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authorMax Filippov <jcmvbkbc@gmail.com>2022-05-13 17:11:14 +0200
committerMax Filippov <jcmvbkbc@gmail.com>2022-05-17 12:35:43 +0200
commitd74862007e0849fad8ba86447e6f05928f920640 (patch)
tree3b4b0e3aa88dbb682fce761e7b4a79fe5f586c0b
parentxtensa: add trap handler for division by zero (diff)
downloadlinux-d74862007e0849fad8ba86447e6f05928f920640.tar.xz
linux-d74862007e0849fad8ba86447e6f05928f920640.zip
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@gmail.com>
-rw-r--r--arch/xtensa/kernel/traps.c23
1 files changed, 23 insertions, 0 deletions
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. */