[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Matthias Klose]

Matthias Klose  added the comment:

I checked with gcc-4.4 from the 4.4 branch, and with a recent build from the 
trunk.  The check fails with -O0, and succeeds with -O1 and higher.

Is the testcode from r82957 really using the optimization flags?

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

I notice (again) that these failures occur on the 2.6 and 3.1 buildslaves 
(where the debug build includes the -O2 compilation flag), but not the 2.7 or 
py3k buildslaves.  So again this looks like a compiler optimization bug.

This should really be reported upstream, but without direct access to the 
machine to produce a small failing example I don't think I can compose a decent 
bug report.

Closing this as 'won't fix'.

--
resolution:  -> wont fix
status: open -> closed

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

Added some test code to the configure script in r82957;  if the corresponding 
configure test fails, this snippet can be used in the gcc bug report.

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

The test_float failure is still extant.

Here's the output of gcc -v on this buildbot, for use in any gcc bug report:

Using built-in specs.
Target: arm-linux-gnueabi
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.4-6' 
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs 
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared 
--enable-multiarch --enable-linker-build-id --with-system-zlib 
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix 
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls 
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc 
--disable-sjlj-exceptions --enable-checking=release --build=arm-linux-gnueabi 
--host=arm-linux-gnueabi --target=arm-linux-gnueabi
Thread model: posix
gcc version 4.4.4 (Debian 4.4.4-6) 

and the relevant compilation line:

gcc -pthread -c  -g -O2 -g -Wall -Wstrict-prototypes  -I. -IInclude -I./Include 
  -DPy_BUILD_CORE -o Objects/floatobject.o Objects/floatobject.c

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

New issue for the Solaris failure opened:  issue 9069.

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

David, thanks for the report.  This looks like a different issue to me, though.

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[David Kirkby]

David Kirkby  added the comment:

I'm seeing this failure on both Solaris 10 (SPARC processor) in 32-bit mode and 
OpenSolaris 06/2009 (Intel Xeon) in 64-bit mode using Python 2.6.4. So it is 
not just an ARM Linux issue. 

See 

http://trac.sagemath.org/sage_trac/ticket/9297
http://trac.sagemath.org/sage_trac/ticket/9299

Note, Solaris supports both a 32 and 64-bit ABI. Not  sure if that is relevant, 
but I see "ABI" in the title, so perhaps it might be. 

Dave

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nosy: +drkirkby

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[STINNER Victor]

Changes by STINNER Victor :


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nosy: +haypo

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

I made a couple of experimental checkins to the release26-maint branch (I 
didn't want to do a temporary checkin to the trunk with a release imminent):  
see r79560 (which didn't work :) and its fix in r79601.  Results:

  MIN = 2.2250738585072014e-308
  TINY = 4.9406564584124654e-324
  3*TINY = 1.4821969375237396e-323
  MIN - 3*TINY = 2.2250738585071984e-308
  ldexp(1.0, -1074) = 4.9406564584124654e-324

The values for MIN, TINY and 3*TINY are correct; the value for MIN - 3*TINY 
(which should be an exact operation) is not:  it's giving something equal to 
MIN - 6*TINY instead.  This should be easily reproducible at the C level, since 
the Python subtraction is just a thin wrapper around the corresponding C 
operation.

So it looks as though the float emulation is buggy on this platform, and this 
bug should be reported upstream.  Matthias, can you take care of this?

For Python, I'm not sure what the appropriate action is, but I'd rather not 
skip the test, or otherwise completely silence the error.  Maybe some sort of 
"expected failure due to platform floating-point bug" output?

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Mark Dickinson]

Mark Dickinson  added the comment:

>From the values in the report, float.fromhex is giving the correct value here, 
>but MIN-3*TINY is somehow coming out incorrectly.

Correct values (with Python 2.6, so old float repr; OS X 10.6.2):

Python 2.6.5+ (release26-maint:79559:79560, Apr  1 2010, 21:54:0) 
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> float.fromhex('0x0.d6p-1022')
2.2250738585071999e-308
>>> MIN = float.fromhex('0x1p-1022')
>>> TINY = float.fromhex('0x0.1p-1022')
>>> MIN
2.2250738585072014e-308
>>> TINY
4.9406564584124654e-324
>>> 3*TINY
1.4821969375237396e-323
>>> MIN - 3*TINY
2.2250738585071999e-308
>>> from math import ldexp
>>> ldexp(1.0, -1074)
4.9406564584124654e-324

It would be helpful to see the corresponding ARM outputs.  I suspect a platform 
bug either in ldexp or in the multiplication or subtraction above.

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[issue8265] test_float fails on ARM Linux EABI with soft floating point

[Matthias Klose]

Matthias Klose  added the comment:

the buildbot labeled "ARM Linux 3.x" is an ARM EABI as well, compiler defaults 
-march=armv7 -math=vfp -float-abi=softfp.

The failing test_float test is an ARM EABI, armv4, ARM mode, soft floating 
point. I never did see the test_float test suceed on this 
platform/configuration.

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title: test_float fails on ARM Linux EABI -> test_float fails on ARM Linux EABI 
with soft floating point

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[issue8265] test_float fails on ARM Linux EABI

[Martin v . Löwis]

Martin v. Löwis  added the comment:

Matthias, can you please take a look?

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nosy: +doko, loewis

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[issue8265] test_float fails on ARM Linux EABI

[Florent Xicluna]

Florent Xicluna  added the comment:

Same failure on trunk:
http://www.python.org/dev/buildbot/all/builders/ARM%20Linux%20EABI%20trunk/builds/12

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[issue8265] test_float fails on ARM Linux EABI

[Florent Xicluna]

New submission from Florent Xicluna :

All the ARM Linux EABI buildbots fail on the same test.

http://www.python.org/dev/buildbot/all/builders/ARM%20Linux%20EABI%202.6/builds/5

test_float
test test_float failed -- Traceback (most recent call last):
  File 
"/home/pybot/buildarea-armeabi/2.6.klose-linux-armeabi/build/Lib/test/test_float.py",
 line 665, in test_from_hex
self.identical(fromHex('0x0.d6p-1022'), MIN-3*TINY)
  File 
"/home/pybot/buildarea-armeabi/2.6.klose-linux-armeabi/build/Lib/test/test_float.py",
 line 375, in identical
self.fail('%r not identical to %r' % (x, y))
AssertionError: 2.2250738585071999e-308 not identical to 2.2250738585071984e-308

--
components: Interpreter Core
keywords: buildbot
messages: 101929
nosy: flox, mark.dickinson
priority: normal
severity: normal
stage: needs patch
status: open
title: test_float fails on ARM Linux EABI
type: behavior
versions: Python 2.6, Python 2.7, Python 3.1, Python 3.2

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