Add common write_memory and read_memory NetBSD routines

Instead of sharing the native-only code with all BSDs with slightly
different semantics of the kernels, share the NetBSD-only behavior beteen
the NetBSD native and gdbserver setup.

NetBSD does not differentiate the address space I and D in the
operations (contrary to OpenBSD). NetBSD handles EACCES that integrates
with NetBSD specific PaX MPROTECT error handling.

Add a verbose message in the native client that an operation could be
cancelled due to PaX MPROTECT setup.

gdb/ChangeLog:

       * nat/netbsd-nat.c (write_memory, read_memory): Add.
       * nat/netbsd-nat.h (write_memory, read_memory): Likewise.
       * nbsd-nat.c (nbsd_nat_target::xfer_partial): Update.

gdbserver/ChangeLog:

       * netbsd-low.cc (netbsd_process_target::read_memory)
       (netbsd_process_target::write_memory): Update.

4 files changed, 131 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6a69e63..4dc729c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-10-07  Kamil Rytarowski  <n54@gmx.com>
+
+	* nat/netbsd-nat.c (write_memory, read_memory): Add.
+	* nat/netbsd-nat.h (write_memory, read_memory): Likewise.
+	* nbsd-nat.c (nbsd_nat_target::xfer_partial): Update.
+
 2020-10-07  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* break-catch-sig.c (signal_catch_counts): Make a static arrray.
diff --git a/gdb/nat/netbsd-nat.c b/gdb/nat/netbsd-nat.c
index 41b67cb..cae9cc2 100644
--- a/gdb/nat/netbsd-nat.c
+++ b/gdb/nat/netbsd-nat.c
@@ -210,4 +210,84 @@ qxfer_siginfo (pid_t pid, const char *annex, unsigned char *readbuf,
   return len;
 }
 
+/* See netbsd-nat.h.  */
+
+int
+write_memory (pid_t pid, unsigned const char *writebuf, CORE_ADDR offset,
+	      size_t len, size_t *xfered_len)
+{
+  struct ptrace_io_desc io;
+  io.piod_op = PIOD_WRITE_D;
+  io.piod_len = len;
+
+  size_t bytes_written = 0;
+
+  /* Zero length write always succeeds.  */
+  if (len > 0)
+    {
+      do
+	{
+	  io.piod_addr = (void *)(writebuf + bytes_written);
+	  io.piod_offs = (void *)(offset + bytes_written);
+
+	  errno = 0;
+	  int rv = ptrace (PT_IO, pid, &io, 0);
+	  if (rv == -1)
+	    {
+	      gdb_assert (errno != 0);
+	      return errno;
+	    }
+	  if (io.piod_len == 0)
+	    return 0;
+
+	  bytes_written += io.piod_len;
+	  io.piod_len = len - bytes_written;
+	}
+      while (bytes_written < len);
+    }
+
+  if (xfered_len != nullptr)
+    *xfered_len = bytes_written;
+
+  return 0;
+}
+
+/* See netbsd-nat.h.  */
+
+int
+read_memory (pid_t pid, unsigned char *readbuf, CORE_ADDR offset,
+	      size_t len, size_t *xfered_len)
+{
+  struct ptrace_io_desc io;
+  io.piod_op = PIOD_READ_D;
+  io.piod_len = len;
+
+  size_t bytes_read = 0;
+
+  /* Zero length read always succeeds.  */
+  if (len > 0)
+    {
+      do
+	{
+	  io.piod_offs = (void *)(offset + bytes_read);
+	  io.piod_addr = readbuf + bytes_read;
+
+	  int rv = ptrace (PT_IO, pid, &io, 0);
+	  if (rv == -1)
+	    return errno;
+	  if (io.piod_len == 0)
+	    return 0;
+
+	  bytes_read += io.piod_len;
+	  io.piod_len = len - bytes_read;
+	}
+      while (bytes_read < len);
+    }
+
+  if (xfered_len != nullptr)
+    *xfered_len = bytes_read;
+
+  return 0;
+}
+
 }
diff --git a/gdb/nat/netbsd-nat.h b/gdb/nat/netbsd-nat.h
index d77119b..594dec1 100644
--- a/gdb/nat/netbsd-nat.h
+++ b/gdb/nat/netbsd-nat.h
@@ -67,6 +67,28 @@ extern void enable_proc_events (pid_t pid);
 extern int qxfer_siginfo (pid_t pid, const char *annex, unsigned char *readbuf,
 			  unsigned const char *writebuf, CORE_ADDR offset,
 			  int len);
+
+/* Write gdb's LEN bytes from WRITEBUF and copy it to OFFSET in inferior
+   process' address space. The inferior is specified by PID.
+   Returns 0 on success or errno on failure and the number of bytes
+   on a successful transfer in XFERED_LEN.
+
+   This function assumes internally that the queried process is stopped and
+   traced.  */
+
+extern int write_memory (pid_t pid, unsigned const char *writebuf,
+			 CORE_ADDR offset, size_t len, size_t *xfered_len);
+
+/* Read inferior process's LEN bytes from OFFSET and copy it to WRITEBUF in
+   gdb's address space.
+   Returns 0 on success or errno on failure and the number of bytes
+   on a successful transfer in XFERED_LEN.
+
+   This function assumes internally that the queried process is stopped and
+   traced.  */
+
+extern int read_memory (pid_t pid, unsigned char *readbuf, CORE_ADDR offset,
+			size_t len, size_t *xfered_len);
 }
 
 #endif
diff --git a/gdb/nbsd-nat.c b/gdb/nbsd-nat.c
index 7a07fbf..46dcfac 100644
--- a/gdb/nbsd-nat.c
+++ b/gdb/nbsd-nat.c
@@ -764,6 +764,29 @@ nbsd_nat_target::xfer_partial (enum target_object object,
 	*xfered_len = len;
 	return TARGET_XFER_OK;
       }
+    case TARGET_OBJECT_MEMORY:
+      {
+	size_t xfered;
+	int res;
+	if (writebuf != nullptr)
+	  res = netbsd_nat::write_memory (pid, writebuf, offset, len, &xfered);
+	else
+	  res = netbsd_nat::read_memory (pid, readbuf, offset, len, &xfered);
+	if (res != 0)
+	  {
+	    if (res == EACCES)
+	      fprintf_unfiltered (gdb_stderr, "Cannot %s process at %s (%s). "
+				  "Is PaX MPROTECT active? See security(7), "
+				  "sysctl(7), paxctl(8)\n",
+				  (writebuf ? "write to" : "read from"),
+				  pulongest (offset), safe_strerror (errno));
+	    return TARGET_XFER_E_IO;
+	  }
+	if (xfered == 0)
+	  return TARGET_XFER_EOF;
+	*xfered_len = (ULONGEST) xfered;
+	return TARGET_XFER_OK;
+      }
     default:
       return inf_ptrace_target::xfer_partial (object, annex,
 					      readbuf, writebuf, offset,