RISCVLinuxkernel启动代码分析之九:initramfs实践

config BLK_DEV_INITRD    bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"    help      The initial RAM filesystem is a ramfs which is loaded by the      boot loader (loadlin or lilo) and that is mounted as root      before the normal boot procedure. It is typically used to      load modules needed to mount the "real" root file system,      etc. See <file:Documentation/admin-guide/initrd.rst> for details.
      If RAM disk support (BLK_DEV_RAM) is also included, this      also enables initial RAM disk (initrd) support and adds      15 Kbytes (more on some other architectures) to the kernel size.      If unsure say Y.

config INITRAMFS_SOURCE    string "Initramfs source file(s)"    default ""    help      This can be either a single cpio archive with a .cpio suffix or a      space-separated list of directories and files for building the      initramfs image.  A cpio archive should contain a filesystem archive      to be used as an initramfs image.  Directories should contain a      filesystem layout to be included in the initramfs image.  Files      should contain entries according to the format described by the      "usr/gen_init_cpio" program in the kernel tree.
      When multiple directories and files are specified then the      initramfs image will be the aggregate of all of them.      See <file:Documentation/driver-api/early-userspace/early_userspace_support.rst> for more details.      If you are not sure, leave it blank.

config INITRAMFS_COMPRESSION_GZIP    bool "Gzip"    depends on RD_GZIP    help      Use the old and well tested gzip compression algorithm. Gzip provides      a good balance between compression ratio and decompression speed and      has a reasonable compression speed. It is also more likely to be      supported by your build system as the gzip tool is present by default      on most distros.
config RD_GZIP    bool "Support initial ramdisk/ramfs compressed using gzip"    default y    select DECOMPRESS_GZIP    help      Support loading of a gzip encoded initial ramdisk or cpio buffer.      If unsure, say Y.

obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o$(obj)/initramfs_data.o: $(obj)/initramfs_inc_dataramfs-input := $(strip $(shell echo $(CONFIG_INITRAMFS_SOURCE)))

# If CONFIG_INITRAMFS_SOURCE specifies a single file, and it is suffixed with# .cpio.*, use it directly as an initramfs, and avoid double compression.ifeq ($(words $(subst .cpio.,$(space),$(ramfs-input))),2)cpio-data := $(ramfs-input)compress-y := shippedendif

$(obj)/initramfs_inc_data: $(cpio-data) FORCE    $(call if_changed,$(compress-y))
targets += initramfs_data.cpio initramfs_inc_data

cmd_usr/initramfs_inc_data := cat /home/qinyunti/sdk/buildroot/enhanced_5.10_glibc_br_defconfig/images/rootfs.cpio.gz > usr/initramfs_inc_data

#ifdef CONFIG_BLK_DEV_INITRD#define INIT_RAM_FS                         \    . = ALIGN(4);                           \    __initramfs_start = .;                      \    KEEP(*(.init.ramfs))                        \    . = ALIGN(8);                           \    KEEP(*(.init.ramfs.info))#else#define INIT_RAM_FS#endif

(gdb) p &__irf_end$7 = (no debug info> *) 0xffffffe0012a0174(gdb) p &__irf_start$8 = (no debug info> *) 0xffffffe000890788(gdb) p &__irf_end-&__irf_startwarning: Type size unknown, assuming 1. Try casting to a known type, or void *.$9 = 10549740(gdb)
(gdb) p &__initramfs_start$10 = (char (*)[]) 0xffffffe000890788(gdb)
(gdb) p &__initramfs_size$11 = (unsigned long *) 0xffffffe0012a0178(gdb)
(gdb) p __initramfs_size$2 = 10549740(gdb)

Breakpoint 1, init_mount_tree () at ../fs/namespace.c:3791␦␦/home/qinyunti/sdk/linux/linux-custom/fs/namespace.c:3791:93171:beg:0xffffffe0000130d0(gdb) bt#0  init_mount_tree () at ../fs/namespace.c:3791#1  mnt_init () at ../fs/namespace.c:3846#2  0xffffffe000012da0 in vfs_caches_init () at ../fs/dcache.c:3234#3  0xffffffe000002bee in start_kernel () at ../init/main.c:1041#4  0xffffffe000002092 in _start_kernel () at ../arch/riscv/kernel/head.S:281Backtrace stopped: frame did not save the PC(gdb)

