U-Boot FIT镜像启动异常问题排查与原因分析

算力阿峰

2026-7-4

问题分析：FIT镜像卡在Starting kernel ...的原因

问题现象

通过Yocto（meta-updater层）构建的U-Boot FIT镜像启动时卡在Starting kernel ...阶段
手动将kernel或device tree复制到其他内存地址后用bootz启动，或者调整.its文件把device tree放在kernel之前，镜像就能正常运行

原始配置与镜像信息

原始.its文件

/dts-v1/;

/ {
        description = "Kernel fitImage for FSLC FrameBuffer/5.10.9+gitAUTOINC+32513c25d8/exappscreen";
        #address-cells = <1>;

        images {
                kernel-1 {
                        description = "Linux kernel";
                        data = /incbin/("linux.bin");
                        type = "kernel";
                        arch = "arm";
                        os = "linux";
                        compression = "none";
                        load = <0x80008000>;
                        entry = <0x80008000>;
                        hash-1 {
                                algo = "sha256";
                        };
                };
                fdt-exappscreen.dtb {
                        description = "Flattened Device Tree blob";
                        data = /incbin/("arch/arm/boot/dts/exappscreen.dtb");
                        type = "flat_dt";
                        arch = "arm";
                        compression = "none";
                        
                        hash-1 {
                                algo = "sha256";
                        };
                };
                ramdisk-1 {
                        description = "initramfs-ostree-image";
                        data = /incbin/("/home/dane/yocto/fsl-community-bsp/exappscreen/tmp/deploy/images/exappscreen/initramfs-ostree-image-exappscreen.cpio.gz");
                        type = "ramdisk";
                        arch = "arm";
                        os = "linux";
                        compression = "none";
                        
                        
                        hash-1 {
                                algo = "sha256";
                        };
                };
    };

        configurations {
                default = "conf-exappscreen.dtb";
                conf-exappscreen.dtb {
                        description = "1 Linux kernel, FDT blob, ramdisk";
                        kernel = "kernel-1";
                        fdt = "fdt-exappscreen.dtb";
                        ramdisk = "ramdisk-1";
                        
                        
                        hash-1 {
                                algo = "sha256";
                        };
                };
    };
};

原始FIT镜像iminfo输出

## Checking Image at 82000000 ...
   FIT image found
   FIT description: Kernel fitImage for FSLC FrameBuffer/5.10.9+gitAUTOINC+32513c25d8/exappscreen
   Created:         2021-03-09   2:17:18 UTC
    Image 0 (kernel-1)
     Description:  Linux kernel
     Created:      2021-03-09   2:17:18 UTC
     Type:         Kernel Image
     Compression:  uncompressed
     Data Start:   0x82000100
     Data Size:    7806336 Bytes = 7.4 MiB
     Architecture: ARM
     OS:           Linux
     Load Address: 0x80008000
     Entry Point:  0x80008000
     Hash algo:    sha256
     Hash value:   cf08dd91b86a8478417c12398866832358463797dc6990be5ae33a48c4fae5d5
    Image 1 (fdt-exappscreen.dtb)
     Description:  Flattened Device Tree blob
     Created:      2021-03-09   2:17:18 UTC
     Type:         Flat Device Tree
     Compression:  uncompressed
     Data Start:   0x82771f8c
     Data Size:    32086 Bytes = 31.3 KiB
     Architecture: ARM
     Hash algo:    sha256
     Hash value:   8f08ffc245d6dd1a70a4c6a85bac46b2007af3594237179f3cdc89c0892522a1
    Image 2 (ramdisk-1)
     Description:  initramfs-ostree-image
     Created:      2021-03-09   2:17:18 UTC
     Type:         RAMDisk Image
     Compression:  uncompressed
     Data Start:   0x82779db0
     Data Size:    1864194 Bytes = 1.8 MiB
     Architecture: ARM
     OS:           Linux
     Load Address: unavailable
     Entry Point:  unavailable
     Hash algo:    sha256
     Hash value:   fb57b408c01ed997e07be816393940ae618b8b20d37b85ac1b47e4a5215bb783
    Default Configuration: 'conf-exappscreen.dtb'
    Configuration 0 (conf-exappscreen.dtb)
     Description:  1 Linux kernel, FDT blob, ramdisk
     Kernel:       kernel-1
     Init Ramdisk: ramdisk-1
     FDT:          fdt-exappscreen.dtb
     Hash algo:    sha256
     Hash value:   unavailable
## Checking hash(es) for FIT Image at 82000000 ...
   Hash(es) for Image 0 (kernel-1): sha256+
   Hash(es) for Image 1 (fdt-exappscreen.dtb): sha256+
   Hash(es) for Image 2 (ramdisk-1): sha256+

修改后可正常运行的配置与镜像信息

修改后的.its文件

/dts-v1/;

/ {
        description = "Kernel fitImage for FSLC FrameBuffer/5.10.9+gitAUTOINC+32513c25d8/exappscreen";
        #address-cells = <1>;

        images {
                fdt-exappscreen.dtb {
                        description = "Flattened Device Tree blob";
                        data = /incbin/("./exappscreen--5.10.9+git0+32513c25d8-r0-exappscreen-20231120190329.dtb");
                        type = "flat_dt";
                        arch = "arm";
                        compression = "none";
                        
