Char* in struct not being written to RAM and hard faults when pointer tries to change value

[dboland]

I am encountering an issue where a hard fault occurs when the "char * pszCommand" variable is written to because it is trying to change data that is not in the RAM.

Here is the related code that gives me the hard fault:

typedef struct
{
	char * pszCommand; // command string
	void (* pfnHandler)(Parsed_t * ParsedCmd); // handler function
	int iParent; // index of command one level up in tree (if any)
	int nRequiredLength; // number of significant chars in command
	int nTreeLevel; // this commands depth in menu tree
	unsigned short bBranchEnd:1; // set if this command is the end of branch
	unsigned short bQueryAllowed: 1; // set if this command accepts queries
} CmdTreeEntry_t;


CmdTreeEntry_t * pTreeEntry;
// initialize the root entry
pTreeEntry = &g_CmdTree[0];
*pTreeEntry->pszCommand = ITEM_SEPARATOR;  <------ The hard fault occurs after execution of this line
pTreeEntry->iParent = -1;
pTreeEntry->nRequiredLength = 1;
pTreeEntry->nTreeLevel = 1;
pTreeEntry->bBranchEnd = FALSE;
pTreeEntry->bQueryAllowed = FALSE;

CmdTreeEntry_t g_CmdTree[] =
{
    /* command string, handler */
    { " ", NULL }, /* MUST BE FIRST ENTRY IN TABLE ! */

    { ":*CAL??",    calibration_query},
    { ":*CLS",      clear_status_cmd},
    .... (A bunch of commands)

    { NULL, NULL} /* MUST BE LAST ENTRY IN TABLE!!! */
};

I believe this is somehow related to the linker file not allocating the memory properly for the pszCommand pointer, but I am unable to find where the issue may be in the linker. 
Here is the linker file:

/* Entry Point */
ENTRY(Reset_Handler)

/* Highest address of the user mode stack */
_estack = ORIGIN(RAM) + LENGTH(RAM); /* end of "RAM" Ram type memory */

_Min_Heap_Size = 0x200; /* required amount of heap */
_Min_Stack_Size = 0x400; /* required amount of stack */

/* Memories definition */
MEMORY
{
  RAM    (xrw)    : ORIGIN = 0x20000000,  LENGTH = 64K
  FLASH  (rx)     : ORIGIN = 0x8000000,   LENGTH = 512K
}

/* Sections */
SECTIONS
{
  /* The startup code into "FLASH" Rom type memory */
  .isr_vector :
  {
    . = ALIGN(4);
    KEEP(*(.isr_vector)) /* Startup code */
    . = ALIGN(4);
  } >FLASH

  /* The program code and other data into "FLASH" Rom type memory */
  .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 into "FLASH" Rom type memory */
  .rodata :
  {
    . = ALIGN(4);
    *(.rodata)         /* .rodata sections (constants, strings, etc.) */
    *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
    . = ALIGN(4);
  } >FLASH

  .ARM.extab   : {
    . = ALIGN(4);
    *(.ARM.extab* .gnu.linkonce.armextab.*)
    . = ALIGN(4);
  } >FLASH

  .ARM : {
    . = ALIGN(4);
    __exidx_start = .;
    *(.ARM.exidx*)
    __exidx_end = .;
    . = ALIGN(4);
  } >FLASH

  .preinit_array     :
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__preinit_array_start = .);
    KEEP (*(.preinit_array*))
    PROVIDE_HIDDEN (__preinit_array_end = .);
    . = ALIGN(4);
  } >FLASH

  .init_array :
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(SORT(.init_array.*)))
    KEEP (*(.init_array*))
    PROVIDE_HIDDEN (__init_array_end = .);
    . = ALIGN(4);
  } >FLASH

  .fini_array :
  {
    . = ALIGN(4);
    PROVIDE_HIDDEN (__fini_array_start = .);
    KEEP (*(SORT(.fini_array.*)))
    KEEP (*(.fini_array*))
    PROVIDE_HIDDEN (__fini_array_end = .);
    . = ALIGN(4);
  } >FLASH

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

  /* Initialized data sections into "RAM" Ram type memory */
  .data :
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */
    *(.RamFunc)        /* .RamFunc sections */
    *(.RamFunc*)       /* .RamFunc* sections */

    . = ALIGN(4);
    _edata = .;        /* define a global symbol at data end */

  } >RAM AT> FLASH

  /* Uninitialized data section into "RAM" Ram type memory */
  . = ALIGN(4);
  .bss :
  {
    /* This is used by the startup in order to initialize the .bss section */
    _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" Ram  type memory left */
  ._user_heap_stack :
  {
    . = ALIGN(8);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(8);
  } >RAM

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

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

This is the memory address of pTreeEntry that is being placed in RAM but the address of pszCommand is not in RAM.

Any help would be appreciated.

Thanks,

Dan

[Tesla DeLorean]

Or make a structure which allocates space? And strcpy() or strcat() into that given sufficient space.

typedef struct
{
	char Command[16]; // command string
	void (* pfnHandler)(Parsed_t * ParsedCmd); // handler function
	int iParent; // index of command one level up in tree (if any)
	int nRequiredLength; // number of significant chars in command
	int nTreeLevel; // this commands depth in menu tree
	unsigned short bBranchEnd:1; // set if this command is the end of branch
	unsigned short bQueryAllowed: 1; // set if this command accepts queries
} CmdTreeEntry_t;

Pointers could be used with malloc/free type use of dynamic memory, or from a pool, but got to watch how you free up resources, and not leak, etc.

You can create systems that don't fragment, but you need to release everything you allocate

[Pavel A.]

Maybe you're confusing char vs string constants -   ':' vs ":"

The first one is a char, the 2nd is a pointer (maybe even points to read-only memory).

Of course one cannot assign a pointer to element of a char array.

[dboland · Accepted solution]

I found a solution that works, thanks to a coworker of mine that had some helpful insight. I created a new function that will allocate RAM space for the character and copy it from ROM.

static char * ROMtoRAM(char pszCommandContents[]){
	size_t len = strlen(pszCommandContents) + 1;
	char * target = malloc(len);
	if (target == NULL) return NULL;
	memcpy(target, pszCommandContents, len);
	return target;
}

 With this function I can change where pTreeEntry->pszCommand is being pointed to and can actually write to the allocated memory.

pTreeEntry->pszCommand = ROMtoRAM(pTreeEntry->pszCommand);
*pTreeEntry->pszCommand = ITEM_SEPARATOR;

I think this is acceptable to use so that it doesn't hard fault.

[Pavel A.]

:face_with_head_bandage: