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my code here:

void _init(void) {return;}    

int main(void)
{
     /* STM32F2xx HAL library initialization:
   - Configure the Flash prefetch, instruction and Data caches
   - Configure the Systick to generate an interrupt each 1 msec
   - Set NVIC Group Priority to 4
   - Global MSP (MCU Support Package) initialization
 */

 HAL_Init();

/* Configure the system clock to 64 MHz */
 SystemClock_Config();

 /* Enable CRC clock */
 __CRC_CLK_ENABLE();
 Example_Status = 1;
 Example_Status = 2;
 Example_Status = 3;
..... 

and my gdb on my stm32 using stlink-texane are as follow:

(gdb) s
main () at main.c:74
 74   __CRC_CLK_ENABLE();
(gdb) s
77    Example_Status = 3;
(gdb) p Example_status
No symbol "Example_status" in current context.
(gdb) p Example_Status
$1 = 139640994
(gdb) n
74    __CRC_CLK_ENABLE();
(gdb) n
77    Example_Status = 3;
(gdb) n
183   Example_Status = ExampleECCKeyGenSignVerif();
(gdb) p Example_Status
$2 = 139640994

i am wondering why the Example_Status outcome not = 3 ?

and the storage of the variable are

arm-none-eabi-objdump --syms main.o | grep Example_Status 
00000000 l    d  .bss.Example_Status    00000000 .bss.Example_Status
00000000 g     O .bss.Example_Status    00000004 Example_Status

and my linker file are here:

/* Entry Point */
ENTRY(Reset_Handler)

/* Highest address of the user mode stack */
_estack = 0x20010000;    /* end of RAM */
/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0x000;;      /* required amount of heap  */
_Min_Stack_Size = 0x000;; /* required amount of stack */

/* Specify the memory areas */
MEMORY
{
FLASH (rx)      : ORIGIN = 0x8000000, LENGTH = 128K
RAM (xrw)      : ORIGIN = 0x20000000, LENGTH = 64K
}

/* Define output sections */
SECTIONS
{
  /* The startup code goes first into FLASH */
  .isr_vector :
  {
    . = ALIGN(4);
    KEEP(*(.isr_vector)) /* Startup code */
    . = ALIGN(4);
  } >FLASH

  /* The program code and other data goes into FLASH */
  .text :
  {
    . = ALIGN(4);
    *(.text)           /* .text sections (code) */
    *(.text*)          /* .text* sections (code) */
    *(.glue_7)         /* glue arm to thumb code */
    *(.glue_7t)        /* glue thumb to arm code */
    *(.eh_frame)

    KEEP (*(.init))
    KEEP (*(.fini))

        . = ALIGN(4);
    _etext = .;        /* define a global symbols at end of code */
  } >FLASH

  /* Constant data goes into FLASH */
  .rodata :
  {
    . = ALIGN(4);
    *(.rodata)         /* .rodata sections (constants, strings, etc.) */
    *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
    . = ALIGN(4);
  } >FLASH

  .ARM.extab   : { *(.ARM.extab* .gnu.linkonce.armextab.*) } >FLASH
  .ARM : {
    __exidx_start = .;
    *(.ARM.exidx*)
    __exidx_end = .;
  } >FLASH

  .preinit_array     :
  {
    PROVIDE_HIDDEN (__preinit_array_start = .);
    KEEP (*(.preinit_array*))
    PROVIDE_HIDDEN (__preinit_array_end = .);
  } >FLASH
  .init_array :
  {
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(SORT(.init_array.*)))
    KEEP (*(.init_array*))
    PROVIDE_HIDDEN (__init_array_end = .);
  } >FLASH
  .fini_array :
  {
    PROVIDE_HIDDEN (__fini_array_start = .);
    KEEP (*(SORT(.fini_array.*)))
    KEEP (*(.fini_array*))
    PROVIDE_HIDDEN (__fini_array_end = .);
  } >FLASH

  /* used by the startup to initialize data */
  _sidata = LOADADDR(.data);

  /* Initialized data sections goes into RAM, load LMA copy after code */
  .data : 
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */

    . = ALIGN(4);
    _edata = .;        /* define a global symbol at data end */
  } >RAM AT> FLASH


  /* Uninitialized data section */
  . = ALIGN(4);
  .bss :
  {
    /* This is used by the startup in order to initialize the .bss secion */
    _sbss = .;         /* define a global symbol at bss start */
    __bss_start__ = _sbss;
    *(.bss)
    *(.bss*)
    *(COMMON)

