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--- jaysnote:android_bootimg [2018/11/21 17:39]
jaylee 创建
+++ jaysnote:android_bootimg [2021/06/22 23:14]
@@ 行 1: / 行 1: @@
-# android boot image
-全志 a64 linux sdk采用了android 的boot image，这里顺着该sdk系统理解android的引导镜像。
-如下`linux-3.10/build.sh `代码片段显示，在完成内核编译后，改脚本直接将kernel的二进制可执行文件和cpio的gzip压缩包rootfs.cpio.gz 一起合并进入boot.img。
-```bash
-#linux-3.10/build.sh line.27
-export MKBOOTIMG=${LICHEE_TOOLS_DIR}/pack/pctools/linux/android/mkbootimg
-local BIMAGE="output/bImage";
-local RAMDISK="output/rootfs.cpio.gz";
-#linux-3.10/build.sh line.287
-${MKBOOTIMG} --kernel ${BIMAGE} \
-    --ramdisk ${RAMDISK} \
-    --board ${CHIP} \
-    --base ${BASE} \
-    --kernel_offset ${KERNEL_OFFSET} \
-    --ramdisk_offset ${RAMDISK_OFFSET} \
-    -o output/boot.img
-```
-对于如上 mkbootimg  通过review [github mkbootimg ](https://github.com/osm0sis/mkbootimg)代码片段确定该应用功能。
-```c
-//mkbootimg.c line466
-if(write(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) goto fail;
-if(write_padding(fd, pagesize, sizeof(hdr))) goto fail;
-if(write(fd, kernel_data, hdr.kernel_size) != (ssize_t) hdr.kernel_size) goto fail;
-if(write_padding(fd, pagesize, hdr.kernel_size)) goto fail;
-if(write(fd, ramdisk_data, hdr.ramdisk_size) != (ssize_t) hdr.ramdisk_size) goto fail;
-if(write_padding(fd, pagesize, hdr.ramdisk_size)) goto fail;
-```
-整合传递参数后，mkbootimg   依次将header（metadata）、kernel、ramdisk、等信息到一个文件。
-```c
-//mkboot.h line.166
-/* When the boot image header has a version of BOOT_HEADER_VERSION_ONE, the structure of the boot
- * image is as follows:
- *
- * +-----------------+
- * | boot header     | 1 page
- * +-----------------+
- * | kernel          | n pages
- * +-----------------+
- * | ramdisk         | m pages
- * +-----------------+
- * | second stage    | o pages
- * +-----------------+
- * | recovery dtbo   | p pages
- * +-----------------+
- * n = (kernel_size + page_size - 1) / page_size
- * m = (ramdisk_size + page_size - 1) / page_size
- * o = (second_size + page_size - 1) / page_size
- * p = (recovery_dtbo_size + page_size - 1) / page_size
- *
- * 0. all entities are page_size aligned in flash
- * 1. kernel and ramdisk are required (size != 0)
- * 2. recovery_dtbo is required for recovery.img in non-A/B devices(recovery_dtbo_size != 0)
- * 3. second is optional (second_size == 0 -> no second)
- * 4. load each element (kernel, ramdisk, second) at
- *    the specified physical address (kernel_addr, etc)
- * 5. If booting to recovery mode in a non-A/B device, extract recovery dtbo and
- *    apply the correct set of overlays on the base device tree depending on the
- *    hardware/product revision.
- * 6. prepare tags at tag_addr.  kernel_args[] is
- *    appended to the kernel commandline in the tags.
- * 7. r0 = 0, r1 = MACHINE_TYPE, r2 = tags_addr
- * 8. if second_size != 0: jump to second_addr
- *    else: jump to kernel_addr
- */
-```
-这里需要深入理解metadata`boot_img_hdr_v1`,它描述这个引导镜像的kernel、ramfs 大小基地址。
-```c
-//bootimg.h line 121
-struct boot_img_hdr_v1 {
-     uint8_t magic[BOOT_MAGIC_SIZE];
-     uint32_t kernel_size; /* size in bytes */
-     uint32_t kernel_addr; /* physical load addr */
-     uint32_t ramdisk_size; /* size in bytes */
-     uint32_t ramdisk_addr; /* physical load addr */
-     uint32_t second_size; /* size in bytes */
-     uint32_t second_addr; /* physical load addr */
-     uint32_t tags_addr; /* physical addr for kernel tags */
-     uint32_t page_size; /* flash page size we assume */
-     /*
-      * version for the boot image header.
-      * alternately this is used as dt_size on some hardware.
-      */
-     union {
-         uint32_t header_version;
-         uint32_t dt_size; /* device tree in bytes */
-     };
-     /* operating system version and security patch level; for
-      * version "A.B.C" and patch level "Y-M-D":
-      * ver = A << 14 | B << 7 | C         (7 bits for each of A, B, C)
-      * lvl = ((Y - 2000) & 127) << 4 | M  (7 bits for Y, 4 bits for M)
-      * os_version = ver << 11 | lvl */
-     uint32_t os_version;
-     uint8_t name[BOOT_NAME_SIZE]; /* asciiz product name */
-     uint8_t cmdline[BOOT_ARGS_SIZE];
-     uint32_t id[8]; /* timestamp / checksum / sha1 / etc */
-     /* Supplemental command line data; kept here to maintain
-      * binary compatibility with older versions of mkbootimg */
-     uint8_t extra_cmdline[BOOT_EXTRA_ARGS_SIZE];
-     uint32_t recovery_dtbo_size;   /* size in bytes for recovery DTBO image */
-     uint64_t recovery_dtbo_offset; /* offset to recovery dtbo in boot image */
-     uint32_t header_size;
- } __attribute__((packed));
-```
-直接dump boot.img 验证如上首地址的metadata。
-```bash
-jay@mxj-build:~/a64_v4l2$ hexdump -n 100 -C /home/jay/a64_v4l2/out/sun50iw1p1/debian/common/boot.img
-00000000  41 4e 44 52 4f 49 44 21  50 4b e8 00 00 00 08 41  |ANDROID!PK.....A|
-00000010  69 d0 29 00 00 00 00 42  00 00 00 00 00 00 f0 41  |i.)....B.......A|
-00000020  00 01 00 41 00 08 00 00  00 00 00 00 00 00 00 00  |...A............|
-00000030  73 75 6e 35 30 69 00 00  00 00 00 00 00 00 00 00  |sun50i..........|
-00000040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
-*
-00000064
-```

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