[glibc/release/2.26/master] aarch64: Remove HWCAP_CPUID from HWCAP_IMPORTANT

[glibc/release/2.26/master] aarch64: Remove HWCAP_CPUID from HWCAP_IMPORTANT

[Wilco Dijkstra]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c6ed5b563c780032a52b7a1cfa0ce75affd4c167

commit c6ed5b563c780032a52b7a1cfa0ce75affd4c167
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Jun 28 14:43:07 2018 +0100

    aarch64: Remove HWCAP_CPUID from HWCAP_IMPORTANT
    
    This partially reverts
    
    commit f82e9672ad89ea1ef40bbe1af71478e255e87c5e
    Author:     Siddhesh Poyarekar <siddhesh@sourceware.org>
    
        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:
    
      GLIBC_TUNABLES=glibc.tune.cpu=generic
    
            * 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)

Diff:
---
 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 5f3df320bc..732e89dcd5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2018-07-06  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+	* 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  <wdijkstr@arm.com>
 
 	* 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 50297bc409..e71d636e46 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;
 
 #if HAVE_TUNABLES
@@ -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));
       else
 	midr = 0;
diff --git a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
index 0333a18267..63bdf75bb5 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.  */
-#define HWCAP_IMPORTANT HWCAP_CPUID
+/* No additional library search paths.  */
+#define HWCAP_IMPORTANT 0
 
 static inline const char *
 __attribute__ ((unused))