llvm dev - Jun 2018 - runStaticConstructorsDestructors() causes crash on exit

Greetings, LLVM wizards.

I am using clang to compile a C++ module, and an ExecutionEngine (MCJIT) to
execute a function it defines. That works (or pretends to). However, if I
call the module's constructors first:

exec_engine->runStaticConstructorsDestructors(false);
exec_engine->runFunctionAsMain(function, argvec, NULL);

execution still works, but my program crashes when it exits, in
__run_exit_handlers(). I can't tell from gdb what exit handler is crashing,
but no calls are made to atexit() or on_exit(); all exit handlers are
installed via __cxa_atexit().

This may or may not be meaningful, but I am forced to compile with
-fno-use-cxa-atexit, otherwise clang complains that __dso_handle could not
be resolved.

Any guidance would be MUCH appreciated. I am at a loss... Also, if you know
of a better place to look for help than this mailing list, that would be
appreciated, too.

Thanks,
Geoff
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Hi Geoff,

I hit the same problem some time ago.
The problem that atexit handlers are registered from the JITted code, and the
handlers point to the memory allocated by JIT.
When the host program exits it calls the atexit handlers, but the memory is
already deallocated by JIT.
That's basically the reason of the crash.

From what I see ExecutionEngine and MCJIT do not provide any helpful API for
this case.
I can only recommend switching to Orc APIs in this case: there you can use
custom symbol resolver and redirect atexit functions to your own function(s).
That function would record atexit handlers, which you can call manually after
running your program.
Orc APIs even provide a class for that: orc::LocalCXXRuntimeOverrides.

I think this is the right place to ask such questions.
Otherwise, feel free to ping me on #llvm (AlexDenisov) if you need some hints on
how to JIT native code using Orc APIs.

I hope it helps.

Cheers,
Alex.
> On 14. Jun 2018, at 12:44, Geoff Levner via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Greetings, LLVM wizards.
> 
> I am using clang to compile a C++ module, and an ExecutionEngine (MCJIT) to
execute a function it defines. That works (or pretends to). However, if I call
the module's constructors first:
> 
> exec_engine->runStaticConstructorsDestructors(false);
> exec_engine->runFunctionAsMain(function, argvec, NULL);
> 
> execution still works, but my program crashes when it exits, in
__run_exit_handlers(). I can't tell from gdb what exit handler is crashing,
but no calls are made to atexit() or on_exit(); all exit handlers are installed
via __cxa_atexit().
> 
> This may or may not be meaningful, but I am forced to compile with
-fno-use-cxa-atexit, otherwise clang complains that __dso_handle could not be
resolved.
> 
> Any guidance would be MUCH appreciated. I am at a loss... Also, if you know
of a better place to look for help than this mailing list, that would be
appreciated, too.
> 
> Thanks,
> Geoff
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
--
AlexDenisov
Software Engineer, https://lowlevelbits.org
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Wow, now that is an answer. Thank you very much!

