On FPU exceptions, pass a useful error code (one of the FPE_...

macros) to the signal handler, for old-style BSD signal handlers as
the second (int) argument, for SA_SIGINFO signal handlers as
siginfo_t->si_code. This is source-compatible with Solaris, except
that we have no <siginfo.h> (which isn't even mentioned in POSIX
1003.1b).

An rather complete example program is at
  http://www3.cons.org/cracauer/freebsd-signal.c
This will be added to the regression tests in src/.

This commit also adds code to disable the (hardware) FPU from
userconfig, so that you can use a software FP emulator on a machine
that has hardware floating point. See LINT.

7 files changed, 258 insertions, 51 deletions

diff --git a/sys/i386/conf/LINT b/sys/i386/conf/LINT
index 51c1411..e71cac9 100644
--- a/sys/i386/conf/LINT
+++ b/sys/i386/conf/LINT
@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.617 1999/07/09 04:29:56 wpaul Exp $
+#	$Id: LINT,v 1.618 1999/07/25 04:32:44 wpaul Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -956,18 +956,20 @@ options 	SC_NO_HISTORY
 options 	SC_NO_SYSMOUSE
 
 #
-# The Numeric Processing eXtension driver.  This should be configured if
-# your machine has a math co-processor, unless the coprocessor is very
-# buggy. If it is not configured then you *must* configure math emulation
-# (see above).  If both npx0 and emulation are configured, then only npx0
-# is used (provided it works).
+# The Numeric Processing eXtension driver. In addition to this, you
+# may configure a math emulator (see above). If your machine has a
+# hardware FPU and the kernel configuration includes the npx device
+# *and* a math emulator compiled into the kernel, the hardware FPU
+# will be used, unless it is found to be broken or unless "flags" to
+# npx0 includes "0x08", which requests preference for the emulator.
 device		npx0	at nexus? port IO_NPX flags 0x0 irq 13
 
 #
 # `flags' for npx0:
-#	0x01	don't use the npx registers to optimize bcopy
-#	0x02	don't use the npx registers to optimize bzero
+#	0x01	don't use the npx registers to optimize bcopy.
+#	0x02	don't use the npx registers to optimize bzero.
 #	0x04	don't use the npx registers to optimize copyin or copyout.
+#	0x08	use emulator even if hardware FPU is available.
 # The npx registers are normally used to optimize copying and zeroing when
 # all of the following conditions are satisfied:
 #	I586_CPU is an option
@@ -978,6 +980,9 @@ device		npx0	at nexus? port IO_NPX flags 0x0 irq 13
 # The flags can be used to control cases where it doesn't work or is slower.
 # Setting them at boot time using userconfig works right (the optimizations
 # are not used until later in the bootstrap when npx0 is attached).
+# Flag 0x08 does not imply any settings of the other flags, you may run
+# with FPU preference set to emulator, but still using the i586 optimized
+# memory routines.
 #
 
 #
@@ -1149,6 +1154,7 @@ device		sio0	at isa? port IO_COM1 flags 0x10 irq 4
 #		higher priority console).  This replaces the COMCONSOLE option.
 #	0x40	reserve this unit for low level console operations.  Do not
 #		access the device in any normal way.
+#	0x80	use this port for serial line gdb support in ddb.
 #
 # PnP `flags' (set via userconfig using pnp x flags y)
 #	0x1	disable probing of this device.  Used to prevent your modem
diff --git a/sys/i386/conf/NOTES b/sys/i386/conf/NOTES
index 51c1411..e71cac9 100644
--- a/sys/i386/conf/NOTES
+++ b/sys/i386/conf/NOTES
@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.617 1999/07/09 04:29:56 wpaul Exp $
+#	$Id: LINT,v 1.618 1999/07/25 04:32:44 wpaul Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -956,18 +956,20 @@ options 	SC_NO_HISTORY
 options 	SC_NO_SYSMOUSE
 
