Problems in implementing a private longjmp on MIPS

["PRC" <panruochen at gmail dot com>]

I want to implement a private longjmp to return quickly from subroutines to the
top routine in our embedded system.

My code looks like this:
----------------------------------------------
int top_routine()
{
	{
		int reg0;
		__asm__ __volatile__(
			"la %0, QUIT\n\t"
			"sw %0, %1\n\t" 
			"sw $29,%2\n\t": "=r"(reg0), "=m"(quit_addr.ra), "=m"(quit_addr.sp)
		);
	}

	...
	sub_routine();
	...

__asm__ __volatile__("QUIT:\n\t");
	write_reg32(mask, 0xb0020004);
	...
	return 0;
}
----------------------------------------------
Before returning, there are some cleaning work to be done (The code following the
label QUIT).
Here I get some problems. On -O2 optimization, gcc may save the value in a register
like s8, and won't reload it again from stack for this statement:
	write_reg32(mask, 0xb0020004);
The registers may be changed during calling to subroutines so that the cleaning work
can't be done properly and the top routine can't quit normally.

It is a solution to declare the variable `mask' volatile. But it is not a general approach.
Is there a way to inform gcc not to do optimization just from the lable QUIT to the end of
top_routine. Or is there another better way to implement longjmp?

Best Regards,
PRC
Apr 22, 2008