Segfault in Pkg.update() in a fresh Julia installation

[Cristóvão Duarte Sousa]

Hi,

I'm using Julia compiled from git in Arch linux, and in the last weeks I've been getting almost random segmentation faults, mainly, but not only, when running Pkg.update().

I've followed the procedures from https://gist.github.com/staticfloat/6188418 (except for the Github issue opening) and I'm posting here the gdb logs. All logs refer to starting Julia with an empty .julia/v0.3 folder.

I started by running versioninfo(true) before Pkg.update(), but somehow in this case it doesn't segfaults; here is a gdb log copypast for that case:

https://gist.github.com/cdsousa/9cfa5307ae221e72f2e2#file-julia_ok_log

If I just run Pkg.update(), also with an empty .julia/v0.3, it segfaults:

https://gist.github.com/cdsousa/9cfa5307ae221e72f2e2#file-julia_nok_log

(the log is huge since there is a lot of llvm code in the middle)

I've also seen segmentation faults when running other commands, and I even have got BoundsErrors from Base functions in a few occasions.

I've also discovered that by removing the precompiled sys.so, the segfaults disappear:

https://gist.github.com/cdsousa/9cfa5307ae221e72f2e2#file-julia_nosysso_ok_log

I have no knowledge about how to further tackle this issue.

What can I do next?

Thanks,

Cristóvão

[Cristóvão Duarte Sousa]

Let me add that the backtrace is not always the same.

If I run Pkg.update() but typing it into the julia realine shell rather than passing it as an execute argument I get this b.t.:

https://gist.github.com/cdsousa/a18439acba05a64d8476

On the other hand if I do exactly the same thing but using julia-debug-basic instead of julia-debug-readline then it doesn't segfaults.

It seems to be some dangling/wild pointer... no?

[Isaiah Norton]

Can you please send the version number of LLVM under julia/deps/llvm-#.#?

[Cristóvão Duarte Sousa]

I'm compiling julia with a slightly modified (forcing debug mode) packaging build file from my distribution, and it makes with USE_SYSTEM_LLVM=1.

My system has LLVM version 3.4.

In the mean time I'll try to compile Julia with USE_SYSTEM_LLVM=0.

[Isaiah Norton]

Yes, you should have better luck with that. MCJIT is enabled when using LLVM 3.4, and there are some bugs.

Please file an issue and link the gists, so this doesn't get lost. (if you have any other reproducible test cases, those might be helpful too)

[Cristóvão Duarte Sousa]

Indeed. I downgrade my system LLVM to v3.3 and now it's working!

Thanks Isaiah!

Looking at Arch Linux LLVM package history, I found it was updated from 3.3 to 3.4 in the begin of January, exactly the time I start having those issues with new Julia builds :)

I opened an issue in Julia GitHub: https://github.com/JuliaLang/julia/issues/5696
And I'll notify the Arch package maintainer about this.

Thank you so much.