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Most Linux distributions still compile against the original x86-64 baseline that was based on the AMD K8 (minus the 3DNow! parts, for Intel EM64T compatibility). There has been an attempt to use the existing AT_PLATFORM-based loading mechanism in the glibc dynamic linker to enable a selection of optimized libraries. But the general selection mechanism in glibc is problematic: hwcaps subdirectory selection in the dynamic loader <https://sourceware.org/pipermail/libc-alpha/2020-May/113757.html> We also...

...r 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,...

...weimer at redhat.com> wrote: > > > > Most Linux distributions still compile against the original x86-64 > > baseline that was based on the AMD K8 (minus the 3DNow! parts, for Intel > > EM64T compatibility). > > > > There has been an attempt to use the existing AT_PLATFORM-based loading > > mechanism in the glibc dynamic linker to enable a selection of optimized > > libraries. But the general selection mechanism in glibc is problematic: > > > > hwcaps subdirectory selection in the dynamic loader > > <https://sourceware.org/piperm...

Hi, after a year, I decided to hack on klibc again. I?ve reworked both the patch to add mkstemp(), discussing to use AT_RANDOM as cheap entropy source on IRC (if there will ever be another entropy consumer, I can quickly write a minimal arc4random() seeded from it, as it has only 16 octets), capable of making a working mksh (static and shared) on amd64/xen, and the m68k support code, leading to