llvm dev - Oct 2017 - Clang/LLVM JIT - When to use "registerEHFrames()"

I'm catching up on this. Does this mean LLVM x64 JITTed code is not
exception friendly or you can't catch exceptions inside LLVM JITTed
code. The first one seems to indicate that the code is not ABI
friendly or that not enough information is present to notify Windows
of unwind tables.

I'll ask the question another way: Does LLVM emit enough information
so that RtlAddFunctionTable can work? Anyone successfully done this in
the wild?

On Sun, Oct 1, 2017 at 7:16 AM, Stefan Gränitz via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi, I checked last year's mails. Back then Timur and me faced the same
issue
> Björn reports (nulled memory in _ThrowInfo).
>
>> Back then I tried to solve a related issue: SEH exceptions thrown from
>> code loaded with RuntimeDyld had to be caught in statically compiled
code.
>> It turned out Windows explicitly prohibits this. I got in touch with
>> Microsoft people and IIRC it's due to security concerns.
>
>
> Stefan -- That's an interesting restriction. :/
> Does it prohibit exceptions thrown in JIT'd code from being caught also
in
> JIT'd code, or does it only apply if an exception crosses the boundary
back
> into statically compiled code?
> Do you know how they were enforcing that?
>
> Igor Minin explained this was due to Data Execution Prevention (DEP) and
> gave pointers to the involved functions in the OS runtime:
> http://lists.llvm.org/pipermail/llvm-dev/2016-June/100901.html
>
> The whole thing gets hairy quickly. It seems like a combination of multiple
> problems. So let's first collect evidence and clarify the goal.
>
> Joseph Tremoulet from Microsoft partially confirmed Igor's statements:
> "I checked with some experts here, and they agree with your/Igor’s
> assessment that it’s not possible to have a dynamically generated handler
on
> x86"
> "the llilc code only handles x86_64, not 32-bit x86; I know the
> implementations of WinEH are quite different between the two"
> First conclusion: No solution for JITed catch handlers on x86.
>
> I think for most of us x86 has little prio anyway, so let's focus on
x86_64.
> In theory both, JITed and static catch handlers, may be possible here.
>
> I disabled DEP globally on my machine and set MEM_EXECUTE_OPTION_ENABLE
> explicitly:
> http://www.thewindowsclub.com/disable-data-execution-prevention
> https://github.com/Sh1ft0x0EF/metahook/blob/master/sys_launcher.cpp#L65
> It didn't fix anything.
> Second conclusion: DEP may be one reason, but there must be something else.
>
> My next guess was an incompatibility between Clang (we used for JITing) and
> MSVC (we used for static compilation). Joseph:
> "One thing that comes to mind is that presumably you’re not trying to
make
> your language/runtime’s exceptions masquerade as MSVC++ exceptions, so I
> guess you’d want your static native code to either have an SEH
> __try/__except or compile with clang’s equivalents of MSVC’s /EHa and
> catch(…)"
>
> I tried all the combinations without success. I also compared the compiled
> code between Clang 3.8 and MSVC, which showed no reasonable difference.
> Second conclusion: No issue with code generation.
>
> At that point we ran out of time we could spend on this. So we postponed
the
> feature, hoping for Microsoft to come up with a solution at some point.
> Giving it another try today, I think this looks promising:
>
https://github.com/dotnet/llilc/blob/master/lib/Jit/EEMemoryManager.cpp#L250
>
> Processing .pdata section entries, it creates and allocates unwind blocks
> and funclets (handlers for catch & finally) for CLR managed exceptions.
It's
> probably not directly applicable to native exception handling, but it may
> provide useful information. Also there is much more documentation available
> now:
>
https://github.com/dotnet/coreclr/blob/master/Documentation/botr/clr-abi.md#exception-handling
>
https://llvm.org/docs/ExceptionHandling.html#exception-handling-using-the-windows-runtime
>
> I could imagine setting up minimal tests would be a useful first step to
> distinguish issues in a reproducible way.
>
> Best
> Stefan
>
> Am 29.09.17 um 19:43 schrieb Lang Hames:
>
> Hi Bjoern,
>
>> I'm trying to make exceptions run. I have an Object file with a
function,
>> throwing a 1 and a second function which should catch the 1. Normal
JITTING
>> under Windows showed me, that I have an unresolved reference to the
virtual
>> table of type_info. Some experiments later I was able to load
"msvcrt.lib"
>> as an archive and could resolve the reference. Nice - but than
>> "??_Etype_info@@UEAPEAXI at Z" was missing too. Ufff! I
decided to ignore this.
>> Because, when I try to load every .lib and .obj provided by Visual
Studio, I
>> get an assertion failure with "Relocation type not implemented
yet!".
>
>
> RuntimeDyldCOFF is missing a lot of relocation support. We need a COFF
> expert to fix that and unfortunately I'm not one.
>
>> I decided to have a look at "_CxxThrowException". I inserted
my own
>> function for the JIT and had a look at the parameters. I got two of
them.
>> The first was the address of the Exception-Object, which was correct.
The
>> second is the address for the "_ThrowInfo". This address was
valid too, but
>> all its members - except from attributes - are null. So I can't
throw this
>> Exception. I tried to pass the address of typeid(1) to it, or
modificate the
>> call. Nothing helped.
>
>
> I don't know windows exception handling well, but if it's anything
like
> DWARF EH then I'd be inclined to blame the missing relocations/fixups
-- the
> _ThrowInfo struct (or whatever data-source ultimately populates it)
probably
> isn't being fixed up.
>
>> I have no clue and no idea anymore. So... Do you have an idea?
>
>
> I'm afraid I don't personally. We need some windows linker / system
experts
> to take an interest in the JIT.
