NetBSD Problem Report #54000

From gson@gson.org  Fri Feb 22 08:40:10 2019
Return-Path: <gson@gson.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 "mail.NetBSD.org CA" (not verified))
	by mollari.NetBSD.org (Postfix) with ESMTPS id 1CB697A151
	for <gnats-bugs@gnats.NetBSD.org>; Fri, 22 Feb 2019 08:40:10 +0000 (UTC)
Message-Id: <20190222084004.167F498A91B@guava.gson.org>
Date: Fri, 22 Feb 2019 10:40:04 +0200 (EET)
From: gson@gson.org (Andreas Gustafsson)
Reply-To: gson@gson.org (Andreas Gustafsson)
To: gnats-bugs@NetBSD.org
Subject: FP tests failing on amd64 since gcc7 import
X-Send-Pr-Version: 3.95

>Number:         54000
>Category:       port-amd64
>Synopsis:       FP tests failing on amd64 since gcc7 import
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-amd64-maintainer
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Feb 22 08:45:00 +0000 2019
>Closed-Date:    Thu Apr 25 12:49:31 +0000 2019
>Last-Modified:  Thu Apr 25 12:49:31 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:

>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

The following tests are failing on amd64 since the import of gcc 7:

  lib/libc/gen/t_fpsetround/fpsetround_basic
  lib/libm/t_fe_round/fe_nearbyint
  lib/libm/t_fe_round/fe_round

They fail both under qemu and on real hardware, but not on i386.
For recent log output, see:

  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#lib_libc_gen_t_fpsetround_fpsetround_basic
  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#lib_libm_t_fe_round_fe_nearbyint
  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#lib_libm_t_fe_round_fe_round
  http://releng.netbsd.org/b5reports/amd64/2019/2019.02.20.19.42.14/test.html#lib_libc_gen_t_fpsetround_fpsetround_basic
  (etc)

>How-To-Repeat:

Run the ATF tests on amd64.

>Fix:

>Release-Note:

>Audit-Trail:
From: coypu@sdf.org
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: port-amd64/54000: FP tests failing on amd64 since gcc7 import
Date: Fri, 22 Feb 2019 09:22:17 +0000

 I built libm.so with some GCC versions:

 GCC6 from pkgsrc:	OK
 GCC7 base:		FAIL
 GCC9 (snapshot):	FAIL


 It's sufficient to revert libm.so to get at least one of the failing
 cases to succeed.

From: coypu@sdf.org
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: port-amd64/54000: FP tests failing on amd64 since gcc7 import
Date: Fri, 22 Feb 2019 09:38:45 +0000

 The difference starts with s_nearbyint.o.
 building this with GCC7 and -O0 also works.

From: coypu@sdf.org
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: port-amd64/54000: FP tests failing on amd64 since gcc7 import
Date: Fri, 22 Feb 2019 09:56:43 +0000

 Also fixed by -fno-builtin-rint.

From: coypu@sdf.org
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: port-amd64/54000: FP tests failing on amd64 since gcc7 import
Date: Fri, 22 Feb 2019 16:38:47 +0000

 --PNTmBPCT7hxwcZjr
 Content-Type: text/plain; charset=us-ascii
 Content-Disposition: inline

 Attached is a standalone test case (non-netbsd-specific)

#!/bin/sh

cat << EOF > round.c
#include <assert.h>
#include <fenv.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#define INT 9223L

#define EPSILON 0.001

static const struct {
	int round_mode;
	double input;
	long int expected;
} values[] = {
	{ FE_DOWNWARD,		-3.7,		-4},
};


double my_nearbyint(double x)
{
	double ret;
	fenv_t env;
	fegetenv(&env);
	ret = rint(x);
	fesetenv(&env);
	return ret;
}

int main(void)
{
	double received;

	fesetround(values[0].round_mode);

	received = my_nearbyint(values[0].input);

	if (!(fabs(received - values[0].expected) < EPSILON))
		printf("nearbyint rounding wrong, difference too large\n"
		    "input: %f (index %d): got %f, expected %ld\n",
		    values[0].input, 0, received, values[0].expected);

	assert((fabs(received - values[0].expected) < EPSILON));

	/* Do we get the same rounding mode out? */
	if (!((fegetround() == values[0].round_mode)))
		printf("Didn't get the same rounding mode out!\n"
		    "(index %d) fed in %d rounding mode, got %d out\n",
		    0, values[0].round_mode, fegetround());

	assert((fegetround() == values[0].round_mode));
}
EOF

gcc -lm round.c -O2 -o round
echo "Executing regular -O2 build:"
./round
echo "returned " $?


gcc -lm round.c -O2 -fno-builtin-rint -o round2
echo "Executing -O2 -fno-builtin-rint build:"
./round2

echo "returned " $?


