Alok Manchanda
2011-Dec-05 07:06 UTC
[LLVMdev] bug in ARMFrameLowering.cpp:processFunctionBeforeCalleeSavedScan
Hello LLVMDev, I've encountered what looks like a bug in LLVM 2.9, it doesn't appear to be fixed in 3.0 either. The problem occurs in function ARMFrameLowering.cpp:processFunctionBeforeCalleeSavedScan. There's a circular dependency in setting the variable BigStack and AFI->setHashStackFrame(true). The expression which initializes BigStack calls estimateRSSStackSizeLimit which in turn checks AFI->hasStackFrame(). Unfortunately setHasStackFrame(true) only gets called after BigStack is initialized. The specific issue this caused in my case was that BigStack got initialized as false because estimateRSSStackSizeLimit returned (1<<12)-1 instead of (1<<8)-1. The code thus never entered the if (BigStack && !ExtraCSSpill) block further down where setScavengingFrameIndex should have been set. As a result of it was not being set there, there was an assertion failure (ScavengingFrameIndex >= 0) and subsequent memory corruption in RegScavenger::scavengeRegister. I fixed this by performing the CanEliminateFrame and RegInfo->cannotEliminateFrame checks before the call to estimateRSSStackSizeLimit, since these values are available before BigStack is initialized. Does that sound reasonable? I've attached a patch with my change. Oh, I should mention that the previous version of LLVM we used, 2.6, didn't include the check to hasStackFrame() in estimateRSSStackSizeLimit and worked on the same input. Thanks, -alok. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20111205/3c7aacd7/attachment.html> -------------- next part -------------- A non-text attachment was scrubbed... Name: ARMFrameLowering.patch Type: application/octet-stream Size: 613 bytes Desc: ARMFrameLowering.patch URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20111205/3c7aacd7/attachment.obj>
Anton Korobeynikov
2011-Dec-05 11:10 UTC
[LLVMdev] bug in ARMFrameLowering.cpp:processFunctionBeforeCalleeSavedScan
Hello Alok,> I fixed this by performing the CanEliminateFrame and > RegInfo->cannotEliminateFrame checks before the call to > estimateRSSStackSizeLimit, since these values are available before BigStack > is initialized. Does that sound reasonable? I’ve attached a patch with my > change.Will you please provide a testcase which reproduces the problem? Thanks! -- With best regards, Anton Korobeynikov Faculty of Mathematics and Mechanics, Saint Petersburg State University
James Molloy
2011-Dec-05 14:44 UTC
[LLVMdev] bug in ARMFrameLowering.cpp:processFunctionBeforeCalleeSavedScan
Hi Alok, Echoing Anton's statements, please provide a testcase! :) Apart from that, looking at your patch and description I actually think that it is estimateRSStackSizeLimit that is wrong. It is performing a check for a Thumb2 addressing mode whether the target has a FP register. That's the main check - for some reason it is appending another check AFI->hasStackFrame() which seems wrong. The function should assume the function has a stack frame, because its entire function is to estimate its size! It looks like that check has been copy-pasted from elsewhere in the file. Anton, would you agree with this? I haven't looked at ARMFrameLowering before. Cheers, James -----Original Message----- From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Anton Korobeynikov Sent: 05 December 2011 11:11 To: Alok Manchanda Cc: llvmdev at cs.uiuc.edu Subject: Re: [LLVMdev] bug in ARMFrameLowering.cpp:processFunctionBeforeCalleeSavedScan Hello Alok,> I fixed this by performing the CanEliminateFrame and > RegInfo->cannotEliminateFrame checks before the call to > estimateRSSStackSizeLimit, since these values are available before BigStack > is initialized. Does that sound reasonable? I’ve attached a patch with my > change.Will you please provide a testcase which reproduces the problem? Thanks! -- With best regards, Anton Korobeynikov Faculty of Mathematics and Mechanics, Saint Petersburg State University _______________________________________________ LLVM Developers mailing list LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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