Gas altmacro macro with a percent sign in a default parameter fails with “% operator needs absolute expression”

Question

I want to create a macro like the following:

.altmacro

.macro assert_eq a, b=%eax
    LOCAL ok
    #...
.endm

To be used as:

Answer 1

You can add

.att_syntax noprefix

and than call the macro as

assert_eq $1, eax