[LLVMdev] A weird, reproducable problem with MCJIT

[Kaylor, Andrew]

Yes, you are correct Yaron.  Before we commit this we ought to put a check in to see what the target OS is.  I just suggested the change below as a quick and easy way to verify that this was the cause of the problem.  I'll clean it up.

-Andy

From: Yaron Keren [mailto:yaron.keren at gmail.com]
Sent: Monday, October 14, 2013 9:09 PM
To: Christian Schafmeister; Kaylor, Andrew; iain at codesourcery.com
Cc: <llvmdev at cs.uiuc.edu>
Subject: Re: [LLVMdev] A weird, reproducable problem with MCJIT

Correct or no I don't know, but this change will affect all x86-64 targets including Linux and Windows as getMaxStubSize() is called from the ELF linker as well as the Mach-O linker.


2013/10/15 Christian Schafmeister <chris.schaf at verizon.net<mailto:chris.schaf at verizon.net>>

With the help of iain at codesourcery.com<mailto:iain at codesourcery.com> and andrew.kaylor at intel.com<mailto:andrew.kaylor at intel.com> we
tracked the problem down to a bad relocation that was clobbering the
first bytes of the eh_frame.   I think this problem/solution may be OS X
specific.

On akaylor's suggestion I made the change below and my reproducable test
case now compiles fine with MCJIT.

As well, my Common Lisp code base now compiles using MCJIT - that's about 1,000
functions at one MCJIT module per function.



In llvm/lib/ExecutionEngine/RuntimeDyld

Index: RuntimeDyldImpl.h
===================================================================
--- RuntimeDyldImpl.h   (revision 192535)
+++ RuntimeDyldImpl.h   (working copy)
@@ -195,7 +195,7 @@
     else if (Arch == Triple::ppc64 || Arch == Triple::ppc64le)
       return 44;
     else if (Arch == Triple::x86_64)
-      return 6; // 2-byte jmp instruction + 32-bit relative address
+       return 8; /* was 6 but akaylor said change to 8 - meister Oct 2013 */ // 2-byte jmp instruction + 32-bit relative address
     else if (Arch == Triple::systemz)
       return 16;
     else

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