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xtensa: support artificial division by 0 exception

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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: Max Filippov <jcmvbkbc@gmail.com>
This commit is contained in:
Max Filippov 2022-05-13 08:11:14 -07:00
parent 408b1d3c0e
commit d74862007e
1 changed files with 23 additions and 0 deletions
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23
arch/xtensa/kernel/traps.c
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@ -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. */