                        hash-1 {
                                algo = "sha256";
                        };
                };
                kernel-1 {
                        description = "Linux kernel";
                        data = /incbin/("./zImage--5.10.9+git0+32513c25d8-r0-exappscreen-20231120190329.bin");
                        type = "kernel";
                        arch = "arm";
                        os = "linux";
                        compression = "none";
                        load = <0x80008000>;
                        entry = <0x80008000>;
                        hash-1 {
                                algo = "sha256";
                        };
                };
                ramdisk-1 {
                        description = "initramfs-ostree-image";
                        data = /incbin/("./initramfs-ostree-image-exappscreen-20231129181607.cpio.gz");
                        type = "ramdisk";
                        arch = "arm";
                        os = "linux";
                        compression = "gzip";
                        
                        
                        hash-1 {
                                algo = "sha256";
                        };
                };
    };

        configurations {
                default = "conf-exappscreen.dtb";
                conf-exappscreen.dtb {
                        description = "1 Linux kernel, FDT blob, ramdisk";
                        kernel = "kernel-1";
                        fdt = "fdt-exappscreen.dtb";
                        ramdisk = "ramdisk-1";
                        
                        
                        hash-1 {
                                algo = "sha256";
                        };
                };
    };
};

修改后FIT镜像iminfo输出

## Checking Image at 82000000 ...
   FIT image found
   FIT description: Kernel fitImage for FSLC FrameBuffer/5.10.9+gitAUTOINC+32513c25d8/exappscreen
   Created:         2023-12-01  13:27:09 UTC
    Image 0 (fdt-exappscreen.dtb)
     Description:  Flattened Device Tree blob
     Created:      2023-12-01  13:27:09 UTC
     Type:         Flat Device Tree
     Compression:  uncompressed
     Data Start:   0x82000114
     Data Size:    32086 Bytes = 31.3 KiB
     Architecture: ARM
     Hash algo:    sha256
     Hash value:   8f08ffc245d6dd1a70a4c6a85bac46b2007af3594237179f3cdc89c0892522a1
    Image 1 (kernel-1)
     Description:  Linux kernel
     Created:      2023-12-01  13:27:09 UTC
     Type:         Kernel Image
     Compression:  uncompressed
     Data Start:   0x82007f30
     Data Size:    7806336 Bytes = 7.4 MiB
     Architecture: ARM
     OS:           Linux
     Load Address: 0x80008000
     Entry Point:  0x80008000
     Hash algo:    sha256
     Hash value:   cf08dd91b86a8478417c12398866832358463797dc6990be5ae33a48c4fae5d5
    Image 2 (ramdisk-1)
     Description:  initramfs-ostree-image
     Created:      2023-12-01  13:27:09 UTC
     Type:         RAMDisk Image
     Compression:  gzip compressed
     Data Start:   0x82779db0
     Data Size:    1864194 Bytes = 1.8 MiB
     Architecture: ARM
     OS:           Linux
     Load Address: unavailable
     Entry Point:  unavailable
     Hash algo:    sha256
     Hash value:   fb57b408c01ed997e07be816393940ae618b8b20d37b85ac1b47e4a5215bb783
    Default Configuration: 'conf-exappscreen.dtb'
    Configuration 0 (conf-exappscreen.dtb)
     Description:  1 Linux kernel, FDT blob, ramdisk
     Kernel:       kernel-1
     Init Ramdisk: ramdisk-1
     FDT:          fdt-exappscreen.dtb
     Hash algo:    sha256
     Hash value:   unavailable

原因分析

从配置和镜像信息对比可以看出，核心差异在于FIT镜像内部的文件存储顺序，以及由此导致的内存覆盖问题：

原始镜像的内存布局冲突
原始FIT镜像加载在0x82000000地址，其中kernel数据从0x82000100开始，大小7.4MiB，结束地址为0x82000100 + 0x76C000 = 0x8276C100。虽然device tree起始地址0x82771F8C看起来和kernel不重叠，但问题出在kernel自身运行时会覆盖FDT所在的内存区域。
ARM内核启动时，会将自身从加载地址0x80008000复制到高端内存（通常是内存末尾附近），或在运行过程中使用FDT所在区域作为临时缓冲区，导致FDT被破坏，内核无法正确解析硬件信息，最终卡在Starting kernel ...阶段。
修改后镜像的内存布局避免了冲突
修改.its文件将FDT放在kernel之前，FDT的起始地址是0x82000114，大小仅31.3KiB，结束地址为0x82000114 + 0x7D56 = 0x82007E6A，而kernel从0x82007F30开始，两者完全不重叠。此时内核启动时，即使操作自身加载区域附近的内存，也不会覆盖FDT的数据，内核能正常读取FDT完成初始化。
手动启动可行的原因
用bootz手动启动时，kernel和FDT被复制到了其他内存地址，避开了原始FIT镜像所在的内存区域，避免了内核运行时对FDT的覆盖，因此能正常启动。

另外注意到修改后的ramdisk启用了gzip压缩，但这不是核心原因——原始镜像中ramdisk的位置和修改后一致，且手动启动时未修改ramdisk压缩方式也能正常运行，所以压缩方式不影响启动结果。

内容的提问来源于stack exchange，提问作者Dane

U-Boot FIT镜像启动异常问题排查与原因分析

问题现象 #

原始配置与镜像信息 #

原始.its文件 #

原始FIT镜像iminfo输出 #

修改后可正常运行的配置与镜像信息 #

修改后的.its文件 #

修改后FIT镜像iminfo输出 #

原因分析 #