Implement remote_bfd_iovec_stat

This commit adds a new packet "vFile:fstat:" to the remote protocol
that can be used by to retrieve information about files that have
been previously opened using vFile:open.  vFile:fstat: support is
added to GDB, and remote_bfd_iovec_stat is implemented using it.  If
vFile:fstat: is not supported by the remote GDB creates a dummy result
by zeroing the supplied stat structure and setting its st_size field
to INT_MAX.  This mimics GDB's previous behaviour, with the exception
that GDB did not previously zero the structure so all other fields
would have been returned unchanged, which is to say very likely
populated with random values from the stack.

gdb/ChangeLog:

	* remote-fileio.h (remote_fileio_to_host_stat): New declaration.
	* remote-fileio.c (remote_fileio_to_host_uint): New function.
	(remote_fileio_to_host_ulong): Likewise.
	(remote_fileio_to_host_mode): Likewise.
	(remote_fileio_to_host_time): Likewise.
	(remote_fileio_to_host_stat): Likewise.
	* remote.c (PACKET_vFile_fstat): New enum value.
	(remote_protocol_features): Register the "vFile:fstat" feature.
	(remote_hostio_fstat): New function.
	(remote_bfd_iovec_stat): Use the above.
	(_initialize_remote): Register new "set/show remote
	hostio-fstat-packet" command.
	* symfile.c (separate_debug_file_exists): Update comment.
	* NEWS: Announce new vFile:fstat packet.

gdb/doc/ChangeLog:

	* gdb.texinfo (Remote Configuration): Document the
	"set/show remote hostio-fstat-packet" command.
	(General Query Packets): Document the vFile:fstat
	qSupported features.
	(Host I/O Packets): Document the vFile:fstat packet.

1 files changed, 83 insertions, 4 deletions

diff --git a/gdb/remote.c b/gdb/remote.c
index 19f56a1..9aaee13 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1258,6 +1258,7 @@ enum {
   PACKET_vFile_close,
   PACKET_vFile_unlink,
   PACKET_vFile_readlink,
+  PACKET_vFile_fstat,
   PACKET_qXfer_auxv,
   PACKET_qXfer_features,
   PACKET_qXfer_libraries,
@@ -4047,7 +4048,9 @@ static const struct protocol_feature remote_protocol_features[] = {
   { "Qbtrace-conf:bts:size", PACKET_DISABLE, remote_supported_packet,
     PACKET_Qbtrace_conf_bts_size },
   { "swbreak", PACKET_DISABLE, remote_supported_packet, PACKET_swbreak_feature },
-  { "hwbreak", PACKET_DISABLE, remote_supported_packet, PACKET_hwbreak_feature }
+  { "hwbreak", PACKET_DISABLE, remote_supported_packet, PACKET_hwbreak_feature },
+  { "vFile:fstat", PACKET_DISABLE, remote_supported_packet,
+    PACKET_vFile_fstat },
 };
 
 static char *remote_support_xml;
@@ -10064,6 +10067,68 @@ remote_hostio_readlink (struct target_ops *self,
   return ret;
 }
 
+/* Read information about the open file FD on the remote target
+   into ST.  Return 0 on success, or -1 if an error occurs (and
+   set *REMOTE_ERRNO).  */
+
+static int
+remote_hostio_fstat (struct target_ops *self,
+		     int fd, struct stat *st,
+		     int *remote_errno)
+{
+  struct remote_state *rs = get_remote_state ();
+  char *p = rs->buf;
+  int left = get_remote_packet_size ();
+  int attachment_len, ret;
+  char *attachment;
+  struct fio_stat fst;
+  int read_len;
+
+  if (packet_support (PACKET_vFile_fstat) != PACKET_ENABLE)
+    {
+      /* Strictly we should return -1, ENOSYS here, but when
+	 "set sysroot remote:" was implemented in August 2008
+	 BFD's need for a stat function was sidestepped with
+	 this hack.  This was not remedied until March 2015
+	 so we retain the previous behavior to avoid breaking
+	 compatibility.
+
+	 Note that the memset is a March 2015 addition; older
+	 GDBs set st_size *and nothing else* so the structure
+	 would have garbage in all other fields.  This might
+	 break something but retaining the previous behavior
+	 here would be just too wrong.  */
+
+      memset (st, 0, sizeof (struct stat));
+      st->st_size = INT_MAX;
+      return 0;
+    }
+
+  remote_buffer_add_string (&p, &left, "vFile:fstat:");
+
+  remote_buffer_add_int (&p, &left, fd);
+
+  ret = remote_hostio_send_command (p - rs->buf, PACKET_vFile_fstat,
+				    remote_errno, &attachment,
+				    &attachment_len);
+  if (ret < 0)
+    return ret;
+
+  read_len = remote_unescape_input ((gdb_byte *) attachment, attachment_len,
+				    (gdb_byte *) &fst, sizeof (fst));
+
+  if (read_len != ret)
+    error (_("vFile:fstat returned %d, but %d bytes."), ret, read_len);
+
+  if (read_len != sizeof (fst))
+    error (_("vFile:fstat returned %d bytes, but expecting %d."),
+	   read_len, (int) sizeof (fst));
+
+  remote_fileio_to_host_stat (&fst, st);
+
+  return 0;
+}
+
 static int
 remote_fileio_errno_to_host (int errnum)
 {
@@ -10208,9 +10273,20 @@ remote_bfd_iovec_pread (struct bfd *abfd, void *stream, void *buf,
 static int
 remote_bfd_iovec_stat (struct bfd *abfd, void *stream, struct stat *sb)
 {
-  /* FIXME: We should probably implement remote_hostio_stat.  */
-  sb->st_size = INT_MAX;
-  return 0;
+  int fd = *(int *) stream;
+  int remote_errno;
+  int result;
+
+  result = remote_hostio_fstat (find_target_at (process_stratum),
+				fd, sb, &remote_errno);
+
+  if (result == -1)
+    {
+      errno = remote_fileio_errno_to_host (remote_errno);
+      bfd_set_error (bfd_error_system_call);
+    }
+
+  return result;
 }
 
 int
@@ -12351,6 +12427,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_readlink],
 			 "vFile:readlink", "hostio-readlink", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_fstat],
+			 "vFile:fstat", "hostio-fstat", 0);
+
   add_packet_config_cmd (&remote_protocol_packets[PACKET_vAttach],
 			 "vAttach", "attach", 0);