test_math.test_fma_zero_result() fails with the musl C library

[prashanthallu]

Bug report

Bug description:

1. While installing Python 3.13 version in docker:dind endingup without installation, getting the issue like as mentioned below

   675.0 0:00:26 load avg: 0.94 [18/44] test_fstring
   675.0 /Python-3.13.2/Lib/test/test_fstring.py:1655: SyntaxWarning: invalid escape sequence '\N'
   675.0   self.assertEqual(f'{b"\N{OX}"=}', 'b"\\N{OX}"=b\'\\\\N{OX}\'')
   691.8 0:00:43 load avg: 0.96 [19/44] test_functools
   692.5 0:00:44 load avg: 0.96 [20/44] test_generators
   692.9 0:00:44 load avg: 0.96 [21/44] test_hashlib
   693.7 0:00:45 load avg: 0.96 [22/44] test_heapq
   694.4 0:00:46 load avg: 0.96 [23/44] test_int
   695.2 0:00:47 load avg: 0.96 [24/44] test_itertools
   699.8 0:00:51 load avg: 0.96 [25/44] test_json
   704.2 0:00:56 load avg: 0.96 [26/44] test_long
   706.7 0:00:58 load avg: 0.97 [27/44] test_lzma
   706.8 0:00:58 load avg: 0.97 [28/44] test_math -- test_lzma skipped
   709.6 test test_math failed
   709.6 0:01:01 load avg: 0.97 [29/44] test_memoryview -- test_math failed (1 failure)
   710.1 0:01:01 load avg: 0.97 [30/44] test_operator
   710.3 0:01:02 load avg: 0.97 [31/44] test_ordered_dict
   711.5 0:01:03 load avg: 0.97 [32/44] test_patma
   711.7 0:01:03 load avg: 0.97 [33/44] test_pickle
   718.3 0:01:10 load avg: 0.97 [34/44] test_pprint
   718.6 0:01:10 load avg: 0.97 [35/44] test_re
   719.7 test test_re failed
   719.7 0:01:11 load avg: 0.98 [36/44] test_set -- test_re failed (2 failures)
   724.7 0:01:16 load avg: 0.98 [37/44] test_sqlite3
   725.6 0:01:17 load avg: 0.98 [38/44] test_statistics
   733.0 0:01:24 load avg: 0.98 [39/44] test_str
   735.1 0:01:26 load avg: 0.98 [40/44] test_struct
   735.8 0:01:27 load avg: 0.98 [41/44] test_tabnanny
   736.3 0:01:28 load avg: 0.98 [42/44] test_time
   739.5 0:01:31 load avg: 0.98 [43/44] test_xml_etree
   740.2 0:01:32 load avg: 0.98 [44/44] test_xml_etree_c
   741.3
   741.3 Total duration: 1 min 33 sec
   741.3 Total tests: run=9,178 failures=3 skipped=203
   741.3 Total test files: run=44/44 failed=2 skipped=2
   741.3 Result: FAILURE
   741.3 make: *** [Makefile:886: profile-run-stamp] Error 2
   

