AArch64: Implement memory tagging target methods for AArch64

The patch implements the memory tagging target hooks for AArch64, so we
can handle MTE.

gdb/ChangeLog:

2021-03-24  Luis Machado  <luis.machado@linaro.org>

	* Makefile.in (ALL_64_TARGET_OBS): Add arch/aarch64-mte-linux.o.
	(HFILES_NO_SRCDIR): Add arch/aarch64-mte-linux.h and
	nat/aarch64-mte-linux-ptrace.h.
	* aarch64-linux-nat.c: Include nat/aarch64-mte-linux-ptrace.h.
	(aarch64_linux_nat_target) <supports_memory_tagging>: New method
	override.
	<fetch_memtags>: New method override.
	<store_memtags>: New method override.
	(aarch64_linux_nat_target::supports_memory_tagging): New method.
	(aarch64_linux_nat_target::fetch_memtags): New method.
	(aarch64_linux_nat_target::store_memtags): New method.
	* arch/aarch64-mte-linux.c: New file.
	* arch/aarch64-mte-linux.h: Include gdbsupport/common-defs.h.
	(AARCH64_MTE_GRANULE_SIZE): Define.
	(aarch64_memtag_type): New enum.
	(aarch64_mte_get_tag_granules): New prototype.
	* configure.nat (NATDEPFILES): Add nat/aarch64-mte-linux-ptrace.o.
	* configure.tgt (aarch64*-*-linux*): Add arch/aarch64-mte-linux.o.
	* nat/aarch64-mte-linux-ptrace.c: New file.
	* nat/aarch64-mte-linux-ptrace.h: New file.

