c demo
#include <unistd.h>
#include <stdio.h>
struct mydyh_desc {
unsigned int nr;
const char *name;
unsigned long price;
void (*fun)(unsigned long, const char *);
};
extern struct mydyh_desc __dyh_info_begin[], __dyh_info_end[];
#define for_each_dyh_desc(p) \
for (p = __dyh_info_begin; p < __dyh_info_end; p++)
#define SECTION_START(_type,_name) \
static const struct mydyh_desc __mydyh_desc_##_type \
__attribute__((used, __section__(".dyh.info.init"))) = { \
.nr = MY_DYH_##_type, \
.name = _name,
#define SECTION_END \
};
#define MY_DYH_PHONE 0
#define MY_DYH_CAR 1
void huawei_phone(unsigned long price, const char *name)
{
printf("hello.\n");
printf("name=%s, price=%ld\n", name, price);
return;
}
void byd_phone(unsigned long price, const char *name)
{
printf("world.\n");
printf("name=%s, price=%ld\n", name, price);
return;
}
SECTION_START(PHONE, "huawei")
.price = 100,
.fun = huawei_phone,
SECTION_END
SECTION_START(CAR, "byd")
.price = 200,
.fun = byd_phone,
SECTION_END
int main()
{
struct mydyh_desc *p;
for_each_dyh_desc(p) {
p->fun(p->price, p->name);
}
return 0;
}
以上代码是新增一个自定义的section，为了使用该section内的函数，需要定义一个起始的位置，这个是在.S链接脚本中实现的。demo中的section存储的数据格式为mydyh_desc结构体，因此sizeof(mydyh_desc) 大小为一个元素。
lds链接脚本
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/* Copyright (C) 2014-2018 Free Software Foundation, Inc.
Copying and distribution of this script, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved. */
OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64",
"elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(_start)
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SECTIONS
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该链接脚本中主要增加了
.mydyh :
{
__dyh_info_begin = .;
*(.dyh.info.init)
__dyh_info_end = .;
}
.dyh.info.init为段名， __dyh_info_begin为段的开始位置，__dyh_info_end为段的结束位置，gcc在编译代码时，会将一些指定的数据放到该段中，然后会计算出__dyh_info_end的位置。而demo中使用到的__dyh_info_end和 __dyh_info_begin则是gcc通过链接脚本连接后的出来的一些地址。
Makefile
CC ?= gcc
all:
$(CC) section.c -T section.lds -o section
clean:
rm -rf section
执行时 ./section 即可运行
以上则是内核代码中 .initcall*.init 的执行原理