State-Changed-From-To: open->analyzed
State-Changed-By: maya@NetBSD.org
State-Changed-When: Fri, 22 Feb 2019 18:00:20 +0000
State-Changed-Why:
Not really a bug. GCC defaults to -fno-rounding-math, we can get correct behaviour with -frounding-math.


From: Jason Thorpe <thorpej@me.com>
To: "gnats-bugs@netbsd.org" <gnats-bugs@NetBSD.org>
Cc: port-amd64-maintainer@netbsd.org,
 netbsd-bugs@netbsd.org,
 gnats-admin@netbsd.org,
 "maya@netbsd.org" <maya@NetBSD.org>,
 Andreas Gustafsson <gson@gson.org>
Subject: Re: port-amd64/54000 (FP tests failing on amd64 since gcc7 import)
Date: Fri, 22 Feb 2019 10:03:45 -0800

 > On Feb 22, 2019, at 10:00 AM, maya@netbsd.org <maya@NetBSD.org> wrote:
 >=20
 > Synopsis: FP tests failing on amd64 since gcc7 import
 >=20
 > State-Changed-From-To: open->analyzed
 > State-Changed-By: maya@NetBSD.org
 > State-Changed-When: Fri, 22 Feb 2019 18:00:20 +0000
 > State-Changed-Why:
 > Not really a bug. GCC defaults to -fno-rounding-math, we can get =
 correct behaviour with -frounding-math.

 Is this a change in GCC=E2=80=99s default?  If so, it seems like this is =
 a binary compatibility issue and that we should switch the default back.

 -- thorpej

From: "Maya Rashish" <maya@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/54000 CVS commit: src/lib/libm
Date: Fri, 22 Feb 2019 18:17:23 +0000

 Module Name:	src
 Committed By:	maya
 Date:		Fri Feb 22 18:17:23 UTC 2019

 Modified Files:
 	src/lib/libm: Makefile

 Log Message:
 Default our libm to -frounding-math, if built with GCC.

 The long-standing GCC default is to not respect rounding mode.
 it looks like GCC 7 optimizes rint to a builtin, causing our few
 rounding mode tests to fail.

 Fixes PR port-amd64/54000: FP tests failing on amd64 since gcc7 import


 To generate a diff of this commit:
 cvs rdiff -u -r1.205 -r1.206 src/lib/libm/Makefile

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

From: Andreas Gustafsson <gson@gson.org>
To: "Maya Rashish" <maya@netbsd.org>
Cc: gnats-bugs@NetBSD.org
Subject: Re: PR/54000 CVS commit: src/lib/libm
Date: Sat, 23 Feb 2019 12:58:44 +0200

 Maya,

 You wrote:
 >  Default our libm to -frounding-math, if built with GCC.
 >  
 >  The long-standing GCC default is to not respect rounding mode.
 >  it looks like GCC 7 optimizes rint to a builtin, causing our few
 >  rounding mode tests to fail.
 >  
 >  Fixes PR port-amd64/54000: FP tests failing on amd64 since gcc7 import

 Thanks for working on this.  Your commit seems to have fixed the
 fe_nearbyint and fe_round tests, but the fpsetround_basic test is
 still failing for me (on real amd64 hardware).
 -- 
 Andreas Gustafsson, gson@gson.org

From: "Christos Zoulas" <christos@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/54000 CVS commit: src/tests/lib/libc/gen
Date: Wed, 24 Apr 2019 11:12:09 -0400

 Module Name:	src
 Committed By:	christos
 Date:		Wed Apr 24 15:12:09 UTC 2019

 Modified Files:
 	src/tests/lib/libc/gen: Makefile

 Log Message:
 PR/54000: Andreag Gustafsson: Compile the rounding test with
 -fround-math since with gcc-7, the default mode ignores fenv settings
 (the same effect can be achieved with -O0 :-)

 https://gcc.gnu.org/wiki/FloatingPointMath


 To generate a diff of this commit:
 cvs rdiff -u -r1.51 -r1.52 src/tests/lib/libc/gen/Makefile

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

State-Changed-From-To: analyzed->closed
State-Changed-By: gson@NetBSD.org
State-Changed-When: Thu, 25 Apr 2019 12:49:31 +0000
State-Changed-Why:
Two of the failures were fixed by maya and the third by christos, thanks!


>Unformatted:

Home	PR Database Search