(gdb) x /64xb 0xffffffe0008907880xffffffe000890788:     0x1f    0x8b    0x08    0x00    0x00    0x00    0x00    0x000xffffffe000890790:     0x02    0x03    0xbc    0x9a    0x79    0x9c    0xcd    0x650xffffffe000890798:     0xfb    0xc7    0xbf    0xe7    0xcc    0x99    0x31    0x260xffffffe0008907a0:     0x71    0xac    0xd9    0x1d    0x8c    0xa5    0x6c    0x670xffffffe0008907a8:     0x06    0x63    0x94    0x98    0x19    0x93    0x2d    0x240xffffffe0008907b0:     0x14    0x92    0xec    0x45    0x59    0xca    0x4e    0xdb0xffffffe0008907b8:     0x58    0xaa    0x21    0x4a    0x85    0x94    0x16    0xa10xffffffe0008907c0:     0x85    0x52    0x48    0x7b    0x09    0x6d    0xb4    0x29(gdb)
hexdump images/rootfs.cpio.gz -n 640000000 8b1f 0008 0000 0000 0302 9abc 9c79 65cd0000010 c7fb e7bf 99cc 2631 ac71 1dd9 a58c 676c0000020 6306 9894 9319 242d 9214 45ec ca59 db4e0000030 aa58 4a21 9485 a116 5285 7b48 6d09 29b40000040

(gdb) hb populate_rootfsHardware assisted breakpoint 1 at 0xffffffe000004c58: file ../init/initramfs.c, line 606.(gdb) cContinuing.
Breakpoint 1, populate_rootfs () at ../init/initramfs.c:606␦␦/home/qinyunti/sdk/linux/linux-custom/init/initramfs.c:606:13203:beg:0xffffffe000004c58(gdb) bt#0  populate_rootfs () at ../init/initramfs.c:606#1  0xffffffe000200762 in do_one_initcall (fn=0xffffffe000004c58 ) at ../init/main.c:1217#2  0xffffffe000002e18 in do_initcall_level (command_line=0xffffffe001e05800 "earlycon", level=5) at ../init/main.c:1290#3  do_initcalls () at ../init/main.c:1306#4  do_basic_setup () at ../init/main.c:1326#5  kernel_init_freeable () at ../init/main.c:1526#6  0xffffffe0008743d6 in kernel_init (unused=) at ../init/main.c:1415#7  0xffffffe000201b5e in handle_exception () at ../arch/riscv/kernel/entry.S:243Backtrace stopped: frame did not save the PC(gdb)
(gdb) hb rest_initHardware assisted breakpoint 1 at 0xffffffe0008742d2: file ../init/main.c, line 681.(gdb) cContinuing.
Breakpoint 1, rest_init () at ../init/main.c:681␦␦/home/qinyunti/sdk/linux/linux-custom/init/main.c:681:16754:beg:0xffffffe0008742d2(gdb) bt#0  rest_init () at ../init/main.c:681#1  0xffffffe0000026e4 in arch_call_rest_init () at ../init/main.c:845#2  0xffffffe000002c12 in start_kernel () at ../init/main.c:1061#3  0xffffffe000002092 in _start_kernel () at ../arch/riscv/kernel/head.S:281Backtrace stopped: frame did not save the PC(gdb)

#define rootfs_initcall(fn)    __define_initcall(fn, rootfs)#define __define_initcall(fn, id) ___define_initcall(fn, id, .initcall##id)#define ___define_initcall(fn, id, __sec) \    static initcall_t __initcall_##fn##id __used \        __attribute__((__section__(#__sec ".init"))) = fn;

    static initcall_t __initcall_populate_rootfsrootfs __used \        __attribute__((__section__(".initcallrootfs.init"))) = populate_rootfs;

(gdb) p __initcall_populate_rootfsrootfs$1 = (initcall_t) 0xffffffe000004c58 (gdb)

static void __init do_initcalls(void){    int level;    size_t len = strlen(saved_command_line) + 1;    char *command_line;
    command_line = kzalloc(len, GFP_KERNEL);    if (!command_line)        panic("%s: Failed to allocate %zu bytes\n", __func__, len);    for (level = 0; level < ARRAY_SIZE(initcall_levels) - 1; level++) {        /* Parser modifies command_line, restore it each time */        strcpy(command_line, saved_command_line);        do_initcall_level(level, command_line);    }    kfree(command_line);}

