Use of ifdef in gas assembly language

问题

I have following assembly file mov.s

 .text
    .macro test_3
     and $3,%eax
    .endm

    movz:
    movzb   %al,%ax
     movzb   (%eax),%ax
     movzb   %al,%eax
        movzb   (%eax),%eax
    .ifdef test_3
        movzb33 %al,%rax
        movzb   (%rax),%rax
.endif

command as -o dump.o movz

In this code I want to test ifdef in assembly language so I have defined macro test_3.

According to my understanding it should print message Error: no such instruction: 'movzb33 %al,%rax' when I use assembler but it is not going inside ifdef so what is the problem?

回答1:

.ifdef checks if a symbol is defined, it does not test macros. In GNU AS and many other assemblers macros can only be used where an instruction is permitted.

来源：https://stackoverflow.com/questions/46272497/use-of-ifdef-in-gas-assembly-language