gcc - 如何在 ARM 程序集中声明一个定义并使用它？

Question

我正在尝试使用icachetest，它有一个名为icache.scontains 的文件：

#define LOOP \
        subs    r2, r2, #1             ; \ 
        mov     r0, r0                 ; \
        mov     r0, r0                 ; \ 
        mov     r0, r0                 ; \
        mov     r0, r0                 ; \
        mov     r0, r0                 ; \
        beq     end_loop               ; \
        mov     r0, r0                 ; \

我 arm-eabi-as用来编译这个项目，但我得到这个错误：

  AS     icache.S
icache.S: Assembler messages:
icache.S:16: Error: junk at end of line, first unrecognized character is `\'
icache.S:17: Error: junk at end of line, first unrecognized character is `\'
icache.S:18: Error: junk at end of line, first unrecognized character is `\'
icache.S:19: Error: junk at end of line, first unrecognized character is `\'
icache.S:20: Error: junk at end of line, first unrecognized character is `\'
icache.S:21: Error: junk at end of line, first unrecognized character is `\'
icache.S:22: Error: junk at end of line, first unrecognized character is `\'
icache.S:23: Error: junk at end of line, first unrecognized character is `\'
icache.S:52: Error: bad instruction `loop LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP'
icache.S:53: Error: bad instruction `loop LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP'
icache.S:54: Error: bad instruction `loop LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP'

Answer 1

正如其他人指出的那样，这LOOP是一个C宏。由于它没有参数或条件，它很容易被gas宏替换。

.macro  LOOP
    subs    r2, r2, #1
    mov     r0, r0
    mov     r0, r0
    mov     r0, r0
    mov     r0, r0
    mov     r0, r0
    beq     end_loop
    mov     r0, r0
.endm

此后它的行为与 a 相同#define，但需要注意的是每行只允许一个。ARM 汇编器确实允许一行中有多个操作码（据我所知）。

您可以使用.rept重复宏。

.rept 2048
   LOOP
.endr