在一些资源受限的MCU中，使用rt-thread时需要进行代码的优化，默认情况下，在map文件中可以看到

6170 156 0 8 0 11738 finsh_compiler.o

56 22 243 64 0 2755 finsh_error.o

552 42 0 8 128 5935 finsh_heap.o

64 6 0 0 0 2100 finsh_init.o

392 8 0 0 320 5966 finsh_node.o

3034 294 196 0 0 25930 finsh_ops.o

2428 32 0 0 0 16363 finsh_parser.o

1644 16 126 0 0 10262 finsh_token.o

296 32 0 4 192 7994 finsh_var.o

176 36 0 12 384 7227 finsh_vm.o

finsh相关的文件占用了很多的flash和ram，

刚开始我找了好久都没有发现是在哪里调用的这些东西，后来才注意到，rt-thread里使用了一些通常MCU代码里不太常用的初始化方式，它使用的是组件的形式，详细介绍可以参考：http://www.cnblogs.com/King-Gentleman/p/4570559.html

核心部分是使用了__attribute__((section(x)))的方式先把一个函数的地址（注意是函数地址，而不是函数本身）输出到一个独立的section中。

然后在rt_hw_board_init ->rt_components_board_init() 直接以函数指针的形式调用的。

/** * This function will initial STM32 board. */ void rt_hw_board_init(void) { /* NVIC Configuration */ NVIC_Configuration(); /* Configure the SysTick */ SysTick_Config( SystemCoreClock / RT_TICK_PER_SECOND ); #if STM32_EXT_SRAM EXT_SRAM_Configuration(); #endif rt_hw_usart_init(); rt_console_set_device(RT_CONSOLE_DEVICE_NAME); #ifdef RT_USING_COMPONENTS_INIT rt_components_board_init(); #endif }

/** * RT-Thread Components Initialization for board */ void rt_components_board_init(void) { #if RT_DEBUG_INIT int result; const struct rt_init_desc *desc; for (desc = &__rt_init_desc_rti_board_start; desc < &__rt_init_desc_rti_board_end; desc ++) { rt_kprintf("initialize %s", desc->fn_name); result = desc->fn(); rt_kprintf(":%d done\n", result); } #else const init_fn_t *fn_ptr; for (fn_ptr = &__rt_init_rti_board_start; fn_ptr < &__rt_init_rti_board_end; fn_ptr++) { (*fn_ptr)(); } #endif }

INIT_COMPONENT_EXPORT(finsh_system_init); 这句话

#define INIT_COMPONENT_EXPORT(fn) INIT_EXPORT(fn, "3")

#define INIT_EXPORT(fn, level) \

const init_fn_t __rt_init_##fn SECTION(".rti_fn."level) = fn

#define SECTION(x) __attribute__((section(x)))

_attribute_((section(x))) 含义如下

__attribute__((section("name"))) function attribute

Non-Confidential		ARM DUI0375E
ARM® Compiler v5.04 for µVision armcc User GuideVersion 5
Home>Compiler-specific Features> __attribute__((section("name"))) function attribute

9.46 __attribute__((section("name"))) function attribute

Thesectionfunction attribute enables you to place code in different sections of the image.

Note

This function attribute is a GNU compiler extension that the ARM compiler supports.

Examples

In the following example,Function_Attributes_section_0is placed into the ROsectionnew_sectionrather than.text.

void Function_Attributes_section_0 (void) __attribute__((section ("new_section"))); void Function_Attributes_section_0 (void) { static int aStatic =0; aStatic++; }

In the following example,sectionfunction attribute overrides the#pragma armsectionsetting.

#pragma arm section code="foo" int f2() { return 1; } // into the 'foo' area __attribute__((section ("bar"))) int f3() { return 1; } // into the 'bar' area int f4() { return 1; } // into the 'foo' area #pragma arm section

它也可以指定变量的属性

__attribute__((section("name"))) variable attribute

Non-Confidential		ARM DUI0375E
ARM® Compiler v5.04 for µVision armcc User GuideVersion 5
Home>Compiler-specific Features> __attribute__((section("name"))) variable attribute

9.64 __attribute__((section("name"))) variable attribute

Thesectionattribute specifies that a variable must be placed in a particular datasection.

Normally, the ARM compiler places the objects it generates in sections like.dataand.bss. However, you might require additional data sections or you might want a variable to appear in a specialsection, for example, to map to special hardware.

If you use thesectionattribute, read-only variables are placed in RO data sections, read-write variables are placed in RW data sections unless you use thezero_initattribute. In this case, the variable is placed in a ZIsection.

Note

This variable attribute is a GNU compiler extension that the ARM compiler supports.

Examples

/* in RO section */ const int descriptor[3] __attribute__((section ("descr"))) = { 1,2,3 }; /* in RW section */ long long rw_initialized[10] __attribute__((section ("INITIALIZED_RW"))) = {5}; /* in RW section */ long long rw[10] __attribute__((section ("RW"))); /* in ZI section */ long long altstack[10] __attribute__((section ("STACK"), zero_init));

所以不使用的话 在rtconfig.h 中将以下这句话注释掉即可

#define RT_USING_COMPONENTS_INIT

或者把这句注释掉

INIT_COMPONENT_EXPORT(finsh_system_init);

这样就可以减少很多flash和ram空间了