On 9 Jan 2025, at 15:12, Diego Nieto Cid <dnie...@gmail.com> wrote: > > Hi, > > On Thu, Jan 09, 2025 at 11:51:27AM +0300, Sergey Bugaev wrote: >> >> "Implementer", "architecture", "variant", "part", "revision" come from >> midr/revidr [0], and "features" are hwcap names. These are privileged >> registers that only EL1 can read, but on AArch64 gnumach, their values >> are obtainable from userland using the aarch64_get_hwcaps RPC (see >> gnumach:aarch64/include/mach/aarch64/mach_aarch64.defs and >> gnumach:aarch64/include/mach/aarch64/mach_aarch64_types.h). > > Looking at the types.h header, I see there are HWCAP2_* definitions for > bits above 32. Since hwcaps_t is an uint32_t and the defs file claims to > return two values (I assume the first for HWCAP_* and the second for > HWCAP2_*), I don't see how to get the higher bits of HWCAP2_*. > > How does that work?
On Linux, FreeBSD and any other OS that implements AT_HWCAP(2), you get hwcaps via auxv, and Elf_Auxinfo’s a_un.a_val is a long, so it’s 64-bit on 64-bit architectures, which aarch64 is. Making hwcaps_t a uint32_t on aarch64 is a mistake. Jess
