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From: Juli Mallett <jmallett@FreeBSD.org>
Date: Thu, 29 Mar 2012 02:04:16 +0000 (UTC)
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Subject: svn commit: r233638 - head/sys/mips/mips
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Author: jmallett
Date: Thu Mar 29 02:04:15 2012
New Revision: 233638
URL: http://svn.freebsd.org/changeset/base/233638

Log:
  Disable FP instruction emulation by default on !o32 because of ABI concerns.
  
  Note that in practice this isn't needed because we get a coprocessor unusable
  exception first, but that's actually something like a bug.

Modified:
  head/sys/mips/mips/trap.c

Modified: head/sys/mips/mips/trap.c
==============================================================================
--- head/sys/mips/mips/trap.c	Thu Mar 29 02:03:06 2012	(r233637)
+++ head/sys/mips/mips/trap.c	Thu Mar 29 02:04:15 2012	(r233638)
@@ -290,6 +290,20 @@ static int allow_unaligned_acc = 1;
 SYSCTL_INT(_vm, OID_AUTO, allow_unaligned_acc, CTLFLAG_RW,
     &allow_unaligned_acc, 0, "Allow unaligned accesses");
 
+/*
+ * FP emulation is assumed to work on O32, but the code is outdated and crufty
+ * enough that it's a more sensible default to have it disabled when using
+ * other ABIs.  At the very least, it needs a lot of help in using
+ * type-semantic ABI-oblivious macros for everything it does.
+ */
+#if defined(__mips_o32)
+static int emulate_fp = 1;
+#else
+static int emulate_fp = 0;
+#endif
+SYSCTL_INT(_machdep, OID_AUTO, emulate_fp, CTLFLAG_RW,
+    &allow_unaligned_acc, 0, "Emulate unimplemented FPU instructions");
+
 static int emulate_unaligned_access(struct trapframe *frame, int mode);
 
 extern void fswintrberr(void); /* XXX */
@@ -988,6 +1002,11 @@ dofault:
 #endif
 
 	case T_FPE + T_USER:
+		if (!emulate_fp) {
+			i = SIGILL;
+			addr = trapframe->pc;
+			break;
+		}
 		MipsFPTrap(trapframe->sr, trapframe->cause, trapframe->pc);
 		goto out;