ARM32 base instruction -- blx

BLX

带返回和状态切换的跳转指令，此指令只适用 ARMv5T*, ARMv6*, ARMv7。

BLX (immediate)

    Branch with Link calls a subroutine at a PC-relative address.
    Branch with Link and Exchange Instruction Sets (immediate) calls a subroutine at a PC-relative address, and changes instruction set from ARM to Thumb, or from Thumb to ARM.

    带链接的分支调用PC相对地址处的子程序。
    带链接和交换指令集的分支（立即）调用PC相对地址处的子程序，并将指令集从ARM更改为Thumb，或从Thumb更改为ARM。

    ARM指令是4字节对齐，最低两位可以用作状态指示，如果最低两位是0，表示切换到ARM状态。

    BLX<c> <label>

BLX (register)

    Branch with Link and Exchange (register) calls a subroutine at an address and instruction set specified by a register.

    带链接和交换（寄存器）的分支在寄存器指定的地址和指令集调用子例程。

    BLX<c> <Rm>

blx immediate :

   10534:       b580            push    {r7, lr}
   10536:       b082            sub     sp, #8
   10538:       af00            add     r7, sp, #0
   1053a:       6078            str     r0, [r7, #4]    /* this 指针 */
                printf("%d, %d\n", v1, v2);
   1053c:       687b            ldr     r3, [r7, #4]    /* r3 = this */
   1053e:       6819            ldr     r1, [r3, #0]    /* r1 = [r3+0] = v1 */
   10540:       687b            ldr     r3, [r7, #4]    /* r3 = this */
   10542:       685b            ldr     r3, [r3, #4]    /* r3 = [r3+4] = v2 */
   10544:       461a            mov     r2, r3          /* r2 = r3 = v2 */
   10546:       f240 50a8       movw    r0, #1448       /* r0 = 0x5a8 */
   1054a:       f2c0 0001       movt    r0, #1           /* r0 = (1 << 16) | 0x05a8 = 0x105a8，此为数据段地址 */
   1054e:       f7ff ef38       blx     103c0 <printf@plt>  /* printf(r0, r1, r2) */

blx register :

   104dc:       e51b3008        ldr     r3, [fp, #-8]   ; x
   104e0:       e1a03103        lsl     r3, r3, #2      ; r3 = x << 2 , [0, 4, 8]
   104e4:       e24b2004        sub     r2, fp, #4      ; r2 = fp - 4
   104e8:       e0823003        add     r3, r2, r3      ; r3 = r2 + r3 [0|4|8] --> (fp-4)+[0|4|8]
   104ec:       e5133014        ldr     r3, [r3, #-20]  ; 0xffffffec    r3 = 0:[(fp-4)-20], 1:[(fp-4)+4-20], 2:[(fp-4)+8-20]
   104f0:       e50b300c        str     r3, [fp, #-12]  ; save function address, 0:r3=(fp-24), 1:r3=(fp-20), 2:r3=(fp-16)
        f();
   104f4:       e51b300c        ldr     r3, [fp, #-12] ; load function address
   104f8:       e12fff33        blx     r3             ; execl