2 files changed, 227 insertions, 0 deletions

diff --git a/gdb/nat/aarch64-mte-linux-ptrace.c b/gdb/nat/aarch64-mte-linux-ptrace.c
new file mode 100644
index 0000000..47f4ab6
--- /dev/null
+++ b/gdb/nat/aarch64-mte-linux-ptrace.c
@@ -0,0 +1,210 @@
+/* Common Linux native ptrace code for AArch64 MTE.
+
+   Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "gdbsupport/common-defs.h"
+#include "gdbsupport/byte-vector.h"
+
+#include "arch/aarch64.h"
+#include "arch/aarch64-mte-linux.h"
+#include "nat/aarch64-linux.h"
+#include "nat/aarch64-mte-linux-ptrace.h"
+
+#include "linux-ptrace.h"
+#include <sys/uio.h>
+
+/* Helper function to display various possible errors when reading
+   MTE tags.  */
+
+static void ATTRIBUTE_NORETURN
+aarch64_mte_linux_peek_error (int error)
+{
+  switch (error)
+    {
+    case EIO:
+      perror_with_name (_("PEEKMTETAGS not supported"));
+      break;
+    case EFAULT:
+      perror_with_name (_("Couldn't fetch allocation tags"));
+      break;
+    case EOPNOTSUPP:
+      perror_with_name (_("PROT_ME not enabled for requested address"));
+    default:
+      perror_with_name (_("Unknown MTE error"));
+      break;
+    }
+}
+
+/* Helper function to display various possible errors when writing
+   MTE tags.  */
+
+static void ATTRIBUTE_NORETURN
+aarch64_mte_linux_poke_error (int error)
+{
+  switch (error)
+    {
+    case EIO:
+      perror_with_name (_("POKEMTETAGS not supported"));
+      break;
+    case EFAULT:
+      perror_with_name (_("Couldn't store allocation tags"));
+      break;
+    case EOPNOTSUPP:
+      perror_with_name (_("PROT_ME not enabled for requested address"));
+    default:
+      perror_with_name (_("Unknown MTE error"));
+      break;
+    }
+}
+
+/* Helper to prepare a vector of tags to be passed on to the kernel.  The
+   main purpose of this function is to optimize the number of calls to
+   ptrace if we're writing too many tags at once, like a pattern fill
+   request.
+
+   Return a vector of tags of up to MAX_SIZE size, containing the tags that
+   must be passed on to the kernel, extracted from TAGS, starting at POS.
+   GRANULES is the number of tag granules to be modified.  */
+
+static gdb::byte_vector
+prepare_tag_vector (size_t granules, const gdb::byte_vector &tags, size_t pos,
+		    size_t max_size)
+{
+  gdb::byte_vector t;
+
+  if (granules == 0)
+    return t;
+
+  gdb_assert (tags.size () > 0 && max_size > 0);
+
+  if (granules > AARCH64_MTE_TAGS_MAX_SIZE)
+    t.resize (AARCH64_MTE_TAGS_MAX_SIZE);
+  else
+    t.resize (granules);
+
+  size_t tag_count = tags.size ();
+
+  for (size_t i = 0; i < t.size (); i++)
+    t[i] = tags[(pos + i) % tag_count];
+
+  return t;
+}
+
+/* See nat/aarch64-mte-linux-ptrace.h */
+
+bool
+aarch64_mte_fetch_memtags (int tid, CORE_ADDR address, size_t len,
+			   gdb::byte_vector &tags)
+{
+  size_t ntags = aarch64_mte_get_tag_granules (address, len,
+					       AARCH64_MTE_GRANULE_SIZE);
+
+  /* If the memory range contains no tags, nothing left to do.  */
+  if (ntags == 0)
+    return true;
+
+  gdb_byte tagbuf[ntags];
+
+  struct iovec iovec;
+  iovec.iov_base = tagbuf;
+  iovec.iov_len = ntags;
+
+  tags.clear ();
+  bool done_reading = false;
+
+  /* The kernel may return less tags than we requested.  Loop until we've read
+     all the requested tags or until we get an error.  */
+  while (!done_reading)
+    {
+      /* Attempt to read ntags allocation tags from the kernel.  */
+      if (ptrace (PTRACE_PEEKMTETAGS, tid, address, &iovec) < 0)
+	aarch64_mte_linux_peek_error (errno);
+
+      /* Make sure the kernel returned at least one tag.  */
+      if (iovec.iov_len <= 0)
+	{
+	  tags.clear ();
+	  return false;
+	}
+
+      /* Copy the tags the kernel returned.  */
+      for (size_t i = 0; i < iovec.iov_len; i++)
+	tags.push_back (tagbuf[i]);
+
+      /* Are we done reading tags?  */
+      if (tags.size () == ntags)
+	done_reading = true;
+      else
+	{
+	  address += iovec.iov_len * AARCH64_MTE_GRANULE_SIZE;
+	  iovec.iov_len = ntags - iovec.iov_len;
+	}
+    }
+  return true;
+}
+
+/* See nat/aarch64-mte-linux-ptrace.h */
+
+bool
+aarch64_mte_store_memtags (int tid, CORE_ADDR address, size_t len,
+			   const gdb::byte_vector &tags)
+{
+  if (tags.size () == 0)
+    return true;
+
+  /* Get the number of tags we need to write.  */
+  size_t ntags = aarch64_mte_get_tag_granules (address, len,
+					       AARCH64_MTE_GRANULE_SIZE);
+
+  /* If the memory range contains no tags, nothing left to do.  */
+  if (ntags == 0)
+    return true;
+
+  bool done_writing = false;
+  size_t tags_written = 0;
+
+  /* Write all the tags, AARCH64_MTE_TAGS_MAX_SIZE blocks at a time.  */
+  while (!done_writing)
+    {
+      gdb::byte_vector t = prepare_tag_vector (ntags - tags_written, tags,
+					       tags_written,
+					       AARCH64_MTE_TAGS_MAX_SIZE);
+
+      struct iovec iovec;
+      iovec.iov_base = t.data ();
+      iovec.iov_len = t.size ();
+
+      /* Request the kernel to update the allocation tags.  */
+      if (ptrace (PTRACE_POKEMTETAGS, tid, address, &iovec) < 0)
+	aarch64_mte_linux_poke_error (errno);
+
+      /* Make sure the kernel wrote at least one tag.  */
+      if (iovec.iov_len <= 0)
+	return false;
+
+      tags_written += iovec.iov_len;
+
+      /* Are we done writing tags?  */
+      if (tags_written == ntags)
+	done_writing = true;
+      else
+	address += iovec.iov_len * AARCH64_MTE_GRANULE_SIZE;
+    }
+
+  return true;
+}
diff --git a/gdb/nat/aarch64-mte-linux-ptrace.h b/gdb/nat/aarch64-mte-linux-ptrace.h
index 65ac141..f8c203b 100644
--- a/gdb/nat/aarch64-mte-linux-ptrace.h
+++ b/gdb/nat/aarch64-mte-linux-ptrace.h
@@ -30,4 +30,21 @@
 #define PTRACE_POKEMTETAGS	  34
 #endif
 
+/* Maximum number of tags to pass at once to the kernel.  */
+#define AARCH64_MTE_TAGS_MAX_SIZE 4096
+
+/* Read the allocation tags from memory range [ADDRESS, ADDRESS + LEN)
+   into TAGS.
+
+   Returns true if successful and false otherwise.  */
+extern bool aarch64_mte_fetch_memtags (int tid, CORE_ADDR address, size_t len,
+				       gdb::byte_vector &tags);
+
+/* Write the allocation tags contained in TAGS into the memory range
+   [ADDRESS, ADDRESS + LEN).
+
+   Returns true if successful and false otherwise.  */
+extern bool aarch64_mte_store_memtags (int tid, CORE_ADDR address, size_t len,
+				       const gdb::byte_vector &tags);
+
 #endif /* NAT_AARCH64_MTE_LINUX_PTRACE_H */