我们在编写驱动或者在啃内核代码时，经常会遇到一些比较奇怪的宏initcall，这些宏一般都放在init.h中，这里简单的笔记下：
CONTENTS
linux-2.6.11\include\linux\init.h
/* These macros are used to mark some functions or
* initialized data (doesn't apply to uninitialized data)
* as `initialization' functions. The kernel can take this
* as hint that the function is used only during the initialization
* phase and free up used memory resources after
*
* Usage:
* For functions:
*
* You should add __init immediately before the function name, like:
*
* static void __init initme(int x, int y)
* {
* extern int z; z = x * y;
* }
*
* If the function has a prototype somewhere, you can also add
* __init between closing brace of the prototype and semicolon:
*
* extern int initialize_foobar_device(int, int, int) __init;
*
* For initialized data:
* You should insert __initdata between the variable name and equal
* sign followed by value, e.g.:
*
* static int init_variable __initdata = 0;
* static char linux_logo[] __initdata = { 0x32, 0x36, ... };
*
* Don't forget to initialize data not at file scope, i.e. within a function,
* as gcc otherwise puts the data into the bss section and not into the init
* section.
*
* Also note, that this data cannot be "const".
*/
/* These are for everybody (although not all archs will actually
discard it in modules) */
/* 编写驱动初始化函数和去初始化函数时我们经常使用底下的这几个宏，
可以发现这里是把这些函数放到了特定的段中
*/
#define __init __attribute__ ((__section__ (".init.text")))
#define __initdata __attribute__ ((__section__ (".init.data")))
#define __exitdata __attribute__ ((__section__(".exit.data")))
#define __exit_call __attribute_used__ __attribute__ ((__section__ (".exitcall.exit")))
#ifdef MODULE
#define __exit __attribute__ ((__section__(".exit.text")))
#else
#define __exit __attribute_used__ __attribute__ ((__section__(".exit.text")))
#endif
/* For assembly routines */
#define __INIT .section ".init.text","ax"
#define __FINIT .previous
#define __INITDATA .section ".init.data","aw"
#ifndef __ASSEMBLY__
/*
定义了两个函数指针
*/
/*
* Used for initialization calls..
*/
typedef int (*initcall_t)(void);
typedef void (*exitcall_t)(void);
/*
以下的这4个变量定义在vmlinux.lds.S 中，用来标记段中函数指针数组的
起始和末尾位置，这样就可以方便的遍历两个变量之间的函数了。
*/
extern initcall_t __con_initcall_start[], __con_initcall_end[];
extern initcall_t __security_initcall_start[], __security_initcall_end[];
/* Defined in init/main.c */
extern char saved_command_line[];
#endif
#ifndef MODULE
#ifndef __ASSEMBLY__
/* initcalls are now grouped by functionality into separate
* subsections. Ordering inside the subsections is determined
* by link order.
* For backwards compatibility, initcall() puts the call in
* the device init subsection.
*/
/* 非常关键的一个工具宏，将函数fn放到段level中 */
#define __define_initcall(level,fn) \
static initcall_t __initcall_##fn __attribute_used__ \
__attribute__((__section__(".initcall" level ".init"))) = fn
/* 根据上面的工具宏定义的不同优先级别的宏*/
#define core_initcall(fn) __define_initcall("1",fn)
#define postcore_initcall(fn) __define_initcall("2",fn)
#define arch_initcall(fn) __define_initcall("3",fn)
#define subsys_initcall(fn) __define_initcall("4",fn)
#define fs_initcall(fn) __define_initcall("5",fn)
#define device_initcall(fn) __define_initcall("6",fn)
#define late_initcall(fn) __define_initcall("7",fn)
#define __initcall(fn) device_initcall(fn)
#define __exitcall(fn) \
static exitcall_t __exitcall_##fn __exit_call = fn
#define console_initcall(fn) \
static initcall_t __initcall_##fn \
__attribute_used__ __attribute__((__section__(".con_initcall.init")))=fn
#define security_initcall(fn) \
static initcall_t __initcall_##fn \
__attribute_used__ __attribute__((__section__(".security_initcall.init"))) = fn
struct obs_kernel_param {
const char *str;
int (*setup_func)(char *);
int early;
};
/*
* Only for really core code. See moduleparam.h for the normal way.
*
* Force the alignment so the compiler doesn't space elements of the
* obs_kernel_param "array" too far apart in .init.setup.