On Fri, 15 Jun 2018 at 11:23, Alex Denisov <1101.debian at gmail.com>
wrote:
> Hi Geoff,
>
> I hit the same problem some time ago.
> The problem that atexit handlers are registered from the JITted code, and
> the handlers point to the memory allocated by JIT.
> When the host program exits it calls the atexit handlers, but the memory
> is already deallocated by JIT.
> That's basically the reason of the crash.
>
> From what I see ExecutionEngine and MCJIT do not provide any helpful API
> for this case.
> I can only recommend switching to Orc APIs in this case: there you can use
> custom symbol resolver and redirect atexit functions to your own
> function(s).
> That function would record atexit handlers, which you can call manually
> after running your program.
> Orc APIs even provide a class for that: orc::LocalCXXRuntimeOverrides.
>
> I think this is the right place to ask such questions.
> Otherwise, feel free to ping me on #llvm (AlexDenisov) if you need some
> hints on how to JIT native code using Orc APIs.
>
> I hope it helps.
>
> Cheers,
> Alex.
>
> > On 14. Jun 2018, at 12:44, Geoff Levner via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Greetings, LLVM wizards.
> >
> > I am using clang to compile a C++ module, and an ExecutionEngine
(MCJIT)
> to execute a function it defines. That works (or pretends to). However, if
> I call the module's constructors first:
> >
> > exec_engine->runStaticConstructorsDestructors(false);
> > exec_engine->runFunctionAsMain(function, argvec, NULL);
> >
> > execution still works, but my program crashes when it exits, in
> __run_exit_handlers(). I can't tell from gdb what exit handler is
crashing,
> but no calls are made to atexit() or on_exit(); all exit handlers are
> installed via __cxa_atexit().
> >
> > This may or may not be meaningful, but I am forced to compile with
> -fno-use-cxa-atexit, otherwise clang complains that __dso_handle could not
> be resolved.
> >
> > Any guidance would be MUCH appreciated. I am at a loss... Also, if you
> know of a better place to look for help than this mailing list, that would
> be appreciated, too.
> >
> > Thanks,
> > Geoff
>
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On Alex's advice I am switching from MCJIT to the Orc API to compile and
execute functions. Starting from the new clang-interpreter example in the
source code (top of the tree!), I am able to execute my functions all
right... as long as there are no constructors and destructors to call.

My question: is there a simple way, with the Orc API, to run a module's
constructors and destructors? I see how OrcMCJITReplacement does it,
calling getConstructors() and getDestructors() when a module is added, and
running them later using a layer, but is there maybe a simpler way that I
am missing? I would prefer to avoid having to invent secret names for
constructors, play with their linkage and visibility, and generally get
involved in things I don't understand...

Thanks,
Geoff

On Fri, 15 Jun 2018 at 11:23, Alex Denisov <1101.debian at gmail.com>
wrote:
> Hi Geoff,
>
> I hit the same problem some time ago.
> The problem that atexit handlers are registered from the JITted code, and
> the handlers point to the memory allocated by JIT.
> When the host program exits it calls the atexit handlers, but the memory
> is already deallocated by JIT.
> That's basically the reason of the crash.
>
> From what I see ExecutionEngine and MCJIT do not provide any helpful API
> for this case.
> I can only recommend switching to Orc APIs in this case: there you can use
> custom symbol resolver and redirect atexit functions to your own
> function(s).
> That function would record atexit handlers, which you can call manually
> after running your program.
> Orc APIs even provide a class for that: orc::LocalCXXRuntimeOverrides.
>
> I think this is the right place to ask such questions.
> Otherwise, feel free to ping me on #llvm (AlexDenisov) if you need some
> hints on how to JIT native code using Orc APIs.
>
> I hope it helps.
>
> Cheers,
> Alex.
>
> > On 14. Jun 2018, at 12:44, Geoff Levner via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Greetings, LLVM wizards.
> >
> > I am using clang to compile a C++ module, and an ExecutionEngine
(MCJIT)
> to execute a function it defines. That works (or pretends to). However, if
> I call the module's constructors first:
> >
> > exec_engine->runStaticConstructorsDestructors(false);
> > exec_engine->runFunctionAsMain(function, argvec, NULL);
> >
> > execution still works, but my program crashes when it exits, in
> __run_exit_handlers(). I can't tell from gdb what exit handler is
crashing,
> but no calls are made to atexit() or on_exit(); all exit handlers are
> installed via __cxa_atexit().
> >
> > This may or may not be meaningful, but I am forced to compile with
> -fno-use-cxa-atexit, otherwise clang complains that __dso_handle could not
> be resolved.
> >
> > Any guidance would be MUCH appreciated. I am at a loss... Also, if you
> know of a better place to look for help than this mailing list, that would
> be appreciated, too.
> >
> > Thanks,
> > Geoff
>
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