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

Historically? I implemented support for exceptions back in LLVM 3.3, before
LLVM had an implementation of a Windows unwinder.

Currently? As recent as LLVM 4.0, I don't think the JIT was fully capable
of handling COFF files, and LLVM wouldn't emit the correct sections (with
the COFF-formatted unwind tables) when used in ELF mode.

The prolog is known to be standard since Julia disables FPO on all code, so
the hand-coded values simply needed to declare that to the unwinder.
Windows doesn't have epilog records (it instead infers them from the
structure of the assembly itself, and requires that LLVM only generate
function returns using a particular finite set of instructions), so that
has to be handled elsewhere during machine code selection/emission.


On Tue, Oct 10, 2017 at 11:07 AM Hayden Livingston <halivingston at
gmail.com>
wrote:
> Julia is a language, and you can use their code.
>
> Jameson Nash, could you please let us know why Julia's code has hard
> coded values for the unwinding? Is your prolog/epilog some standard
> one?
>
> On Fri, Oct 6, 2017 at 2:47 AM,  <bjoern.gaier at horiba.com> wrote:
> > Hello everyone,
> >
> > I was following the discussion, but I have to admit, that my skills
> aren't
> > high enough to follow you guys. For my current exception problem, I
don't
> > have to stick around with the PECOFF format, so I used clang to
don't
> > compile to a PECOFF, but to a ELF file. Interesting, now I'm
missing the
> > functions:
> > __cxa_allocate_exception
> > __cxa_throw
> > _ZTI
> >
> > I loaded the DLL "libstdc++.dll" and found all of the
addresses - but the
> > application still crashes when the exception is thrown.
> >
> > So... Do you think, that "Julias Code" could help me? You
mentioned her
> in
> > one of the mails, but I don't know her - or her code.
> >
> > Also, is it a better idea to compile all dynamic code to the ELF
format,
> > because PECOFF isn't fully supported?
> >
> > 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.
>
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I'm losing track a little bit...

So... there is no way to make throw and catch working in a jitted code 
under Windows?

Also - to get rid of reallocation problems, it's no help to compile to 
.elf files?

(Sorry Mr. Nash >.<)



From:   Jameson Nash <vtjnash at gmail.com>
To:     Hayden Livingston <halivingston at gmail.com>, 
bjoern.gaier at horiba.com
Cc:     LLVM Developers Mailing List <llvm-dev at lists.llvm.org>, Stefan 
Gränitz <stefan.graenitz at gmail.com>
Date:   16.10.2017 23:04
Subject:        Re: [llvm-dev] Clang/LLVM JIT - When to use 
"registerEHFrames()"



Historically? I implemented support for exceptions back in LLVM 3.3, 
before LLVM had an implementation of a Windows unwinder.

Currently? As recent as LLVM 4.0, I don't think the JIT was fully capable 
of handling COFF files, and LLVM wouldn't emit the correct sections (with 
the COFF-formatted unwind tables) when used in ELF mode.

The prolog is known to be standard since Julia disables FPO on all code, 
so the hand-coded values simply needed to declare that to the unwinder. 
Windows doesn't have epilog records (it instead infers them from the 
structure of the assembly itself, and requires that LLVM only generate 
function returns using a particular finite set of instructions), so that 
has to be handled elsewhere during machine code selection/emission.


On Tue, Oct 10, 2017 at 11:07 AM Hayden Livingston <halivingston at
gmail.com
> wrote:
Julia is a language, and you can use their code.

Jameson Nash, could you please let us know why Julia's code has hard
coded values for the unwinding? Is your prolog/epilog some standard
one?

