[llvm-dev] LLJIT vs. thread-local storage

Lang Hames via llvm-dev llvm-dev at lists.llvm.org
Thu Jan 16 19:06:03 PST 2020

Hi Geoff,

Thanks for your patience — I’ve been out on vacation and am still catching up on emails.

If this was working for you on ORCv1 then it could be as simple as ORCv2 not enabling TLS emulation by default (where I believe ORCv1 did) — I will investigate this tomorrow.

You said you were on an older LLVM version right? Whatever fix I make may have to be backported.

— Lang.

Sent from my iPad

> On Jan 7, 2020, at 10:33 AM, David Blaikie <dblaikie at gmail.com> wrote:
> (just adding Lang here for visibility)
>> On Tue, Jan 7, 2020 at 2:29 AM Geoff Levner via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> So, picking up this thread again after the holidays (burp)... Is there any chance that ORC v2 will support thread-local variables in the foreseeable future? Is there some way of configuring it today to ensure they are handled correctly? Or are we better off sticking with ORC v1?
>>> On Fri, Dec 20, 2019 at 9:59 PM Jameson Nash via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>> I don't think it's especially hard, but just not specifically unimplemented because nobody's had a strong need for it. There's probably some combinations of code models and machines that does happen to work (e.g. emutls+linux+large-code+large-data+no-PIC). Julia has some support for thread locals, but as a JIT in control of the language we currently try to generate better code than would otherwise happen (often bits of inline assembly that's more similar to the initial-exec model than a dynamic library would normally be able to use)—but also with more limitations on how it may be used and requiring some additional support from the runtime.
>>>> On Fri, Dec 20, 2019 at 1:17 PM Praveen Velliengiri <praveenvelliengiri at gmail.com> wrote:
>>>> Hi Jameson,
>>>> Why thread local support is hard to support in JITs? Whether Julia supports Thread locals? If so, it would be very much helpful to know how.
>>>> Thanks
>>>>> On Fri, 20 Dec 2019 at 23:31, Jameson Nash via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>>> This had also came up at llvm-devmtg briefly at the JIT roundtable. One of the collaborators on my project had started a patch years ago to implement some of it https://reviews.llvm.org/D8815, but then we went a different direction with TLS in our frontend and it became unnecessary.
>>>>>> On Fri, Dec 20, 2019 at 12:36 PM David Blaikie via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>>>> +Lang for visibility
>>>>>>> On Fri, Dec 20, 2019 at 5:09 AM Geoff Levner via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>>>>> I am in the process of porting our ORC code to ORC v2 and LLJIT. Now that I have worked around a problem getting global constructors to be called, everything seems to work unless a module declares a static thread-local variable. In that case I get a "JIT session error" saying that the symbol __emutls_v.xyz was not found (substitute the mangled variable name for "xyz").
>>>>>>> Does that mean anything to anybody out there?
>>>>>>> (I don't know if it's relevant, but we are using LLVM 8, and we are using Clang to compile C++ modules that are all put into a single JITDylib.)
>>>>>>> Geoff
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