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Message-Id: <20220517104458.257799-3-jcmvbkbc@gmail.com>
Date: Tue, 17 May 2022 03:44:57 -0700
From: Max Filippov <jcmvbkbc@...il.com>
To: linux-xtensa@...ux-xtensa.org
Cc: Chris Zankel <chris@...kel.net>, linux-kernel@...r.kernel.org,
Max Filippov <jcmvbkbc@...il.com>
Subject: [PATCH v3 2/3] 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: Max Filippov <jcmvbkbc@...il.com>
---
Changes v2->v3:
- simplify check_div0 by dropping check for the specific illegal
instruction and only verifying the 'DIV0' signature
Changes v1->v2:
- split ABI probing improvement from the artificial division by 0
- don't limit artificial division by 0 pattern detection to
configurations without HW division opcodes, do it always
arch/xtensa/kernel/traps.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
index 24d11b44fa57..2b75b252b626 100644
--- a/arch/xtensa/kernel/traps.c
+++ b/arch/xtensa/kernel/traps.c
@@ -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. */
--
2.30.2
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