Hard Fault Assembly Code PC-relative load warning

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1

Hi,

I used the example on this page which shows some handy assembly for debugging hard faults on ARM Cortex-M devices. I have this placed in a cpp file, and the code looks like this.

//The hard fault interrupt is configured to call this    
extern "C" void HardFaultHandler() __attribute__ (( naked ));

extern "C" void HardFaultHandler(){
	__asm volatile
	(
		" tst lr, #4\n"
		" ite eq\n"
		" mrseq r0, msp\n"
		" mrsne r0, psp\n"
		" ldr r1, [r0, #24]\n"
		" ldr r2, hard_fault_handler_address_const\n"
		" bx r2\n"
		" hard_fault_handler_address_const: .word HardFaultCrash"
	);
}

extern "C" void HardFaultCrash(uint32_t* sp_addr){
	CrashStart();
	CrashPrint("Hard fault at "); CrashPrintHex32(sp_addr[6]); CrashPrint("\r\n");
	CrashPrintFaultRegisters();
	CrashFinish();
}

This seems to work, but when I compile it, an intermediately assembly file outputs the following assembler warning:

C:\Users\user\AppData\Local\Temp\ccM7txKR.s:1619: Warning: section does not have enough alignment to ensure safe PC-relative loads

It seems to be referring to the branch instruction. Iā€™m using ARM GCC, is there a attribute or some other way I can use to assure alignment?

Thank you

2

Can you decorate the function prototype with

"__attribute__((aligned (8)))"?

It may be possible to add an assembly directive into the inline assembly too - not sure though. Try adding

ā€œ.align 8ā€

above the first assembly line.

1 Like
3

I changed the declaration like this:

extern "C" void HardFaultHandler() __attribute__ (( naked, aligned(8) ));

That did the trick. Nice one! Thank you!