What causes signal 'SIGILL'?

Question

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?

Max Klint · Answer 1 · 2020-05-05T12:13:19.003

50

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.

edited May 05 '20 at 12:13

answered Jul 11 '19 at 16:12

Max Klint

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You have no idea to what lengths I went searching for a reason behind SIGILL (QT + Android) just to find a missing return statement in a function (inspired by your reply). Thank you. – Vega4 Jul 28 '20 at 22:09
@Vega4 What compiler you were using? Thanks! – Feng. Ma Apr 10 '21 at 04:58

score 36 · Answer 2 · answered Oct 26 '11 at 11:20

36

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.

answered Oct 26 '11 at 11:20

trojanfoe

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Another cause of execing an invalid instruction is jumping to an address that isn't in the program area. – Paul Nathan Jan 10 '12 at 16:56
Weird, I got this, when I compiled with clang, but it worked fine with gcc – Post Self Mar 02 '18 at 19:45

Basile Starynkevitch · Answer 3 · 2016-09-13T17:30:57.220

26

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.

edited Sep 13 '16 at 17:30

answered Oct 26 '11 at 11:31

Basile Starynkevitch

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For me, I wasn't returning any value from a function that was supposed to return an int. So somewhat related to this answer. No idea how it managed to compile. – Chris Watts Dec 17 '18 at 18:41

pkamb · Answer 4 · 2022-02-01T21:25:23.307

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

What causes signal 'SIGILL'?

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