Source: scipy Version: 1.13.1-5 Severity: important Tags: ftbfs upstream X-Debbugs-Cc: debian-med-packag...@lists.alioth.debian.org, debian-ri...@lists.debian.org User: debian-ri...@lists.debian.org Usertags: riscv64 Control: affects -1 + src:nipy Control: found -1 scipy/1.14.0-1exp5
Dear maintainer, I have been debugging the cause of the FTBFS of nipy on riscv64. It fails with [1]: | nipy/core/reference/tests/test_matrix_groups.py . | E: Build killed with signal TERM after 600 minutes of inactivity I have been able to extract a minimal reproducer calling the SciPy expm function: | #!/usr/bin/python3 | | import numpy as np | from scipy.linalg import expm | | Z = np.array([[-0.83555296, 1.23536117, -0.54084919], | [ 0.48341885, -0.55882754, -0.53693891], | [-0.14802191, -0.43249490, 0.53730155]]) | # Z = np.random.standard_normal((3,3)) | | orth = expm(Z - Z.T) The original code uses np.random.standard_normal but I changed that into a static array to always use to the same code path. Debugging further, it happens that the pick_pade_structure() in the Cython expm support code is relying on undefined behaviour (UB) to convert a non-finite floating point value to int in a few places [2]. According to the C++ standard this is an undefined behaviour: | When a finite value of real floating type is converted to an integer | type other than _Bool, the fractional part is discarded (i.e., the | value is truncated toward zero). If the value of the integral part | cannot be represented by the integer type, the behavior is undefined. On x86, the conversion returns 0, but on RISC-V it returns either INT_MIN or INT_MAX depending on the sign of the floating point value. As the result of this conversion is then used in a loop [3], this takes an eternity to execute and just appears as endless. The problem has been fixed upstream as part of the rewrite of the Cython code into C [4][5]. For what I understand this will go into SciPy 1.15. I am not sure how you want to get that fixed in the Debian package. I see two options: - Backport the upstream commits [4][5] - Change the Cython code to check if number are finite before conversion to int, and if not return 0. Please tell me what do you prefer, and I will work on the corresponding patch. Note that the build failures on mips64el and sparc64 are very likely to be same issue. Regards Aurelien [1] https://buildd.debian.org/status/fetch.php?pkg=nipy&arch=riscv64&ver=0.6.1-1&stamp=1729595150&raw=0 [2] https://sources.debian.org/src/scipy/1.13.1-5/scipy/linalg/_matfuncs_expm.pyx.in/#L224 [3] https://sources.debian.org/src/scipy/1.13.1-5/scipy/linalg/_matfuncs.py/#L345 [4] https://github.com/scipy/scipy/pull/21553 [5] https://github.com/scipy/scipy/commit/424708ed018cae6b6584d7d992940fd39f2ebcc0 [6] https://github.com/scipy/scipy/commit/84d4bd91213a89cc59d67dd9045625055c2cc463