 #
-# The Numeric Processing eXtension driver.  This should be configured if
-# your machine has a math co-processor, unless the coprocessor is very
-# buggy. If it is not configured then you *must* configure math emulation
-# (see above).  If both npx0 and emulation are configured, then only npx0
-# is used (provided it works).
+# The Numeric Processing eXtension driver. In addition to this, you
+# may configure a math emulator (see above). If your machine has a
+# hardware FPU and the kernel configuration includes the npx device
+# *and* a math emulator compiled into the kernel, the hardware FPU
+# will be used, unless it is found to be broken or unless "flags" to
+# npx0 includes "0x08", which requests preference for the emulator.
 device		npx0	at nexus? port IO_NPX flags 0x0 irq 13
 
 #
 # `flags' for npx0:
-#	0x01	don't use the npx registers to optimize bcopy
-#	0x02	don't use the npx registers to optimize bzero
+#	0x01	don't use the npx registers to optimize bcopy.
+#	0x02	don't use the npx registers to optimize bzero.
 #	0x04	don't use the npx registers to optimize copyin or copyout.
+#	0x08	use emulator even if hardware FPU is available.
 # The npx registers are normally used to optimize copying and zeroing when
 # all of the following conditions are satisfied:
 #	I586_CPU is an option
@@ -978,6 +980,9 @@ device		npx0	at nexus? port IO_NPX flags 0x0 irq 13
 # The flags can be used to control cases where it doesn't work or is slower.
 # Setting them at boot time using userconfig works right (the optimizations
 # are not used until later in the bootstrap when npx0 is attached).
+# Flag 0x08 does not imply any settings of the other flags, you may run
+# with FPU preference set to emulator, but still using the i586 optimized
+# memory routines.
 #
 
 #
@@ -1149,6 +1154,7 @@ device		sio0	at isa? port IO_COM1 flags 0x10 irq 4
 #		higher priority console).  This replaces the COMCONSOLE option.
 #	0x40	reserve this unit for low level console operations.  Do not
 #		access the device in any normal way.
+#	0x80	use this port for serial line gdb support in ddb.
 #
 # PnP `flags' (set via userconfig using pnp x flags y)
 #	0x1	disable probing of this device.  Used to prevent your modem
diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
index 1d9d216..e717563 100644
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -35,7 +35,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)trap.c	7.4 (Berkeley) 5/13/91
- *	$Id: trap.c,v 1.138 1999/06/01 18:19:47 jlemon Exp $
+ *	$Id: trap.c,v 1.139 1999/06/18 14:32:16 bde Exp $
  */
 
 /*
@@ -360,7 +360,7 @@ restart:
 			break;
 
 		case T_DIVIDE:		/* integer divide fault */
-			ucode = FPE_INTDIV_TRAP;
+			ucode = FPE_INTDIV;
 			i = SIGFPE;
 			break;
 
@@ -382,12 +382,12 @@ restart:
 #endif /* NISA > 0 */
 
 		case T_OFLOW:		/* integer overflow fault */
-			ucode = FPE_INTOVF_TRAP;
+			ucode = FPE_INTOVF;
 			i = SIGFPE;
 			break;
 
 		case T_BOUND:		/* bounds check fault */
-			ucode = FPE_SUBRNG_TRAP;
+			ucode = FPE_FLTSUB;
 			i = SIGFPE;
 			break;
 
diff --git a/sys/i386/i386/userconfig.c b/sys/i386/i386/userconfig.c
index 9c842a2..85360f0 100644
--- a/sys/i386/i386/userconfig.c
+++ b/sys/i386/i386/userconfig.c
@@ -46,7 +46,7 @@
  ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  ** THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  **
- **      $Id: userconfig.c,v 1.148 1999/07/09 04:29:54 wpaul Exp $
+ **      $Id: userconfig.c,v 1.149 1999/07/25 04:32:46 wpaul Exp $
  **/
 
 /**
@@ -459,7 +459,7 @@ static DEV_INFO device_info[] = {
 
 {"apm",         "Advanced Power Management",		FLG_FIXED,	CLS_MISC},
 {"labpc",       "National Instruments Lab-PC/Lab-PC+",	0,		CLS_MISC},
-{"npx",	        "Math coprocessor",			FLG_INVISIBLE,	CLS_MISC},
+{"npx",	        "Math coprocessor",			FLG_IMMUTABLE,	CLS_MISC},
 {"lkm",		"Loadable PCI driver support",		FLG_INVISIBLE,	CLS_MISC},
 {"vga",	        "Catchall PCI VGA driver",		FLG_INVISIBLE,	CLS_MISC},
 {"chip",        "PCI chipset support",			FLG_INVISIBLE,	CLS_MISC},
@@ -2544,7 +2544,7 @@ visuserconfig(void)
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *      $Id: userconfig.c,v 1.148 1999/07/09 04:29:54 wpaul Exp $
+ *      $Id: userconfig.c,v 1.149 1999/07/25 04:32:46 wpaul Exp $
  */
 
