Hi All,
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.
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.
The 20,000 ft overview, for those who want to get straight to the code:
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.
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*.
You'll find the new headers in
llvm/include/llvm/ExecutionEngine/OrcJIT/*.h, and the implementation files
in lib/ExecutionEngine/OrcJIT/*.
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.
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.
Cheers,
Lang.
Possible questions:
(1)
Q. Are you trying to kill off MCJIT?
A. There are no plans to remove MCJIT. The new APIs are designed to live
alongside it.
(2)
Q. What do "JIT components" look like, and how do you compose them?
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:
class SomeLayer {
private:
// Implementation details
public:
// Implementation details
typedef ??? Handle;
template <typename ModuleSet>
Handle addModuleSet(ModuleSet&& Ms);
void removeModuleSet(Handle H);
uint64_t getSymbolAddress(StringRef Name, bool ExportedSymbolsOnly);
uint64_t lookupSymbolAddressIn(Handle H, StringRef Name, bool
ExportedSymbolsOnly);
};
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.
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.
Clients are free to use utilities directly, or compose layers, or implement
new utilities or layers.
(3)
Q. Why "addModuleSet" rather than "addModule"?
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.
(4)
Q. What happened to "finalize"?
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.
(5)
Q. What does "removeModuleSet" do?
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'.
(5a)
Q. How are the linked sections freed? RTDyldMemoryManager doesn't have any
"free.*Section" methods.
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.
(6)
Q. How does the CompileOnDemand layer redirect calls to the JIT?
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.
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).
(7)
Q. Do the new APIs support cross-target JITing like MCJIT does?
A. Yes.
(7.a)
Q. Do the new APIs support cross-target (or cross process) lazy-jitting?
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.
(8)
Q. Do any of the components implement the ExecutionEngine interface?
A. None of the components do, but the MCJITReplacement class does.
(9)
Q. Does this address any of the long-standing issues with MCJIT - Stackmap
parsing? Debugging? Thread-local-storage?
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.
(10)
Q. Why is part X of the patch (ugly | buggy | in the wrong place) ?
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.
---
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.
* Marketing slogans abound: "Very MachO". "Some warts".
"Surprisingly
friendly with ELF". "Not yet on speaking terms with DWARF".
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On 01/14/2015 12:05 AM, Lang Hames wrote:> Hi All, > > 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. > > 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.In terms of the overall idea, I like what your proposing. However, I want to be very clear: you are not planning on removing any functionality from the existing (fairly low level) MCJIT interface right? We've built our own infrastructure around that and require a few features it doesn't sounds like you're planning on supporting in the new abstractions. (The biggest one is that we "install" code into a different location from where it was compiled.) I really like the idea of having a low level JIT interface for advanced users and an easy starting point for folks getting started.> > The 20,000 ft overview, for those who want to get straight to the code: > > 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. > > 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*. > > You'll find the new headers in > llvm/include/llvm/ExecutionEngine/OrcJIT/*.h, and the implementation > files in lib/ExecutionEngine/OrcJIT/*. > > 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. > > 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. > > Cheers, > Lang. > > Possible questions: > > (1) > Q. Are you trying to kill off MCJIT? > A. There are no plans to remove MCJIT. The new APIs are designed to > live alongside it. > > (2) > Q. What do "JIT components" look like, and how do you compose them? > 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: > > class SomeLayer { > private: > // Implementation details > public: > // Implementation details > > typedef ??? Handle; > > template <typename ModuleSet> > Handle addModuleSet(ModuleSet&& Ms); > > void removeModuleSet(Handle H); > > uint64_t getSymbolAddress(StringRef Name, bool ExportedSymbolsOnly); > > uint64_t lookupSymbolAddressIn(Handle H, StringRef Name, bool > ExportedSymbolsOnly); > }; > > 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. > > 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. > > Clients are free to use utilities directly, or compose layers, or > implement new utilities or layers. > > (3) > Q. Why "addModuleSet" rather than "addModule"? > 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.Please add a utility function for a single Module if you haven't already. For a method based JIT use case, multiple Modules just aren't that useful.> > (4) > Q. What happened to "finalize"? > 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.As long as this is true for the high level API and *not* the low level one (as is true today), this seems fine. I don't really like the finalize mechanism we have, but we do need a mechanism to get at the code before relocations have been applied.> > (5) > Q. What does "removeModuleSet" do? > 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'. > > (5a) > Q. How are the linked sections freed? RTDyldMemoryManager doesn't have > any "free.