[issue44728] Testsuite fails on x86_64

[Mark Dickinson]

Mark Dickinson  added the comment:

One more thought on the libm issues - from the logs, it looks as though the 
libm implementation is coming from a fairly recent version of glibc (glibc 
2.33, which was released in February 2021). There were updates to the 'exp' 
implementation in glibc in 2018[1], but I'm not seeing anything more recent 
than that. Is it possible that glibc was miscompiled somehow on this platform - 
e.g., that it's using code designed to work with the x87 FPU with its extended 
precision, but was compiled with flags that force use of SSE2 instead?

If not, and if there's a genuine accuracy problem in glibc itself, we should 
expect to see more Python test_math and test_cmath failures in the future.

If anyone is able to run test_math or test_cmath on a machine using glibc 2.33 
or glibc 2.34 and report results, that would be useful.




[1] 
https://sourceware.org/git/?p=glibc.git;a=commit;h=e70c17682518fab2fad164fecf73341443bc2ed3

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[issue44728] Testsuite fails on x86_64

[Mark Dickinson]

Mark Dickinson  added the comment:

Here's the test_posix failure, extracted from the attachment:

==
ERROR: test_sched_rr_get_interval (test.test_posix.PosixTester)
--
Traceback (most recent call last):
  File "/build/python/src/Python-3.9.6/Lib/test/test_posix.py", line 1347, in 
test_sched_rr_get_interval
interval = posix.sched_rr_get_interval(0)
PermissionError: [Errno 1] Operation not permitted

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[issue44728] Testsuite fails on x86_64

[Mark Dickinson]

Mark Dickinson  added the comment:

Update: test_turtle is fixed (44734); I think test_math and test_cmath should 
be resolved as either "third party" or "wont fix", since the issue is almost 
certainly the platform libm.

That leaves test_posix, which we should probably open a fresh issue for.

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[issue44728] Testsuite fails on x86_64

[Mark Dickinson]

Mark Dickinson  added the comment:

Looks like the turtle code was changed to use `math.hypot` instead of `** 0.5` 
in issue #41528. That will likely also fix the test failure, but I've opened 
#44734 to fix the unnecessarily strict test.

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[issue44728] Testsuite fails on x86_64

[Mark Dickinson]

Mark Dickinson  added the comment:

The test_posix failure appears to be unrelated; I'll let others look into that 
one.

The test_turtle failure looks again like a libm issue, perhaps combined with an 
overeager test: we're expecting a `** 0.5` operation (which translates to a 
libm pow call) to give exact results when the square root is exactly 
representable.

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[issue44728] Testsuite fails on x86_64

[Mark Dickinson]

Mark Dickinson  added the comment:

Extract from the log - from the configure output:

> checking for expm1... yes

and from the test output

> expm10118: expm1(27.0): expected 532048240600.79865, got 532048240600.7976 
> (error = 0.00104 (17 ulps); permitted error = 0 or 5 ulps)
> expm10119: expm1(123.0): expected 2.6195173187490626e+53, got 
> 2.619517318749054e+53 (error = 8.51e+38 (20 ulps); permitted error = 0 or 5 
> ulps)
> expm10300: expm1(300.0): expected 1.9424263952412558e+130, got 
> 1.942426395241274e+130 (error = 1.82e+116 (74 ulps); permitted error = 0 or 5 
> ulps)
> expm10301: expm1(700.0): expected 1.0142320547350045e+304, got 
> 1.0142320547349733e+304 (error = 3.12e+290 (256 ulps); permitted error = 0 or 
> 5 ulps)
> expm10307: expm1(709.5): expected 1.3549863193146328e+308, got 
> 1.354986319314675e+308 (error = 4.21e+294 (211 ulps); permitted error = 0 or 
> 5 ulps)

The first part indicates that your math library does provide expm1, so Python 
goes ahead and uses it. The errors from test_math show that the expm1 
implementation provided by your math library has accuracy problems for large 
inputs. From the other failures, I suspect that the underlying issue is 
actually an issue with exp (but our tests for exp are not so thorough as those 
for expm1).

In short, the tests represent issues with the underlying C math library. What 
OS is this, and who supplies the libm?

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nosy: +mark.dickinson

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[issue44728] Testsuite fails on x86_64

[Erich Eckner]

New submission from Erich Eckner :

The following tests fails on x86 32 bit:

test_cmath test_math test_posix test_turtle - looks, like the expected 
precision is too high.

Full log is attached.

--
components: Tests
files: build-log.php?a=pentium4&p=python
messages: 398084
nosy: deep42thought
priority: normal
severity: normal
status: open
title: Testsuite fails on x86_64
versions: Python 3.9
Added file: https://bugs.python.org/file50175/build-log.php?a=pentium4&p=python

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