 #include "scbus.h"
diff --git a/sys/i386/include/ieeefp.h b/sys/i386/include/ieeefp.h
index f81ff31..ab4d529 100644
--- a/sys/i386/include/ieeefp.h
+++ b/sys/i386/include/ieeefp.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  * 	from: @(#) ieeefp.h 	1.0 (Berkeley) 9/23/93
- *	$Id$
+ *	$Id: ieeefp.h,v 1.5 1997/02/22 09:34:41 peter Exp $
  */
 
 /*
@@ -72,6 +72,7 @@ typedef enum {
 #define FP_X_OFL	0x08	/* overflow */
 #define FP_X_UFL	0x10	/* underflow */
 #define FP_X_IMP	0x20	/* (im)precision */
+#define FP_X_STK	0x40	/* stack fault */
 
 /*
  * FP registers
diff --git a/sys/i386/include/trap.h b/sys/i386/include/trap.h
index 9d49054..5740379 100644
--- a/sys/i386/include/trap.h
+++ b/sys/i386/include/trap.h
@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)trap.h	5.4 (Berkeley) 5/9/91
- *	$Id$
+ *	$Id: trap.h,v 1.7 1997/02/22 09:35:19 peter Exp $
  */
 
 #ifndef _MACHINE_TRAP_H_
@@ -76,13 +76,29 @@
 #define	    ILL_ALIGN_FAULT	T_ALIGNFLT
 #define	    ILL_FPOP_FAULT	T_FPOPFLT	/* coprocessor operand fault */
 
-/* codes for SIGFPE/ARITHTRAP */
+/* 
+ * codes for SIGFPE/ARITHTRAP 
+ *
+ */
+/* portable macros */
+#define FPE_INTDIV	1	/* integer divide by zero */
+#define FPE_INTOVF	2	/* integer overflow */
+#define FPE_FLTDIV	3	/* floating point divide by zero */
+#define FPE_FLTOVF	4	/* floating point overflow */
+#define FPE_FLTUND	5	/* floating point underflow */
+#define FPE_FLTRES	6	/* floating point inexact result */
+#define FPE_FLTINV	7	/* invalid floating point operation */
+#define FPE_FLTSUB	8	/* subscript out of range */
+
+/* old FreeBSD macros, deprecated */
 #define	    FPE_INTOVF_TRAP	0x1	/* integer overflow */
 #define	    FPE_INTDIV_TRAP	0x2	/* integer divide by zero */
 #define	    FPE_FLTDIV_TRAP	0x3	/* floating/decimal divide by zero */
 #define	    FPE_FLTOVF_TRAP	0x4	/* floating overflow */
 #define	    FPE_FLTUND_TRAP	0x5	/* floating underflow */
-#define	    FPE_FPU_NP_TRAP	0x6	/* floating point unit not present */
+#define	    FPE_FPU_NP_TRAP	0x6	/* floating point unit not present 
+					 * - won't happen in practice
+					 */
 #define	    FPE_SUBRNG_TRAP	0x7	/* subrange out of bounds */
 
 /* codes for SIGBUS */
diff --git a/sys/i386/isa/npx.c b/sys/i386/isa/npx.c
index ce4a077..2f2709d 100644
--- a/sys/i386/isa/npx.c
+++ b/sys/i386/isa/npx.c
@@ -32,7 +32,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)npx.c	7.2 (Berkeley) 5/12/91
- *	$Id: npx.c,v 1.72 1999/05/11 16:29:18 luoqi Exp $
+ *	$Id: npx.c,v 1.73 1999/05/15 17:58:58 peter Exp $
  */
 
 #include "npx.h"
@@ -86,6 +86,7 @@
 #define	NPX_DISABLE_I586_OPTIMIZED_BCOPY	(1 << 0)
 #define	NPX_DISABLE_I586_OPTIMIZED_BZERO	(1 << 1)
 #define	NPX_DISABLE_I586_OPTIMIZED_COPYIO	(1 << 2)
+#define	NPX_PREFER_EMULATOR			(1 << 3)
 
