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<div class="moz-cite-prefix">Hi Lang,<br>
<br>
Lang Hames schrieb:<br>
</div>
<blockquote
cite="mid:CALLttgr14eASd989Vdw_UG-=Rdq1rZwEA0_nzx3kz-rLSnbcPw@mail.gmail.com"
type="cite">
<div dir="ltr">Hi Armin,
<div><br>
</div>
<div>> The MCJIT API can only be used once to JIT compile
external souces to excuteable code into the address space of a
running process.<br>
</div>
</div>
</blockquote>
<br>
That means: after the first successfull JIT compile it isn't
possible to do it again (within the same active process) ... because
of some resource issues.<br>
<br>
<blockquote
cite="mid:CALLttgr14eASd989Vdw_UG-=Rdq1rZwEA0_nzx3kz-rLSnbcPw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">I'm not sure exactly what you mean by
"can only be used once" in this context. Regardless, the new
APIs are definitely designed to make it easier to lead, unload
and replace modules, and I hope they will support a wider
range of use cases off-the-shelf than MCJIT does.</div>
</div>
</blockquote>
<br>
OK ... sound interesting, I will test it.<br>
<br>
<br>
Regards<br>
<br>
Armin <br>
<br>
<br>
<blockquote
cite="mid:CALLttgr14eASd989Vdw_UG-=Rdq1rZwEA0_nzx3kz-rLSnbcPw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">Cheers,</div>
<div class="gmail_extra">Lang.</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Jan 16, 2015 at 2:41 AM,
Armin Steinhoff <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:armin@steinhoff.de"
target="_blank">armin@steinhoff.de</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div><br>
Hi Lang,<br>
<br>
we are using the JIT API of TCC and the MCJIT API in
order to import external code into a running control
application process.<br>
<br>
The MCJIT API can only be used once to JIT compile
external souces to excuteable code into the address
space of a running process.<br>
<br>
Has your JIT API the same restriction ? It would be
very nice if your JIT API could provide a similar
functionalty as provided by TCC.<br>
<br>
Best Regards<br>
<br>
Armin<br>
<br>
<br>
Lang Hames schrieb:<br>
</div>
<blockquote type="cite">
<div dir="ltr"><span class="">
<div style="font-size:13px">Hi All,<br>
</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">The attached patch
(against r225842) contains some new JIT APIs
that I've been working on. I'm going to start
breaking it up, tidying it up, and submitting
patches to llvm-commits soon, but while I'm
working on that I thought I'd put the whole
patch out for the curious to start playing
around with and/or commenting on.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">The aim of these new
APIs is to cleanly support a wider range of JIT
use cases in LLVM, and to recover some of the
functionality lost when the legacy JIT was
removed. In particular, I wanted to see if I
could re-enable lazy compilation while following
MCJIT's design philosophy of relying on the MC
layer and module-at-a-time compilation. The
attached patch goes some way to addressing these
aims, though there's a lot still to do.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">The 20,000 ft
overview, for those who want to get straight to
the code:</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">The new APIs are not
built on top of the MCJIT class, as I didn't
want a single class trying to be all things to
all people. Instead, the new APIs consist of a
set of software components for building JITs.
The idea is that you should be able to take
these off the shelf and compose them reasonably
easily to get the behavior that you want. In the
future I hope that people who are working on
LLVM-based JITs, if they find this approach
useful, will contribute back components that
they've built locally and that they think would
be useful for a wider audience. As a
demonstration of the practicality of this
approach the attached patch contains a class,
MCJITReplacement, that composes some of the
components to re-create the behavior of MCJIT.
This works well enough to pass all MCJIT
regression and unit tests on Darwin, and all but
four regression tests on Linux. The patch also
contains the desired "new" feature:
Function-at-a-time lazy jitting in roughly the
style of the legacy JIT. The attached
lazydemo.tgz file contains a program which
composes the new JIT components (including the
lazy-jitting component) to lazily execute
bitcode. I've tested this program on Darwin and
it can run non-trivial benchmark programs, e.g.