>
>> Back then I tried to solve a related issue: SEH exceptions thrown from
>> code loaded with RuntimeDyld had to be caught in statically compiled
code.
>> It turned out Windows explicitly prohibits this. I got in touch with
>> Microsoft people and IIRC it's due to security concerns.
>
>
> Stefan -- That's an interesting restriction. :/
> Does it prohibit exceptions thrown in JIT'd code from being caught also
in
> JIT'd code, or does it only apply if an exception crosses the boundary
back
> into statically compiled code?
> Do you know how they were enforcing that?
>
> Cheers,
> Lang.
>
>
>
>
>
> On Thu, Sep 28, 2017 at 12:37 PM, Stefan Gränitz via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> I tried loading the "msvcrt.lib" as a archive. That was... a
bad idea! I
>> get a Exception while loading:
>> Assertion failed: ((int64_t)Result <= INT32_MAX) &&
"Relocation overflow",
>> file \lib\executionengine\runtimedyld\Targets/RuntimeDyldCOFFX86_64.h,
line
>> 81
>>
>> It's a limitation of the COFF/PE format and unrelated to
exceptions. This
>> patch explains it and shows a workaround:
>>
>>
https://github.com/weliveindetail/pj-llvm/commit/97cd336d458ae9c73232d1b539ceefcdb2f5eb0f
>>
>> Is there no hope left?
>>
>> Well at least I am not aware of a solution.
>>
>> Am 28.09.17 um 16:04 schrieb bjoern.gaier at horiba.com:
>>
>> Hello Stefan,
>>
>> I'm happy someone replied to my problem! Many thanks! To be
honest... I
>> didn't understood much of your mail. I'm a beginner with the
JIT - so I will
>> explain what I've done.
>>
>> To manage the memory and resolve symbols, I'm using my own
Resolver-Class,
>> which overloads the allocation and the findSymbol functions. I've
noticed
>> today, that the "registerEHFrames" function of my class gets
called
>> automatically, with correct values. I'm remapping my code and the
address
>> are still correct. Great! But, what should I do with it? I pass the
values
>> to the original function, but my exception won't be caught!
It's an
>> exception raised inside the JITTED code and should also catched there.
>>
>> I tried loading the "msvcrt.lib" as a archive. That was... a
bad idea! I
>> get a Exception while loading:
>> Assertion failed: ((int64_t)Result <= INT32_MAX) &&
"Relocation overflow",
>> file \lib\executionengine\runtimedyld\Targets/RuntimeDyldCOFFX86_64.h,
line
>> 81
>>
>> Research didn't helped me! My code was compiled with /MD, but it
didn't
>> changed. So I'm still stupid D:
>> The JITTED code must be loaded to shared memory later - there
aren't
>> libraries, so even if this would work, it wouldn't help me. I tried
>> compiling my code with sjlj-exceptions. Didn't worked...
>>
>> Is there no hope left?
>>
>> Kind regards
>> Björn
>>
>>
>>
>> From:        Stefan Gränitz <stefan.graenitz at gmail.com>
>> To:        bjoern.gaier at horiba.com, llvm-dev at lists.llvm.org
>> Date:        27.09.2017 23:09
>> Subject:        Re: [llvm-dev] Clang/LLVM JIT - When to use
>> "registerEHFrames()"
>> ________________________________
>>
>>
>>
>> Hi Björn
>>
>> To first answer your questionin the subject: For x86 registerEHFrames()
is
>> only a stub. For x86_64 registerEHFrames() is implemented properly in
>> RuntimeDyldCOFFX86_64, calling MemMgr.registerEHFrames() for each EH
frame
>> section. It should be called and work out of the box without your
>> involvement, but unfortunately it won't solve your issue. All the
essential
>> information is there in the comments, just check the base classes.
>>
>> This thread from last year helps with your unresolved symbol:
>> http://lists.llvm.org/pipermail/llvm-dev/2016-October/106458.html
>>
>> Back then I tried to solve a related issue: SEH exceptions thrown from
>> code loaded with RuntimeDyld had to be caught in statically compiled
code.
>> It turned out Windows explicitly prohibits this. I got in touch with
>> Microsoft people and IIRC it's due to security concerns.
>>
>> Depending on your specific case, you may want to fall back to vectored
>> exception handling. In my experience this was a dead end though. If you
need
>> a solution for arbitrary situations, you just can't jump back to a
"safe"
>> place to continue execution. I tried setjump (on each entry point to
the
>> dynamically loaded code) / longjmp (in the vectored exception handler),
but
>> the address was invalidated when I accessed it. I suspect it's kind
of
>> undefined behavior to call longjmp outside a child frame of the
function
>> that called setjmp. Anyway it turned all far too hacky.
>>
>> If you are willing to do research, compare implementations and behavior
>> with the MachO and ELF versions. At least one of them works, just not
on
>> Windows ;)
>> Also check the LLILC project: https://github.com/dotnet/llilc I heard
>> about some solution that uses trampolines to push exceptions back to
>> dynamically loaded code and handle them there.
>>
>> AND disclaimer: I did not follow recent developments in this area. If
>> there's news please let me know!
>>
>> Cheers & Good Luck!
>> Stefan
>>
>> Am 25.09.17 um 11:31 schrieb via llvm-dev:
>> Hello friendly LLVM-World,
>>
>> because I don't know if I had send my problem to the correct
Mailing-List,
>> I will send my problem to this address too. I'm not subscribed to
this list,
>> so please add my in CC if you response.