 #ifdef	__GNUC__
 
@@ -396,34 +397,44 @@ int
 npx_attach(dev)
 	device_t dev;
 {
-#ifdef I586_CPU
 	int flags;
-#endif
+
+	if (resource_int_value("npx", 0, "flags", &flags) != 0)
+		flags = 0;
 
 	device_print_prettyname(dev);
 	if (npx_irq13) {
 		printf("using IRQ 13 interface\n");
 	} else {
-		if (npx_ex16)
-			printf("INT 16 interface\n");
 #if defined(MATH_EMULATE) || defined(GPL_MATH_EMULATE)
-		else if (npx_exists) {
+		if (npx_ex16) {
+			if (!(flags & NPX_PREFER_EMULATOR))
+				printf("INT 16 interface\n");
+			else {
+				printf("FPU exists, but flags request "
+				    "emulator\n");
+				hw_float = npx_exists = 0;
+			}
+		} else if (npx_exists) {
 			printf("error reporting broken; using 387 emulator\n");
 			hw_float = npx_exists = 0;
 		} else
 			printf("387 emulator\n");
 #else
-		else
-			printf("no 387 emulator in kernel!\n");
+		if (npx_ex16) {
+			printf("INT 16 interface\n");
+			if (flags & NPX_PREFER_EMULATOR) {
+				printf("emulator requested, but none compiled "
+				    "into kernel, using FPU\n");
+			}
+		} else
+			printf("no 387 emulator in kernel and no FPU!\n");
 #endif
 	}
 	npxinit(__INITIAL_NPXCW__);
 
 #ifdef I586_CPU
-	if (resource_int_value("npx", 0, "flags", &flags) != 0)
-		flags = 0;
-
-	if (cpu_class == CPUCLASS_586 && npx_ex16 &&
+	if (cpu_class == CPUCLASS_586 && npx_ex16 && npx_exists &&
 	    timezero("i586_bzero()", i586_bzero) <
 	    timezero("bzero()", bzero) * 4 / 5) {
 		if (!(flags & NPX_DISABLE_I586_OPTIMIZED_BCOPY)) {
@@ -494,6 +505,179 @@ npxexit(p)
 #endif
 }
 
