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Ubsan is fantastic, but ASAN and the rest have serious caveats. They're not suitable for production use and they have a tendency to break in mysterious, intermittent ways. For example, Ubuntu 24.04 unknowingly broke Clang <=15ish when it increased mmap_rnd_bits. ASAN on Windows will actually check if you have ASLR enabled, disable it, and restart at entry. They interact in fun ways with LD_PRELOAD too.

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I'm on Clang 19 and still have a bunch of those sysctl commands sitting around.

I'm not in a position to look up exactly when it was merged, but I'm pretty confident that shouldn't be needed anymore. The entry point on 19 should do the same restart juggling it does on Windows if the environment isn't correct for some other reason. I can double check later if you want to provide details.

I encountered the issue when our (not Ubuntu, not 24.04) LTS upstream backported security fixes that included the mmap changes without updating universe to include a clang version with the fixes. Any developers diligent enough to update and run sanitisers locally started seeing intermittent crashes.

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