[PATCH v2 2/8] AArch64: Use HWCAP to detect pauth feature

[Alan Hayward]

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

gdb/ChangeLog:

2019-03-06  Alan Hayward  <alan.hayward@arm.com>
	    Jiong Wang  <jiong.wang@arm.com>

	* 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:

2019-03-06  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.
---
 gdb/aarch64-linux-nat.c           |  7 +++++--
 gdb/aarch64-linux-tdep.c          | 16 +++++++++++----
 gdb/aarch64-linux-tdep.h          |  6 ++++++
 gdb/gdbserver/linux-aarch64-low.c | 33 +++++++++++++++++++++++++++++--
 4 files changed, 54 insertions(+), 8 deletions(-)

diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
index f58a41e195..8a7006165e 100644
--- a/gdb/aarch64-linux-nat.c
+++ b/gdb/aarch64-linux-nat.c
@@ -606,8 +606,11 @@ aarch64_linux_nat_target::read_description ()
   if (ret == 0)
     return tdesc_arm_with_neon;
 
-  /* pauth not yet supported.  */
-  return aarch64_read_description (aarch64_sve_get_vq (tid), false);
+  CORE_ADDR hwcap = 0;
+  bool pauth_p = aarch64_linux_get_hwcap (&hwcap)
+		 && (hwcap & AARCH64_HWCAP_PACA);
+
+  return aarch64_read_description (aarch64_sve_get_vq (tid), pauth_p);
 }
 
 /* Convert a native/host siginfo object, into/from the siginfo in the
diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 445019accc..5eeafa456c 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -637,12 +637,11 @@ aarch64_linux_core_read_description (struct gdbarch *gdbarch,
 {
   CORE_ADDR aarch64_hwcap = 0;
 
-  if (target_auxv_search (target, AT_HWCAP, &aarch64_hwcap) != 1)
-    return NULL;
+  if (!aarch64_linux_get_hwcap (&aarch64_hwcap))
+    return nullptr;
 
-  /* pauth not yet supported.  */
   return aarch64_read_description (aarch64_linux_core_read_vq (gdbarch, abfd),
-				   false);
+				   aarch64_hwcap & AARCH64_HWCAP_PACA);
 }
 
 /* Implementation of `gdbarch_stap_is_single_operand', as defined in
@@ -1420,6 +1419,15 @@ aarch64_linux_gcc_target_options (struct gdbarch *gdbarch)
   return NULL;
 }
 
+/* See aarch64-linux-tdep.h.  */
+
+bool
+aarch64_linux_get_hwcap (CORE_ADDR *hwcap)
+{
+  *hwcap = 0;
+  return target_auxv_search (current_top_target (), AT_HWCAP, hwcap) == 1;
+}
+
 static void
 aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
diff --git a/gdb/aarch64-linux-tdep.h b/gdb/aarch64-linux-tdep.h
index 814222ead0..244095cbca 100644
--- a/gdb/aarch64-linux-tdep.h
+++ b/gdb/aarch64-linux-tdep.h
@@ -36,4 +36,10 @@
 extern const struct regset aarch64_linux_gregset;
 extern const struct regset aarch64_linux_fpregset;
 
+/* 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.  */
+bool aarch64_linux_get_hwcap (CORE_ADDR *hwcap);
+
 #endif /* AARCH64_LINUX_TDEP_H */
diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index db329da4dc..e2e25f0e27 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;
-- 
2.17.2 (Apple Git-113)