+/* 
+ * The following mechanism is used to ensure that the FPE_... value
+ * that is passed as a trapcode to the signal handler of the user
+ * process does not have more than one bit set.
+ * 
+ * Multiple bits may be set if the user process modifies the control
+ * word while a status word bit is already set. While this is a sign
+ * of bad coding, we have no choise than to narrow them down to one
+ * bit, since we must not send a trapcode that is not exactly one of
+ * the FPE_ macros.
+ *
+ * The mechanism has a static table with 127 entries. Each combination
+ * of the 7 FPU status word exception bits directly translates to a
+ * position in this table, where a single FPE_... value is stored.
+ * This FPE_... value stored there is considered the "most important"
+ * of the exception bits and will be sent as the signal code. The
+ * precedence of the bits is based upon Intel Document "Numerical
+ * Applications", Chapter "Special Computational Situations".
+ *
+ * The macro to choose one of these values does these steps: 1) Throw
+ * away status word bits that cannot be masked. 2) Throw away the bits
+ * currently masked in the control word, assuming the user isn't
+ * interested in them anymore. 3) Reinsert status word bit 7 (stack
+ * fault) if it is set, which cannot be masked but must be presered.
+ * 4) Use the remaining bits to point into the trapcode table.
+ *
+ * The 6 maskable bits in order of their preference, as stated in the
+ * above referenced Intel manual:
+ * 1  Invalid operation (FP_X_INV)
+ * 1a   Stack underflow
+ * 1b   Stack overflow
+ * 1c   Operand of unsupported format
+ * 1d   SNaN operand.
+ * 2  QNaN operand (not an exception, irrelavant here)
+ * 3  Any other invalid-operation not mentioned above or zero divide
+ *      (FP_X_INV, FP_X_DZ)
+ * 4  Denormal operand (FP_X_DNML)
+ * 5  Numeric over/underflow (FP_X_OFL, FP_X_UFL)
+ * 6  Inexact result (FP_X_IMP) */
+
+static char fpetable[128] = {
+	0,
+	FPE_FLTINV, /*  1 - INV */
+	FPE_FLTUND, /*  2 - DNML */
+	FPE_FLTINV, /*  3 - INV | DNML */
+	FPE_FLTDIV, /*  4 - DZ */
+	FPE_FLTINV, /*  5 - INV | DZ */
+	FPE_FLTDIV, /*  6 - DNML | DZ */
+	FPE_FLTINV, /*  7 - INV | DNML | DZ */
+	FPE_FLTOVF, /*  8 - OFL */
+	FPE_FLTINV, /*  9 - INV | OFL */
+	FPE_FLTUND, /*  A - DNML | OFL */
+	FPE_FLTINV, /*  B - INV | DNML | OFL */
+	FPE_FLTDIV, /*  C - DZ | OFL */
+	FPE_FLTINV, /*  D - INV | DZ | OFL */
+	FPE_FLTDIV, /*  E - DNML | DZ | OFL */
+	FPE_FLTINV, /*  F - INV | DNML | DZ | OFL */
+	FPE_FLTUND, /* 10 - UFL */
+	FPE_FLTINV, /* 11 - INV | UFL */
+	FPE_FLTUND, /* 12 - DNML | UFL */
+	FPE_FLTINV, /* 13 - INV | DNML | UFL */
+	FPE_FLTDIV, /* 14 - DZ | UFL */
+	FPE_FLTINV, /* 15 - INV | DZ | UFL */
+	FPE_FLTDIV, /* 16 - DNML | DZ | UFL */
+	FPE_FLTINV, /* 17 - INV | DNML | DZ | UFL */
+	FPE_FLTOVF, /* 18 - OFL | UFL */
+	FPE_FLTINV, /* 19 - INV | OFL | UFL */
+	FPE_FLTUND, /* 1A - DNML | OFL | UFL */
+	FPE_FLTINV, /* 1B - INV | DNML | OFL | UFL */
+	FPE_FLTDIV, /* 1C - DZ | OFL | UFL */
+	FPE_FLTINV, /* 1D - INV | DZ | OFL | UFL */
+	FPE_FLTDIV, /* 1E - DNML | DZ | OFL | UFL */
