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代码自动初始化
代码自动初始化
说明：本文针对嵌入式开发编写，其他开发可作为参考
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1. 概述
初始化代码如何做到自动化调用？
在我们开发程序过程中，往往需要对 bsp 部分进行外设配置，以及一些模块、参数进行初始化，比较常见的作法便是：
- 将各个部分的初始化代码分别封装成一个单独的函数，然后再main函数刚开始的地方进行调用已实现初始化；
这种方法比较简单、常用，亦能解决问题，但是此类写法在一些方面仍然存在不足：
- 所有初始化均需要在main函数内调用，不能做到彻底解耦
- 框架设计不友好，部分非业务部分初始化，如软件框架类的初始化，往往不希望还需要业务在main函数内调用初始化
- 等…
那是否有比较完美的方式来解决此问题呢？
答案是肯定的，本文将向大家介绍一种自动初始化的实现方式，注意，此方案在不同的平台，由于链接器使用的链接脚本可能不一致，容易出现问题，需要大家重点注意，细节在下文中将详细介绍。
2. 方案分析
为了更好的阐述此方案的实现方式，接下来将通过给大家展示一个demo程序，之后对此demo进行细致讲解的方式来阐述此方案的实现，以下是此demo程序：
#includeint a = 0; int b = 0; int c = 0; typedef void (*init_func)(void); //#define SECTION(x) __attribute__((used, section(x))) //#define INIT_FUNC(fn, level) const func_test init_##fn SECTION(".duan."#level) = fn #define INIT_PORT(fn, level) const init_func init_##fn __attribute__((used, section(".init."level))) = fn void start(void) { a = 1; return; } INIT_PORT(start, "1"); void end(void) { a = 2; return; } INIT_PORT(end, "3"); void test1(void) { b = 1; } INIT_PORT(test1, "1"); void test2(void) { b = 2; } INIT_PORT(test2, "2"); void system_init(void) { const init_func *func_p; for (func_p = &init_start; func_p < &init_end; func_p ++) { (*func_p)(); } } - 1
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关于宏：
#define INIT_PORT(fn, level) const init_func init_##fn __attribute__((used, section(".init."level))) = fn
代码分析如下：- 首先定义一个函数指针
typedef void (*init_func)(void);，所有初始化函数此指针类型 - 之后定义宏
#define INIT_PORT(fn, level)作为一个接口，后续初始化函数可以通过此接口加入自动初始化列表内const init_func init_##fn，其中##为连接符，假设参数fn为test，则init_##fn为init_test；init_func为指针类型const init_func init_##fn与const int *p是同一概念，只不过指针类型不一样
const init_func init_##fn定义了一个init_func类型的指针变量，此指针还没有赋值，因此将参数fn赋值给此变量，宏定义可以简化为#define INIT_PORT(fn, level) const init_func init_##fn = fn（__attribute__先忽略）__attribute__((used, section(".init."level)))这也是一个关键字进行修饰用的，可以拆解为__attribute__((used))和__attribute__((section(".init."level)))__attribute__((used))用来告诉编译器，此函数如果没有被调用，也不要被优化__attribute__((section(".init."level)))用来将修饰的内容放入指定的段".init."level中（编译器在你编译的时候帮你去完成的），注意这里level为宏的第二个传入参数，传入进来的时候他是一个字符串，所用不用加#进行拼接，两个字符串会自动拼接- 关于attribute的其他相关知识，可以参考：attribute((section(x))) 使用详解 和attribute((section(x))) 使用详解
综上分析，因此宏
#define INIT_PORT(fn, level) const init_func init_##fn __attribute__((used, section(".init."level))) = fn，其实就是定义了一个init_func类型的函数指针，并将此函数指针通过__attribute__((section(".init."level)))指定存放到特定的段内。Demo程序中定义了四个函数：
void start(void)void end(void)void test1(void)void test2(void)
并分别通过宏
INIT_PORT(fn, level)添加到自动初始化段内INIT_PORT(start, "1");INIT_PORT(end, "3");INIT_PORT(test1, "1");INIT_PORT(test2, "2");
这里大家注意观察下，有几个注意点：
level参数是一个字符串，而不是数字- 用户的自定义初始化函数
test1和test2的level需要在start和end的level值中间，这是由于编译器采用__attribute__((section(".init."level)))指定放入到指定段的时候，还会针对其进行排序，keil默认采用根据名称的方式排序，因此需要放置在用户自定义的，放置在用start和end中间，方便后续遍历start和end中间部分进行完整初始化
说明下，顺带发现了一个可能出现的bug，
INIT_PORT(test1, "1");的level建议不要设置为1，如果这么设置，在map文件里面排序是按照".init"level的值进行排序的，那么test1和start的顺序不能百分百确定，虽然这里侥幸没有出问题，但是建议大家不要这么操作最后看到
system_init初始化函数void system_init(void) { const init_func *func_p; for (func_p = &init_start; func_p < &init_end; func_p ++) { (*func_p)(); } }- 1
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此函数实现的便是通过
for循环，遍历start和end中间的段，并进行调用进行初始化这样用户初始化函数只需要调用宏
INIT_PORT(fn, level)即可完成自动初始化，当然system_init函数肯定是需要在main里面调用的此方案的好处是将各模块的初始化顺利实现了解耦，不用每个初始化都去动main函数了，此外系统框架类的初始化也可以做到不让业务感知！
针对不同类型的初始化，可以在此基础上稍微改动点，将start和end之间距离拉大点，一部分做外设初始化，一部分做参数初始化，直接挂代码吧
INIT_PORT(start, "1"); INIT_PORT(end, "4");- 1
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再对外开放接口宏
#define INIT_BSP_PORT(func) INIT_PORT(func, "2"); #define INIT_DATA_PORT(func) INIT_PORT(func, "3");- 1
