Arguments between the BL1 and BL2 is overlap by zeromem when BL2 start.

1. BL2 save r3 to r12

arm-trusted-firmware/bl2/aarch32/bl2_entrypoint.S

    /*---------------------------------------------
     * Save arguments x0 - x3 from BL1 for future
     * use.
     * ---------------------------------------------
     */
    mov r9, r0
    mov r10, r1
    mov r11, r2
    mov r12, r3

2. BL2 call zeromem to clear bss

arm-trusted-firmware/bl2/aarch32/bl2_entrypoint.S

    ldr r0, =__BSS_START__
    ldr r1, =__BSS_END__
    sub     r1, r1, r0
    bl  zeromem

arm-trusted-firmware/lib/aarch32/misc_helpers.S

    tmp      .req r12 /* Temporary scratch register */

r12 used as scratch register

3. r3 restore from r12

arm-trusted-firmware/bl2/aarch32/bl2_entrypoint.S

    mov r0, r9
    mov r1, r10
    mov r2, r11
    mov r3, r12

I can try to save it in other registers, but can not guarantee that the register will not be damaged. Is there any better way to deal with this problem?

Thanks.