SIGILL with clang

Clang Frontend
1

Hey folks,

I am migrating our huge Android code base from GCC(Eclipse IDE) to clang(Android Studio).

Error: SIGILL (signal SIGILL: illegal instruction)

At a weird line in the code, I am getting this error. which points to a closing curly bracket of an if condition. After googling, I am assuming it is some kind of architecture flag issue. I am using same flags which were used for GCC.

Note: I am currently working on Arm build.

Here are the architecture flags for ARM7:

-march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -mtune=cortex-a8 -mthumb -DTARGET_THUMB2

Can anyone help me debug this issue? Is there any issue with the flags with clang?

Thanks,
Rohit Kumar

2

Glad to help. CCing ML for the record.

3

Hi,
foo() has undefined behavior if i==0 (lack of return statement)

6.6.3 para 2:
Flowing off the end of a function is equivalent to a return with no
value; this results in undefined behavior
in a value-returning function.

clang generates an invalid instruction for undefined behavior.
This is not ARM-specific.

Compiler Explorer’)),version:4

That ud2 instruction is the machine code for undefined behavior.

Csaba

4

Hi,
foo() has undefined behavior if i==0 (lack of return statement)

6.6.3 para 2:
Flowing off the end of a function is equivalent to a return with no
value; this results in undefined behavior
in a value-returning function.

clang generates an invalid instruction for undefined behavior.
This is not ARM-specific.

Note that this is C++-specific; it is only undefined behavior in C if the result is used by the caller.

John.

5

Thanks guys, the issue is resolved now. It was a more trivial fix. Gcc was not giving any error neither on compile time nor on run time. Clang was giving error on runtime.
It was an issue with a function which was supposed to return a Boolean but it wasn’t. I could not figure it out earlier because debugging was not working. But when I got it working I could pinpoint the function, someone from llvm-dev thread suggested to check for such a function. So, finally it got fixed.