NetBSD Problem Report #51368

From www@NetBSD.org  Wed Jul 27 15:08:05 2016
Return-Path: <www@NetBSD.org>
Received: from mail.netbsd.org (mail.netbsd.org [199.233.217.200])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(Client CN "mail.netbsd.org", Issuer "Postmaster NetBSD.org" (verified OK))
	by mollari.NetBSD.org (Postfix) with ESMTPS id 230807A219
	for <gnats-bugs@gnats.NetBSD.org>; Wed, 27 Jul 2016 15:08:05 +0000 (UTC)
Message-Id: <20160727150803.888BC7A264@mollari.NetBSD.org>
Date: Wed, 27 Jul 2016 15:08:03 +0000 (UTC)
From: rokuyama@rk.phys.keio.ac.jp
Reply-To: rokuyama@rk.phys.keio.ac.jp
To: gnats-bugs@NetBSD.org
Subject: powerpc FPU emulation fails for single precision floating point arithmetic
X-Send-Pr-Version: www-1.0

>Number:         51368
>Category:       port-powerpc
>Synopsis:       powerpc FPU emulation fails for single precision floating point arithmetic
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-powerpc-maintainer
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jul 27 15:10:01 +0000 2016
>Closed-Date:    Mon Jan 09 00:09:39 +0000 2017
>Last-Modified:  Mon Jan 09 00:09:39 +0000 2017
>Originator:     Rin Okuyama
>Release:        HEAD
>Organization:
Faculty of Science and Technology, Keio University
>Environment:
NetBSD obs266 7.99.34 NetBSD 7.99.34 (OPENBLOCKS266) #1: Wed Jul 27 22:09:26 JST 2016  rin@XXX:XXX evbppc
>Description:
FPU emulation of powerpc fails for single precision floating point
arithmetic. On a machine without FPU (e.g., ibm4xx like
evbppc/OPENBLOCKS266),

====================
  % cat fp.c
  #include <stdio.h>
  int main(){
          double dx = 1.0, dy = 2.0;
          float  sx = 1.0, sy = 2.0;
          printf("DP: %f / %f = %f\n", dx, dy, dx / dy);
          printf("SP: %f / %f = %f\n", sx, sy, sx / sy);
          return 0;
  }
  % cc fp.c && ./a.out
  DP: 1.000000 / 2.000000 = 0.500000
  SP: 1.000000 / 2.000000 = 0.003906
====================

This failure triggers corrupted display output of X clients, e.g., xterm
or oclock, where single precision calculation is utilized.
>How-To-Repeat:
Described above.
>Fix:
FreeBSD also uses FPU emulation codes derived from ours, and they fixed
this bug by commit r258250:

====================
  https://svnweb.freebsd.org/base?view=revision&revision=258250

  Make single precision floating point arithmetic actually work -- I think
  it never did -- and fix an obvious missing line. Floating point emulation
  on Book-E still needs some work but this gets it basically functional on
  soft-FPU systems (hard FPU for Book-E is not yet implemented).

  MFC after:	1 week
====================

With this fix, X clients as well as the test above works fine.

====================
--- src/sys/arch/powerpc/fpu/fpu_emu.c.orig	2016-07-27 10:04:00.737524067 +0900
+++ src/sys/arch/powerpc/fpu/fpu_emu.c	2016-07-27 10:03:44.803486129 +0900
@@ -626,9 +626,11 @@
 			rb = instr.i_a.i_frb;
 			rc = instr.i_a.i_frc;

