[PATCH v1] gdbserver: widen the stat fields returned by the vFile packets

[Abhay Kandpal <abhay@linux.ibm.com>]

The struct sent by the vFile:fstat, vFile:stat and vFile:lstat packets
declares st_dev, st_ino, st_nlink, st_rdev and the three timestamps as
4-byte fields, while the corresponding struct stat members are 8 bytes
on a 64-bit host.  The values are silently truncated.

This is not visible on a filesystem whose inode numbers stay below
2^32, but it is on a large one.  On an 86 TB xfs volume,
gdb.server/fileio-packets.exp fails because the inode reported by
vFile:lstat does not match the one reported locally:

  remote = {..., 'st_ino': 2161233200, ...}
  local  = {..., 'st_ino': 122420317488, ...}

The field widths cannot simply be changed, as that would alter the wire
layout and break communication between different versions of GDB and
gdbserver.  Add a new 'stat64' qSupported feature instead.  When both
sides report it, the vFile stat packets return struct fio_stat_wide, in
which the six too-narrow fields are 8 bytes; otherwise the existing
struct fio_stat is used, exactly as before.

Internally both GDB and gdbserver now work with the wide struct, and
the conversion happens at the wire boundary: gdbserver narrows the
result before sending it if the feature was not negotiated, and GDB
selects the unpacker by the length of the reply.  Narrowing a value
which does not fit now produces a warning rather than truncating
silently.

Only the vFile packets are changed.  The F-packet file-i/o protocol
uses the same struct, but writes it directly into inferior memory,
where the target reads it as the layout documented in the manual under
"struct stat"; that layout is left alone.

While here, drop a duplicate include of gdbsupport/fileio.h from
gdbserver/hostio.cc.

Tested on powerpc64le-linux; gdb.server/fileio-packets.exp now passes on
a filesystem with inode numbers above 2^32 and continues to pass on one
without, with no unexpected failures in the full testsuite.

gdb/
	* NEWS: Mention the stat64 feature.
	* doc/gdb.texinfo (General Query Packets): Document the stat64
	feature.
	(Host I/O Packets): Mention the wide reply format.
	(struct stat64): New node.
	* remote-fileio.c (remote_fileio_to_host_ulong8): New function.
	(remote_fileio_wide_to_host_stat): New function.
	* remote-fileio.h (remote_fileio_wide_to_host_stat): Declare.
	* remote.c (PACKET_stat64_feature): New enum value.
	(remote_features::stat64_feature): New method.
	(remote_protocol_features): Add stat64.
	(remote_target::remote_query_supported): Send stat64+.
	(fileio_process_fstat_and_lstat_reply): Handle both formats.
	(INIT_GDB_FILE): Add the stat64-feature packet command.
	* testsuite/gdb.server/fileio-packets.py (decode_stat_reply):
	Handle both the narrow and wide reply formats.

gdbserver/
	* hostio.cc (handle_fstat, handle_stat, handle_lstat): Send the
	wide struct when the feature is negotiated.
	* server.cc (handle_query): Handle and report stat64.
	* server.h (client_state::stat64_feature): New member.

gdbsupport/
	* fileio.cc (host_to_fileio_stat_wide): New function.
	(narrow_field, fileio_stat_wide_to_narrow): New functions.
	* fileio.h (struct fio_stat_wide): New struct.
	(bigendian_to_host): New function.
	(host_to_fileio_stat_wide, fileio_stat_wide_to_narrow): Declare.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34567
---
This patch is reg tested.

 gdb/NEWS                                   |  12 +++
 gdb/doc/gdb.texinfo                        |  49 ++++++++++
 gdb/remote-fileio.c                        |  35 ++++++-
 gdb/remote-fileio.h                        |   4 +
 gdb/remote.c                               |  36 +++++--
 gdb/testsuite/gdb.server/fileio-packets.py |  59 +++++++-----
 gdbserver/hostio.cc                        | 106 +++++++++++++++------
 gdbserver/server.cc                        |   4 +-
 gdbserver/server.h                         |   5 +
 gdbsupport/fileio.cc                       |  70 ++++++++++++++
 gdbsupport/fileio.h                        |  54 ++++++++++-
 11 files changed, 368 insertions(+), 66 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index 222f38e3d52..de8346350ab 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,18 @@
 
