On 20 January 2014 18:44, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > On Mon, 20 Jan 2014, Catalin Marinas wrote: > >> On Mon, Dec 23, 2013 at 02:06:27PM +0000, Ard Biesheuvel wrote: >> > This series is a followup to the patch that was recently merged by Catalin >> > that >> > allocates hwcaps bits for CRC and Crypto Extensions instructions so >> > userland can >> > discover whether the current CPU has any of those capabilities. >> > >> > Patch #1 enables ARM support for the ELF_HWCAP2/AT_HWCAP2 ELF auxv entry >> > that >> > was recently added to the kernel and glibc (2.18). It extends the feature >> > bit >> > space to 64 bits (on 32-bit architectures) >> > >> > Patch #2 adds generic support for ELF_HWCAP2/AT_HWCAP2 to the 32-bit ELF >> > compat >> > mode for 64-bit architectures. >> > >> > Patch #3 adds support for ELF_HWCAP2/AT_HWCAP2 to arm64's 32-bit ELF >> > compat mode >> > >> > Patch #4 allocates the HWCAP2 bits in the arch/arm tree. This is necessary >> > because 32-bit ARM binaries can execute both under ARM and under arm64 >> > kernels, >> > so there should be agreement about the meaning of feature bits, even if >> > the ARM >> > kernel has no support yet for ARMv8 32-bit only hardware (such as ARMv8-R). >> >> It looks a bit strange to start filling HWCAP2 before HWCAP is full but >> I guess we want to preserve some future extensions in HWCAP for older >> glibc. > > How could older glibc possibly care about future extensions? >
Calling getauxval(AT_HWCAP) on an outdated libc.so will give you the whole value, not just the bits whose meaning was known to glibc at the time. So if desired, a program can interpret AT_HWCAP itself. AT_HWCAP2 is completely new, so you won't be able to retrieve it using getauxval() on an older libc. -- Ard. -- 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/
