Learn ARM development(9)

Last time, I finished reading the boot assembly and prepared the C operating environment. Now I will start to learn the C source code and jump from the start.S file to the file
lib_arm/board.c to run.
/*
The boot program jumps from the assembly start.S to here to execute.
Cai Junsheng 2005/07/19
*/
void start_armboot (void)
{
/* Declare a global pointer, which points to a data structure for storing parameters.
And it occupies the r8 register, which is used to store memory addresses for global use.
*/
DECLARE_GLOBAL_DATA_PTR;

ulong size;
init_fnc_t **init_fnc_ptr;
char *s;

#if defined(CONFIG_VFD) || defined(CONFIG_LCD)
unsigned long addr;
#endif

/* The gd pointer can be written because a register has been assigned to it as a variable.
This is equivalent to saving the address calculated later to the r8 register.
*/
gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));

/* The following sentence prevents GCC versions above 3.4 from optimizing the code and deletes the following code. */
__asm__ __volatile__("": ​​: :"memory");

/* Clear the structure pointed to by gd*/
memset ((void*)gd, 0, sizeof (gd_t));

/* */
gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
memset (gd->bd, 0, sizeof (bd_t));

monitor_flash_len = _bss_start - _armboot_start;
This section prepares the global variable area for saving parameters.
The following is a series of initializations and obtaining the correct parameters.