<div dir="ltr"><div>Hi Christian,<br><br>> I don’t see anything in the Itanium ABI that says I need to call
the function that throws an exception with “invoke” to get exception
handling to work!<br><br></div>AFAICT, it is the design of LLVM IR and its implementation. To catch the exceptions thrown by the callee functions, we should use the invoke instruction along with the landingpad instruction. If you are calling a function with a call instruction, the LLVM backend will simply assumes frame unwinding when the callee throws an exception.<br><br><br>FYI, according to LLVM reference manual, an <a href="http://llvm.org/docs/LangRef.html#invoke-instruction">invoke-instruction</a> has following semantics:<br><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex" class="gmail_quote"><p>The ‘<tt class=""><span class="">invoke</span></tt>‘ instruction causes control to transfer to a specified
function, with the possibility of control flow transfer to either the
‘<tt class=""><span class="">normal</span></tt>‘ label or the ‘<tt class=""><span class="">exception</span></tt>‘ label. If the callee function
returns with the “<tt class=""><span class="">ret</span></tt>” instruction, control flow will return to the
“normal” label. If the callee (or any indirect callees) returns via the
“<a class="" href="http://llvm.org/docs/LangRef.html#i-resume"><em>resume</em></a>” instruction or other exception handling
mechanism, control is interrupted and continued at the dynamically
nearest “exception” label.</p></blockquote><div>OTOH, here's the description for <a href="http://llvm.org/docs/LangRef.html#call-instruction">call instruction</a>: <br><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex" class="gmail_quote"><p>The ‘<tt class=""><span class="">call</span></tt>‘ instruction represents a simple function call.</p></blockquote><div><br>Hope this is helpful.<br><br></div><div>Best regards,<br></div><div>Logan<br></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Apr 12, 2015 at 6:33 AM, Christian Schafmeister <span dir="ltr"><<a href="mailto:chris.schaf@verizon.net" target="_blank">chris.schaf@verizon.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><br></div>It appears that I've found a very curious effect where if I JIT a function that throws an exception and I use "call" to call it the throw fails despite there being a "catch" clause on the stack. But if I use “invoke” it works fine!<div><br></div><div> If I call the function (@cc_invoke) that throws a “core::CatchThrow” exception like this:</div><div><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;margin-top:0px;margin-bottom:0px;width:748px;color:rgb(51,51,51);line-height:16px"><div>call void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64 2, {}* %4, {}* %5, {}* null, {}* null, {}* null)
</div><div>;; Comment out the next two lines and
</div><div>; to label %return0 unwind label %landing-pad1
</div><div>;return0:</div><div>ret void
</div><div>
</div><div>landing-pad1: ; No predecessors!
</div><div> %6 = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
</div><div> cleanup
</div><div> resume { i8*, i32 } %6
</div><div>}</div></pre><div><br></div></div><div>It fails with: libc++abi.dylib: terminating with uncaught exception of type core::CatchThrow</div><div><br></div><div>If instead I convert the “call” into an “invoke” and hook in a dummy landing-pad like this:</div><div><br></div><div><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;margin-top:0px;margin-bottom:0px;width:748px;color:rgb(51,51,51);line-height:16px"><div>invoke void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64 2, {}* %4, {}* %5, {}* null, {}* null, {}* null)
</div><div> to label %return0 unwind label %landing-pad1
</div><div>return0:
</div><div> ret void
</div><div>
</div><div>landing-pad1: ; No predecessors!
