aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK

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.

HWCAP_CPUID is also now set in HWCAP_IMPORTANT so that it is set by
default.  With this patch, this feature is only usable with
dyanmically linked binaries because LD_HWCAP_MASK is not read for
static binaries.  A future patch fixes that.

	* sysdeps/unix/sysv/linux/aarch64/cpu-features.c
	(init_cpu_features): Use glibc.tune.hwcap_mask.
	* sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h: New file.

1 files changed, 6 insertions, 4 deletions

diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
index 702506249d..ef6eecd17e 100644
--- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
@@ -18,18 +18,20 @@
 
 #include <cpu-features.h>
 #include <sys/auxv.h>
+#include <elf/dl-hwcaps.h>
 
 static inline void
 init_cpu_features (struct cpu_features *cpu_features)
 {
-  if (GLRO(dl_hwcap) & HWCAP_CPUID)
+  uint64_t hwcap_mask = GET_HWCAP_MASK();
+  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;
 }