aarch64: Guess L1 cache linesize for aarch64

Using the cache hierarchy linesize minimum in CTR_EL0.
See the comment within the code for rationale.

	* sysdeps/unix/sysv/linux/aarch64/sysconf.c: New file.

2 files changed, 59 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index e1146ba..d0ef94c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2017-11-03  Richard Henderson  <rth@twiddle.net>
+
+	* sysdeps/unix/sysv/linux/aarch64/sysconf.c: New file.
+
 2017-11-03  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	* sysdeps/aarch64/dl-tlsdesc.S (_dl_tlsdesc_dynamic): Optimize.
diff --git a/sysdeps/unix/sysv/linux/aarch64/sysconf.c b/sysdeps/unix/sysv/linux/aarch64/sysconf.c
new file mode 100644
index 0000000..30608dd
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/aarch64/sysconf.c
@@ -0,0 +1,55 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+static long int linux_sysconf (int name);
+
+/* Get the value of the system variable NAME.  */
+long int
+__sysconf (int name)
+{
+  unsigned ctr;
+
+  /* Unfortunately, the registers that contain the actual cache info
+     (CCSIDR_EL1, CLIDR_EL1, and CSSELR_EL1) are protected by the Linux
+     kernel (though they need not have been).  However, CTR_EL0 contains
+     the *minimum* linesize in the entire cache hierarchy, and is
+     accessible to userland, for use in __aarch64_sync_cache_range,
+     and it is a reasonable assumption that the L1 cache will have that
+     minimum line size.  */
+  switch (name)
+    {
+    case _SC_LEVEL1_ICACHE_LINESIZE:
+      asm("mrs\t%0, ctr_el0" : "=r"(ctr));
+      return 4 << (ctr & 0xf);
+    case _SC_LEVEL1_DCACHE_LINESIZE:
+      asm("mrs\t%0, ctr_el0" : "=r"(ctr));
+      return 4 << ((ctr >> 16) & 0xf);
+    }
+
+  return linux_sysconf (name);
+}
+
+/* Now the generic Linux version.  */
+#undef __sysconf
+#define __sysconf static linux_sysconf
+#include <sysdeps/unix/sysv/linux/sysconf.c>