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用户通过调用
BSP_INIT_PORT和DATA_INIT_PORT进行注册3. 检查MAP文件
在上述方法中，我们使用
__attribute__((section(".init."level)))将数据存入指定的段内，那么是否成功了呢，以及排序方式是否符合我们的预期呢？接下来我们需要通过检查map文件进行确认3.1 keil / MDK 环境检查
keil/mdk编译完程序之后，双击工程栏处的工程，可以查看map文件，还不知道的可以网上搜下
以下是上述demo的map文件中关键字段，我们可以看到我们需要的数据存放在正确的段内，并且排序也是正常的，注意一定要检查排序和字段是否完整！
大家也可以尝试下修改，把__attribute__((used, section(".init."level)))修改为__attribute__(( section(".init."level)))去掉used，看看有什么不一样，条件允许的话，还可以单步调试下，看下程序怎么跑的，加深下理解3.2 gcc环境检查
auto_init.c源文件：#includetypedef void (*func_test)(void); //#define SECTION(x) __attribute__((used, section(x))) //#define INIT_FUNC(fn, level) const func_test test_##fn SECTION(".duan."#level) = fn //#define INIT_FUNC(fn, level) const func_test test_##fn __attribute__((used, section(".duan."level))) = fn #define INIT_FUNC(fn, level) __attribute__((used)) const func_test test_##fn __attribute__((section(".duan."level))) = fn #define STRING(level) ("string"#level) //__attribute__((used, section(".duan")))void start(void) void start(void) { printf("start\n"); return; } INIT_FUNC(start, "1"); void end(void) { return; } INIT_FUNC(end, "6"); void test1(void) { printf("test1"); } INIT_FUNC(test1, "1"); void test2(void) { printf("test2"); } INIT_FUNC(test2, "2"); int main() { func_test a = NULL; a = start; a(); printf("Hello world\n"); return 0; } - 1
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- 生成map文件命令：
gcc auto_init.c -Wl,-Map=auto_init.map - 查看链接文件命令：
gcc auto_init.c -Wl,--verbose
生成的Map文件如下：
Archive member included to satisfy reference by file (symbol) /usr/lib/x86_64-linux-gnu/libc_nonshared.a(elf-init.oS) /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o (__libc_csu_init) Merging program properties As-needed library included to satisfy reference by file (symbol) libc.so.6 /tmp/ccDz4GV7.o (puts@@GLIBC_2.2.5) Discarded input sections .note.GNU-stack 0x0000000000000000 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o .note.gnu.property 0x0000000000000000 0x20 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o .note.GNU-stack 0x0000000000000000 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o .note.GNU-stack 0x0000000000000000 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o .note.gnu.property 0x0000000000000000 0x20 /usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o .note.GNU-stack 0x0000000000000000 0x0 /tmp/ccDz4GV7.o .note.gnu.property 0x0000000000000000 0x20 /tmp/ccDz4GV7.o .note.GNU-stack 0x0000000000000000 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[!provide] PROVIDE (edata = .) 0x0000000000004030 . = . 0x0000000000004030 __bss_start = . .bss 0x0000000000004030 0x8 *(.dynbss) .dynbss 0x0000000000004030 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o *(.bss .bss.* .gnu.linkonce.b.*) .bss 0x0000000000004030 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o .bss 0x0000000000004030 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o .bss 0x0000000000004030 0x1 /usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o .bss 0x0000000000004031 0x0 /tmp/ccDz4GV7.o .bss 0x0000000000004031 0x0 /usr/lib/x86_64-linux-gnu/libc_nonshared.a(elf-init.oS) .bss 0x0000000000004031 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/crtendS.o .bss 0x0000000000004031 0x0 /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crtn.o *(COMMON) 0x0000000000004038 . = ALIGN ((. != 0x0)?0x8:0x1) *fill* 0x0000000000004031 0x7 .lbss *(.dynlbss) *(.lbss .lbss.* .gnu.linkonce.lb.*) *(LARGE_COMMON) 0x0000000000004038 . = ALIGN (0x8) 0x0000000000004038 . = SEGMENT_START ("ldata-segment", .) .lrodata *(.lrodata .lrodata.* .gnu.linkonce.lr.*) .ldata 0x0000000000006038 0x0 *(.ldata .ldata.* .gnu.linkonce.l.*) 0x0000000000006038 . = ALIGN ((. != 0x0)?0x8:0x1) 0x0000000000006038 . = ALIGN (0x8) 0x0000000000004038 _end = . 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检查上述map文件，我们可以发现段 段排序和Keil采用的方式不一样，因此在gcc环境下直接使用会存在问题