>>
>> Kind regards
>> Björn
>>
>>
>> From:        Bjoern Gaier/HE/HORIBA
>> To:        Clang Dev <cfe-dev at lists.llvm.org>,
"cfe-dev"
>> <cfe-dev-bounces at lists.llvm.org>
>> Date:        19.09.2017 08:05
>> Subject:        Clang/LLVM JIT - When to use
"registerEHFrames()"
>>
>> ________________________________
>>
>>
>> Hello friendly Clang-World,
>>
>> I was experimenting with Clang and the JIT capabilities of LLVM. Most
of
>> my attempts were successfully but, I still fail miserably at
exceptions.
>> Doing research I found the function "registerEHFrames()"
which should assist
>> me supporting exceptions - but sadly the documentation I found
wasn't
>> helpful.
>> I looked at into the "notifyObjectLoaded" function and
discovered that
>> there appear some symbol names starting with "$" - I expected
them to be
>> connected to my try and catch block. But what now? As usually, at this
point
>> I have there names, but can't get there address to register them
with the
>> "registerEHFrames()" function. Also the JITTER still wants an
address for
>> "??_7type_info@@6B@" which is the virtual table of the
type_info struct.
>>
>> Confusing! So friendly Clang-World, could you please help?
>>
>> Not so important - but has the dragon which decorates clang and LLVM a
>> name?
>>
>> Kind regards
>> Björn
>>
>> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
>> USt.ID-Nr. DE 114 165 789
>> Geschäftsführer: Hiroshi Kawamura, Dr Hiroshi Nakamura, Markus Bode,
Heiko
>> Lampert, Takashi Nagano, Takeshi Fukushima.
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>> --
>> https://weliveindetail.github.io/blog/
>> https://cryptup.org/pub/stefan.graenitz at gmail.com
>>
>>
>> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
>> USt.ID-Nr. DE 114 165 789
>> Geschäftsführer: Hiroshi Kawamura, Dr Hiroshi Nakamura, Markus Bode,
Heiko
>> Lampert, Takashi Nagano, Takeshi Fukushima.
>>
>>
>> --
>> https://weliveindetail.github.io/blog/
>> https://cryptup.org/pub/stefan.graenitz at gmail.com
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
>
> --
> https://weliveindetail.github.io/blog/
> https://cryptup.org/pub/stefan.graenitz at gmail.com
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

In partial answer to your question, I can state that JuliaLang has been
successfully registering and handling exceptions in JIT code since LLVM
3.3, when I implemented support (with varying levels of hackiness over time
to support all of the JIT and other changes to LLVM since then). However
note that to hook it all up we use the ELF format and have our own
exception format + personality routine and a custom memory manager.


On Tue, Oct 3, 2017 at 12:36 AM Hayden Livingston via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I'm catching up on this. Does this mean LLVM x64 JITTed code is not
> exception friendly or you can't catch exceptions inside LLVM JITTed
> code. The first one seems to indicate that the code is not ABI
> friendly or that not enough information is present to notify Windows
> of unwind tables.
>
> I'll ask the question another way: Does LLVM emit enough information
> so that RtlAddFunctionTable can work? Anyone successfully done this in
> the wild?
>
> On Sun, Oct 1, 2017 at 7:16 AM, Stefan Gränitz via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Hi, I checked last year's mails. Back then Timur and me faced the
same
> issue
> > Björn reports (nulled memory in _ThrowInfo).
> >
> >> Back then I tried to solve a related issue: SEH exceptions thrown
from
> >> code loaded with RuntimeDyld had to be caught in statically
compiled
> code.
> >> It turned out Windows explicitly prohibits this. I got in touch
with
> >> Microsoft people and IIRC it's due to security concerns.
> >
> >
> > Stefan -- That's an interesting restriction. :/
> > Does it prohibit exceptions thrown in JIT'd code from being caught
also
> in
> > JIT'd code, or does it only apply if an exception crosses the
boundary
> back
> > into statically compiled code?
> > Do you know how they were enforcing that?
> >
> > Igor Minin explained this was due to Data Execution Prevention (DEP)
and
> > gave pointers to the involved functions in the OS runtime:
> > http://lists.llvm.org/pipermail/llvm-dev/2016-June/100901.html
> >
> > The whole thing gets hairy quickly. It seems like a combination of
> multiple
> > problems. So let's first collect evidence and clarify the goal.
> >
> > Joseph Tremoulet from Microsoft partially confirmed Igor's
statements:
> > "I checked with some experts here, and they agree with
your/Igor’s
> > assessment that it’s not possible to have a dynamically generated
> handler on
> > x86"
> > "the llilc code only handles x86_64, not 32-bit x86; I know the
> > implementations of WinEH are quite different between the two"
> > First conclusion: No solution for JITed catch handlers on x86.
> >
> > I think for most of us x86 has little prio anyway, so let's focus
on
> x86_64.
> > In theory both, JITed and static catch handlers, may be possible here.
> >
> > I disabled DEP globally on my machine and set
MEM_EXECUTE_OPTION_ENABLE
> > explicitly:
> > http://www.thewindowsclub.com/disable-data-execution-prevention
> >
https://github.com/Sh1ft0x0EF/metahook/blob/master/sys_launcher.cpp#L65
> > It didn't fix anything.
> > Second conclusion: DEP may be one reason, but there must be something
> else.
> >
> > My next guess was an incompatibility between Clang (we used for
JITing)
> and
> > MSVC (we used for static compilation). Joseph:
> > "One thing that comes to mind is that presumably you’re not
trying to
> make
> > your language/runtime’s exceptions masquerade as MSVC++ exceptions, so
I
> > guess you’d want your static native code to either have an SEH
> > __try/__except or compile with clang’s equivalents of MSVC’s /EHa and
> > catch(…)"
> >
> > I tried all the combinations without success. I also compared the
> compiled
> > code between Clang 3.8 and MSVC, which showed no reasonable
difference.
> > Second conclusion: No issue with code generation.
> >
> > At that point we ran out of time we could spend on this. So we
postponed
> the
> > feature, hoping for Microsoft to come up with a solution at some
point.