*/
#define __setup_param(str, unique_id, fn, early) \
static char __setup_str_##unique_id[] __initdata = str; \
static struct obs_kernel_param __setup_##unique_id \
__attribute_used__ \
__attribute__((__section__(".init.setup"))) \
__attribute__((aligned((sizeof(long))))) \
= { __setup_str_##unique_id, fn, early }
#define __setup_null_param(str, unique_id) \
__setup_param(str, unique_id, NULL, 0)
#define __setup(str, fn) \
__setup_param(str, fn, fn, 0)
#define __obsolete_setup(str) \
__setup_null_param(str, __LINE__)
/* NOTE: fn is as per module_param, not __setup! Emits warning if fn
* returns non-zero. */
#define early_param(str, fn) \
__setup_param(str, fn, fn, 1)
/* Relies on saved_command_line being set */
void __init parse_early_param(void);
#endif /* __ASSEMBLY__ */
/**
* module_init() - driver initialization entry point
* @x: function to be run at kernel boot time or module insertion
*
* module_init() will either be called during do_initcalls (if
* builtin) or at module insertion time (if a module). There can only
* be one per module.
*/
#define module_init(x) __initcall(x);
/**
* module_exit() - driver exit entry point
* @x: function to be run when driver is removed
*
* module_exit() will wrap the driver clean-up code
* with cleanup_module() when used with rmmod when
* the driver is a module. If the driver is statically
* compiled into the kernel, module_exit() has no effect.
* There can only be one per module.
*/
#define module_exit(x) __exitcall(x);
#else /* MODULE */
/* Don't use these in modules, but some people do... */
#define core_initcall(fn) module_init(fn)
#define postcore_initcall(fn) module_init(fn)
#define arch_initcall(fn) module_init(fn)
#define subsys_initcall(fn) module_init(fn)
#define fs_initcall(fn) module_init(fn)
#define device_initcall(fn) module_init(fn)
#define late_initcall(fn) module_init(fn)
#define security_initcall(fn) module_init(fn)
/* These macros create a dummy inline: gcc 2.9x does not count alias
as usage, hence the `unused function' warning when __init functions
are declared static. We use the dummy __*_module_inline functions
both to kill the warning and check the type of the init/cleanup
function. */
/* Each module must use one module_init(), or one no_module_init */
#define module_init(initfn) \
static inline initcall_t __inittest(void) \
{ return initfn; } \
int init_module(void) __attribute__((alias(#initfn)));
/* This is only required if you want to be unloadable. */
#define module_exit(exitfn) \
static inline exitcall_t __exittest(void) \
{ return exitfn; } \
void cleanup_module(void) __attribute__((alias(#exitfn)));
#define __setup_param(str, unique_id, fn) /* nothing */
#define __setup_null_param(str, unique_id) /* nothing */
#define __setup(str, func) /* nothing */
#define __obsolete_setup(str) /* nothing */
#endif
/* Data marked not to be saved by software_suspend() */
#define __nosavedata __attribute__ ((__section__ (".data.nosave")))
/* This means "can be init if no module support, otherwise module load
may call it." */
#ifdef CONFIG_MODULES
#define __init_or_module
#define __initdata_or_module
#else
#define __init_or_module __init
#define __initdata_or_module __initdata
#endif /*CONFIG_MODULES*/
#ifdef CONFIG_HOTPLUG
#define __devinit
#define __devinitdata
#define __devexit
#define __devexitdata
#else
#define __devinit __init
#define __devinitdata __initdata
#define __devexit __exit
#define __devexitdata __exitdata
#endif
/* Functions marked as __devexit may be discarded at kernel link time, depending
on config options. Newer versions of binutils detect references from
retained sections to discarded sections and flag an error. Pointers to
__devexit functions must use __devexit_p(function_name), the wrapper will
insert either the function_name or NULL, depending on the config options.