+	FPE_FLTINV, /* 1F - INV | DNML | DZ | OFL | UFL */
+	FPE_FLTRES, /* 20 - IMP */
+	FPE_FLTINV, /* 21 - INV | IMP */
+	FPE_FLTUND, /* 22 - DNML | IMP */
+	FPE_FLTINV, /* 23 - INV | DNML | IMP */
+	FPE_FLTDIV, /* 24 - DZ | IMP */
+	FPE_FLTINV, /* 25 - INV | DZ | IMP */
+	FPE_FLTDIV, /* 26 - DNML | DZ | IMP */
+	FPE_FLTINV, /* 27 - INV | DNML | DZ | IMP */
+	FPE_FLTOVF, /* 28 - OFL | IMP */
+	FPE_FLTINV, /* 29 - INV | OFL | IMP */
+	FPE_FLTUND, /* 2A - DNML | OFL | IMP */
+	FPE_FLTINV, /* 2B - INV | DNML | OFL | IMP */
+	FPE_FLTDIV, /* 2C - DZ | OFL | IMP */
+	FPE_FLTINV, /* 2D - INV | DZ | OFL | IMP */
+	FPE_FLTDIV, /* 2E - DNML | DZ | OFL | IMP */
+	FPE_FLTINV, /* 2F - INV | DNML | DZ | OFL | IMP */
+	FPE_FLTUND, /* 30 - UFL | IMP */
+	FPE_FLTINV, /* 31 - INV | UFL | IMP */
+	FPE_FLTUND, /* 32 - DNML | UFL | IMP */
+	FPE_FLTINV, /* 33 - INV | DNML | UFL | IMP */
+	FPE_FLTDIV, /* 34 - DZ | UFL | IMP */
+	FPE_FLTINV, /* 35 - INV | DZ | UFL | IMP */
+	FPE_FLTDIV, /* 36 - DNML | DZ | UFL | IMP */
+	FPE_FLTINV, /* 37 - INV | DNML | DZ | UFL | IMP */
+	FPE_FLTOVF, /* 38 - OFL | UFL | IMP */
+	FPE_FLTINV, /* 39 - INV | OFL | UFL | IMP */
+	FPE_FLTUND, /* 3A - DNML | OFL | UFL | IMP */
+	FPE_FLTINV, /* 3B - INV | DNML | OFL | UFL | IMP */
+	FPE_FLTDIV, /* 3C - DZ | OFL | UFL | IMP */
+	FPE_FLTINV, /* 3D - INV | DZ | OFL | UFL | IMP */
+	FPE_FLTDIV, /* 3E - DNML | DZ | OFL | UFL | IMP */
+	FPE_FLTINV, /* 3F - INV | DNML | DZ | OFL | UFL | IMP */
+	FPE_FLTSUB, /* 40 - STK */
+	FPE_FLTSUB, /* 41 - INV | STK */
+	FPE_FLTUND, /* 42 - DNML | STK */
+	FPE_FLTSUB, /* 43 - INV | DNML | STK */
+	FPE_FLTDIV, /* 44 - DZ | STK */
+	FPE_FLTSUB, /* 45 - INV | DZ | STK */
+	FPE_FLTDIV, /* 46 - DNML | DZ | STK */
+	FPE_FLTSUB, /* 47 - INV | DNML | DZ | STK */
+	FPE_FLTOVF, /* 48 - OFL | STK */
+	FPE_FLTSUB, /* 49 - INV | OFL | STK */
+	FPE_FLTUND, /* 4A - DNML | OFL | STK */
+	FPE_FLTSUB, /* 4B - INV | DNML | OFL | STK */
+	FPE_FLTDIV, /* 4C - DZ | OFL | STK */
+	FPE_FLTSUB, /* 4D - INV | DZ | OFL | STK */
+	FPE_FLTDIV, /* 4E - DNML | DZ | OFL | STK */
+	FPE_FLTSUB, /* 4F - INV | DNML | DZ | OFL | STK */
+	FPE_FLTUND, /* 50 - UFL | STK */
+	FPE_FLTSUB, /* 51 - INV | UFL | STK */
+	FPE_FLTUND, /* 52 - DNML | UFL | STK */
+	FPE_FLTSUB, /* 53 - INV | DNML | UFL | STK */
+	FPE_FLTDIV, /* 54 - DZ | UFL | STK */
+	FPE_FLTSUB, /* 55 - INV | DZ | UFL | STK */
+	FPE_FLTDIV, /* 56 - DNML | DZ | UFL | STK */
+	FPE_FLTSUB, /* 57 - INV | DNML | DZ | UFL | STK */
+	FPE_FLTOVF, /* 58 - OFL | UFL | STK */
+	FPE_FLTSUB, /* 59 - INV | OFL | UFL | STK */
+	FPE_FLTUND, /* 5A - DNML | OFL | UFL | STK */
+	FPE_FLTSUB, /* 5B - INV | DNML | OFL | UFL | STK */
+	FPE_FLTDIV, /* 5C - DZ | OFL | UFL | STK */
+	FPE_FLTSUB, /* 5D - INV | DZ | OFL | UFL | STK */
+	FPE_FLTDIV, /* 5E - DNML | DZ | OFL | UFL | STK */
+	FPE_FLTSUB, /* 5F - INV | DNML | DZ | OFL | UFL | STK */
+	FPE_FLTRES, /* 60 - IMP | STK */
+	FPE_FLTSUB, /* 61 - INV | IMP | STK */
+	FPE_FLTUND, /* 62 - DNML | IMP | STK */
+	FPE_FLTSUB, /* 63 - INV | DNML | IMP | STK */
+	FPE_FLTDIV, /* 64 - DZ | IMP | STK */
