运行时覆盖框架将可执行有效载荷从 eMMC FATFS 加载到共享的 SRAM 覆盖槽中。加载过程由 BootApp_emmcOverlayLoadAndRun() 函数实现。

加载器首先读取并验证覆盖包标头。然后，清除共享 SRAM 覆盖槽，并将可执行有效载荷映像从包文件复制到覆盖执行区域。

有效载荷映像加载到 SRAM 后，由 BootApp_emmcOverlayExecute() 函数执行。执行完成后，有效载荷会将控制权交还给驻留的 boot_app 运行时。然后，相同的 SRAM 覆盖槽可重复用于另一个有效载荷包。

下面是一个与有效载荷加载和执行相关的代码片段。

int32_t BootApp_emmcOverlayLoadAndRun(const char *payloadFile,
                                      BootApp_EmmcOverlayCtx *ctx)
{
    BootApp_EmmcOverlayPkgHeader hdr;
    int32_t status;
    void *slotBase = (void *)((uintptr_t)BOOTAPP_EMMC_OVERLAY_SLOT_BASE);

    if ((payloadFile == NULL) || (ctx == NULL))
    {
        return CSL_EBADARGS;
    }

    memset(&hdr, 0, sizeof(hdr));
    status = BootApp_emmcOverlayReadFile(payloadFile, 0U, &hdr, sizeof(hdr));
    if (status != CSL_PASS)
    {
        return status;
    }

    status = BootApp_emmcOverlayValidateHeader(payloadFile, &hdr);
    if (status != CSL_PASS)
    {
        return status;
    }

    memset(slotBase, 0, BOOTAPP_EMMC_OVERLAY_SLOT_SIZE);
    CacheP_wbInv(slotBase, BOOTAPP_EMMC_OVERLAY_SLOT_SIZE);

    status = BootApp_emmcOverlayReadFile(payloadFile,
                                         (uint32_t)sizeof(hdr),
                                         slotBase,
                                         hdr.codeSize);
    if (status != CSL_PASS)
    {
        return status;
    }

    UART_printf("emmc_overlay: loaded %s code=%u entryOffset=%u slot=0x%x\r\n",
                payloadFile,
                hdr.codeSize,
                hdr.entryOffset,
                (uint32_t)((uintptr_t)slotBase));

    status = BootApp_emmcOverlayExecute(slotBase, hdr.codeSize, hdr.entryOffset, ctx);
    return status;
}

static void BootApp_emmcOverlaySyncForExec(void *addr, uint32_t size)
{
    CacheP_wbInv(addr, size);
    CSL_armR5CacheInvalidateAllIcache();
    CSL_armR5Dsb();
    CSL_armR5Isb();
}

int32_t BootApp_emmcOverlayExecute(void *slotBase,
                                   uint32_t codeSize,
                                   uint32_t entryOffset,
                                   BootApp_EmmcOverlayCtx *ctx)
{
    uintptr_t entryAddr;
    BootApp_EmmcOverlayEntry entry;

    if ((slotBase == NULL) || (ctx == NULL) || (codeSize == 0U) || (entryOffset >= codeSize))
    {
        return CSL_EBADARGS;
    }

    BootApp_emmcOverlaySyncForExec(slotBase, codeSize);

    entryAddr = ((uintptr_t)slotBase) + ((uintptr_t)entryOffset);

    /* R5F executes Thumb code. Force bit[0] for function pointer call. */
    entryAddr |= (uintptr_t)0x1U;
    entry = (BootApp_EmmcOverlayEntry)entryAddr;

    UART_printf("emmc_overlay: execute entry=0x%x codeSize=%u entryOffset=%u\r\n",
                (uint32_t)entryAddr,
                codeSize,
                entryOffset);

    entry(ctx);

    CSL_armR5Dsb();
    CSL_armR5Isb();

    return CSL_PASS;
}