-			type = FTYPE_SNG;
-			if (instr.i_any.i_opcd & 0x4)
-				type = FTYPE_DBL;
+			/*
+			 * All arithmetic operations work on registers, which
+			 * are stored as doubles.
+			 */
+			type = FTYPE_DBL;
 			switch ((unsigned int)instr.i_a.i_xo) {
 			case	OPC59_FDIVS:
 				FPU_EMU_EVCNT_INCR(fdiv);
@@ -745,6 +747,13 @@
 				return (NOTFPU);
 				break;
 			}
+
+			/* If the instruction was single precision, round */
+			if (!(instr.i_any.i_opcd & 0x4)) {
+				fpu_implode(fe, fp, FTYPE_SNG, 
+					(u_int *)&fs->fpreg[rt]);
+				fpu_explode(fe, fp = &fe->fe_f1, FTYPE_SNG, rt);
+			}
 		}
 	} else {
 		return (NOTFPU);
--- src/sys/arch/powerpc/fpu/fpu_explode.c.orig	2016-07-27 10:00:01.060507066 +0900
+++ src/sys/arch/powerpc/fpu/fpu_explode.c	2016-07-27 10:00:12.431852649 +0900
@@ -235,6 +235,7 @@
 		s = fpu_dtof(fp, s, space[1]);
 		break;

+	default:
 		panic("fpu_explode");
 		panic("fpu_explode: invalid type %d", type);
 	}
====================

>Release-Note:

>Audit-Trail:
From: "Rin Okuyama" <rin@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/51368 CVS commit: src/sys/arch/powerpc/fpu
Date: Wed, 28 Dec 2016 10:52:30 +0000

 Module Name:	src
 Committed By:	rin
 Date:		Wed Dec 28 10:52:30 UTC 2016

 Modified Files:
 	src/sys/arch/powerpc/fpu: fpu_emu.c

 Log Message:
 PR port-powerpc/51368: powerpc FPU emulation fails for single precision
 floating point arithmetic

 For single precision instruction, calculate first in double precision,
 and then round it. With this fix, single precision arithmetic gets sane
 on ibm4xx and booke.

 Taken from FreeBSD commit r258250:
   https://svnweb.freebsd.org/base?view=revision&revision=258250

 Ok matt and simonb.


 To generate a diff of this commit:
 cvs rdiff -u -r1.18 -r1.19 src/sys/arch/powerpc/fpu/fpu_emu.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->pending-pullups
State-Changed-By: rin@NetBSD.org
State-Changed-When: Wed, 28 Dec 2016 20:57:18 +0000
State-Changed-Why:
Fix committed. Pull-up requested to netbsd-7.


From: "Soren Jacobsen" <snj@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/51368 CVS commit: [netbsd-7] src/sys/arch/powerpc/fpu
Date: Tue, 3 Jan 2017 06:19:21 +0000

 Module Name:	src
 Committed By:	snj
 Date:		Tue Jan  3 06:19:21 UTC 2017

 Modified Files:
 	src/sys/arch/powerpc/fpu [netbsd-7]: fpu_emu.c fpu_explode.c

 Log Message:
 Pull up following revision(s) (requested by rin in ticket #1341):
 	sys/arch/powerpc/fpu/fpu_emu.c: revision 1.19
 	sys/arch/powerpc/fpu/fpu_explode.c: revision 1.7
 - add missing default from FreeBSD
 - remove duplicate panic pointed out by matt
 --
 PR port-powerpc/51368: powerpc FPU emulation fails for single precision
 floating point arithmetic
 For single precision instruction, calculate first in double precision,
 and then round it. With this fix, single precision arithmetic gets sane
 on ibm4xx and booke.
 Taken from FreeBSD commit r258250:
    https://svnweb.freebsd.org/base?view=revision&revision=258250
 Ok matt and simonb.


 To generate a diff of this commit:
 cvs rdiff -u -r1.16 -r1.16.14.1 src/sys/arch/powerpc/fpu/fpu_emu.c
 cvs rdiff -u -r1.6 -r1.6.140.1 src/sys/arch/powerpc/fpu/fpu_explode.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: pending-pullups->closed
State-Changed-By: rin@NetBSD.org
State-Changed-When: Mon, 09 Jan 2017 00:09:39 +0000
State-Changed-Why:
The fix is to be in NetBSD 7.1.


>Unformatted:

Home	PR Database Search