+	FPE_FLTSUB, /* 65 - INV | DZ | IMP | STK */
+	FPE_FLTDIV, /* 66 - DNML | DZ | IMP | STK */
+	FPE_FLTSUB, /* 67 - INV | DNML | DZ | IMP | STK */
+	FPE_FLTOVF, /* 68 - OFL | IMP | STK */
+	FPE_FLTSUB, /* 69 - INV | OFL | IMP | STK */
+	FPE_FLTUND, /* 6A - DNML | OFL | IMP | STK */
+	FPE_FLTSUB, /* 6B - INV | DNML | OFL | IMP | STK */
+	FPE_FLTDIV, /* 6C - DZ | OFL | IMP | STK */
+	FPE_FLTSUB, /* 6D - INV | DZ | OFL | IMP | STK */
+	FPE_FLTDIV, /* 6E - DNML | DZ | OFL | IMP | STK */
+	FPE_FLTSUB, /* 6F - INV | DNML | DZ | OFL | IMP | STK */
+	FPE_FLTUND, /* 70 - UFL | IMP | STK */
+	FPE_FLTSUB, /* 71 - INV | UFL | IMP | STK */
+	FPE_FLTUND, /* 72 - DNML | UFL | IMP | STK */
+	FPE_FLTSUB, /* 73 - INV | DNML | UFL | IMP | STK */
+	FPE_FLTDIV, /* 74 - DZ | UFL | IMP | STK */
+	FPE_FLTSUB, /* 75 - INV | DZ | UFL | IMP | STK */
+	FPE_FLTDIV, /* 76 - DNML | DZ | UFL | IMP | STK */
+	FPE_FLTSUB, /* 77 - INV | DNML | DZ | UFL | IMP | STK */
+	FPE_FLTOVF, /* 78 - OFL | UFL | IMP | STK */
+	FPE_FLTSUB, /* 79 - INV | OFL | UFL | IMP | STK */
+	FPE_FLTUND, /* 7A - DNML | OFL | UFL | IMP | STK */
+	FPE_FLTSUB, /* 7B - INV | DNML | OFL | UFL | IMP | STK */
+	FPE_FLTDIV, /* 7C - DZ | OFL | UFL | IMP | STK */
+	FPE_FLTSUB, /* 7D - INV | DZ | OFL | UFL | IMP | STK */
+	FPE_FLTDIV, /* 7E - DNML | DZ | OFL | UFL | IMP | STK */
+	FPE_FLTSUB, /* 7F - INV | DNML | DZ | OFL | UFL | IMP | STK */
+};
+
+#define ENCODE(_sw, _cw) (fpetable[(_sw & ~_cw & 0x3f) | (_sw & 0x40)])
+
 /*
  * Preserve the FP status word, clear FP exceptions, then generate a SIGFPE.
  *
@@ -501,13 +685,9 @@ npxexit(p)
  * depend on longjmp() restoring a usable state.  Restoring the state
  * or examining it might fail if we didn't clear exceptions.
  *
- * XXX there is no standard way to tell SIGFPE handlers about the error
- * state.  The old interface:
- *
- *	void handler(int sig, int code, struct sigcontext *scp);
- *
- * is broken because it is non-ANSI and because the FP state is not in
- * struct sigcontext.
+ * The error code chosen will be one of the FPE_... macros. It will be
+ * sent as the second argument to old BSD-style signal handlers and as
+ * "siginfo_t->si_code" (second argument) to SA_SIGINFO signal handlers.
  *
  * XXX the FP state is not preserved across signal handlers.  So signal
  * handlers cannot afford to do FP unless they preserve the state or
@@ -520,6 +700,7 @@ npx_intr(dummy)
 	void *dummy;
 {
 	int code;
+	u_long cw;
 	struct intrframe *frame;
 
 	if (npxproc == NULL || !npx_exists) {
@@ -535,6 +716,7 @@ npx_intr(dummy)
 
 	outb(0xf0, 0);
 	fnstsw(&curpcb->pcb_savefpu.sv_ex_sw);
+	fnstcw(&cw);
 	fnclex();
 
 	/*
@@ -554,15 +736,11 @@ npx_intr(dummy)
 		 * just before it is used).
 		 */
 		curproc->p_md.md_regs = INTR_TO_TRAPFRAME(frame);
-#ifdef notyet
 		/*
 		 * Encode the appropriate code for detailed information on
 		 * this exception.
 		 */
-		code = XXX_ENCODE(curpcb->pcb_savefpu.sv_ex_sw);
-#else
-		code = 0;	/* XXX */
-#endif
+		code = ENCODE(curpcb->pcb_savefpu.sv_ex_sw, cw);
 		trapsignal(curproc, SIGFPE, code);
 	} else {
 		/*