AArch64: Use HWCAP to detect pauth feature

Add aarch64_get_hwcap functions for reading the HWCAP.
From this extract the PACA value and use this to enable pauth.

gdb/ChangeLog:

	* aarch64-linux-nat.c
	(aarch64_linux_nat_target::read_description): Read PACA hwcap.
	* aarch64-linux-tdep.c
	(aarch64_linux_core_read_description): Likewise.
	(aarch64_linux_get_hwcap): New function.
	* aarch64-linux-tdep.h (AARCH64_HWCAP_PACA): New define.
	(aarch64_linux_get_hwcap): New declaration.

gdb/gdbserver/ChangeLog:

	* linux-aarch64-low.c (AARCH64_HWCAP_PACA): New define.
	(aarch64_get_hwcap): New function.
	(aarch64_arch_setup): Read APIA hwcap.

2 files changed, 38 insertions, 2 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 9fdbe1d..3b585ca 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,6 +1,13 @@
 2019-03-22  Alan Hayward  <alan.hayward@arm.com>
 	    Jiong Wang  <jiong.wang@arm.com>
 
+	* linux-aarch64-low.c (AARCH64_HWCAP_PACA): New define.
+	(aarch64_get_hwcap): New function.
+	(aarch64_arch_setup): Read APIA hwcap.
+
+2019-03-22  Alan Hayward  <alan.hayward@arm.com>
+	    Jiong Wang  <jiong.wang@arm.com>
+
 	* linux-aarch64-ipa.c (get_ipa_tdesc): Add pauth param.
 	(initialize_low_tracepoint): Likewise.
 	* linux-aarch64-low.c (aarch64_arch_setup): Likewise.
diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index db329da..e2e25f0 100644
--- a/gdb/gdbserver/linux-aarch64-low.c
+++ b/gdb/gdbserver/linux-aarch64-low.c
@@ -485,6 +485,33 @@ aarch64_linux_new_fork (struct process_info *parent,
   *child->priv->arch_private = *parent->priv->arch_private;
 }
 
+/* Matches HWCAP_PACA in kernel header arch/arm64/include/uapi/asm/hwcap.h.  */
+#define AARCH64_HWCAP_PACA (1 << 30)
+
+/* Fetch the AT_HWCAP entry from the auxv vector.  */
+
+static bool
+aarch64_get_hwcap (unsigned long *valp)
+{
+  unsigned char *data = (unsigned char *) alloca (16);
+  int offset = 0;
+
+  while ((*the_target->read_auxv) (offset, data, 16) == 16)
+    {
+      unsigned long *data_p = (unsigned long *)data;
+      if (data_p[0] == AT_HWCAP)
+	{
+	  *valp = data_p[1];
+	  return true;
+	}
+
+      offset += 16;
+    }
+
+  *valp = 0;
+  return false;
+}
+
 /* Implementation of linux_target_ops method "arch_setup".  */
 
 static void
@@ -501,8 +528,10 @@ aarch64_arch_setup (void)
   if (is_elf64)
     {
       uint64_t vq = aarch64_sve_get_vq (tid);
-      /* pauth not yet supported.  */
-      current_process ()->tdesc = aarch64_linux_read_description (vq, false);
+      unsigned long hwcap = 0;
+      bool pauth_p = aarch64_get_hwcap (&hwcap) && (hwcap & AARCH64_HWCAP_PACA);
+
+      current_process ()->tdesc = aarch64_linux_read_description (vq, pauth_p);
     }
   else
     current_process ()->tdesc = tdesc_arm_with_neon;