extern initcall_entry_t __initcall_start[];extern initcall_entry_t __initcall0_start[];extern initcall_entry_t __initcall1_start[];extern initcall_entry_t __initcall2_start[];extern initcall_entry_t __initcall3_start[];extern initcall_entry_t __initcall4_start[];extern initcall_entry_t __initcall5_start[];extern initcall_entry_t __initcall6_start[];extern initcall_entry_t __initcall7_start[];extern initcall_entry_t __initcall_end[];
static initcall_entry_t *initcall_levels[] __initdata = {    __initcall0_start,    __initcall1_start,    __initcall2_start,    __initcall3_start,    __initcall4_start,    __initcall5_start,    __initcall6_start,    __initcall7_start,    __initcall_end,};

static void __init do_initcall_level(int level, char *command_line){    initcall_entry_t *fn;
    parse_args(initcall_level_names[level],           command_line, __start___param,           __stop___param - __start___param,           level, level,           NULL, ignore_unknown_bootoption);
    trace_initcall_level(initcall_level_names[level]);    for (fn = initcall_levels[level]; fn < initcall_levels[level+1]; fn++)        do_one_initcall(initcall_from_entry(fn));}

int __init_or_module do_one_initcall(initcall_t fn){    int count = preempt_count();    char msgbuf[64];    int ret;
    if (initcall_blacklisted(fn))        return -EPERM;    do_trace_initcall_start(fn);    ret = fn();    do_trace_initcall_finish(fn, ret);    msgbuf[0] = 0;    if (preempt_count() != count) {        sprintf(msgbuf, "preemption imbalance ");        preempt_count_set(count);    }    if (irqs_disabled()) {        strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));        local_irq_enable();    }    WARN(msgbuf[0], "initcall %pS returned with %s\n", fn, msgbuf);    add_latent_entropy();    return ret;}

.init.data : AT(ADDR(.init.data) - 0xffffffe000000000) { KEEP(*(SORT(___kentry+*))) *(.init.data init.data.*) *(.meminit.data*) *(.init.rodata .init.rodata.*) . = ALIGN(8); __start_ftrace_events = .; KEEP(*(_ftrace_events)) __stop_ftrace_events = .; __start_ftrace_eval_maps = .; KEEP(*(_ftrace_eval_map)) __stop_ftrace_eval_maps = .; *(.meminit.rodata) . = ALIGN(8); __clk_of_table = .; KEEP(*(__clk_of_table)) KEEP(*(__clk_of_table_end)) . = ALIGN(8); __reservedmem_of_table = .; KEEP(*(__reservedmem_of_table)) KEEP(*(__reservedmem_of_table_end)) . = ALIGN(8); __timer_of_table = .; KEEP(*(__timer_of_table)) KEEP(*(__timer_of_table_end)) . = ALIGN(8); __cpu_method_of_table = .; KEEP(*(__cpu_method_of_table)) KEEP(*(__cpu_method_of_table_end)) . = ALIGN(32); __dtb_start = .; KEEP(*(.dtb.init.rodata)) __dtb_end = .; . = ALIGN(8); __irqchip_of_table = .; KEEP(*(__irqchip_of_table)) KEEP(*(__irqchip_of_table_end)) . = ALIGN(8); __earlycon_table = .; KEEP(*(__earlycon_table)) __earlycon_table_end = .; . = ALIGN(8); __kunit_suites_start = .; KEEP(*(.kunit_test_suites)) __kunit_suites_end = .; . = ALIGN(16); __setup_start = .; KEEP(*(.init.setup)) __setup_end = .; __initcall_start = .; KEEP(*(.initcallearly.init)) __initcall0_start = .; KEEP(*(.initcall0.init)) KEEP(*(.initcall0s.init)) __initcall1_start = .; KEEP(*(.initcall1.init)) KEEP(*(.initcall1s.init)) __initcall2_start = .; KEEP(*(.initcall2.init)) KEEP(*(.initcall2s.init)) __initcall3_start = .; KEEP(*(.initcall3.init)) KEEP(*(.initcall3s.init)) __initcall4_start = .; KEEP(*(.initcall4.init)) KEEP(*(.initcall4s.init)) __initcall5_start = .; KEEP(*(.initcall5.init)) KEEP(*(.initcall5s.init)) __initcallrootfs_start = .; KEEP(*(.initcallrootfs.init)) KEEP(*(.initcallrootfss.init)) __initcall6_start = .; KEEP(*(.initcall6.init)) KEEP(*(.initcall6s.init)) __initcall7_start = .; KEEP(*(.initcall7.init)) KEEP(*(.initcall7s.init)) __initcall_end = .; __con_initcall_start = .; KEEP(*(.con_initcall.init)) __con_initcall_end = .; . = ALIGN(4); __initramfs_start = .; KEEP(*(.init.ramfs)) . = ALIGN(8); KEEP(*(.init.ramfs.info)) }

