Commit d7486200 authored by Max Filippov's avatar Max Filippov
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xtensa: support artificial division by 0 exception 



On xtensa cores wihout hardware division option division support
functions from libgcc react to division by 0 attempt by executing
illegal instruction followed by the characters 'DIV0'. Recognize this
pattern in illegal instruction exception handler and convert it to
division by 0.

Signed-off-by: default avatarMax Filippov <jcmvbkbc@gmail.com>
parent 408b1d3c

arch/xtensa/kernel/traps.c

+23 −0
Original line number Diff line number Diff line
@@ -293,12 +293,35 @@ static void do_interrupt(struct pt_regs *regs) 
	set_irq_regs(old_regs);

}



static bool check_div0(struct pt_regs *regs)

{

	static const u8 pattern[] = {'D', 'I', 'V', '0'};

	const u8 *p;

	u8 buf[5];



	if (user_mode(regs)) {

		if (copy_from_user(buf, (void __user *)regs->pc + 2, 5))

			return 0;

		p = buf;

	} else {

		p = (const u8 *)regs->pc + 2;

	}



	return memcmp(p, pattern, sizeof(pattern)) == 0 ||

		memcmp(p + 1, pattern, sizeof(pattern)) == 0;

}



/*

 * Illegal instruction. Fatal if in kernel space.

 */



static void do_illegal_instruction(struct pt_regs *regs)

{

	if (check_div0(regs)) {

		do_div0(regs);

		return;

	}



	__die_if_kernel("Illegal instruction in kernel", regs, SIGKILL);



	/* If in user mode, send SIGILL signal to current process. */