Linux源码与编译出的目标文件汇编代码的一致性问题

start_kernel是内核启动时比较重要的一个函数，然而我发现一个问题，我编译出来的目标文件中的汇编代码与C源码并不完全对应，这是怎么一回事呢？

asmlinkage void __init start_kernel(void)
{
        char * command_line;
        extern const struct kernel_param __start___param[], __stop___param[];

        /*
         * Need to run as early as possible, to initialize the
         * lockdep hash:
         */
        lockdep_init();
        smp_setup_processor_id();
        debug_objects_early_init();

        /*
         * Set up the the initial canary ASAP:
         */
        boot_init_stack_canary();

        cgroup_init_early();

        local_irq_disable();
        early_boot_irqs_disabled = true;
/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
        boot_cpu_init();
        page_address_init();
        pr_notice("%s", linux_banner);
        setup_arch(&command_line);
        mm_init_owner(&init_mm, &init_task);
        mm_init_cpumask(&init_mm);
        setup_command_line(command_line);
        setup_nr_cpu_ids();
        setup_per_cpu_areas();
        smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */

objdump -d main.o

00000337 <start_kernel>:
 337:	55                   	push   %ebp
 338:	89 e5                	mov    %esp,%ebp
 33a:	53                   	push   %ebx
 33b:	83 ec 14             	sub    $0x14,%esp
 33e:	e8 fc ff ff ff       	call   33f <start_kernel+0x8>
 343:	e8 fc ff ff ff       	call   344 <start_kernel+0xd>
 348:	ff 15 08 00 00 00    	call   *0x8
 34e:	64 8b 1d 00 00 00 00 	mov    %fs:0x0,%ebx
 355:	ba 01 00 00 00       	mov    $0x1,%edx
 35a:	89 d8                	mov    %ebx,%eax
 35c:	c6 05 00 00 00 00 01 	movb   $0x1,0x0
 363:	e8 fc ff ff ff       	call   364 <start_kernel+0x2d>
 368:	89 d8                	mov    %ebx,%eax
 36a:	ba 01 00 00 00       	mov    $0x1,%edx
 36f:	e8 fc ff ff ff       	call   370 <start_kernel+0x39>
 374:	89 d8                	mov    %ebx,%eax
 376:	ba 01 00 00 00       	mov    $0x1,%edx
 37b:	e8 fc ff ff ff       	call   37c <start_kernel+0x45>
 380:	ba 01 00 00 00       	mov    $0x1,%edx
 385:	89 d8                	mov    %ebx,%eax
 387:	e8 fc ff ff ff       	call   388 <start_kernel+0x51>
 38c:	e8 fc ff ff ff       	call   38d <start_kernel+0x56>
 391:	c7 44 24 04 00 00 00 	movl   $0x0,0x4(%esp)

objdump -r main.o

00000309 R_386_32          boot_command_line
0000030e R_386_32          .init.data
00000313 R_386_PC32        strlcpy
00000318 R_386_32          .init.data
0000031d R_386_PC32        parse_early_options
00000324 R_386_32          .init.data
0000033f R_386_PC32        smp_setup_processor_id
00000344 R_386_PC32        cgroup_init_early
0000034a R_386_32          pv_irq_ops
00000351 R_386_32          cpu_number
0000035e R_386_32          early_boot_irqs_disabled
00000364 R_386_PC32        set_cpu_online
00000370 R_386_PC32        set_cpu_active
0000037c R_386_PC32        set_cpu_present
00000388 R_386_PC32        set_cpu_possible
0000038d R_386_PC32        page_address_init
00000395 R_386_32          linux_banner
0000039c R_386_32          .rodata.str1.1
000003a1 R_386_PC32        printk
000003a9 R_386_PC32        setup_arch
000003ae R_386_32          init_task
000003b3 R_386_32          init_mm
000003b8 R_386_PC32        mm_init_owner
000003bd R_386_32          boot_command_line

那么，lockdep_init函数哪里去了呢，start_kernel究竟有没有调用到它呢。

首先可以肯定的是，lockdep_init没有被内核导出，因为在System.map中找不到它。

然后，在重定位信息中也找不到lockdep_init。

lockdep_init是在哪个文件中定义的？

kernel/locking/lockdep.c

但是在kernel/locking目录下并没有生成lockdep.o，这又是为什么？

void lockdep_init(void)
{
        int i;

        /*
         * Some architectures have their own start_kernel()
         * code which calls lockdep_init(), while we also
         * call lockdep_init() from the start_kernel() itself,
         * and we want to initialize the hashes only once:
         */
        if (lockdep_initialized)
                return;

        for (i = 0; i < CLASSHASH_SIZE; i++)
                INIT_LIST_HEAD(classhash_table + i);

        for (i = 0; i < CHAINHASH_SIZE; i++)
                INIT_LIST_HEAD(chainhash_table + i);

        lockdep_initialized = 1;
}