tunables, aarch64: New tunable to override cpu

Add a new tunable (glibc.tune.cpu) to override CPU identification on
aarch64.  This is useful in two cases: one where it is desirable to
pretend to be another CPU for purposes of testing or because routines
written for that CPU are beneficial for specific workloads and second
where the underlying kernel does not support emulation of MRS to get
the MIDR of the CPU.

	* elf/dl-tunables.h (tunable_is_name): Move from...
	* elf/dl-tunables.c (is_name): ... here.
	(parse_tunables, __tunables_init): Adjust.
	* manual/tunables.texi: Document glibc.tune.cpu.
	* sysdeps/aarch64/dl-tunables.list: New file.
	* sysdeps/unix/sysv/linux/aarch64/cpu-features.c (struct
	cpu_list): New type.
	(cpu_list): New list of CPU names and their MIDR.
	(get_midr_from_mcpu): New function.
	(init_cpu_features): Override MIDR if necessary.

2 files changed, 21 insertions, 20 deletions

diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index b3c1392..44c160c 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -33,22 +33,6 @@
 # define GLIBC_TUNABLES "GLIBC_TUNABLES"
 #endif
 
-/* Compare environment or tunable names, bounded by the name hardcoded in
-   glibc.  */
-static bool
-is_name (const char *orig, const char *envname)
-{
-  for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
-    if (*orig != *envname)
-      break;
-
-  /* The ENVNAME is immediately followed by a value.  */
-  if (*orig == '\0' && *envname == '=')
-    return true;
-  else
-    return false;
-}
-
 #if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
 static char *
 tunables_strdup (const char *in)
@@ -235,7 +219,7 @@ parse_tunables (char *tunestr, char *valstring)
 	{
 	  tunable_t *cur = &tunable_list[i];
 
-	  if (is_name (cur->name, name))
+	  if (tunable_is_name (cur->name, name))
 	    {
 	      /* If we are in a secure context (AT_SECURE) then ignore the tunable
 		 unless it is explicitly marked as secure.  Tunable values take
@@ -318,7 +302,7 @@ __tunables_init (char **envp)
 			       &prev_envp)) != NULL)
     {
 #if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
-      if (is_name (GLIBC_TUNABLES, envname))
+      if (tunable_is_name (GLIBC_TUNABLES, envname))
 	{
 	  char *new_env = tunables_strdup (envname);
 	  if (new_env != NULL)
@@ -341,7 +325,7 @@ __tunables_init (char **envp)
 	  const char *name = cur->env_alias;
 
 	  /* We have a match.  Initialize and move on to the next line.  */
-	  if (is_name (name, envname))
+	  if (tunable_is_name (name, envname))
 	    {
 	      /* For AT_SECURE binaries, we need to check the security settings of
 		 the tunable and decide whether we read the value and also whether
@@ -356,7 +340,7 @@ __tunables_init (char **envp)
 
 		      while (*ep != NULL)
 			{
-			  if (is_name (name, *ep))
+			  if (tunable_is_name (name, *ep))
 			    {
 			      char **dp = ep;
 
diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
index 6c49dcb..c92882a 100644
--- a/elf/dl-tunables.h
+++ b/elf/dl-tunables.h
@@ -111,5 +111,22 @@ rtld_hidden_proto (__tunable_get_val)
 # define TUNABLES_FRONTEND_valstring 1
 /* The default value for TUNABLES_FRONTEND.  */
 # define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
+
+/* Compare two name strings, bounded by the name hardcoded in glibc.  */
+static inline bool
+__always_inline
+tunable_is_name (const char *orig, const char *envname)
+{
+  for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
+    if (*orig != *envname)
+      break;
+
+  /* The ENVNAME is immediately followed by a value.  */
+  if (*orig == '\0' && *envname == '=')
+    return true;
+  else
+    return false;
+}
+
 #endif
 #endif