这是由于采用gcc编译.c文件时，默认通过链接文件生成链接脚本，生成的这个链接脚本，对于数据段采用的排序方式未采用按照名称排序的方式，我们可以通过指令查看采用的
gcc auto_init.c -Wl,--verbose链接脚本内容，如下所示：GNU ld (GNU Binutils for Ubuntu) 2.34 Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 elf_iamcu elf_l1om elf_k1om i386pep i386pe using internal linker script: ================================================== /* Script for -pie -z combreloc -z separate-code -z relro -z now */ /* Copyright (C) 2014-2020 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) SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu64"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib"); SECTIONS { PROVIDE (__executable_start = SEGMENT_START("text-segment", 0)); . = SEGMENT_START("text-segment", 0) + SIZEOF_HEADERS; .interp : { *(.interp) } .note.gnu.build-id : { *(.note.gnu.build-id) } .hash : { *(.hash) } .gnu.hash : { *(.gnu.hash) } .dynsym : { *(.dynsym) } .dynstr : { *(.dynstr) } .gnu.version : { *(.gnu.version) } .gnu.version_d : { *(.gnu.version_d) } .gnu.version_r : { *(.gnu.version_r) } .rela.dyn : { *(.rela.init) *(.rela.text .rela.text.* .rela.gnu.linkonce.t.*) *(.rela.fini) *(.rela.rodata .rela.rodata.* .rela.gnu.linkonce.r.*) *(.rela.data .rela.data.* .rela.gnu.linkonce.d.*) *(.rela.tdata .rela.tdata.* .rela.gnu.linkonce.td.*) *(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*) *(.rela.ctors) *(.rela.dtors) *(.rela.got) *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) *(.rela.ldata .rela.ldata.* .rela.gnu.linkonce.l.*) *(.rela.lbss .rela.lbss.* .rela.gnu.linkonce.lb.*) *(.rela.lrodata .rela.lrodata.* .rela.gnu.linkonce.lr.*) *(.rela.ifunc) } .rela.plt : { *(.rela.plt) *(.rela.iplt) } . = ALIGN(CONSTANT (MAXPAGESIZE)); .init : { KEEP (*(SORT_NONE(.init))) } .plt : { *(.plt) *(.iplt) } .plt.got : { *(.plt.got) } .plt.sec : { *(.plt.sec) } .text : { *(.text.unlikely .text.*_unlikely .text.unlikely.*) *(.text.exit .text.exit.*) *(.text.startup .text.startup.*) *(.text.hot .text.hot.*) *(SORT(.text.sorted.*)) *(.text .stub .text.* .gnu.linkonce.t.*) /* .gnu.warning sections are handled specially by elf.em. */ *(.gnu.warning) } .fini : { KEEP (*(SORT_NONE(.fini))) } PROVIDE (__etext = .); PROVIDE (_etext = .); PROVIDE (etext = .); . = ALIGN(CONSTANT (MAXPAGESIZE)); /* Adjust the address for the rodata segment. 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Symbols in the DWARF debugging sections are relative to the beginning of the section so we begin them at 0. */ /* DWARF 1 */ .debug 0 : { *(.debug) } .line 0 : { *(.line) } /* GNU DWARF 1 extensions */ .debug_srcinfo 0 : { *(.debug_srcinfo) } .debug_sfnames 0 : { *(.debug_sfnames) } /* DWARF 1.1 and DWARF 2 */ .debug_aranges 0 : { *(.debug_aranges) } .debug_pubnames 0 : { *(.debug_pubnames) } /* DWARF 2 */ .debug_info 0 : { *(.debug_info .gnu.linkonce.wi.*) } .debug_abbrev 0 : { *(.debug_abbrev) } .debug_line 0 : { *(.debug_line .debug_line.* .debug_line_end) } .debug_frame 0 : { *(.debug_frame) } .debug_str 0 : { *(.debug_str) } .debug_loc 0 : { *(.debug_loc) } .debug_macinfo 0 : { *(.debug_macinfo) } /* SGI/MIPS DWARF 2 extensions */ .debug_weaknames 0 : { *(.debug_weaknames) } .debug_funcnames 0 : { *(.debug_funcnames) } .debug_typenames 0 : { *(.debug_typenames) } .debug_varnames 0 : { *(.debug_varnames) } /* DWARF 3 */ .debug_pubtypes 0 : { *(.debug_pubtypes) } .debug_ranges 0 : { *(.debug_ranges) } /* DWARF Extension. */ .debug_macro 0 : { *(.debug_macro) } .debug_addr 0 : { *(.debug_addr) } .gnu.attributes 0 : { KEEP (*(.gnu.attributes)) } /DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) } } ================================================== /usr/bin/ld: