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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Dear All,
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<div>I think adding metadata and expecting transforms to repect it is a bad idea. It is just too easy for someone who does not know about the metadata to add a transform that ignores it.</div>
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<div>As for SAFECode, I think we have one of several options for handling load-widening. The most obvious one is to have a pass that just boosts the allocation size of any alloca with an align 16 attribute; this pass would only be scheduled to execute when
the other SAFECode instrumentation passes are scheduled to execute. Another option would be to just disable the load-widening transform or to use a specialized version that only widens when the allocation size does not cause a problem.</div>
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<div>-- John T.</div>
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<div id="divRpF691606" style="direction: ltr; "><font face="Tahoma" size="2" color="#000000"><b>From:</b> llvmdev-bounces@cs.uiuc.edu [llvmdev-bounces@cs.uiuc.edu] on behalf of Kostya Serebryany [kcc@google.com]<br>
<b>Sent:</b> Tuesday, December 27, 2011 12:57 PM<br>
<b>To:</b> Chris Lattner<br>
<b>Cc:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] load widening conflicts with AddressSanitizer<br>
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<div class="gmail_quote">On Mon, Dec 19, 2011 at 4:27 PM, Chris Lattner <span dir="ltr">
<<a href="mailto:clattner@apple.com" target="_blank">clattner@apple.com</a>></span> wrote:<br>
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On Dec 17, 2011, at 7:40 AM, Rafael Ávila de Espíndola wrote:<br>
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> On 16/12/11 08:46 PM, Chris Lattner wrote:<br>
>> I'm not opposed to disabling this transformation when asan is on, we just need a clean way to express this in the IR.<br>
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> Could clang be aware of asan being on and introduce a "please don't<br>
> widen" metadata on local variable accesses?<br>
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Yes, "we just need a clean way to express this in the IR."<br>
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LLVM can't have a global "bool ASANIsOn;" that the optimizers listen to.<br>
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<div>A global is bad.</div>
<div>What about a metadata attached to a Function saying that transformations which will read out of bounds (even "safely") are illegal? </div>
<div>asan and SAFEcode will add this metadata, optimizers will listen to it. </div>
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<div>Any other suggestion? </div>
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<div>--kcc </div>
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