Keil Debug cannot trace HardFault handler

I am not expert on Cortex-M3. I recently test the memory handle using mbed LPC1768. It is strange that the debugger cannot jump into the hardfault_handler function. But the exceptional code execuated when it run in non-debug mode.

The code was exported from mbed online compiler and then opened by Keil uvision 5. I rewrite the HardFault_Handler function to capture an exception. The debugger is set as CMSIS-DAP. When I compile the code and load to the chip. It will flash LEDs after few seconds which means it jumps to the Hardfault_handler as expected. However, when I run in debug mode, the code paused at following line. The LED is not flashing as expected.

0x0000263E BEAB BKPT 0xAB

and I check the peripherals->core peripherals->fault report, the HARD_FAULT_STAT is 0x0 which means it didn't catch the interrupt. The BKPT bit as DBG_FAULT_STAT is 1. However, I didn't set any break point.

In the registers view, the ISR is 0 as well which means there is no interrupt caught!

Anyone can help on this problem? If a debugger cannot catch Hard_Fault_stat. It will be very difficult.

Here is the code.

 #include "mbed.h"


Serial pc(USBTX, USBRX);
BusOut leds(LED1, LED2, LED3, LED4);

extern "C" void HardFault_Handler()
{
    pc.printf("Hard fault!\r\n");
    while(1) {
        leds = 0x09;
        wait(0.1);
        leds = 0x06;
        wait(0.1);
    }
}


void fail()
{
    pc.printf("Caught the failure\r\n");
    while(1) {
        leds = 0x09;
        wait(0.4);
        leds = 0x06;
        wait(0.4);
    }
}


class Test
{
    public:
        int something;
        char woot[28];
};


int main() {
    Test *dummy;
    int index = 0;

    while(1) {
        dummy = new Test;
        if (dummy == NULL) fail();
        pc.printf("%u\r\n", index);
        ++index;
    }
}