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Re: [PATCH 7/7] aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK
On 11/05/2017 11:51, Siddhesh Poyarekar wrote:
> Now that LD_HWCAP_MASK (or glibc.tune.hwcap_mask) is read early enough
> to influence cpu feature check in aarch64, use it to influence
> multiarch selection. Setting LD_HWCAP_MASK such that it clears
> HWCAP_CPUID will now disable multiarch for the binary.
>
> * sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> (init_cpu_features): Use glibc.tune.hwcap_mask.
LGTM.
>
> Change-Id: Ia801ed6b8166b79a0cae184ee7417272f2f60593
> ---
> sysdeps/unix/sysv/linux/aarch64/cpu-features.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> index 7025062..0478fcc 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> @@ -18,18 +18,25 @@
>
> #include <cpu-features.h>
> #include <sys/auxv.h>
> +#include <elf/dl-tunables.h>
>
> static inline void
> init_cpu_features (struct cpu_features *cpu_features)
> {
> - if (GLRO(dl_hwcap) & HWCAP_CPUID)
> +#if HAVE_TUNABLES
> + uint64_t hwcap_mask = TUNABLE_GET (glibc, tune, hwcap_mask, uint64_t);
> +#else
> + uint64_t hwcap_mask = GLRO (dl_hwcap_mask);
> +#endif
I noted the hwcap_mask get logic is duplicated over various places. Should we
define a helper macro for it?
> +
> + uint64_t hwcap = GLRO (dl_hwcap) & hwcap_mask;
> +
> + if (hwcap & HWCAP_CPUID)
> {
> register uint64_t id = 0;
> asm volatile ("mrs %0, midr_el1" : "=r"(id));
> cpu_features->midr_el1 = id;
> }
> else
> - {
> - cpu_features->midr_el1 = 0;
> - }
> + cpu_features->midr_el1 = 0;
> }
>