> > Giving it another try today, I think this looks promising:
> >
>
https://github.com/dotnet/llilc/blob/master/lib/Jit/EEMemoryManager.cpp#L250
> >
> > Processing .pdata section entries, it creates and allocates unwind
blocks
> > and funclets (handlers for catch & finally) for CLR managed
exceptions.
> It's
> > probably not directly applicable to native exception handling, but it
may
> > provide useful information. Also there is much more documentation
> available
> > now:
> >
>
https://github.com/dotnet/coreclr/blob/master/Documentation/botr/clr-abi.md#exception-handling
> >
>
https://llvm.org/docs/ExceptionHandling.html#exception-handling-using-the-windows-runtime
> >
> > I could imagine setting up minimal tests would be a useful first step
to
> > distinguish issues in a reproducible way.
> >
> > Best
> > Stefan
> >
> > Am 29.09.17 um 19:43 schrieb Lang Hames:
> >
> > Hi Bjoern,
> >
> >> I'm trying to make exceptions run. I have an Object file with
a
> function,
> >> throwing a 1 and a second function which should catch the 1.
Normal
> JITTING
> >> under Windows showed me, that I have an unresolved reference to
the
> virtual
> >> table of type_info. Some experiments later I was able to load
> "msvcrt.lib"
> >> as an archive and could resolve the reference. Nice - but than
> >> "??_Etype_info@@UEAPEAXI at Z" was missing too. Ufff! I
decided to ignore
> this.
> >> Because, when I try to load every .lib and .obj provided by Visual
> Studio, I
> >> get an assertion failure with "Relocation type not
implemented yet!".
> >
> >
> > RuntimeDyldCOFF is missing a lot of relocation support. We need a COFF
> > expert to fix that and unfortunately I'm not one.
> >
> >> I decided to have a look at "_CxxThrowException". I
inserted my own
> >> function for the JIT and had a look at the parameters. I got two
of
> them.
> >> The first was the address of the Exception-Object, which was
correct.
> The
> >> second is the address for the "_ThrowInfo". This address
was valid too,
> but
> >> all its members - except from attributes - are null. So I
can't throw
> this
> >> Exception. I tried to pass the address of typeid(1) to it, or
> modificate the
> >> call. Nothing helped.
> >
> >
> > I don't know windows exception handling well, but if it's
anything like
> > DWARF EH then I'd be inclined to blame the missing
relocations/fixups --
> the
> > _ThrowInfo struct (or whatever data-source ultimately populates it)
> probably
> > isn't being fixed up.
> >
> >> I have no clue and no idea anymore. So... Do you have an idea?
> >
> >
> > I'm afraid I don't personally. We need some windows linker /
system
> experts
> > to take an interest in the JIT.
> >
> >> Back then I tried to solve a related issue: SEH exceptions thrown
from
> >> code loaded with RuntimeDyld had to be caught in statically
compiled
> code.
> >> It turned out Windows explicitly prohibits this. I got in touch
with
> >> Microsoft people and IIRC it's due to security concerns.
> >
> >
> > Stefan -- That's an interesting restriction. :/
> > Does it prohibit exceptions thrown in JIT'd code from being caught
also
> in
> > JIT'd code, or does it only apply if an exception crosses the
boundary
> back
> > into statically compiled code?
> > Do you know how they were enforcing that?
> >
> > Cheers,
> > Lang.
> >
> >
> >
> >
> >
> > On Thu, Sep 28, 2017 at 12:37 PM, Stefan Gränitz via llvm-dev
> > <llvm-dev at lists.llvm.org> wrote:
> >>
> >> I tried loading the "msvcrt.lib" as a archive. That
was... a bad idea! I
> >> get a Exception while loading:
> >> Assertion failed: ((int64_t)Result <= INT32_MAX) &&
"Relocation
> overflow",
> >> file
\lib\executionengine\runtimedyld\Targets/RuntimeDyldCOFFX86_64.h,
> line
> >> 81
> >>
> >> It's a limitation of the COFF/PE format and unrelated to
exceptions.
> This
> >> patch explains it and shows a workaround:
> >>
> >>
>
https://github.com/weliveindetail/pj-llvm/commit/97cd336d458ae9c73232d1b539ceefcdb2f5eb0f
> >>
> >> Is there no hope left?
> >>
> >> Well at least I am not aware of a solution.
> >>
> >> Am 28.09.17 um 16:04 schrieb bjoern.gaier at horiba.com:
> >>
> >> Hello Stefan,
> >>
> >> I'm happy someone replied to my problem! Many thanks! To be
honest... I
> >> didn't understood much of your mail. I'm a beginner with
the JIT - so I
> will
> >> explain what I've done.
> >>
> >> To manage the memory and resolve symbols, I'm using my own
> Resolver-Class,
> >> which overloads the allocation and the findSymbol functions.
I've
> noticed
> >> today, that the "registerEHFrames" function of my class
gets called
> >> automatically, with correct values. I'm remapping my code and
the
> address
> >> are still correct. Great! But, what should I do with it? I pass
the
> values
> >> to the original function, but my exception won't be caught!
It's an
> >> exception raised inside the JITTED code and should also catched
there.
> >>
> >> I tried loading the "msvcrt.lib" as a archive. That
was... a bad idea! I
> >> get a Exception while loading:
> >> Assertion failed: ((int64_t)Result <= INT32_MAX) &&
"Relocation
> overflow",
> >> file
\lib\executionengine\runtimedyld\Targets/RuntimeDyldCOFFX86_64.h,
> line
> >> 81
> >>
> >> Research didn't helped me! My code was compiled with /MD, but
it didn't
> >> changed. So I'm still stupid D:
> >> The JITTED code must be loaded to shared memory later - there
aren't
> >> libraries, so even if this would work, it wouldn't help me. I
tried
> >> compiling my code with sjlj-exceptions. Didn't worked...
