From 37d02ff3fae3fe9be2e3ed207dfb940914780271 Mon Sep 17 00:00:00 2001
From: miod <miod@openbsd.org>
Date: Sun, 3 Mar 2024 11:14:34 +0000
Subject: [PATCH] Cope with the rare case of an imprecise FPU exception caught
 when reenabling the FPU as part of the regular processing of another
 exception.

---
 sys/arch/m88k/m88k/m88100_fp.c | 15 +++++++++++----
 sys/arch/m88k/m88k/trap.c      | 11 ++++++++++-
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/sys/arch/m88k/m88k/m88100_fp.c b/sys/arch/m88k/m88k/m88100_fp.c
index 250cfe3fc14..c227f8be328 100644
--- a/sys/arch/m88k/m88k/m88100_fp.c
+++ b/sys/arch/m88k/m88k/m88100_fp.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: m88100_fp.c,v 1.6 2024/03/03 11:03:13 miod Exp $	*/
+/*	$OpenBSD: m88100_fp.c,v 1.7 2024/03/03 11:14:34 miod Exp $	*/
 
 /*
  * Copyright (c) 2007, 2014, Miodrag Vallat.
@@ -442,9 +442,16 @@ m88100_fpu_imprecise_exception(struct trapframe *frame)
 	 */
 	__asm__ volatile ("fstcr %0, %%fcr62" :: "r"(frame->tf_fpsr));
 
-	/* Check for a SIGFPE condition */
-	if (frame->tf_fpsr & frame->tf_fpcr)
-		m88100_fpu_checksig(frame, SIGFPE, 0 /* SI_NOINFO */);
+	/*
+	 * Check for a SIGFPE condition.
+	 *
+	 * XXX If the exception was caught while in kernel mode, we can't
+	 * XXX send a signal at this point... what to do?
+	 */
+	if ((frame->tf_fpsr & PSR_MODE) == 0) {
+		if (frame->tf_fpsr & frame->tf_fpcr)
+			m88100_fpu_checksig(frame, SIGFPE, 0 /* SI_NOINFO */);
+	}
 }
 
 /*
diff --git a/sys/arch/m88k/m88k/trap.c b/sys/arch/m88k/m88k/trap.c
index 02fa56109ff..66677e280ee 100644
--- a/sys/arch/m88k/m88k/trap.c
+++ b/sys/arch/m88k/m88k/trap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: trap.c,v 1.134 2024/02/18 21:27:38 miod Exp $	*/
+/*	$OpenBSD: trap.c,v 1.135 2024/03/03 11:14:34 miod Exp $	*/
 /*
  * Copyright (c) 2004, Miodrag Vallat.
  * Copyright (c) 1998 Steve Murphree, Jr.
@@ -511,6 +511,15 @@ user_fault:
 	case T_FPEPFLT+T_USER:
 		m88100_fpu_precise_exception(frame);
 		goto userexit;
+	case T_FPEIFLT:
+		/*
+		 * Although the kernel does not use FPU instructions,
+		 * userland-triggered FPU imprecise exceptions may be
+		 * raised during exception processing, when the FPU gets
+		 * reenabled (i.e. immediately when returning to
+		 * m88100_fpu_enable).
+		 */
+		/* FALLTHROUGH */
 	case T_FPEIFLT+T_USER:
 		m88100_fpu_imprecise_exception(frame);
 		goto userexit;
-- 
2.20.1