Electronic – Problem on NVIC STM32F100

I am using STM32VL discovery board(STM32f100rb6)..
I wrote following code for NVIC:

void Interrupt_Init(void)
{
    __enable_irq();
    /*Core Base(NVIC)*/

    //set priority to 0
    //NVIC->IP[6] &= ~((uint32_t)0xff00);

    //Activate Interrupts
    NVIC->ISER[0] |= BIT6;

    //Enable Pending BIT for Interrupt 6
    NVIC->ISPR[0] |= BIT6;
    lcd_writechar('1');
} 

and

int main(void)
{
Interrupt_Init();
    while (1)
    {

    }
}
void EXTI0_IRQHandler(void)
{
    //NVIC->ICPR[0] |= BIT6;

    lcd_writechar('2');
}

as you see under Interrupt_Init() I user NVIC->ISPR[0] |= BIT6; phrase to soft-enable exti0-IRQ. so void EXTI0_IRQHandler(void) subroutine must executed and I got '2' on LCD. but as NVIC->ISPR[0] |= BIT6; execute next line(lcd_writechar('1');) never runs.. but when I commented (NVIC->ISPR[0] |= BIT6;) I got '1' on LCD… whats going on??

Update:

I look further into "startup_stm32f10x_md_vl.s" file in my project as
startup file:

.section  .text.Default_Handler,"ax",%progbits
Default_Handler:
Infinite_Loop:
  b  Infinite_Loop
  .size  Default_Handler, .-Default_Handler

and:

g_pfnVectors:
  .word  _estack
  .word  Reset_Handler
  .word  NMI_Handler
  .word  HardFault_Handler
  .word  MemManage_Handler
  .word  BusFault_Handler
  .word  UsageFault_Handler
  .word  0
  .word  0
  .word  0
  .word  0
  .word  SVC_Handler
  .word  DebugMon_Handler
  .word  0
  .word  PendSV_Handler
  .word  SysTick_Handler
  .word  WWDG_IRQHandler
  .word  PVD_IRQHandler
  .word  TAMPER_IRQHandler
  .word  RTC_IRQHandler
  .word  FLASH_IRQHandler
  .word  RCC_IRQHandler
  .word  EXTI0_IRQHandler
...

and:

.weak  EXTI0_IRQHandler
.thumb_set EXTI0_IRQHandler,Default_Handler

It seems that "EXTI0_IRQHandler" always equal to "Default_Handler" in
my projects so it cause infinite loop as we define above.

I think this part:

void EXTI0_IRQHandler(void)
{
  NVIC->ICPR[0] |= BIT6;

  lcd_writechar('2');
}

never influences the "EXTI0_IRQHandler" definition. why?

Update:

Is there any way to jump to
EXTI0_IRQHandler without implementing anything in peripheral?? Like asm("B
0x58")? my purpose is to be sure from core configurations then work
on peripheral configurations ?

Update:

I nearly found problem but needs help to fix it.. after many
examination and using debug features I found this piece of code is
faulty:

    void EXTI0_IRQHandler()
    {
      lcd_writechar('2');
      LED_ON();
      NVIC->ICPR[0] |= BIT6;
    }

in detail lcd_writechar('2'); cause to issue because inside function
I am using delay() function.This is that piece of code
involving delay by SycTick feature:

/*Enable SysTick*/
  //Processor clock (AHB)
  SysTick->CTRL |= BIT2;
  //Counting down to zero to asserts the SysTick exception request.
  SysTick->CTRL |= BIT1;
  SysTick->LOAD = 8000 - 1;
void SysTick_Handler(void)
{
  SysTick_Tick++;
  //lcd_writechar('7');
  SCB->ICSR |= BIT25;
}
void delay(int ms)
{
  SysTick_Tick = 0;
  //Enable Systick Counter
  SysTick->CTRL |= BIT0;
  while (SysTick_Tick < ms) {}
  //Disable Systick Counter
  SysTick->CTRL &= ~BIT0;
  SCB->ICSR |= BIT25;
  return;
}

as you see I am trying to clear pending bit of SysTick by SCB->ICSR
|= BIT25; but clearly after running of delay() function
from inside of EXTI0_IRQHandler() everything hangs..