2. Which is happening in only docker:dind, when I am trying in centos, ubuntu able to install.

3. And one more with the Python 3.12.9 version able to install in in docker:dind and logs are

   #15 578.8 0:00:21 load avg: 1.50 [18/44] test_fstring
   #15 578.8 /Python-3.12.9/Lib/test/test_fstring.py:1769: SyntaxWarning: invalid escape sequence '\N'
   #15 578.8   self.assertEqual(f'{b"\N{OX}"=}', 'b"\\N{OX}"=b\'\\\\N{OX}\'')
   #15 593.3 0:00:35 load avg: 1.39 [19/44] test_functools
   #15 593.8 0:00:36 load avg: 1.36 [20/44] test_generators
   #15 594.1 0:00:36 load avg: 1.36 [21/44] test_hashlib
   #15 594.8 0:00:37 load avg: 1.36 [22/44] test_heapq
   #15 595.3 0:00:37 load avg: 1.36 [23/44] test_int
   #15 595.7 0:00:38 load avg: 1.36 [24/44] test_itertools
   #15 599.2 0:00:41 load avg: 1.33 [25/44] test_json
   #15 629.5 0:01:11 load avg: 1.20 [26/44] test_long -- test_json passed in 30.3 sec
   #15 631.7 0:01:13 load avg: 1.20 [27/44] test_lzma
   #15 631.8 0:01:14 load avg: 1.20 [28/44] test_math -- test_lzma skipped
   #15 633.8 0:01:16 load avg: 1.20 [29/44] test_memoryview
   #15 634.4 0:01:16 load avg: 1.18 [30/44] test_operator
   #15 634.5 0:01:16 load avg: 1.18 [31/44] test_ordered_dict
   #15 635.5 0:01:17 load avg: 1.18 [32/44] test_patma
   #15 635.8 0:01:18 load avg: 1.18 [33/44] test_pickle
   #15 641.0 0:01:23 load avg: 1.17 [34/44] test_pprint
   #15 641.3 0:01:23 load avg: 1.17 [35/44] test_re
   #15 642.1 test test_re failed
   #15 642.1 0:01:24 load avg: 1.17 [36/44] test_set -- test_re failed (2 failures)
   #15 646.1 0:01:28 load avg: 1.15 [37/44] test_sqlite3
   #15 646.9 0:01:29 load avg: 1.15 [38/44] test_statistics
   #15 648.3 0:01:30 load avg: 1.15 [39/44] test_struct
   #15 648.9 0:01:31 load avg: 1.22 [40/44] test_tabnanny
   #15 649.4 0:01:31 load avg: 1.22 [41/44] test_time
   #15 652.5 0:01:34 load avg: 1.22 [42/44] test_unicode
   #15 654.5 0:01:36 load avg: 1.20 [43/44] test_xml_etree
   #15 655.0 0:01:37 load avg: 1.20 [44/44] test_xml_etree_c
   #15 655.9 
   #15 655.9 Total duration: 1 min 38 sec
   #15 655.9 Total tests: run=8,930 failures=2 skipped=192
   #15 655.9 Total test files: run=44/44 failed=1 skipped=2
   #15 655.9 Result: FAILURE
   #15 656.0 true
   #15 656.0 # Remove profile generation binary since we are done with it.
   #15 656.0 make clean-retain-profile
   #15 656.1 make[1]: Entering directory '/Python-3.12.9'
   #15 656.1 find . -depth -name '__pycache__' -exec rm -rf {} ';'
   #15 656.2 find . -name '*.py[co]' -exec rm -f {} ';'
   #15 656.2 find . -name '*.[oa]' -exec rm -f {} ';'
   #15 656.5 find . -name '*.s[ol]' -exec rm -f {} ';'
   #15 656.6 find . -name '*.so.[0-9]*.[0-9]*' -exec rm -f {} ';'
   #15 656.7 find . -name '*.lto' -exec rm -f {} ';'
   #15 656.7 find . -name '*.wasm' -exec rm -f {} ';'
   #15 656.7 find . -name '*.lst' -exec rm -f {} ';'
   #15 656.8 find build -name 'fficonfig.h' -exec rm -f {} ';' || true
   #15 656.8 find build -name '*.py' -exec rm -f {} ';' || true
   #15 656.8 find build -name '*.py[co]' -exec rm -f {} ';' || true
   #15 656.8 rm -f pybuilddir.txt
   #15 656.8 rm -f Lib/lib2to3/*Grammar*.pickle
   

4. So what could be the issue ?.

5. I am using following Dockerfile code to install Python

   # Use the official Docker DinD image as the base image
   ARG PYTHON_VERSION=3.13.2
   FROM docker:dind
   
   # Install necessary packages and dependencies
   RUN apk add --no-cache \
   	build-base \
   	bzip2-dev \
   	ncurses-dev \
   	gdbm-dev \
   	xz-dev \
   	tk-dev \
   	util-linux-dev \
   	readline-dev \
   	zlib-dev \
   	openssl-dev \
   	libffi-dev \
   	wget
   
   RUN wget https://www.python.org/ftp/python/${PYTHON_VERSION}/Python-${PYTHON_VERSION}.tgz \
   	&& tar xvf Python-${PYTHON_VERSION}.tgz \
   	&& cd Python-${PYTHON_VERSION} \
   	&& ./configure --enable-optimizations \
   	&& make altinstall \
   	&& pip3.13 install --upgrade pip
   

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-131032: Add support.linked_to_musl() function #131071
• gh-131032: Fix math.fma(x, y, z) zero sign #131134
• [3.13] gh-131032: Add support.linked_to_musl() function (#131071) #131179

[vstinner]

Can you try to re-run test_math in verbose mode? Something like: ./python -m test test_math -v in the directory where you built Python.

[prashanthallu]

the following is the result for the verbose mode.

