<div dir="ltr">Hi All,<div><br></div><div>Stage 1 landed just after I sent this and it looks like there was minimal fallout from that for MCJIT users, but it broke common symbol support in the ORC Lazy JIT. To fix this I've replaced RuntimeDyld::SymbolInfo with the lazily-materializing JITSymbol (which I've moved from ORC to ExecutionEngine) in r277386. Most clients won't see any breakage due to this (neither Swift nor LLDB required updates), but ORC users will need to rename RuntimeDyld::SymbolInfo to JITSymbol to get their code compiling again. My apologies for the breakage, but this should be a big improvement in the long run: it will allow me to fix common symbol support, and should also make it possible to support weak symbols correctly.</div><div><br></div><div>The changes I mentioned in stages 2 and 3 in my original email are still in the works, but I don't have schedule for them yet.</div><div><br></div><div>Cheers,</div><div>Lang.</div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, May 27, 2016 at 4:02 AM, Stefan Gränitz <span dir="ltr"><<a href="mailto:stefan.graenitz@gmail.com" target="_blank">stefan.graenitz@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<p>Hi Lang, thanks for announcing. Would be great if you could send
another short notice as soon as the actual patch exists.<br>
Best, Stefan<br>
</p>
<div>Am 24.05.16 um 23:06 schrieb Lang Hames
via llvm-dev:<br>
</div>
<blockquote type="cite"><div><div class="h5">
<div dir="ltr">Hi All,
<div><br>
</div>
<div>I'm going to be making some API breaking changes to the ORC
APIs, and to the RuntimeDyld class (which underlies MCJIT).
The changes may affect MCJIT clients but are unlikely to.
Where they do the fixes are likely to be trivial. ORC clients
will be affected, but the fixes should also be
straightforward.</div>
<div><br>
</div>
<div>I have three upcoming changes in mind:</div>
<div><br>
</div>
<div>1) RuntimeDyld (the linker underlying MCJIT and ORC) will
now search for symbols using the SymbolResolver's
findSymbolInLogicalDylib first, before falling back to the
findSymbol method if findSymbolInLogicalDylib returns a null
result.</div>
<div><br>
</div>
<div>This is a step towards making RuntimeDyld behave more like
a static linker: we prefer to link against symbols defined in
the same "logical dylib" as the module being JIT'd, before
linking against external symbols.</div>
<div><br>
</div>
<div>For clients that have not implemented
findSymbolInLogicalDylib (I suspect this covers most clients)
this change will have no effect: the default version of
findSymbolInLogicalDylib will be called and will return null,
and RuntimeDyld will fall back to calling findSymbol as it did
before.</div>
<div><br>
</div>
<div>For clients that have implemented findSymbolInLogicalDylib:
Beware that any symbol found via this call will now shadow
symbols that might have been found via findSymbol. It is
unlikely that anyone is relying on non-shadowing so I don't
expect any trouble here, but if you do see any changes in
symbol resolution after this change (which I expect to land
today) this is something to have in mind.</div>
<div><br>
</div>
<div>2) MemoryManager deregisterEHFrames will be removed.</div>
<div><br>
</div>
<div>Memory managers should own their registered EH frames and
deregister them on destruction. This will bring EH frame
ownership in line with memory ownership: memory managers are
already responsible for freeing the memory that they've
allocated when they are destructed.</div>
<div> <br>
</div>
<div>To transition, clients should track the frames registered
by their class, then deregister them in the destructor. For
in-tree memory managers (and RuntimeDyld itself) this bug is
being tracked by <a href="https://llvm.org/PR23991" target="_blank">https://llvm.org/PR23991</a>
.</div>
<div><br>
</div>
<div>3) Some operations in the ORC APIs, RuntimeDyld,
SymbolResolver and MemoryManager will be modified to return
Error/Expected.</div>
<div><br>
</div>
<div>MCJIT and ORC both support remote execution of JIT'd code
via RPC, but there is currently no way to cleanly bail out and
report failure in the case of an RPC error. Adding error
returns provides the mechanism we need.</div>
<div><br>
</div>
<div>When the interfaces are changed to add error returns
clients will see compile-time errors for any custom ORC-based
stacks, derived symbol resolvers, or memory managers. Most
clients will just be able to update their offending return
types and leave their function body as-is (for
Expected<T> returns) or return llvm::Error::success()
(for Error returns). Clients who are actually using the
remote-JITing features will now be able to return any errors
that they had previously been dropping or bailing out on. This
change is being tracked by <a href="https://llvm.org/PR22612" target="_blank">https://llvm.org/PR22612</a>
.</div>
<div><br>
</div>
<div>I've held off making these changes for a while, because I
know there are a lot of out-of-tree JIT clients and I want to
avoid breaking your code. I think this churn is worth the pain
though - the resulting APIs will have less historical baggage,
be more error-proof, and enable some new features.</div>
<div><br>
</div>
<div>Please let me know if you have any questions or run into
any trouble as these changes land - I'll be happy to help out.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Lang.</div>
</div>
<br>
<fieldset></fieldset>
<br>
</div></div><pre>_______________________________________________
LLVM Developers mailing list
<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>
<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><span class="HOEnZb"><font color="#888888">
</font></span></pre><span class="HOEnZb"><font color="#888888">
</font></span></blockquote><span class="HOEnZb"><font color="#888888">
<br>
<pre cols="72">--
<a href="https://about.me/stefan.graenitz" target="_blank">https://about.me/stefan.graenitz</a></pre>
</font></span></div>
</blockquote></div><br></div>