> >>
> >> Is there no hope left?
> >>
> >> Kind regards
> >> Björn
> >>
> >>
> >>
> >> From:        Stefan Gränitz <stefan.graenitz at gmail.com>
> >> To:        bjoern.gaier at horiba.com, llvm-dev at lists.llvm.org
> >> Date:        27.09.2017 23:09
> >> Subject:        Re: [llvm-dev] Clang/LLVM JIT - When to use
> >> "registerEHFrames()"
> >> ________________________________
> >>
> >>
> >>
> >> Hi Björn
> >>
> >> To first answer your questionin the subject: For x86
registerEHFrames()
> is
> >> only a stub. For x86_64 registerEHFrames() is implemented properly
in
> >> RuntimeDyldCOFFX86_64, calling MemMgr.registerEHFrames() for each
EH
> frame
> >> section. It should be called and work out of the box without your
> >> involvement, but unfortunately it won't solve your issue. All
the
> essential
> >> information is there in the comments, just check the base classes.
> >>
> >> This thread from last year helps with your unresolved symbol:
> >> http://lists.llvm.org/pipermail/llvm-dev/2016-October/106458.html
> >>
> >> Back then I tried to solve a related issue: SEH exceptions thrown
from
> >> code loaded with RuntimeDyld had to be caught in statically
compiled
> code.
> >> It turned out Windows explicitly prohibits this. I got in touch
with
> >> Microsoft people and IIRC it's due to security concerns.
> >>
> >> Depending on your specific case, you may want to fall back to
vectored
> >> exception handling. In my experience this was a dead end though.
If you
> need
> >> a solution for arbitrary situations, you just can't jump back
to a
> "safe"
> >> place to continue execution. I tried setjump (on each entry point
to the
> >> dynamically loaded code) / longjmp (in the vectored exception
handler),
> but
> >> the address was invalidated when I accessed it. I suspect it's
kind of
> >> undefined behavior to call longjmp outside a child frame of the
function
> >> that called setjmp. Anyway it turned all far too hacky.
> >>
> >> If you are willing to do research, compare implementations and
behavior
> >> with the MachO and ELF versions. At least one of them works, just
not on
> >> Windows ;)
> >> Also check the LLILC project: https://github.com/dotnet/llilc I
heard
> >> about some solution that uses trampolines to push exceptions back
to
> >> dynamically loaded code and handle them there.
> >>
> >> AND disclaimer: I did not follow recent developments in this area.
If
> >> there's news please let me know!
> >>
> >> Cheers & Good Luck!
> >> Stefan
> >>
> >> Am 25.09.17 um 11:31 schrieb via llvm-dev:
> >> Hello friendly LLVM-World,
> >>
> >> because I don't know if I had send my problem to the correct
> Mailing-List,
> >> I will send my problem to this address too. I'm not subscribed
to this
> list,
> >> so please add my in CC if you response.
> >>
> >> Kind regards
> >> Björn
> >>
> >>
> >> From:        Bjoern Gaier/HE/HORIBA
> >> To:        Clang Dev <cfe-dev at lists.llvm.org>,
"cfe-dev"
> >> <cfe-dev-bounces at lists.llvm.org>
> >> Date:        19.09.2017 08:05
> >> Subject:        Clang/LLVM JIT - When to use
"registerEHFrames()"
> >>
> >> ________________________________
> >>
> >>
> >> Hello friendly Clang-World,
> >>
> >> I was experimenting with Clang and the JIT capabilities of LLVM.
Most of
> >> my attempts were successfully but, I still fail miserably at
exceptions.
> >> Doing research I found the function "registerEHFrames()"
which should
> assist
> >> me supporting exceptions - but sadly the documentation I found
wasn't
> >> helpful.
> >> I looked at into the "notifyObjectLoaded" function and
discovered that
> >> there appear some symbol names starting with "$" - I
expected them to be
> >> connected to my try and catch block. But what now? As usually, at
this
> point
> >> I have there names, but can't get there address to register
them with
> the
> >> "registerEHFrames()" function. Also the JITTER still
wants an address
> for
> >> "??_7type_info@@6B@" which is the virtual table of the
type_info
> struct.
> >>
> >> Confusing! So friendly Clang-World, could you please help?
> >>
> >> Not so important - but has the dragon which decorates clang and
LLVM a
> >> name?
> >>
> >> Kind regards
> >> Björn
> >>
> >> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB
9816,
> >> USt.ID-Nr. DE 114 165 789
> >> Geschäftsführer: Hiroshi Kawamura, Dr Hiroshi Nakamura, Markus
Bode,
> Heiko
> >> Lampert, Takashi Nagano, Takeshi Fukushima.
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
> >> --
> >> https://weliveindetail.github.io/blog/
> >> https://cryptup.org/pub/stefan.graenitz at gmail.com
> >>
> >>
> >> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB
9816,
> >> USt.ID-Nr. DE 114 165 789
> >> Geschäftsführer: Hiroshi Kawamura, Dr Hiroshi Nakamura, Markus
Bode,
> Heiko
> >> Lampert, Takashi Nagano, Takeshi Fukushima.
> >>
> >>
> >> --
> >> https://weliveindetail.github.io/blog/
> >> https://cryptup.org/pub/stefan.graenitz at gmail.com
> >>
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
> >
> >
> > --
> > https://weliveindetail.github.io/blog/
> > https://cryptup.org/pub/stefan.graenitz at gmail.com
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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That's encouraging.

Assuming that all access to the JITted code is going to be done
through a function pointer, and all JIT code is ephemeral, why is the
object container format important? In fact, why is it even needed? I
found it somewhat odd that MCJIT generates an object file for even the
JIT case.

