What causes signal 'SIGILL'?
AndroidC++Android NdkPortingAndroid Problem Overview
I'm porting some C++ code to Android using NDK and GCC. The code basically runs. At one point, when debugging in Eclipse, the call
Dabbler::Android::Factory* pFactory = new Dabbler::Android::Factory;
causes this error:
Thread [1] (Suspended: Signal 'SIGILL' received. Description: Illegal instruction.)
1 <symbol is not available> 0x812feb44
What does that mean? Has the compiler generated illegal code for some reason? I have a breakpoint in the constructor (which does nothing), and it's not hit. I have already done a full rebuild.
What could I be doing wrong to cause this problem?
Android Solutions
Solution 1 - Android
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 - Android
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 - Android
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 - Android
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