401.bzip2 from SPEC2006.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">These new APIs are
named after the motivating feature: On Request
Compilation, or ORC. I believe the logo
potential is outstanding. I'm picturing an Orc
riding a Dragon. If I'm honest this was at least
45% of my motivation for doing this project*.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">You'll find the new
headers in
llvm/include/llvm/ExecutionEngine/OrcJIT/*.h,
and the implementation files in
lib/ExecutionEngine/OrcJIT/*.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">I imagine there will
be a number of questions about the design and
implementation. I've tried to preempt a few
below, but please fire away with anything I've
left out.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">Also, thanks to Jim
Grosbach, Michael Illseman, David Blaikie, Pete
Cooper, Eric Christopher, and Louis Gerbarg for
taking time out to review, discuss and test this
thing as I've worked on it.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">Cheers,</div>
<div style="font-size:13px">Lang.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">Possible questions:</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(1)</div>
<div style="font-size:13px">Q. Are you trying to
kill off MCJIT?</div>
<div style="font-size:13px">A. There are no plans
to remove MCJIT. The new APIs are designed to
live alongside it.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(2)</div>
<div style="font-size:13px">Q. What do "JIT
components" look like, and how do you compose
them?<br>
</div>
<div style="font-size:13px">A. The classes and
functions you'll find in OrcJIT/*.h fall into
two rough categories: Layers and Utilities.
Layers are classes that implement a small common
interface that makes them easy to compose:<br>
</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">class SomeLayer {</div>
<div style="font-size:13px">private:</div>
</span>
<div style="font-size:13px"> // Implementation
details</div>
<div style="font-size:13px">public:</div>
<div style="font-size:13px"> // Implementation
details</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px"> typedef ??? Handle;</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px"> template
<typename ModuleSet></div>
<div style="font-size:13px"> Handle
addModuleSet(ModuleSet&& Ms);</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px"> void
removeModuleSet(Handle H);</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px"> uint64_t
getSymbolAddress(StringRef Name, bool
ExportedSymbolsOnly);</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px"> uint64_t
lookupSymbolAddressIn(Handle H, StringRef Name,
bool ExportedSymbolsOnly);</div>
<span class="">
<div style="font-size:13px">};</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">Layers are usually
designed to sit one-on-top-of-another, with each
doing some sort of useful work before handing
off to the layer below it. The layers that are
currently included in the patch are the the
CompileOnDemandLayer, which breaks up modules
and redirects calls to not-yet-compiled
functions back into the JIT; the LazyEmitLayer,
which defers adding modules to the layer below
until a symbol in the module is actually
requested; the IRCompilingLayer, which compiles
bitcode to objects; and the ObjectLinkingLayer,
which links sets of objects in memory using
RuntimeDyld.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">Utilities are
everything that's not a layer. Ideally the heavy
lifting is done by the utilities. Layers just
wrap certain uses-cases to make them easy to
compose.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">Clients are free to
use utilities directly, or compose layers, or
implement new utilities or layers.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(3)</div>
<div style="font-size:13px">Q. Why "addModuleSet"
rather than "addModule"?</div>
<div style="font-size:13px">A. Allowing multiple
modules to be passed around together allows
layers lower in the stack to perform interesting
optimizations. E.g. direct calls between objects
that are allocated sufficiently close in memory.
To add a single Module you just add a
single-element set.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(4)</div>
<div style="font-size:13px">Q. What happened to
"finalize"?</div>
<div style="font-size:13px">A. In the Orc APIs,
getSymbolAddress automatically finalizes as
necessary before returning addresses to the
client. When you get an address back from
getSymbolAddress, that address is ready to call.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(5)</div>
<div style="font-size:13px">Q. What does
"removeModuleSet" do?</div>
<div style="font-size:13px">A. It removes the
modules represented by the handle from the JIT.