/Python-3.13.2 # ./python -m unittest -v test.test_math
test_fma_infinities (test.test_math.FMATests.test_fma_infinities) ... ok
test_fma_nan_results (test.test_math.FMATests.test_fma_nan_results) ... ok
test_fma_overflow (test.test_math.FMATests.test_fma_overflow) ... ok
test_fma_single_round (test.test_math.FMATests.test_fma_single_round) ... ok
test_fma_zero_result (test.test_math.FMATests.test_fma_zero_result) ... FAIL
test_random (test.test_math.FMATests.test_random) ... ok
test_asymmetry (test.test_math.IsCloseTests.test_asymmetry) ... ok
test_decimals (test.test_math.IsCloseTests.test_decimals) ... ok
test_eight_decimal_places (test.test_math.IsCloseTests.test_eight_decimal_places) ... ok
test_fractions (test.test_math.IsCloseTests.test_fractions) ... ok
test_identical (test.test_math.IsCloseTests.test_identical) ... ok
test_identical_infinite (test.test_math.IsCloseTests.test_identical_infinite) ... ok
test_inf_ninf_nan (test.test_math.IsCloseTests.test_inf_ninf_nan) ... ok
test_integers (test.test_math.IsCloseTests.test_integers) ... ok
test_near_zero (test.test_math.IsCloseTests.test_near_zero) ... ok
test_negative_tolerances (test.test_math.IsCloseTests.test_negative_tolerances) ... ok
test_zero_tolerance (test.test_math.IsCloseTests.test_zero_tolerance) ... ok
testAcos (test.test_math.MathTests.testAcos) ... ok
testAcosh (test.test_math.MathTests.testAcosh) ... ok
testAsin (test.test_math.MathTests.testAsin) ... ok
testAsinh (test.test_math.MathTests.testAsinh) ... ok
testAtan (test.test_math.MathTests.testAtan) ... ok
testAtan2 (test.test_math.MathTests.testAtan2) ... ok
testAtanh (test.test_math.MathTests.testAtanh) ... ok
testCbrt (test.test_math.MathTests.testCbrt) ... ok
testCeil (test.test_math.MathTests.testCeil) ... ok
testComb (test.test_math.MathTests.testComb) ... ok
testConstants (test.test_math.MathTests.testConstants) ... ok
testCopysign (test.test_math.MathTests.testCopysign) ... ok
testCos (test.test_math.MathTests.testCos) ... ok
testCosh (test.test_math.MathTests.testCosh) ... ok
testDegrees (test.test_math.MathTests.testDegrees) ... ok
testDist (test.test_math.MathTests.testDist) ... ok
testExp (test.test_math.MathTests.testExp) ... ok
testExp2 (test.test_math.MathTests.testExp2) ... ok
testFabs (test.test_math.MathTests.testFabs) ... ok
testFactorial (test.test_math.MathTests.testFactorial) ... ok
testFactorialHugeInputs (test.test_math.MathTests.testFactorialHugeInputs) ... ok
testFactorialNonIntegers (test.test_math.MathTests.testFactorialNonIntegers) ... ok
testFloor (test.test_math.MathTests.testFloor) ... ok
testFmod (test.test_math.MathTests.testFmod) ... ok
testFrexp (test.test_math.MathTests.testFrexp) ... ok
testFsum (test.test_math.MathTests.testFsum) ... ok
testGcd (test.test_math.MathTests.testGcd) ... ok
testHypot (test.test_math.MathTests.testHypot) ... ok
testHypotAccuracy (test.test_math.MathTests.testHypotAccuracy) ... ok
testIsfinite (test.test_math.MathTests.testIsfinite) ... ok
testIsinf (test.test_math.MathTests.testIsinf) ... ok
testIsnan (test.test_math.MathTests.testIsnan) ... ok
testIsqrt (test.test_math.MathTests.testIsqrt) ... ok
testLdexp (test.test_math.MathTests.testLdexp) ... ok
testLog (test.test_math.MathTests.testLog) ... ok
testLog10 (test.test_math.MathTests.testLog10) ... ok
testLog1p (test.test_math.MathTests.testLog1p) ... ok
testLog2 (test.test_math.MathTests.testLog2) ... ok
testLog2Exact (test.test_math.MathTests.testLog2Exact) ... ok
testModf (test.test_math.MathTests.testModf) ... ok
testPerm (test.test_math.MathTests.testPerm) ... ok
testPow (test.test_math.MathTests.testPow) ... ok
testRadians (test.test_math.MathTests.testRadians) ... ok
testRemainder (test.test_math.MathTests.testRemainder) ... ok
testSin (test.test_math.MathTests.testSin) ... ok
testSinh (test.test_math.MathTests.testSinh) ... ok
testSqrt (test.test_math.MathTests.testSqrt) ... ok
testSumProd (test.test_math.MathTests.testSumProd) ... ok
testTan (test.test_math.MathTests.testTan) ... ok
testTanh (test.test_math.MathTests.testTanh) ... ok
testTanhSign (test.test_math.MathTests.testTanhSign) ... ok
test_exceptions (test.test_math.MathTests.test_exceptions) ... ok
test_inf_constant (test.test_math.MathTests.test_inf_constant) ... ok
test_input_exceptions (test.test_math.MathTests.test_input_exceptions) ... ok
test_issue39871 (test.test_math.MathTests.test_issue39871) ... ok
test_lcm (test.test_math.MathTests.test_lcm) ... ok
test_math_dist_leak (test.test_math.MathTests.test_math_dist_leak) ... ok
test_mtestfile (test.test_math.MathTests.test_mtestfile) ... ok
test_nan_constant (test.test_math.MathTests.test_nan_constant) ... ok
test_nextafter (test.test_math.MathTests.test_nextafter) ... ok
test_prod (test.test_math.MathTests.test_prod) ... ok
test_sumprod_accuracy (test.test_math.MathTests.test_sumprod_accuracy) ... ok
test_sumprod_extended_precision_accuracy (test.test_math.MathTests.test_sumprod_extended_precision_accuracy) ... ok
test_sumprod_stress (test.test_math.MathTests.test_sumprod_stress) ... ok
test_testfile (test.test_math.MathTests.test_testfile) ... ok
test_trunc (test.test_math.MathTests.test_trunc) ... ok
test_ulp (test.test_math.MathTests.test_ulp) ... ok
/Python-3.13.2/Lib/test/mathdata/ieee754.txt
Doctest: ieee754.txt ... ok