To answer my own question, could it be that advanced JIT's may
need/want to use things available inside the object code format?

So I guess my real question is what are the practical limitations of
using the ELF object code format to generate JIT code when all
observable access to the code will be through its entry point.

P.S. - I'm also assuming that the ELF object container format does not
drive the code-generation triple, i.e. we generate Windows ABI
Compatible code even when using the RuntimeDyIDELF.

On Tue, Oct 3, 2017 at 10:17 PM, Jameson Nash <vtjnash at gmail.com>
wrote:
> In partial answer to your question, I can state that JuliaLang has been
> successfully registering and handling exceptions in JIT code since LLVM
3.3,
> when I implemented support (with varying levels of hackiness over time to
> support all of the JIT and other changes to LLVM since then). However note
> that to hook it all up we use the ELF format and have our own exception
> format + personality routine and a custom memory manager.
>
>
> On Tue, Oct 3, 2017 at 12:36 AM Hayden Livingston via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> I'm catching up on this. Does this mean LLVM x64 JITTed code is not
>> exception friendly or you can't catch exceptions inside LLVM JITTed
>> code. The first one seems to indicate that the code is not ABI
>> friendly or that not enough information is present to notify Windows
>> of unwind tables.
>>
>> I'll ask the question another way: Does LLVM emit enough
information
>> so that RtlAddFunctionTable can work? Anyone successfully done this in
>> the wild?
>>
>> On Sun, Oct 1, 2017 at 7:16 AM, Stefan Gränitz via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > Hi, I checked last year's mails. Back then Timur and me faced
the same
>> > issue
>> > Björn reports (nulled memory in _ThrowInfo).
>> >
>> >> Back then I tried to solve a related issue: SEH exceptions
thrown from
>> >> code loaded with RuntimeDyld had to be caught in statically
compiled
>> >> code.
>> >> It turned out Windows explicitly prohibits this. I got in
touch with
>> >> Microsoft people and IIRC it's due to security concerns.
>> >
>> >
>> > Stefan -- That's an interesting restriction. :/
>> > Does it prohibit exceptions thrown in JIT'd code from being
caught also
>> > in
>> > JIT'd code, or does it only apply if an exception crosses the
boundary
>> > back
>> > into statically compiled code?
>> > Do you know how they were enforcing that?
>> >
>> > Igor Minin explained this was due to Data Execution Prevention
(DEP) and
>> > gave pointers to the involved functions in the OS runtime:
>> > http://lists.llvm.org/pipermail/llvm-dev/2016-June/100901.html
>> >
>> > The whole thing gets hairy quickly. It seems like a combination of
>> > multiple
>> > problems. So let's first collect evidence and clarify the
goal.
>> >
>> > Joseph Tremoulet from Microsoft partially confirmed Igor's
statements:
>> > "I checked with some experts here, and they agree with
your/Igor’s
>> > assessment that it’s not possible to have a dynamically generated
>> > handler on
>> > x86"
>> > "the llilc code only handles x86_64, not 32-bit x86; I know
the
>> > implementations of WinEH are quite different between the two"
>> > First conclusion: No solution for JITed catch handlers on x86.
>> >
>> > I think for most of us x86 has little prio anyway, so let's
focus on
>> > x86_64.
>> > In theory both, JITed and static catch handlers, may be possible
here.
>> >
>> > I disabled DEP globally on my machine and set
MEM_EXECUTE_OPTION_ENABLE
>> > explicitly:
>> > http://www.thewindowsclub.com/disable-data-execution-prevention
>> >
https://github.com/Sh1ft0x0EF/metahook/blob/master/sys_launcher.cpp#L65
>> > It didn't fix anything.
>> > Second conclusion: DEP may be one reason, but there must be
something
>> > else.
>> >
>> > My next guess was an incompatibility between Clang (we used for
JITing)
>> > and
>> > MSVC (we used for static compilation). Joseph:
>> > "One thing that comes to mind is that presumably you’re not
trying to
>> > make
>> > your language/runtime’s exceptions masquerade as MSVC++
exceptions, so I
>> > guess you’d want your static native code to either have an SEH
>> > __try/__except or compile with clang’s equivalents of MSVC’s /EHa
and
>> > catch(…)"
>> >
>> > I tried all the combinations without success. I also compared the
>> > compiled
>> > code between Clang 3.8 and MSVC, which showed no reasonable
difference.
>> > Second conclusion: No issue with code generation.
>> >
>> > At that point we ran out of time we could spend on this. So we
postponed
>> > the
>> > feature, hoping for Microsoft to come up with a solution at some
point.
>> > Giving it another try today, I think this looks promising:
>> >
>> >
https://github.com/dotnet/llilc/blob/master/lib/Jit/EEMemoryManager.cpp#L250
>> >
>> > Processing .pdata section entries, it creates and allocates unwind
>> > blocks
>> > and funclets (handlers for catch & finally) for CLR managed
exceptions.
>> > It's
>> > probably not directly applicable to native exception handling, but
it
>> > may
>> > provide useful information. Also there is much more documentation
>> > available
>> > now:
>> >
>> >
https://github.com/dotnet/coreclr/blob/master/Documentation/botr/clr-abi.md#exception-handling
>> >
>> >
https://llvm.org/docs/ExceptionHandling.html#exception-handling-using-the-windows-runtime
>> >
>> > I could imagine setting up minimal tests would be a useful first
step to
>> > distinguish issues in a reproducible way.
>> >
>> > Best
>> > Stefan
>> >
>> > Am 29.09.17 um 19:43 schrieb Lang Hames:
>> >
>> > Hi Bjoern,
>> >
>> >> I'm trying to make exceptions run. I have an Object file
with a
>> >> function,
>> >> throwing a 1 and a second function which should catch the 1.
