未知的寄存器名“r3”

void
ble_phy_rxpdu_copy(uint8_t *dptr, struct os_mbuf *rxpdu)
{
    uint32_t rem_len;
    uint32_t copy_len;
    uint32_t block_len;
    uint32_t block_rem_len;
    void *dst;
    void *src;
    struct os_mbuf * om;
    /* Better be aligned */
    assert(((uint32_t)dptr & 3) == 0);
    block_len = rxpdu->om_omp->omp_databuf_len;
    rem_len = OS_MBUF_PKTHDR(rxpdu)->omp_len;
    src = dptr;
    /*
     * Setup for copying from first mbuf which is shorter due to packet header
     * and extra leading space
     */
    copy_len = block_len - rxpdu->om_pkthdr_len - 4;
    om = rxpdu;
    dst = om->om_data;
    while (true) {
        /*
         * Always copy blocks of length aligned to word size, only last mbuf
         * will have remaining non-word size bytes appended.
         */
        block_rem_len = copy_len;
        copy_len = min(copy_len, rem_len);
        copy_len &= ~3;
        dst = om->om_data;
        om->om_len = copy_len;
        rem_len -= copy_len;
        block_rem_len -= copy_len;
        __asm__ volatile (".syntax unified              \n"
                          "   mov  r4, %[len]           \n"
                          "   b    2f                   \n"
                          "1: ldr  r3, [%[src], %[len]] \n"
                          "   str  r3, [%[dst], %[len]] \n"
                          "2: subs %[len], #4           \n"
                          "   bpl  1b                   \n"
                          "   adds %[src], %[src], r4   \n"
                          "   adds %[dst], %[dst], r4   \n"
                          : [dst] "+r" (dst), [src] "+r" (src),
                            [len] "+r" (copy_len)
                          :
                          : "r3","r4" , "memory"
                         );
        if ((rem_len < 4) && (block_rem_len >= rem_len)) {
            break;
        }
        /* Move to next mbuf */
        om = SLIST_NEXT(om, om_next);
        copy_len = block_len;
    }
    /* Copy remaining bytes, if any, to last mbuf */
    om->om_len += rem_len;
    __asm__ volatile (".syntax unified              \n"
                      "   b    2f                   \n"
                      "1: ldrb r3, [%[src], %[len]] \n"
                      "   strb r3, [%[dst], %[len]] \n"
                      "2: subs %[len], #1           \n"
                      "   bpl  1b                   \n"
                      : [len] "+r" (rem_len)
                      : [dst] "r" (dst), [src] "r" (src)
                      : "r3", "memory"
                     );
    /* Copy header */
    memcpy(BLE_MBUF_HDR_PTR(rxpdu), &g_ble_phy_data.rxhdr,
           sizeof(struct ble_mbuf_hdr));
}