stm32中.bss和.data段是在哪里初始化的

  • Z时代
  • 2024-01-10
  • 分类：IT

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？

回答：

.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
    image001.png

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  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

以上是 stm32中.bss和.data段是在哪里初始化的 的全部内容， 来源链接： utcz.com/p/195898.html

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