Homebrew: AVX instructions in Big Sur bottles crash when run in Rosetta 2

Re:Homebrew: AVX instructions in Big Sur bottles crash when ... by klodolph on Saturday December 26, 2020 @09:54PM (#25548408)

This is fascinating. I can understand why the Homebrew devs might make the decision, but it seems the right way to do this is just to, e.g.,

    cc -dM -E -xc /dev/null | less

Anything with a preprocessor macro is supported on all OS configurations that you are targeting. You can see, for example, that __SSE4_1__ is defined, so SSE 4.1 is ok to use without checking it at runtime with e.g. sysctlbyname("hw.optional.sse4_1", &enabled, ...)

I have always thought that it is worth a bit of paranoia to try and do the check for optional features the “correct” way, whatever method the OS advertises (like sysctl for macOS) rather than doing something like cpuid. After all, every once in a while it’s possible to run into a configuration where the CPU does support some particular feature but the OS does not, and if you rely on cpuid you could be up shit creek without a paddle.

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Re:Homebrew: AVX instructions in Big Sur bottles crash when ... by bodyfour on Sunday December 27, 2020 @01:54AM (#25549380)

It was a mistaken assumption from the Homebrew developers who didn't realize AVX would cause problems with Rosetta2.

Within a few days problems became evident and Homebrew turned the compiler flag back off. Now it's just a question of the best way of remediating the already-compiled packages in the simplest way possible.

Really the fact that this is now a front-page-of-HN story is going to cause more confusion to people. It was just a short-lived bug.

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