Can a segmentation fault be attributed to OpenPiton?

[Ioannis Galanommatis]

Hello all

I have a strange issue. I use a four-core OpenPiton/Ariane with Linux and I receive a segmentation fault but cannot attribute it to user bug. The pattern is that I launch a multithreaded application, in this case lmbench, full log of execution under strace: https://pastebin.com/bVnFprwd.

• Crash is non-deterministic but if I set to 1 or 2 threads it is rare but if set to 3 and 4 it is likely within less than minute.
• Frequently, the error text at syslog contains mixed characters, indicating concurrent crash at all four cores.
• Typically it is the running app that crashes but it can happen that sshd or ntpd to be the crashing application, hinting the cause to be outside of the userspace.
• The offending address is always 0x4 irrespectively of the triggering program. It could be an offset to a struct, e.g. dereference of ptr->second_int with ptr being NULL, I suppose a kernel structure passed via ioctl, but how could it be possible the kernel would ever provide a NULL pointer in a syscall and no-one checked the return value, including widely used system daemons?

My question is, have you seen that behaviour, could this be possibly caused by OpenPiton's hardware support for multithreading/atomicity or a cache coherency issue? Or it is more likely the kernel to be held responsible?

Any advice is welcome!

Regards,

Ioannis Galanommatis

[Jonathan Balkind]

Hm, this is not familiar to me. Generally we haven't had any major surprises of this nature, but there is one weird thing with booting CVA6 on some boards that we'd still like to resolve and I do wonder if it could be a broader manifestation of whatever is going on there.

Could you give some more info on your environment? i.e. Which FPGA, core, Linux kernel, opensbi, etc? That might help jog my thinking on it.

Thanks,

Jon

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