Patchwork [8/8] aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK

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Submitter Siddhesh Poyarekar
Date May 10, 2017, 2:47 p.m.
Message ID <1494427637-14555-9-git-send-email-siddhesh@sourceware.org>
Download mbox | patch
Permalink /patch/20376/
State New
Headers show

Comments

Siddhesh Poyarekar - May 10, 2017, 2:47 p.m.
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.

Change-Id: Ia801ed6b8166b79a0cae184ee7417272f2f60593
---
 sysdeps/unix/sysv/linux/aarch64/cpu-features.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

Patch

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
+
+  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;
 }