*Section" methods. > 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. > > (6) > Q. How does the CompileOnDemand layer redirect calls to the JIT? > 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. > > 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). > > (7) > Q. Do the new APIs support cross-target JITing like MCJIT does? > A. Yes. > > (7.a) > Q. Do the new APIs support cross-target (or cross process) lazy-jitting? > 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. > > (8) > Q. Do any of the components implement the ExecutionEngine interface? > A. None of the components do, but the MCJITReplacement class does. > > (9) > Q. Does this address any of the long-standing issues with MCJIT - > Stackmap parsing? Debugging? Thread-local-storage? > 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. > > (10) > Q. Why is part X of the patch (ugly | buggy | in the wrong place) ? > 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. > > --- > > 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. > > > * Marketing slogans abound: "Very MachO". "Some warts". "Surprisingly > friendly with ELF". "Not yet on speaking terms with DWARF". > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150114/afa51146/attachment.html>
Hi Philip, In terms of the overall idea, I like what your proposing. However, I want> to be very clear: you are not planning on removing any functionality from > the existing (fairly low level) MCJIT interface right? >To confirm - I have no plans to remove MCJIT. I don't want to change any behavior for existing clients. The new stuff is opt-in.> We've built our own infrastructure around that and require a few > features it doesn't sounds like you're planning on supporting in the new > abstractions. (The biggest one is that we "install" code into a different > location from where it was compiled.) >Can you clarify what you mean by "install" here? As it stands in the patch, Orc already supports cross-target and out-of-process JITing. The ObjectLinkingLayer exposes the mapSectionAddress call for mapping sections to new locations, and the MCJITReplacement demo passes all remote-jitting regression tests on Darwin. The intent is that Orc should eventually provide a superset of the functionality provided by MCJIT, but with the various features broken out into separate components. I'd be interested to hear about anything that's missing so that I can, if possible, add support for it.> I really like the idea of having a low level JIT interface for advanced > users and an easy starting point for folks getting started. >Ideally I would like Orc to cover the whole spectrum. I'm hoping we can quickly advance to the point where new JIT developers would use Orc by default, rather than MCJIT, and not miss any features. I expect advanced users will want to compose their stacks directly, while beginners would take some common configuration off the shelf. Once these patches are in tree I'm planning to add a basic lazy-jitting stack for Kaleidoscope that beginners could use as a starting point. (3)> Q. Why "addModuleSet" rather than "addModule"? > 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. > > Please add a utility function for a single Module if you haven't already. > For a method based JIT use case, multiple Modules just aren't that useful. >Sure. This problem should be tackled in the wrappers around the components, rather than the components themselves. See MCJITReplacement::addModule for an example.> (4) > Q. What happened to "finalize"? > 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. > > As long as this is true for the high level API and *not* the low level one > (as is true today), this seems fine. I don't really like the finalize > mechanism we have, but we do need a mechanism to get at the code before > relocations have been applied. >You should still be able to intercept events to access memory before finalization. If you can be more specific about your use-case I'd be keen to figure out if/how it could be supported in Orc. - Lang. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150114/bdb366a1/attachment.html>
Hi Lang, we are using the JIT API of TCC and the MCJIT API in order to import external code into a running control application process. The MCJIT API can only be used once to JIT compile external souces to excuteable code into the address space of a running process. 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. Best Regards Armin Lang Hames schrieb:> Hi All, > > 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. > > 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. > > The 20,000 ft overview, for those who want to get straight to the code: > > 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. > > 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*. > > You'll find the new headers in > llvm/include/llvm/ExecutionEngine/OrcJIT/*.h, and the implementation > files in lib/ExecutionEngine/OrcJIT/*. > > 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. > > 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. > > Cheers, > Lang. > > Possible questions: > > (1) > Q. Are you trying to kill off MCJIT? > A. There are no plans to remove MCJIT. The new APIs are designed to > live alongside it. > > (2) > Q. What do "JIT components" look like, and how do you compose them? > 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: > > class SomeLayer { > private: >  // Implementation details > public: >  // Implementation details > >  typedef ??? Handle; > >  template <typename ModuleSet> >  Handle addModuleSet(ModuleSet&& Ms); > >  void removeModuleSet(Handle H); > >  uint64_t getSymbolAddress(StringRef Name, bool ExportedSymbolsOnly); > >  uint64_t lookupSymbolAddressIn(Handle H, StringRef Name, bool > ExportedSymbolsOnly); > }; > > 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. > > 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. > > Clients are free to use utilities directly, or compose layers, or > implement new utilities or layers. > > (3) > Q. Why "addModuleSet" rather than "addModule"? > 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. > > (4) > Q. What happened to "finalize"? > 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. > > (5) > Q. What does "removeModuleSet" do? > 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'. > > (5a) > Q. How are the linked sections freed? RTDyldMemoryManager doesn't have > any "free.