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

[David Blaikie via llvm-dev]

(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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