mode elf_x86_64 attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o succeeded /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o succeeded /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o succeeded /usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o attempt to open /tmp/cc86xswz.o succeeded /tmp/cc86xswz.o attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.so failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a succeeded /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so succeeded opened script file /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so opened script file /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so attempt to open libgcc_s.so.1 failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so.1 failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libgcc_s.so.1 succeeded /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libgcc_s.so.1 attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.so failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a succeeded /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libc.so failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libc.a failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libc.so succeeded opened script file /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libc.so /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libc.so opened script file /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libc.so attempt to open /lib/x86_64-linux-gnu/libc.so.6 succeeded /lib/x86_64-linux-gnu/libc.so.6 attempt to open /usr/lib/x86_64-linux-gnu/libc_nonshared.a succeeded /usr/lib/x86_64-linux-gnu/libc_nonshared.a (/usr/lib/x86_64-linux-gnu/libc_nonshared.a)elf-init.oS attempt to open /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 succeeded /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 /usr/lib/x86_64-linux-gnu/libc_nonshared.a /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.so failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a succeeded /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so succeeded opened script file /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so opened script file /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so attempt to open libgcc_s.so.1 failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc_s.so.1 failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libgcc_s.so.1 succeeded /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libgcc_s.so.1 attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.so failed attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a succeeded /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/crtendS.o succeeded /usr/lib/gcc/x86_64-linux-gnu/9/crtendS.o attempt to open /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crtn.o succeeded /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crtn.o ld-linux-x86-64.so.2 needed by /lib/x86_64-linux-gnu/libc.so.6 found ld-linux-x86-64.so.2 at /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2- 1
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关键描述字段如下：
其中 text 段由于配置了*(SORT(.text.sorted.*))，因此采用了按名称排序的方式，而 data 段没有采用此排序方式，而我们定义的函数指针实际上是存放在data数据段，所以才会出现上述问题如果要实现data段也采用按照名称大小的排序方式，大家可以将此链接脚本保存在工程路径下，之后修改.data段的描述，之后gcc编译的时候指定此链接脚本即可
4. 补充
定义宏的时候注意
const int *p与int *const p的区别：const int *pconst修饰的是int *p，表明指针指向的对象不可以修改，但是指针可以修改，称之为指针常量int *const pconst修饰的是p，表明指针不可以修改，但是指向的内容可以被修改，称之为常量指针const int *p和int const *p一致
5. 参考
参考RT-thread内核代码初始化设计，如果大家直接上手rtthread的自动初始化部分代码，可能会是一头雾水，那么现在再去看应该就很清楚了哈
-
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- 原文地址：https://blog.csdn.net/qq_43332314/article/details/126033631
