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List:       glibc-cvs
Subject:    [glibc/release/2.27/master] aarch64: Remove HWCAP_CPUID from HWCAP_IMPORTANT
From:       Wilco Dijkstra via Glibc-cvs <glibc-cvs () sourceware ! org>
Date:       2020-03-25 17:54:51
Message-ID: 20200325175451.2304A385E00B () sourceware ! org
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=599ebfacc0dbe4171eb83f179ae235badd593ee6


commit 599ebfacc0dbe4171eb83f179ae235badd593ee6
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 3682637c78..b8db0f270c 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 e3fb09edd8..540e93be27 100644
--- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
@@ -53,9 +53,6 @@ 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
@@ -69,7 +66,7 @@ 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 6887713149..c0dcce15a2 100644
--- a/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
+++ b/sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
@@ -27,9 +27,8 @@
 /* We cannot provide a general printing function.  */
 #define _dl_procinfo(type, word) -1
 
-/* 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))


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