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@ 2020-03-25 18:37 Wilco Dijkstra
  0 siblings, 0 replies; only message in thread
From: Wilco Dijkstra @ 2020-03-25 18:37 UTC (permalink / raw)
  To: libc-stable

This partially reverts

commit f82e9672ad89ea1ef40bbe1af71478e255e87c5e
Author:     Siddhesh Poyarekar <>

    aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK

The idea was to make it possible to disable cpuid based ifunc resolution
in glibc by changing the hwcap mask which the user could already control.

However the hwcap mask has an orthogonal role: it specifies additional
library search paths for the dynamic linker.  So "cpuid" got added to
the search paths when it was set in the default mask (HWCAP_IMPORTANT),
which is not useful behaviour, the hwcap masking should not be reused
in the cpu features code.

Meanwhile there is a tunable to set the cpu explicitly so it is possible
to disable the cpuid based dispatch without using a hwcap mask:


        * sysdeps/unix/sysv/linux/aarch64/cpu-features.c (init_cpu_features):
        Use dl_hwcap without masking.
        * sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h (HWCAP_IMPORTANT):
        Remove HWCAP_CPUID.

(cherry picked from commit d0cd79807157e399ff58e67cb51651f90442122e)
 ChangeLog                                      | 7 +++++++
 sysdeps/unix/sysv/linux/aarch64/cpu-features.c | 5 +----
 sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h  | 5 ++---
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 5f3df32..732e89d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2018-07-06  Szabolcs Nagy  <>
+       * sysdeps/unix/sysv/linux/aarch64/cpu-features.c (init_cpu_features):
+       Use dl_hwcap without masking.
+       * sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h (HWCAP_IMPORTANT):
+       Remove HWCAP_CPUID.
 2019-09-13  Wilco Dijkstra  <>

         * string/memmem.c (__memmem): Rewrite to improve performance.
diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
index 50297bc..e71d636 100644
--- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
@@ -48,9 +48,6 @@ get_midr_from_mcpu (const char *mcpu)
 static inline void
 init_cpu_features (struct cpu_features *cpu_features)
-  uint64_t hwcap_mask = GET_HWCAP_MASK();
-  uint64_t hwcap = GLRO (dl_hwcap) & hwcap_mask;
   register uint64_t midr = UINT64_MAX;

@@ -64,7 +61,7 @@ init_cpu_features (struct cpu_features *cpu_features)
      allows it.  */
   if (midr == UINT64_MAX)
-      if (hwcap & HWCAP_CPUID)
+      if (GLRO (dl_hwcap) & HWCAP_CPUID)
         asm volatile ("mrs %0, midr_el1" : "=r"(midr));
         midr = 0;
diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
index 0333a18..63bdf75 100644
--- a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
+++ b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
@@ -33,9 +33,8 @@
 /* Offset of the last bit allocated in HWCAP.  */
 #define _DL_HWCAP_LAST 15

-/* HWCAP_CPUID should be available by default to influence IFUNC as well as
-   library search.  */
+/* No additional library search paths.  */

 static inline const char *
 __attribute__ ((unused))

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2020-03-25 18:37 [2.26 COMMITTED] aarch64: Remove HWCAP_CPUID from HWCAP_IMPORTANT Wilco Dijkstra

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