While running a program I've written in assembly, I get Illegal instruction
error. Is there a way to know which instruction is causing the error, without debugging that is, because the machine I'm running on does not have a debugger or any developement system. In other words, I compile in one machine and run on another. I cannot test my program on the machine I'm compiling because they don't support SSE4.2. The machine I'm running the program on does support SSE4.2 instructions nevertheless.
I think it maybe because I need to tell the assembler (YASM) to recognize the SSE4.2 instructions, just like we do with gcc by passing it the -msse4.2
flag. Or do you think its not the reason? Any idea how to tell YASM to recognize SSE4.2 instructions?
Maybe I should trap the SIGILL signal and then decode the SA_SIGINFO to see what kind of illegal operation the program does.
Illegal Instruction errors occur when you try to run a program that was compiled with some processor-specific optimizations, and is then running on a processor that fails to meet those requirements.
Illegal instruction and crashing errors on UNIX are usually due to a bad FTP or wrong file permissions. Mar 16, 2022•Knowledge.
Illegal instruction errors don't come from C++, they come instead from the operating system. They arise because not every possible memory value corresponds to a valid instruction. For instance, if instruction opcodes were one byte, there would be 256 distinct instructions possible.
Recently I experienced a crash due to a 132 exit status code (128 + 4: program interrupted by a signal + illegal instruction signal). Here's how I figured out what instruction was causing the crash.
First, I enabled core dumps:
$ ulimit -c unlimited
Interestingly, the folder from where I was running the binary contained a folder named core
. I had to tell Linux to add the PID to the core dump:
$ sudo sysctl -w kernel.core_uses_pid=1
Then I run my program and got a core named core.23650
. I loaded the binary and the core with gdb.
$ gdb program core.23650
Once I got into gdb, it showed up the following information:
Program terminated with signal SIGILL, Illegal instruction. #0 0x00007f58e9efd019 in ?? ()
That means my program crashed due to an illegal instruction at 0x00007f58e9efd019
address memory. Then I switched to asm layout to check the last instruction executed:
(gdb) layout asm >|0x7f58e9efd019 vpmaskmovd (%r8),%ymm15,%ymm0 |0x7f58e9efd01e vpmaskmovd %ymm0,%ymm15,(%rdi) |0x7f58e9efd023 add $0x4,%rdi |0x7f58e9efd027 add $0x0,%rdi
It was instruction vpmaskmovd
that caused the error. Apparently, I was trying to run a program aimed for AVX2 architecture on a system which lacks support for AVX2 instruction set.
$ cat /proc/cpuinfo | grep avx2
Lastly, I confirmed vpmaskmovd is an AVX2 only instruction.
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