[cfe-dev] clang crashes when running in VM

[George Burgess IV via cfe-dev]

> I guess it might be due to parallel linking, the memory usage would skyrocket?

Yup, that would do it. :)

> Is there a graceful way to avoid this?

If your project uses CMake, you might be able to have it generate
files for `ninja` instead of Makefiles. Ninja has job pools just for
cases like this: https://ninja-build.org/manual.html#ref_pool (and
I've heard many LLVM devs talk about how using `ninja` instead of
`make` made incremental rebuilds of LLVM/clang faster for them, so...)

If you're stuck with Makefiles, though, I don't know of a great way to
limit to N parallel link jobs. If you don't mind linking being 100%
serial, you may find the (nonstandard, apparently) .NOTPARALLEL
target useful.

Good luck!
George

On Wed, Jul 26, 2017 at 10:17 AM, chen hsu <chenxuz at outlook.com> wrote:
> Thanks for replying, George.
>
> I allocated 16GB to the VM, as well as 4GB swap. Our
> executable/shared-library are pretty big, usually 500MB to 2GB in size with
> debug symbols, and we use "make -j 12" for the 6-core (12 hyperthread) CPU
> to be fully used. I guess it might be due to parallel linking, the memory
> usage would skyrocket? Is there a graceful way to avoid this?
>
> ________________________________
> From: George Burgess IV <george.burgess.iv at gmail.com>
> Sent: Wednesday, July 26, 2017 2:20:21 AM
> To: chen hsu
> Cc: Clang Dev
> Subject: Re: [cfe-dev] clang crashes when running in VM
>
> Hello!
>
> "error: unable to execute command: Killed" sounds a lot like what I
> get when clang gets killed for eating all of my system's memory. Are
> you sure that your VM has enough RAM to handle linking whatever it is
> that you're linking?
>
> Thanks,
> George
>
> On Tue, Jul 25, 2017 at 5:24 PM, chen hsu via cfe-dev
> <cfe-dev at lists.llvm.org> wrote:
>> Hi,
>>
>>
>> we have clang 3.6.2 on ubuntu 16.04 to build our project and it works well
>> on physical machines. but when running in VM (HyperV on Windows Server
>> 2012R2), it crashes quite often in linking. Is this a known issue? It
>> seems
>> possibly related to memory, as the crash happens more frequently when the
>> memory size of the VM is relatively small. Thanks.
>>
>>
>> clang-3.6: error: unable to execute command: Killed
>>
>> clang-3.6: error: clang frontend command failed due to signal (use -v to
>> see
>> invocation)
>>
>> clang version 3.6.2 (tags/RELEASE_362/final 252038)
>>
>> Target: x86_64-unknown-linux-gnu
>>
>> Thread model: posix
>>
>> clang-3.6: note: diagnostic msg: PLEASE submit a bug report to
>> http://llvm.org/bugs/ and include the crash backtrace, preprocessed
>> source,
>> and associated run script.
>>
>> ********************
>>
>>
>>
>>
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