======================================================================
FAIL: test_fma_zero_result (test.test_math.FMATests.test_fma_zero_result)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Python-3.13.2/Lib/test/test_math.py", line 2744, in test_fma_zero_result
    self.assertIsNegativeZero(math.fma(tiny, -tiny, 0.0))
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Python-3.13.2/Lib/test/test_math.py", line 2860, in assertIsNegativeZero
    self.assertTrue(
    ~~~~~~~~~~~~~~~^
        value == 0 and math.copysign(1, value) < 0,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        msg="Expected a negative zero, got {!r}".format(value)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
AssertionError: False is not true : Expected a negative zero, got 0.0

----------------------------------------------------------------------
Ran 85 tests in 77.598s

FAILED (failures=1)

[vstinner]

You're building a docker image using Alpine Linux which uses the musl C library. It seems like musl has a bug in the fma() function.

[prashanthallu]

is there any plan to release new version of python because of this change?

[vstinner]

is there any plan to release new version of python because of this change?

My fix is not merged yet, and no, there will not be a new release just because of this fix.

You can tune the PGO task to ignore the failing test: see PROFILE_TASK variable in configure. Default:

PROFILE_TASK=   -m test --pgo --timeout=$(TESTTIMEOUT)

You can ignore the failing test using -i option. Example:

./configure --enable-optimizations PROFILE_TASK='-m test --pgo -i test_fma_zero_result'

[skirpichev]

@prashanthallu, maybe you can try this patch?

diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index b4c15a143f..39e34307dc 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -2344,7 +2344,19 @@ static PyObject *
 math_fma_impl(PyObject *module, double x, double y, double z)
 /*[clinic end generated code: output=4fc8626dbc278d17 input=e3ad1f4a4c89626e]*/
 {
-    double r = fma(x, y, z);
+    double r;
+
+    if (z) {
+        r = fma(x, y, z);
+    }
+    else {
+        if (x && y) {
+            r = x * y;
+        }
+        else {
+            r = copysign(1, z) == 1 ? x*y + z : x*y;
+        }
+    }
 
     /* Fast path: if we got a finite result, we're done. */
     if (isfinite(r)) {

[vstinner]

@prashanthallu, maybe you can try this patch?

This patch works with musl (test_math pass). Do you suggest to apply it on all platforms? musl has no #ifdef.

[skirpichev]

Do you suggest to apply it on all platforms?

I would think of it, if this really solves problem on a lot of platforms. It might be the case: no other fma tests are skipped, thus there is a chance that problems restricted to few corner cases.

[vstinner]

Ok, I converted your patch to a PR: #131134. Let's see if test_math still pass on buildbots (ex: FreeBSD and WASI).