*/
#if defined(MODULE) || defined(CONFIG_HOTPLUG)
#define __devexit_p(x) x
#else
#define __devexit_p(x) NULL
#endif
#ifdef MODULE
#define __exit_p(x) x
#else
#define __exit_p(x) NULL
#endif
#endif /* _LINUX_INIT_H */
看init.h文件需要配合vmlinux，这里笔记下i386的实现：
linux-2.6.11\arch\i386\kernel\vmlinux.lds.S
#include <asm-generic/vmlinux.lds.h>
#include <asm/thread_info.h>
#include <asm/page.h>
OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
OUTPUT_ARCH(i386)
ENTRY(startup_32)
jiffies = jiffies_64;
SECTIONS
{
. = __PAGE_OFFSET + 0x100000;
/* read-only */
_text = .; /* Text and read-only data */
.text : {
*(.text)
SCHED_TEXT
LOCK_TEXT
*(.fixup)
*(.gnu.warning)
} = 0x9090
_etext = .; /* End of text section */
. = ALIGN(16); /* Exception table */
__start___ex_table = .;
__ex_table : { *(__ex_table) }
__stop___ex_table = .;
RODATA
/* writeable */
.data : { /* Data */
*(.data)
CONSTRUCTORS
}
. = ALIGN(4096);
__nosave_begin = .;
.data_nosave : { *(.data.nosave) }
. = ALIGN(4096);
__nosave_end = .;
. = ALIGN(4096);
.data.page_aligned : { *(.data.idt) }
. = ALIGN(32);
.data.cacheline_aligned : { *(.data.cacheline_aligned) }
_edata = .; /* End of data section */
. = ALIGN(THREAD_SIZE); /* init_task */
.data.init_task : { *(.data.init_task) }
/* will be freed after init */
. = ALIGN(4096); /* Init code and data */
__init_begin = .;
.init.text : {
_sinittext = .;
*(.init.text)
_einittext = .;
}
.init.data : { *(.init.data) }
. = ALIGN(16);
__setup_start = .;
.init.setup : { *(.init.setup) }
__setup_end = .;
__initcall_start = .; ;;可以看到这里函数段initcall的排列顺序，首先是initcall1，最后是initcall7，因此
.initcall.init : { ;;当遍历执行里面的函数时，initcall1会首先执行
*(.initcall1.init)
*(.initcall2.init)
*(.initcall3.init)
*(.initcall4.init)
*(.initcall5.init)
*(.initcall6.init)
*(.initcall7.init)
}
__initcall_end = .;
__con_initcall_start = .;
.con_initcall.init : { *(.con_initcall.init) }
__con_initcall_end = .;
SECURITY_INIT
. = ALIGN(4);
__alt_instructions = .;
.altinstructions : { *(.altinstructions) }
__alt_instructions_end = .;
.altinstr_replacement : { *(.altinstr_replacement) }
/* .exit.text is discard at runtime, not link time, to deal with references
from .altinstructions and .eh_frame */
.exit.text : { *(.exit.text) }
.exit.data : { *(.exit.data) }
. = ALIGN(4096);
__initramfs_start = .;
.init.ramfs : { *(.init.ramfs) }
__initramfs_end = .;
. = ALIGN(32);
__per_cpu_start = .;
.data.percpu : { *(.data.percpu) }
__per_cpu_end = .;
. = ALIGN(4096);
__init_end = .;
/* freed after init ends here */
__bss_start = .; /* BSS */
.bss : {
*(.bss.page_aligned)
*(.bss)
}
. = ALIGN(4);
__bss_stop = .;
_end = . ;
/* This is where the kernel creates the early boot page tables */
. = ALIGN(4096);
pg0 = .;
/* Sections to be discarded */
/DISCARD/ : {
*(.exitcall.exit)
}
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
}
linux-2.6.11\init\main.c
/* Linux内核初始化时会执行到该函数 */
static void __init do_initcalls(void)
{
initcall_t *call;
int count = preempt_count();
/* 这里遍历函数指针数组，进行执行。
排列在数组前面的会优先执行
*/
for (call = __initcall_start; call < __initcall_end; call++) {
char *msg;
if (initcall_debug) {
printk(KERN_DEBUG "Calling initcall 0x%p", *call);
print_fn_descriptor_symbol(": %s()", (unsigned long) *call);
printk("\n");
}
(*call)();
msg = NULL;
if (preempt_count() != count) {
msg = "preemption imbalance";
preempt_count() = count;
}
if (irqs_disabled()) {
msg = "disabled interrupts";
local_irq_enable();
}
if (msg) {
printk("error in initcall at 0x%p: "
"returned with %s\n", *call, msg);
}
}
/* Make sure there is no pending stuff from the initcall sequence */
flush_scheduled_work();
}
发表评论