Sage startup crashes on some systems with a SignalError: Illegal instruction

[E. M. Bray]

Some users reported that Sage crashes at startup. The full traceback isn't very interesting, but the last frame is:

/opt/sagemath-7.4/src/sage/libs/ntl/ntl_ZZ.pyx in sage.libs.ntl.ntl_ZZ.ntl_ZZ.__init__ (build/cythonized/sage/libs/ntl/ntl_ZZ.cpp:3245)()
     85             self.x = (<ntl_ZZ>v).x
     86         elif isinstance(v, int):
     87             ZZ_conv_from_int(self.x, PyInt_AS_LONG(v))
     88         elif isinstance(v, long):
     89             PyLong_to_ZZ(&self.x, v)
     90         elif isinstance(v, Integer):
     91             self.set_from_sage_int(v)
     92         elif v is not None:
     93             v = str(v)
     94             if len(v) == 0:
     95                 v = '0'
     96             if not ((v[0].isdigit() or v[0] == '-') and \
     97                     (v[1:-1].isdigit() or (len(v) <= 2)) and \
     98                     (v[-1].isdigit() or (v[-1].lower() in ['l','r']))):
     99                raise ValueError("invalid integer: %s" % v)
--> 100             sig_on()
        global sig_on = undefined
    101             ZZ_from_str(&self.x, v)
    102             sig_off()
    103 
    104     def __repr__(self):
    105         """
    106         Return the string representation of self.
    107 
    108         EXAMPLES:
    109             sage: ntl.ZZ(5).__repr__()
    110             '5'
    111         """
    112         return ZZ_to_PyString(&self.x)
    113 
    114     def __reduce__(self):
    115         """

src/cysignals/signals.pyx in cysignals.signals.sig_raise_exception (build/src/cysignals/signals.c:1225)()

SignalError: Illegal instruction

This shows that cysignals caught and raised an exception for a SIGILL, as the CPU tried to execute an unknown instruction. I built NTL on my machine which probably has support for certain instructions that other machines may not. Building Sage with SAGE_FAT_BINARY will, among other things that probably should be done for the default installer, will build an NTL without certain CPU-specific instructions, so will work on a broader range of machines (the question remains at what cost, and if architecture-specific builds should be made available).

[E. M. Bray]

SAGE_FAT_BINARY=yes alone did not resolve the issue, as there are some packages in Sage 7.4 that do no respect that environment variable properly. I have backported the following fixes to my 7.4 branch and built a new binary:

https://trac.sagemath.org/ticket/21849
https://trac.sagemath.org/ticket/21772

[E. M. Bray]

Forgot to update this issue: With the backported fixes for supporting SAGE_FAT_BINARY the issue was resolved for the users who reported it. Future releases will all be built, for now, with SAGE_FAT_BINARY (perhaps in the future we can also cross-compile releases for specific architectures).