*Section" methods. > 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. > > (6) > Q. How does the CompileOnDemand layer redirect calls to the JIT? > 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. > > 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). > > (7) > Q. Do the new APIs support cross-target JITing like MCJIT does? > A. Yes. > > (7.a) > Q. Do the new APIs support cross-target (or cross process) lazy-jitting? > 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. > > (8) > Q. Do any of the components implement the ExecutionEngine interface? > A. None of the components do, but the MCJITReplacement class does. > > (9) > Q. Does this address any of the long-standing issues with MCJIT - > Stackmap parsing? Debugging? Thread-local-storage? > 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. > > (10) > Q. Why is part X of the patch (ugly | buggy | in the wrong place) ? > 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. > > --- > > 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. > > > * Marketing slogans abound: "Very MachO". "Some warts". "Surprisingly > friendly with ELF". "Not yet on speaking terms with DWARF". > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150116/3f1967f4/attachment.html>
Hi Armin,> The MCJIT API can only be used once to JIT compile external souces toexcuteable code into the address space of a running process. 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. Cheers, Lang. On Fri, Jan 16, 2015 at 2:41 AM, Armin Steinhoff <armin at steinhoff.de> wrote:> > Hi Lang, > > we are using the JIT API of TCC and the MCJIT API in order to import > external code into a running control application process. > > The MCJIT API can only be used once to JIT compile external souces to > excuteable code into the address space of a running process. > > 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. > > Best Regards > > Armin > > > Lang Hames schrieb: > > Hi All, > > 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. > > 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. > > The 20,000 ft overview, for those who want to get straight to the code: > > 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. > > 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*. > > You'll find the new headers in > llvm/include/llvm/ExecutionEngine/OrcJIT/*.h, and the implementation files > in lib/ExecutionEngine/OrcJIT/*. > > 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. > > 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. > > Cheers, > Lang. > > Possible questions: > > (1) > Q. Are you trying to kill off MCJIT? > A. There are no plans to remove MCJIT. The new APIs are designed to live > alongside it. > > (2) > Q. What do "JIT components" look like, and how do you compose them? > 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: > > class SomeLayer { > private: >  // Implementation details > public: >  // Implementation details > >  typedef ??? Handle; > >  template <typename ModuleSet> >  Handle addModuleSet(ModuleSet&& Ms); > >  void removeModuleSet(Handle H); > >  uint64_t getSymbolAddress(StringRef Name, bool ExportedSymbolsOnly); > >  uint64_t lookupSymbolAddressIn(Handle H, StringRef Name, bool > ExportedSymbolsOnly); > }; > > 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. > > 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. > > Clients are free to use utilities directly, or compose layers, or > implement new utilities or layers. > > (3) > Q. Why "addModuleSet" rather than "addModule"? > 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. > > (4) > Q. What happened to "finalize"? > 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. > > (5) > Q. What does "removeModuleSet" do? > 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'. > > (5a) > Q. How are the linked sections freed? RTDyldMemoryManager doesn't have any > "free.*Section" methods. > 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. > > (6) > Q. How does the CompileOnDemand layer redirect calls to the JIT? > 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. > > 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). > > (7) > Q. Do the new APIs support cross-target JITing like MCJIT does? > A. Yes. > > (7.a) > Q. Do the new APIs support cross-target (or cross process) lazy-jitting? > 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. > > (8) > Q. Do any of the components implement the ExecutionEngine interface? > A. None of the components do, but the MCJITReplacement class does. > > (9) > Q. Does this address any of the long-standing issues with MCJIT - Stackmap > parsing? Debugging? Thread-local-storage? > 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. > > (10) > Q. Why is part X of the patch (ugly | buggy | in the wrong place) ? > 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. > > --- > > 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. > > > * Marketing slogans abound: "Very MachO". "Some warts". "Surprisingly > friendly with ELF". "Not yet on speaking terms with DWARF". > > > _______________________________________________ > LLVM Developers mailing listLLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.eduhttp://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150116/c8e16081/attachment.html>