On Fri, Oct 6, 2017 at 2:47 AM,  <bjoern.gaier at horiba.com>
wrote:
> Hello everyone,
>
> I was following the discussion, but I have to admit, that my skills 
aren't
> high enough to follow you guys. For my current exception problem, I 
don't
> have to stick around with the PECOFF format, so I used clang to don't
> compile to a PECOFF, but to a ELF file. Interesting, now I'm missing
the
> functions:
> __cxa_allocate_exception
> __cxa_throw
> _ZTI
>
> I loaded the DLL "libstdc++.dll" and found all of the addresses -
but
the
> application still crashes when the exception is thrown.
>
> So... Do you think, that "Julias Code" could help me? You
mentioned her
in
> one of the mails, but I don't know her - or her code.
>
> Also, is it a better idea to compile all dynamic code to the ELF format,
> because PECOFF isn't fully supported?
>
> 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.

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.
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> So... there is no way to make throw and catch working in a jitted code
> under Windows?
>
I have used throw and catch in jitted code, so "no way" is too strong.
But
there's a large range of possible states between "no way" and
"always
enabled OOTB". Currently, this is pretty close to the "mostly
unimplemented" side of the spectrum in LLVM.

Also - to get rid of reallocation problems, it's no help to compile to
.elf
> files?
>
I never dug through the spec fully, but if I remember correctly, ELF does
not support the relocation type that is required by the Windows unwind
table specification (specifically, 32-bit image-base relative). So yes,
this would get rid of relocation problems. But it might then be tricky to
build the unwind information. (Perhaps this wouldn't be feasible in a
static environment, but it's possible in a JIT environment, since this is
indeed how it's done in JuliaLang).

>
> From:        Jameson Nash <vtjnash at gmail.com>
> To:        Hayden Livingston <halivingston at gmail.com>,
> bjoern.gaier at horiba.com
> Cc:        LLVM Developers Mailing List <llvm-dev at lists.llvm.org>,
Stefan
> Gränitz <stefan.graenitz at gmail.com>
> Date:        16.10.2017 23:04
> Subject:        Re: [llvm-dev] Clang/LLVM JIT - When to use
> "registerEHFrames()"
> ------------------------------
>
>
>
> Historically? I implemented support for exceptions back in LLVM 3.3,
> before LLVM had an implementation of a Windows unwinder.
>
> Currently? As recent as LLVM 4.0, I don't think the JIT was fully
capable
> of handling COFF files, and LLVM wouldn't emit the correct sections
(with
> the COFF-formatted unwind tables) when used in ELF mode.
>
> The prolog is known to be standard since Julia disables FPO on all code,
> so the hand-coded values simply needed to declare that to the unwinder.
> Windows doesn't have epilog records (it instead infers them from the
> structure of the assembly itself, and requires that LLVM only generate
> function returns using a particular finite set of instructions), so that
> has to be handled elsewhere during machine code selection/emission.
>
>
> On Tue, Oct 10, 2017 at 11:07 AM Hayden Livingston <
> *halivingston at gmail.com* <halivingston at gmail.com>> wrote:
> Julia is a language, and you can use their code.
>
> Jameson Nash, could you please let us know why Julia's code has hard
> coded values for the unwinding? Is your prolog/epilog some standard
> one?
>
> On Fri, Oct 6, 2017 at 2:47 AM,  <*bjoern.gaier at horiba.com*
> <bjoern.gaier at horiba.com>> wrote:
> > Hello everyone,
> >
> > I was following the discussion, but I have to admit, that my skills
> aren't
> > high enough to follow you guys. For my current exception problem, I
don't
> > have to stick around with the PECOFF format, so I used clang to
don't
> > compile to a PECOFF, but to a ELF file. Interesting, now I'm
missing the
> > functions:
> > __cxa_allocate_exception
> > __cxa_throw
> > _ZTI
> >
> > I loaded the DLL "libstdc++.dll" and found all of the
addresses - but the
> > application still crashes when the exception is thrown.
> >
> > So... Do you think, that "Julias Code" could help me? You
mentioned her
> in
> > one of the mails, but I don't know her - or her code.
> >
> > Also, is it a better idea to compile all dynamic code to the ELF
format,
> > because PECOFF isn't fully supported?
> >
> > 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.
>
>
> 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.
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