The meaning of this is specific to each layer,
but generally speaking it means that any memory
allocated for those modules (and their
corresponding Objects, linked sections, etc) has
been freed, and the symbols those modules
provided are now undefined. Calling
getSymbolAddress for a symbol that was defined
in a module that has been removed is expected to
return '0'.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(5a)</div>
<div style="font-size:13px">Q. How are the linked
sections freed? RTDyldMemoryManager doesn't have
any "free.*Section" methods.</div>
<div style="font-size:13px">A. Each ModuleSet gets
its own RTDyldMemoryManager, and that is
destroyed when the module set is freed. The
choice of RTDyldMemoryManager is up to the
client, but the standard memory managers will
free the memory allocated for the linked
sections when they're destroyed.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(6)</div>
<div style="font-size:13px">Q. How does the
CompileOnDemand layer redirect calls to the JIT?</div>
<div style="font-size:13px">A. It currently uses
double-indirection: Function bodies are
extracted into new modules, and the body of the
original function is replaced with an indirect
call to the extracted body. The pointer for the
indirect call is initialized by the JIT to point
at some inline assembly which is injected into
the module, and this calls back in to the JIT to
trigger compilation of the extracted body. In
the future I plan to make the redirection
strategy a parameter of the CompileOnDemand
layer. Double-indirection is the safest: It
preserves function-pointer equality and works
with non-writable executable memory, however
there's no reason we couldn't use single
indirection (for extra speed where
pointer-equality isn't required), or patchpoints
(for clients who can allocate
writable/executable memory), or any combination
of the three. My intent is that this should be
up to the client.</div>
<div style="font-size:13px"><br>
</div>
</span>
<div style="font-size:13px">As a brief note: it's
worth noting that the CompileOnDemand layer
doesn't handle lazy compilation itself, just lazy
symbol resolution (i.e. symbols are resolved on
first call, not when compiling). If you've put the
CompileOnDemand layer on top of the LazyEmitLayer
then deferring symbol lookup automatically defers
compilation. (E.g. You can remove the
LazyEmitLayer in main.cpp of the lazydemo and
you'll get indirection and callbacks, but no lazy
compilation). </div>
<span class="">
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(7)</div>
<div style="font-size:13px">Q. Do the new APIs
support cross-target JITing like MCJIT does?</div>
<div style="font-size:13px">A. Yes.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(7.a)</div>
<div style="font-size:13px">Q. Do the new APIs
support cross-target (or cross process)
lazy-jitting?</div>
<div style="font-size:13px">A. Not yet, but all
that is required is for us to add a small amount
of runtime to the JIT'd process to call back in
to the JIT via some RPC mechanism. There are no
significant barriers to implementing this that
I'm aware of.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(8)</div>
<div style="font-size:13px">Q. Do any of the
components implement the ExecutionEngine
interface?</div>
<div style="font-size:13px">A. None of the
components do, but the MCJITReplacement class
does.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(9)</div>
<div style="font-size:13px">Q. Does this address
any of the long-standing issues with MCJIT -
Stackmap parsing? Debugging?
Thread-local-storage?</div>
<div style="font-size:13px">A. No, but it doesn't
get in the way either. These features are still
on the road-map (such as it exists) and I'm
hoping that the modular nature of Orc will us to
play around with new features like this without
any risk of disturbing existing clients, and so
allow us to make faster progress.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">(10)</div>
<div style="font-size:13px">Q. Why is part X of
the patch (ugly | buggy | in the wrong place) ?</div>
<div style="font-size:13px">A. I'm still tidying
the patch up - please save patch specific
feedback for for llvm-commits, otherwise we'll
get cross-talk between the threads. The patches
should be coming soon.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">---</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">As mentioned above,
I'm happy to answer further general questions
about what these APIs can do, or where I see
them going. Feedback on the patch itself should
be directed to the llvm-commits list when I
start posting patches there for discussion.</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px"><br>
</div>
<div style="font-size:13px">* Marketing slogans
abound: "Very MachO". "Some warts".
"Surprisingly friendly with ELF". "Not yet on
speaking terms with DWARF".</div>
</span></div>
<br>
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