Normal
>> >> JITTING
>> >> under Windows showed me, that I have an unresolved reference
to the
>> >> virtual
>> >> table of type_info. Some experiments later I was able to load
>> >> "msvcrt.lib"
>> >> as an archive and could resolve the reference. Nice - but than
>> >> "??_Etype_info@@UEAPEAXI at Z" was missing too.
Ufff! I decided to ignore
>> >> this.
>> >> Because, when I try to load every .lib and .obj provided by
Visual
>> >> Studio, I
>> >> get an assertion failure with "Relocation type not
implemented yet!".
>> >
>> >
>> > RuntimeDyldCOFF is missing a lot of relocation support. We need a
COFF
>> > expert to fix that and unfortunately I'm not one.
>> >
>> >> I decided to have a look at "_CxxThrowException". I
inserted my own
>> >> function for the JIT and had a look at the parameters. I got
two of
>> >> them.
>> >> The first was the address of the Exception-Object, which was
correct.
>> >> The
>> >> second is the address for the "_ThrowInfo". This
address was valid too,
>> >> but
>> >> all its members - except from attributes - are null. So I
can't throw
>> >> this
>> >> Exception. I tried to pass the address of typeid(1) to it, or
>> >> modificate the
>> >> call. Nothing helped.
>> >
>> >
>> > I don't know windows exception handling well, but if it's
anything like
>> > DWARF EH then I'd be inclined to blame the missing
relocations/fixups --
>> > the
>> > _ThrowInfo struct (or whatever data-source ultimately populates
it)
>> > probably
>> > isn't being fixed up.
>> >
>> >> I have no clue and no idea anymore. So... Do you have an idea?
>> >
>> >
>> > I'm afraid I don't personally. We need some windows linker
/ system
>> > experts
>> > to take an interest in the JIT.
>> >
>> >> Back then I tried to solve a related issue: SEH exceptions
thrown from
>> >> code loaded with RuntimeDyld had to be caught in statically
compiled
>> >> code.
>> >> It turned out Windows explicitly prohibits this. I got in
touch with
>> >> Microsoft people and IIRC it's due to security concerns.
>> >
>> >
>> > Stefan -- That's an interesting restriction. :/
>> > Does it prohibit exceptions thrown in JIT'd code from being
caught also
>> > in
>> > JIT'd code, or does it only apply if an exception crosses the
boundary
>> > back
>> > into statically compiled code?
>> > Do you know how they were enforcing that?
>> >
>> > Cheers,
>> > Lang.
>> >
>> >
>> >
>> >
>> >
>> > On Thu, Sep 28, 2017 at 12:37 PM, Stefan Gränitz via llvm-dev
>> > <llvm-dev at lists.llvm.org> wrote:
>> >>
>> >> I tried loading the "msvcrt.lib" as a archive. That
was... a bad idea!
>> >> I
>> >> get a Exception while loading:
>> >> Assertion failed: ((int64_t)Result <= INT32_MAX) &&
"Relocation
>> >> overflow",
>> >> file
\lib\executionengine\runtimedyld\Targets/RuntimeDyldCOFFX86_64.h,
>> >> line
>> >> 81
>> >>
>> >> It's a limitation of the COFF/PE format and unrelated to
exceptions.
>> >> This
>> >> patch explains it and shows a workaround:
>> >>
>> >>
>> >>
https://github.com/weliveindetail/pj-llvm/commit/97cd336d458ae9c73232d1b539ceefcdb2f5eb0f
>> >>
>> >> Is there no hope left?
>> >>
>> >> Well at least I am not aware of a solution.
>> >>
>> >> Am 28.09.17 um 16:04 schrieb bjoern.gaier at horiba.com:
>> >>
>> >> Hello Stefan,
>> >>
>> >> I'm happy someone replied to my problem! Many thanks! To
be honest... I
>> >> didn't understood much of your mail. I'm a beginner
with the JIT - so I
>> >> will
>> >> explain what I've done.
>> >>
>> >> To manage the memory and resolve symbols, I'm using my own
>> >> Resolver-Class,
>> >> which overloads the allocation and the findSymbol functions.
I've
>> >> noticed
>> >> today, that the "registerEHFrames" function of my
class gets called
>> >> automatically, with correct values. I'm remapping my code
and the
>> >> address
>> >> are still correct. Great! But, what should I do with it? I
pass the
>> >> values
>> >> to the original function, but my exception won't be
caught! It's an
>> >> exception raised inside the JITTED code and should also
catched there.
>> >>
>> >> I tried loading the "msvcrt.lib" as a archive. That
was... a bad idea!
>> >> I
>> >> get a Exception while loading:
>> >> Assertion failed: ((int64_t)Result <= INT32_MAX) &&
"Relocation
>> >> overflow",
>> >> file
\lib\executionengine\runtimedyld\Targets/RuntimeDyldCOFFX86_64.h,
>> >> line
>> >> 81
>> >>
>> >> Research didn't helped me! My code was compiled with /MD,
but it didn't
>> >> changed. So I'm still stupid D:
>> >> The JITTED code must be loaded to shared memory later - there
aren't
>> >> libraries, so even if this would work, it wouldn't help
me. I tried
>> >> compiling my code with sjlj-exceptions. Didn't worked...
>> >>
>> >> Is there no hope left?