#define INIT_DATA_SECTION(initsetup_align)              \    .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {       \        INIT_DATA                       \        INIT_SETUP(initsetup_align)             \        INIT_CALLS                      \        CON_INITCALL                        \        INIT_RAM_FS                     \    }
#define INIT_CALLS                          \        __initcall_start = .;                   \        KEEP(*(.initcallearly.init))                \        INIT_CALLS_LEVEL(0)                 \        INIT_CALLS_LEVEL(1)                 \        INIT_CALLS_LEVEL(2)                 \        INIT_CALLS_LEVEL(3)                 \        INIT_CALLS_LEVEL(4)                 \        INIT_CALLS_LEVEL(5)                 \        INIT_CALLS_LEVEL(rootfs)                \        INIT_CALLS_LEVEL(6)                 \        INIT_CALLS_LEVEL(7)                 \        __initcall_end = .;

static initcall_entry_t *initcall_levels[] __initdata = {    __initcall0_start,    __initcall1_start,    __initcall2_start,    __initcall3_start,    __initcall4_start,    __initcall5_start,    __initcall6_start,    __initcall7_start,    __initcall_end,};

  for (fn = initcall_levels[level]; fn < initcall_levels[level+1]; fn++)        do_one_initcall(initcall_from_entry(fn));

(gdb) p buf$6 = 0xffffffe000890788 "\037\213\b"(gdb) p len$7 = 10549740(gdb) p buf$8 = 0xffffffe000890788 "\037\213\b"(gdb)

(gdb) p compress_name$10 = 0xffffffe00158c1a8 "gzip"(gdb) p decompress$11 = (decompress_fn) 0xffffffe000018c7a (gdb)

(gdb) bt#0  run_init_process (init_filename=0xffffffe001543f90 "/init") at ../init/main.c:1342#1  0xffffffe000874438 in kernel_init (unused=) at ../init/main.c:1437#2  0xffffffe000201b5e in handle_exception () at ../arch/riscv/kernel/entry.S:243Backtrace stopped: frame did not save the PC(gdb)

 if (ramdisk_execute_command) {        ret = run_init_process(ramdisk_execute_command);        if (!ret)            return 0;        pr_err("Failed to execute %s (error %d)\n",               ramdisk_execute_command, ret);    }
    /*     * We try each of these until one succeeds.     *     * The Bourne shell can be used instead of init if we are     * trying to recover a really broken machine.     */    if (execute_command) {        ret = run_init_process(execute_command);        if (!ret)            return 0;        panic("Requested init %s failed (error %d).",              execute_command, ret);    }
    if (CONFIG_DEFAULT_INIT[0] != '\0') {        ret = run_init_process(CONFIG_DEFAULT_INIT);        if (ret)            pr_err("Default init %s failed (error %d)\n",                   CONFIG_DEFAULT_INIT, ret);        else            return 0;    }
    if (!try_to_run_init_process("/sbin/init") ||        !try_to_run_init_process("/etc/init") ||        !try_to_run_init_process("/bin/init") ||        !try_to_run_init_process("/bin/sh"))        return 0;
    panic("No working init found.  Try passing init= option to kernel. "          "See Linux Documentation/admin-guide/init.rst for guidance.");

 tree -L 1.├── bin├── dev├── etc├── init├── lib├── lib64 -> lib├── lib64v_xthead├── linuxrc -> bin/busybox├── media├── mnt├── opt├── proc├── root├── rootfs.cpio├── run├── sbin├── sys├── tmp├── usr└── var
17 directories, 3 files

#include int main(int argc,char argv[]) {     printf("hello world, from initramfs.\n");     return 0; }

/* Open /dev/console, for stdin/stdout/stderr, this should never fail */void __init console_on_rootfs(void){    struct file *file = filp_open("/dev/console", O_RDWR, 0);
    if (IS_ERR(file)) {        pr_err("Warning: unable to open an initial console.\n");        return;    }    init_dup(file);    init_dup(file);    init_dup(file);    fput(file);}