    . = ALIGN(4);
    _ebss = .;         /* define a global symbol at bss end */
    __bss_end__ = _ebss;
  } >RAM

  /* User_heap_stack section, used to check that there is enough RAM left */
  ._user_heap_stack :
  {
    . = ALIGN(8);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(8);
  } >RAM



  /* Remove information from the standard libraries */
  /DISCARD/ :
  {
    libc.a ( * )
    libm.a ( * )
    libgcc.a ( * )
  }

  .ARM.attributes 0 : { *(.ARM.attributes) }
}

This is my first linux project, i would appreicate if someone can help~ thanks

Edited for adding "disassemble /m"

75    Example_Status = 1;
0x080002ac <+24>:   and.w   r3, r3, #33554432   ; 0x2000000
0x080002b0 <+28>:   cmp r3, #0

---Type <return> to continue, or q <return> to quit---
76    Example_Status = 2;
0x080002b2 <+30>:   beq.n   0x80002a8 <main+20>
0x080002b4 <+32>:   ldr r3, [pc, #60]   ; (0x80002f4 <main+96>)
0x080002b6 <+34>:   movw    r2, #1795   ; 0x703

77    Example_Status = 3;
0x080002b8 <+36>:   strb    r3, [r0, #8]
0x080002ba <+38>:   str r2, [r3, #0]
0x080002bc <+40>:   ldr r2, [pc, #44]   ; (0x80002ec <main+88>)

//
(gdb) n
75    Example_Status = 1;
(gdb) n
76    Example_Status = 2;
(gdb) p Example_Status
$1 = 140166176
(gdb) s
Apex Yu
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  • Can you add the output of `(gdb) disassemble /m` for the code from lines 74 to 77? It's not clear why the gdb `n` command would skip over two of the assignment statements to `Example_Status`... unless some aggressive optimization was done. And if the assignment statements were optimized out, it could be the case that `p Example_Status` won't show an accurate value until execution reaches a part of your program where the variable is read, not just written. Also, is `Example_Status ` declared as `volatile`? – Mark Plotnick Jan 20 '17 at 19:23
  • @MarkPlotnick. Thank you! One of my mistake was using optimization Os instead of O0. thank you ! Also, is Example_Status declared as volatile? I wanna ask that all my variable (both local and global need to set to volatile?. And i added the (gdb) disassemble /m and upload the code for you. Thanks~ – Apex Yu Jan 21 '17 at 03:22
  • Not all variables need to be declared as volatile, but if a variable refers to something other than traditional RAM, such as an i/o register, declaring it volatile may help. In your code, a C compiler can eliminate the first two assignments to `Example_Status` if it's not declared volatile. See [Why is volatile needed in C](http://stackoverflow.com/questions/246127/why-is-volatile-needed-in-c). – Mark Plotnick Jan 21 '17 at 08:32
  • Your new edits show a gdb session in which you can step through successive assignments to `Example_Status`; did you recompile the program with different options? In any case, the assembly code looks unrelated to the source code, so there's something else weird going in with your compilation and I don't know the cause offhand. – Mark Plotnick Jan 21 '17 at 08:37
  • If you're cross-debugging, can you double-check that the source code that gdb is looking at is the same as the source code used to produce your executable? – Mark Plotnick Jan 21 '17 at 10:19
  • @MarkPlotnick. Thank you again. As out i am aways from PC , i remember my CFLAGS is CFLAGS += -DUSE_STDPERIPH_DRIVER -fno-common -Wall -O0 -g -mcpu=cortex-m3 -mthumb can you double-check that the source code that gdb is looking at is the same as the source code used to produce your executable? how can i do so ? many thx – Apex Yu Jan 21 '17 at 15:01
  • Just make sure that, if you have multiple versions of the source code of your program on the system where you run gdb, that gdb is looking at the correct version. Looking at an old version is a common cause of mismatched assembly/source code and breakpoint confusion. When the source code and target process are on the same system, Gdb can actually warn you if it sees that the source code has a modification time that is later than the modification time of the executable. – Mark Plotnick Jan 23 '17 at 15:33

1 Answers1

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When compiling, and you want reliable debugging, do not compile with optimization-level higher than 0:

gcc -O0 mycode.c -o mycode.o -c

Stian Skjelstad
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