Q:

STM32的启动文件startup_stm32f10x_hd.s中的描述是

This module performs:

• Set the initial SP

• Set the initial PC == Reset_Handler

• Set the vector table entries with the exceptions ISR address

• Configure the clock system and also configure the external SRAM mounted on STM3210E-EVAL board to be used as data memory (optional, to be enabled by user)

• Branches to __main in the C library (which eventually calls main()).

我没有看到初始化.data和.bss段的描述
stm32应该是从中断向量Reset_Handler开始执行的

; Reset handler
Reset_Handler PROC
EXPORT Reset_Handler [WEAK]
IMPORT __main
IMPORT SystemInit
LDR R0, =SystemInit
BLX R0 
LDR R0, =__main
BX R0
ENDP

SystemInit里面没有初始化代码，然后就到__main了，难道是在__main里进行的初始化？

因为上面说Branches to __main in the C library (which eventually calls main()),如果不在这里的话就进入C语言的main()函数了，我看到很多地方都说这个初始化在C语言运行之前。
如果是在__main里那具体是在哪里呢？
不同的编译器像gcc和Keil MDK都是在这里吗？

A:

.data和.bss是在__main里进行初始化的。

我是搜索的 “c library startup code”

1. 对于ARM Compiler，__main主要执行以下函数
   

其中__scatterload会对.data和.bss进行初始化

Application code and data can be in a root region or a non-root region. Root regions 
have the same load-time and execution-time addresses. Non-root regions
have different load-time and execution-time addresses. The root region
contains a region table output by the ARM linker. The region table
contains the addresses of the non-root code and data regions that
require initialization. The region table also contains a function
pointer that indicates what initialization is needed for the region,
for example a copying, zeroing, or decompressing function.

__scatterload goes through the region table and initializes the various execution-time regions. The function:

• Initializes the Zero Initialized (ZI) regions to zero

• Copies or decompresses the non-root code and data region from their load-time locations to the execute-time regions.

__main always calls this function during startup before calling __rt_entry.

详细内容见：ARM Compiler C Library Startup and Initialization

1. 对于gcc
   汇编文件startup_stm32f10x_hd.s里面Reset_Handler已经对.data和.bss进行了初始化

Reset_Handler:  /* Copy the data segment initializers from flash to SRAM */    movs  r1, #0  b  LoopCopyDataInitCopyDataInit:  ldr  r3, =_sidata  ldr  r3, [r3, r1]  str  r3, [r0, r1]  adds  r1, r1, #4    LoopCopyDataInit:  ldr  r0, =_sdata  ldr  r3, =_edata  adds  r2, r0, r1  cmp  r2, r3  bcc  CopyDataInit  ldr  r2, =_sbss  b  LoopFillZerobss/* Zero fill the bss segment. */  FillZerobss:  movs  r3, #0  str  r3, [r2], #4    LoopFillZerobss:  ldr  r3, = _ebss  cmp  r2, r3  bcc  FillZerobss/* Call the clock system intitialization function.*/  bl  SystemInit   /* Call the application‘s entry point.*/  bl  main  bx  lr