How do I create a macro with conditional assembly

Question

How do I create a macro where you can leave out a parameter? When left out it should remove a piece of code.

Answer 1

From https://sourceware.org/binutils/docs/as/If.html we can use .ifnb "if not blank"

.macro mymacro arg1, arg2
  li a0, arg1

.ifnb arg2
  li a1, arg2
.endif
  call my_fun
.endm

mymacro 0xdead, 0xbeef // will include li a1, arg2
mymacro 0xdead // will not include li a1, arg2