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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang-cl doesn't support /Qspectre"
href="https://bugs.llvm.org/show_bug.cgi?id=40964">40964</a>
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<th>Summary</th>
<td>clang-cl doesn't support /Qspectre
</td>
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Frontend
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>nicolasweber@gmx.de
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<pre>cl.exe has spectre type 1 mitigation under /Qspectre, and apparently cmake now
(sometimes?) sets this, leading to stuff like
<a href="https://twitter.com/never_released/status/1101439626357686272">https://twitter.com/never_released/status/1101439626357686272</a>
<a href="https://devblogs.microsoft.com/cppblog/spectre-mitigations-in-msvc/">https://devblogs.microsoft.com/cppblog/spectre-mitigations-in-msvc/</a> describes
what the flag does.
We could maybe map it to -mspeculative-load-hardening
There's also a declspec for disabling spectre mitigations on a per-function
level: <a href="https://docs.microsoft.com/en-us/cpp/cpp/spectre?view=vs-2017">https://docs.microsoft.com/en-us/cpp/cpp/spectre?view=vs-2017</a>
<a href="https://reviews.llvm.org/D51157">https://reviews.llvm.org/D51157</a> suggests that we already have something like
this on the IR level, so adding a declspec might not be too difficult.
Finally, there's a warning (C5045) which flags where the mitigation would be
inserted:
<a href="https://devblogs.microsoft.com/cppblog/spectre-diagnostic-in-visual-studio-2017-version-15-7-preview-4/">https://devblogs.microsoft.com/cppblog/spectre-diagnostic-in-visual-studio-2017-version-15-7-preview-4/</a>
This part might be difficult.</pre>
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