>> >>
>> >> Kind regards
>> >> Björn
>> >>
>> >>
>> >>
>> >> From:        Stefan Gränitz <stefan.graenitz at
gmail.com>
>> >> To:        bjoern.gaier at horiba.com, llvm-dev at
lists.llvm.org
>> >> Date:        27.09.2017 23:09
>> >> Subject:        Re: [llvm-dev] Clang/LLVM JIT - When to use
>> >> "registerEHFrames()"
>> >> ________________________________
>> >>
>> >>
>> >>
>> >> Hi Björn
>> >>
>> >> To first answer your questionin the subject: For x86
registerEHFrames()
>> >> is
>> >> only a stub. For x86_64 registerEHFrames() is implemented
properly in
>> >> RuntimeDyldCOFFX86_64, calling MemMgr.registerEHFrames() for
each EH
>> >> frame
>> >> section. It should be called and work out of the box without
your
>> >> involvement, but unfortunately it won't solve your issue.
All the
>> >> essential
>> >> information is there in the comments, just check the base
classes.
>> >>
>> >> This thread from last year helps with your unresolved symbol:
>> >>
http://lists.llvm.org/pipermail/llvm-dev/2016-October/106458.html
>> >>
>> >> Back then I tried to solve a related issue: SEH exceptions
thrown from
>> >> code loaded with RuntimeDyld had to be caught in statically
compiled
>> >> code.
>> >> It turned out Windows explicitly prohibits this. I got in
touch with
>> >> Microsoft people and IIRC it's due to security concerns.
>> >>
>> >> Depending on your specific case, you may want to fall back to
vectored
>> >> exception handling. In my experience this was a dead end
though. If you
>> >> need
>> >> a solution for arbitrary situations, you just can't jump
back to a
>> >> "safe"
>> >> place to continue execution. I tried setjump (on each entry
point to
>> >> the
>> >> dynamically loaded code) / longjmp (in the vectored exception
handler),
>> >> but
>> >> the address was invalidated when I accessed it. I suspect
it's kind of
>> >> undefined behavior to call longjmp outside a child frame of
the
>> >> function
>> >> that called setjmp. Anyway it turned all far too hacky.
>> >>
>> >> If you are willing to do research, compare implementations and
behavior
>> >> with the MachO and ELF versions. At least one of them works,
just not
>> >> on
>> >> Windows ;)
>> >> Also check the LLILC project: https://github.com/dotnet/llilc
I heard
>> >> about some solution that uses trampolines to push exceptions
back to
>> >> dynamically loaded code and handle them there.
>> >>
>> >> AND disclaimer: I did not follow recent developments in this
area. If
>> >> there's news please let me know!
>> >>
>> >> Cheers & Good Luck!
>> >> Stefan
>> >>
>> >> Am 25.09.17 um 11:31 schrieb via llvm-dev:
>> >> Hello friendly LLVM-World,
>> >>
>> >> because I don't know if I had send my problem to the
correct
>> >> Mailing-List,
>> >> I will send my problem to this address too. I'm not
subscribed to this
>> >> list,
>> >> so please add my in CC if you response.
>> >>
>> >> Kind regards
>> >> Björn
>> >>
>> >>
>> >> From:        Bjoern Gaier/HE/HORIBA
>> >> To:        Clang Dev <cfe-dev at lists.llvm.org>,
"cfe-dev"
>> >> <cfe-dev-bounces at lists.llvm.org>
>> >> Date:        19.09.2017 08:05
>> >> Subject:        Clang/LLVM JIT - When to use
"registerEHFrames()"
>> >>
>> >> ________________________________
>> >>
>> >>
>> >> Hello friendly Clang-World,
>> >>
>> >> I was experimenting with Clang and the JIT capabilities of
LLVM. Most
>> >> of
>> >> my attempts were successfully but, I still fail miserably at
>> >> exceptions.
>> >> Doing research I found the function
"registerEHFrames()" which should
>> >> assist
>> >> me supporting exceptions - but sadly the documentation I found
wasn't
>> >> helpful.
>> >> I looked at into the "notifyObjectLoaded" function
and discovered that
>> >> there appear some symbol names starting with "$" - I
expected them to
>> >> be
>> >> connected to my try and catch block. But what now? As usually,
at this
>> >> point
>> >> I have there names, but can't get there address to
register them with
>> >> the
>> >> "registerEHFrames()" function. Also the JITTER still
wants an address
>> >> for
>> >> "??_7type_info@@6B@" which is the virtual table of
the type_info
>> >> struct.
>> >>
>> >> Confusing! So friendly Clang-World, could you please help?
>> >>
>> >> Not so important - but has the dragon which decorates clang
and LLVM a
>> >> name?
>> >>
>> >> Kind regards
>> >> Björn
>> >>
>> >> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB
9816,
>> >> USt.ID-Nr. DE 114 165 789
>> >> Geschäftsführer: Hiroshi Kawamura, Dr Hiroshi Nakamura, Markus
Bode,
>> >> Heiko
>> >> Lampert, Takashi Nagano, Takeshi Fukushima.
>> >>
>> >> _______________________________________________
>> >> LLVM Developers mailing list
>> >> llvm-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >> --
>> >> https://weliveindetail.github.io/blog/
>> >> https://cryptup.org/pub/stefan.graenitz at gmail.com
>> >>
>> >>
>> >> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB
9816,
>> >> USt.ID-Nr. DE 114 165 789
>> >> Geschäftsführer: Hiroshi Kawamura, Dr Hiroshi Nakamura, Markus
Bode,
>> >> Heiko
>> >> Lampert, Takashi Nagano, Takeshi Fukushima.
>> >>
>> >>
>> >> --
>> >> https://weliveindetail.github.io/blog/
>> >> https://cryptup.org/pub/stefan.graenitz at gmail.com
>> >>
>> >>
>> >> _______________________________________________
>> >> LLVM Developers mailing list
>> >> llvm-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >
>> >
>> > --
>> > https://weliveindetail.github.io/blog/
>> > https://cryptup.org/pub/stefan.graenitz at gmail.com
>> >
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev