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<p class="MsoNormal"><span lang="EN-GB">Hello everyone,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">(There is a TL;DR down there)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I started to look into the Spectre Mitigation features of the MSVC compiler - we are planning to apply those to our code base finally. I was able to find out, that the MSVC compiler supports 3 flags for this:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">/Qspectre -> "Specifies compiler generation of instructions to mitigate certain Spectre variant 1 security vulnerabilities."<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">/Qspectre-load -> "Specifies compiler generation of serializing instructions for every load instruction."<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">/Qspectre-load-cf -> "Specifies compiler generation of serializing instructions for every control-flow instruction that contains a load."<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">That was surprisingly helpful! However, we are also using the Clang-Cl compiler, so I wanted to find out which features are supported in terms of the Spectre Mitigation. This was difficult! I found at least this website:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">https://llvm.org/docs/SpeculativeLoadHardening.html - Which is really interesting but... too much for me >o<<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Next hint I got was the attribute "speculative_load_hardening" but there the 'frustration' started. On the site, the compiler flag "-mno-speculative-load-hardening" was mentioned - I figured that the flag "-mspeculative-load-hardening"
would be a thing. The link https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-mspeculative-load-hardening was of no help however, because the flag isn't mentioned there as it seems. Sooo... Next thing I did was executing "clang -help"
and "clang --help-hidden" to my surprise the flag wasn't mentioned there as well...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">So I went to one of our projects and added it by hand, checking if it will throw an error or not - it did not.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">TL;DR:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">My problem as a user is... I'm really unsure how many undocumented flags are supported by Clang and which one might be of interested for me. For example, do I know all the flags now that are related to the spectre mitigation?
I know that there is also -mreptoline (or something), but I can't know about the flags I don't know about - and when not even Clang itself dumps them, then I'm really screwed.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Also, how can I be sure, that the flag is also supported by Clang-Cl? Or by Clang-Cl -Xclang?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Also a kinda confusing thing... When I go to the LLVM/Clang online documentation, then it says Clang 11, when I ask my Clang about the version it replies with Clang 9 - also on the website I can only download LLVM 9 -
That makes me feel like I missed 2 Versions already - even though I think to recall that LLVM 10 is next.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Yet it seems like I'm the only one with that issue .w.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Kind greetings<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Björn<o:p></o:p></span></p>
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