Will Deacon <will.dea...@arm.com> writes: > Perhaps it would be better to consider exposing the ID registers to > userspace in some manner? This could be done either via an undef handler, or > using the vdso. We would add a (final) hwcap advertising this cpuid support. > For big/little systems, the kernel would need to expose a suitable subset of > the features (we already have the sanity checking code from Rutland).
This was discussed a few years ago, and some people raised various objections. Off the top of my head: - Some features (e.g. VFP/NEON) need kernel support, and if this is not enabled, the actual system capabilities will not match the raw register value. Fudging the values exposed to userspace would be fragile. (This argument has some merit.) - Only v7 and newer CPUs have the CPUID registers. Ridiculously old CPUs don't even have a CP15. Providing synthetic values might be tricky. Software thus needs to support alternate feature detection methods for such hardware. (This is true enough.) - It would only be available on new kernels, so software would still need a fallback to another method for the foreseeable future. (This is a rather lazy argument.) - It would be specific to Linux, so software can't rely on it anyway. (This is an even lazier argument.) -- Måns Rullgård m...@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