</div><div> %6 = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0
</div><div> cleanup
</div><div> resume { i8*, i32 } %6
</div><div>}</div></pre><div><br></div><div>The CatchThrow exception is caught and everything works fine! I don’t need to call the caller or any outer function with “invoke” except for in the function that has the landing pad that recognizes core::CatchThrow.</div><div><br></div><div>I don’t see anything in the Itanium ABI that says I need to call the function that throws an exception with “invoke” to get exception handling to work!</div><div><br></div><div>Does anyone have any ideas what I might be doing wrong?</div><div><br></div><div><br></div><br></div><div><div class="h5"><div><br></div><div><br></div><div><br></div><div><br><div><div>On Apr 9, 2015, at 6:59 PM, Lang Hames <<a href="mailto:lhames@gmail.com" target="_blank">lhames@gmail.com</a>> wrote:</div><br><blockquote type="cite"><div dir="ltr">Hi Christian,<div><br></div><div>Andy's already covered the major points, but you could consider filing a bug at <a href="http://llvm.org/bugs" target="_blank">http://llvm.org/bugs</a> too, especially if you've got a small test-case that demonstrates the issue. Exception handling hasn't been a priority in the past, but as more people adopt LLVM's JIT APIs I suspect it will get more attention, and bug reports will help us figure out what needs doing. </div><div><br></div><div>Cheers,</div><div>Lang.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Apr 9, 2015 at 11:43 AM, Kaylor, Andrew <span dir="ltr"><<a href="mailto:andrew.kaylor@intel.com" target="_blank">andrew.kaylor@intel.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div link="blue" vlink="purple" lang="EN-US">
<div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi Christian,<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I suspect that at least some of the details depend on what platform you’re working on. I believe that MCJIT attempts to register eh frame information for either
MachO or ELF objects (though for some ELF platforms nothing actually happens). What happens to it after that is a darker area, at least for me.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Apparently there was a GDB command that did just what you want -- “info catch” -- but I had never used it and it has been removed. It’s too bad because it
sounds like a nice feature. It was supposed to dump a list of catch handlers for whatever frame you’re looking at. I suspect, however, that it would have just confirmed that your catch handler isn’t properly hooked up without being helpful in figuring out
why.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">You could try debugging the RuntimeDyld code that registers eh frames and see if that looks right. RuntimeDyld::registerEHFrames() might be a helpful starting
point.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">-Andy<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<div>
<div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> <a href="mailto:llvmdev-bounces@cs.uiuc.edu" target="_blank">llvmdev-bounces@cs.uiuc.edu</a> [mailto:<a href="mailto:llvmdev-bounces@cs.uiuc.edu" target="_blank">llvmdev-bounces@cs.uiuc.edu</a>]
<b>On Behalf Of </b>Christian Schafmeister<br>
<b>Sent:</b> Wednesday, April 08, 2015 10:09 PM<br>
<b>To:</b> LLVM Developers Mailing List<br>
<b>Subject:</b> [LLVMdev] Looking for advice on how to debug a problem with C++ style exception handling code that my compiler generates.<u></u><u></u></span></p>
</div>
</div><div><div><p class="MsoNormal"><u></u> <u></u></p>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div><p class="MsoNormal">Hi,<u></u><u></u></p>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div><p class="MsoNormal">I’m looking for advice on how to debug a problem with my exception handling code. <u></u><u></u></p>
</div>
<div><p class="MsoNormal">I’m asking a specific question here - but general advice on how to debug something like this would be greatly appreciated.<u></u><u></u></p>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div><p class="MsoNormal">Is there any way to get a list of landing pad clauses that are active at a particular point in a program?<br>
I'd like to get something like a backtrace but listing all active landing pad clauses. The typeids of the C++ types <br>
I'm trying to debug a problem where an exception that I'm throwing is not being caught. <u></u><u></u></p>
<div><p class="MsoNormal">I'm generating JITed code with LLVM and landing pads and I've got shared libraries - lots of things going on that could potentially be going wrong.<u></u><u></u></p>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div><p class="MsoNormal">A list of the pointer values like @_ZTIN4core9DynamicGoE is what I’m looking for. Then I could compare that to the typeids that I know should be in that list.<u></u><u></u></p>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<div><p class="MsoNormal"><span style="font-family:Courier">"(TRY-0).landing-pad": ; preds = %"(TRY-0).normal-dest14", %"(TRY-0).tagbody-B-1", %"(TRY-0).normal-dest10", %"(TRY-0).normal-dest9", %"(TRY-0).normal-dest8", %"(TRY-0).normal-dest",
%"(TRY-0).tagbody-#:G1621-0"</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> %14 = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> catch i8* @_ZTIN4core9DynamicGoE</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> catch i8* @_ZTIN4core10ReturnFromE, !dbg !26</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> %15 = extractvalue { i8*, i32 } %14, 0, !dbg !26</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> %16 = extractvalue { i8*, i32 } %14, 1, !dbg !26</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> %17 = call i32 @llvm.eh.typeid.for(i8* @_ZTIN4core9DynamicGoE), !dbg !26</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> %18 = icmp eq i32 %16, %17, !dbg !26</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"> br i1 %18, label %"(TRY-0).handler-block14470", label %"(TRY-0).dispatch-header19", !dbg !26</span><u></u><u></u></p>
</div>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">I’m getting this error when I throw a core::Unwind exception and I’m certain that there is a landing pad with that clause.</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div>
<div><p class="MsoNormal"><span style="font-family:Courier">libc++abi.dylib: terminating with uncaught exception of type core::Unwind</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier">../../src/gctools/<a href="http://memorymanagement.cc/" target="_blank">memoryManagement.cc</a>:75 Trapped SIGABRT - starting debugger</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier">ABORT was called!!!!!!!!!!!!</span><u></u><u></u></p>
</div>
<div><p class="MsoNormal"><span style="font-family:Courier"><u></u> <u></u></span></p>
</div>
</div>
<div><p class="MsoNormal"><u></u> <u></u></p>
</div>
<div><p class="MsoNormal">I’ve written a Common Lisp compiler that uses LLVM as the backend and it interoperates with C++ code and I use C++ exception handling for non-local exits.<u></u><u></u></p>
</div>
</div></div></div>
</div>
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