[llvm-dev] New x86-64 micro-architecture levels

[Mark Wielaard via llvm-dev]

Hi Florian,

I understand you want to discuss the x86_64 micro-architecture levels
only in this thread, but it would be nice to have a similar discussion
for other architectures.

One thing that wasn't clear to me from this proposal is how the glibc
dynamic loader checks for the CPU feature flags. This is important for
valgrind since it can communicate those through different means. cpuid
interception, auxv AT_HWCAP/AT_HWCAP2 interception (but not AT_PLATFORM
at the moment) and of course we can generate SIGILL for unsupported
instructions. We currently don't intercept /proc/cpuinfo (but could).

I think it is important to be precise here, because in the past this
has sometimes caused confusion. For example for how to check correctly
for avx, lzcnt, or fma[4] support.

Thanks,

Mark

P.S. I don't particular like the numbered names, but well, bike-shed...