llvm dev - Feb 2021 - How to use thread local storage with ORC JIT?

Hello everyone,

I'm using the ORC JIT to load and execute some IR files which I compiled
with Clang-Cl from some source files - the host is Windows 64bit. Apparently,
clang decided to generate code using the thread local storage for some of the
code. When now loading and jitting those files I get the following undefined
references:
__emutls_get_address
__emutls_v._Init_thread_epoch

A while ago I was told, that those references are coming from compiler-rt - so I
build that project and at least I found "__emutls_get_address" in the
"clang_rt.builtins-x86_64.lib" file. However, I haven't found
"__emutls_v._Init_thread_epoch" anyway and don't know what to do
with this symbol.

Any ideas?

Also, in case you see double - I asked this question in the LLVM Discord already
with no big success...

Kind greetings
Björn
Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr.
DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus
Bode, Takashi Nagano, Junichi Tajika, Ergin Cansiz.
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I am no expert, so take anything I say with a pinch of salt, but my
understanding is that Orc JIT does not support native thread-local storage,
it just emulates it. I think what you have to do is to compile your source
code with Clang's -femulated-tls option, to avoid native thread-local
storage calls.

Geoff

On Mon, Feb 15, 2021 at 9:07 AM Gaier, Bjoern via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hello everyone,
>
>
>
> I'm using the ORC JIT to load and execute some IR files which I
compiled
> with Clang-Cl from some source files - the host is Windows 64bit.
> Apparently, clang decided to generate code using the thread local storage
> for some of the code. When now loading and jitting those files I get the
> following undefined references:
>
> __emutls_get_address
>
> __emutls_v._Init_thread_epoch
>
>
>
> A while ago I was told, that those references are coming from compiler-rt
> - so I build that project and at least I found
"__emutls_get_address" in
> the "clang_rt.builtins-x86_64.lib" file. However, I haven't
found
> "__emutls_v._Init_thread_epoch" anyway and don't know what to
do with this
> symbol.
>
>
>
> Any ideas?
>
>
>
> Also, in case you see double - I asked this question in the LLVM Discord
> already with no big success...
>
>
>
> Kind greetings
>
> Björn
> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
> USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert
> Plank, Markus Bode, Takashi Nagano, Junichi Tajika, Ergin Cansiz.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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+Lang Hames <lhames at gmail.com> (though I think he's not got much
bandwidth
for a few months - so responses may be delayed)

On Mon, Feb 15, 2021 at 12:07 AM Gaier, Bjoern via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hello everyone,
>
>
>
> I'm using the ORC JIT to load and execute some IR files which I
compiled
> with Clang-Cl from some source files - the host is Windows 64bit.
> Apparently, clang decided to generate code using the thread local storage
> for some of the code. When now loading and jitting those files I get the
> following undefined references:
>
> __emutls_get_address
>
> __emutls_v._Init_thread_epoch
>
>
>
> A while ago I was told, that those references are coming from compiler-rt
> - so I build that project and at least I found
"__emutls_get_address" in
> the "clang_rt.builtins-x86_64.lib" file. However, I haven't
found
> "__emutls_v._Init_thread_epoch" anyway and don't know what to
do with this
> symbol.
>
>
>
> Any ideas?
>
>
>
> Also, in case you see double - I asked this question in the LLVM Discord
> already with no big success...
>
>
>
> Kind greetings
>
> Björn
> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
> USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert
> Plank, Markus Bode, Takashi Nagano, Junichi Tajika, Ergin Cansiz.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi All,

Björn -- I know we discussed this on discord already, but something just
occurred to me: Are you compiling your target executable (whatever you're
JITing in to, probably the same process as your JIT) with -femulated-tls?
If so, have you made sure to include at least one thread local variable
that is either used or marked as used (to ensure it's not dead stripped)?
JIT'd code will be looking for those symbols in your executable so
you'll
need to make sure they're linked in there.

I am no expert, so take anything I say with a pinch of salt, but
my
> understanding is that Orc JIT does not support native thread-local storage,
> it just emulates it.

That is true for now, but I hope to have native thread locals supported (on
MachO at least) by LLVM 12. The ORC runtime prototype [1] already contains
support for POD thread locals, and I will be aiming to add support for
thread locals with nontrivial constructors in the near future.

-- Lang.

On Tue, Feb 23, 2021 at 7:11 AM David Blaikie <dblaikie at gmail.com>
wrote:
> +Lang Hames <lhames at gmail.com> (though I think he's not got
much
> bandwidth for a few months - so responses may be delayed)
>
> On Mon, Feb 15, 2021 at 12:07 AM Gaier, Bjoern via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hello everyone,
>>
>>
>>
>> I'm using the ORC JIT to load and execute some IR files which I
compiled
>> with Clang-Cl from some source files - the host is Windows 64bit.
>> Apparently, clang decided to generate code using the thread local
storage
>> for some of the code. When now loading and jitting those files I get
the
>> following undefined references:
>>
>> __emutls_get_address
>>
>> __emutls_v._Init_thread_epoch
>>
>>
>>
>> A while ago I was told, that those references are coming from
compiler-rt
>> - so I build that project and at least I found
"__emutls_get_address" in
>> the "clang_rt.builtins-x86_64.lib" file. However, I
haven't found
>> "__emutls_v._Init_thread_epoch" anyway and don't know
what to do with this
>> symbol.
>>
>>
>>
>> Any ideas?
>>
>>
>>
>> Also, in case you see double - I asked this question in the LLVM
Discord
>> already with no big success...
>>
>>
>>
>> Kind greetings
>>
>> Björn
>> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
>> USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr.
Robert
>> Plank, Markus Bode, Takashi Nagano, Junichi Tajika, Ergin Cansiz.
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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