将链接寄存器设置到ARM组件中的标签

Question

_start:
     mov    r0, #0                 @ Function number (index) to use
     mov    r1, #3                 @ First parameter
     mov    r2, #2                 @ Second parameter
     bl     arithfunc              @ Call the function

     swi    0x11                   @ Terminate

arithfunc:
     cmp    r0, #num_func
     bhs    DoAND                  @ If code is >=7, do operation 0
     adr    r3, JumpTable          @ Get the address of the jump table
     ldr    pc, [r3,r0,lsl #2] @ Jump to the routine (PC = R3 + R0*4)
     add    r0,r0, #1
     bne arithfunc

JumpTable:                             @ Table of function addresses
     .word  DoAND
     .word  DoOR
     .word  DoEOR
     .word  DoANDNOT
     .word  DoNOTAND
     .word  DoNOTOR
     .word  DoNOTEOR
DoAND:
     and    r11,r1,r2
     mov    pc, lr                 @ Return

DoOR:
     orr    r11,r1,r2             @ Operation 1 (R0 = R1 - R2)
     mov    pc,lr                  @ Return
DoEOR:
     eor    r11,r1,r2
     mov    pc,lr

如何将lr设置为不只运行一次就终止？

它一直运行到DoAND:，然后返回到开头。我知道这就是它的工作原理，但我想不出其他的方法。

我试着让它在arithfunc中循环。

Answer 1

不要使用mov pc, lr继续，因为这些不是子例程。只需使用一个简单的无条件分支back，例如：

arithfunc:
     cmp    r0, #num_func
     bhs    DoAND                  @ If code is >=7, do operation 0
     adr    r3, JumpTable          @ Get the address of the jump table
     ldr    pc, [r3,r0,lsl #2] @ Jump to the routine (PC = R3 + R0*4)
next:
     add    r0,r0, #1
     bne arithfunc

JumpTable:                             @ Table of function addresses
     .word  DoAND
     .word  DoOR
     .word  DoEOR
     .word  DoANDNOT
     .word  DoNOTAND
     .word  DoNOTOR
     .word  DoNOTEOR
DoAND:
     and    r11,r1,r2
     b next

DoOR:
     orr    r11,r1,r2             @ Operation 1 (R0 = R1 - R2)
     b next

DoEOR:
     eor    r11,r1,r2
     b next