stm32中.bss和.data段是在哪裡初始化的

https://segmentfault.com/q/1010000004829859/a-1020000004850311

Q:

STM32的啟動檔案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()).

我沒有看到初始化.data和.bss段的描述

stm32應該是從中斷向量Reset_Handler開始執行的

; 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裡面沒有初始化代碼，然後就到__main了，難道是在__main裡進行的初始化？

因為上面說

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

,如果不在這裡的話就進入C語言的main()函數了，我看到很多地方都說這個初始化在C語言運作之前。

如果是在__main裡那具體是在哪裡呢？

不同的編譯器像gcc和Keil MDK都是在這裡嗎？

A:

.data和.bss是在__main裡進行初始化的。

我是搜尋的 “c library startup code”

1. 對于ARM Compiler，__main主要執行以下函數

   

其中__scatterload會對.data和.bss進行初始化

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.

詳細内容見：ARM Compiler C Library Startup and Initialization

1. 對于gcc

   彙編檔案startup_stm32f10x_hd.s裡面

   Reset_Handler

   已經對.data和.bss進行了初始化

Reset_Handler:  

/* Copy the data segment initializers from flash to SRAM */  
  movs  r1, #0 b LoopCopyDataInit CopyDataInit: 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 
           

轉載于:https://www.cnblogs.com/aardvark/p/5808936.html