          ; repeat for number of params
    %1              ; expand the first param on a line by itself
    %rotate 1       ; rotate the params so the second one is now first
  %endrep
%endmacro