What causes signal 'SIGILL'?
Solution 1:
Make sure that all functions with non-void return type have a return
statement.
While some compilers automatically provide a default return value, others will send a SIGILL or SIGTRAP at runtime when trying to leave a function without a return value.
Solution 2:
It means the CPU attempted to execute an instruction it didn't understand. This could be caused by corruption I guess, or maybe it's been compiled for the wrong architecture (in which case I would have thought the O/S would refuse to run the executable). Not entirely sure what the root issue is.
Solution 3:
It could be some un-initialized function pointer, in particular if you have corrupted memory (then the bogus vtable of C++ bad pointers to invalid objects might give that).
BTW gdb
watchpoints & tracepoints, and also valgrind might be useful (if available) to debug such issues. Or some address sanitizer.
Solution 4:
LeetCode's online compiler and dev environment generates SIGILL
errors for mistakes that do not generate the same error in my desktop IDE.
For example, array access with an out-of-bounds index:
["foo", "bar"][2]
LeetCode's compiler shows only the error:
Runtime Error process exited with signal
SIGILL
in a local Xcode playground this same code instead results in the error:
error: Execution was interrupted, reason: EXC_BREAKPOINT (code=1, subcode=0x18f2ea5d8).
The process has been left at the point where it was interrupted, use "thread return -x" to return to the state before expression evaluation.
Only in a full Xcode project compilation and run does it report the actual error:
Thread 1: Fatal error: Index out of range