 *** Changes since GDB 18
 
+* Changed remote packets
+
+stat64 in qSupported
+
+  The new stat64 feature within the qSupported packet allows GDB and
+  the stub to agree on a wider form of the stat structure returned by
+  the vFile:fstat, vFile:stat and vFile:lstat packets, in which st_dev,
+  st_ino, st_nlink, st_rdev and the three timestamps are 8 bytes rather
+  than 4.  The wider form is used only when both sides report the
+  feature; otherwise the existing format is used and values which do
+  not fit are truncated as before.
+
 *** Changes in GDB 18
 
 * Support for the Common Trace Format (CTF) has been removed.  GDB now
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 0030698dcee..cebf1fb3017 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -46112,6 +46112,11 @@ inspected, if @samp{qIsAddressTagged} (@pxref{qIsAddressTagged}) packet
 is not supported by the stub.  Access to the @file{/proc/@var{pid}/smaps}
 file is done via @samp{vFile} requests.
 
+@item stat64
+The remote stub supports the wider form of the stat structure returned
+by the @samp{vFile:fstat}, @samp{vFile:stat} and @samp{vFile:lstat}
+packets, as described in @ref{struct stat64}.
+
 @item error-message
 The remote stub supports replying with an error in a
 @samp{E.@var{errtext}} (@xref{textual error reply}) format from the
@@ -47358,6 +47363,9 @@ On success the information is returned as a binary attachment
 and the return value is the size of this attachment in bytes.
 If an error occurs the return value is -1.  The format of the
 returned binary attachment is as described in @ref{struct stat}.
+If both @value{GDBN} and the stub report the @samp{stat64} feature in
+the @samp{qSupported} exchange, the wider format described in
+@ref{struct stat64} is used instead.
 
 @item vFile:stat: @var{filename}
 Get information about the file @var{filename} on the target as if from
@@ -47365,6 +47373,9 @@ a @samp{stat} call.  On success the information is returned as a binary
 attachment and the return value is the size of this attachment in
 bytes.  If an error occurs the return value is -1.  The format of the
 returned binary attachment is as described in @ref{struct stat}.
+If both @value{GDBN} and the stub report the @samp{stat64} feature in
+the @samp{qSupported} exchange, the wider format described in
+@ref{struct stat64} is used instead.
 
 If @var{filename} is a symbolic link, then the information returned is
 about the file the link refers to, this is inline with the @samp{stat}
@@ -47376,6 +47387,9 @@ an @samp{lstat} call.  On success the information is returned as a
 binary attachment and the return value is the size of this attachment
 in bytes.  If an error occurs the return value is -1.  The format of
 the returned binary attachment is as described in @ref{struct stat}.
+If both @value{GDBN} and the stub report the @samp{stat64} feature in
+the @samp{qSupported} exchange, the wider format described in
+@ref{struct stat64} is used instead.
 
 This packet is identical to @samp{vFile:stat}, except if
 @var{filename} is a symbolic link, then this packet returns
@@ -48570,6 +48584,7 @@ protocol.
 * Pointer Values::
 * Memory Transfer::
 * struct stat::
+* struct stat64::
 * struct timeval::
 @end menu
 
@@ -48696,6 +48711,40 @@ Note that due to size differences between the host, target, and protocol
 representations of @code{struct stat} members, these members could eventually
 get truncated on the target.
 
+@node struct stat64
+@unnumberedsubsubsec struct stat64
+@cindex struct stat64, in file-i/o protocol
+
+When the @samp{stat64} feature has been negotiated, the buffer returned
+by the @samp{vFile:fstat}, @samp{vFile:stat} and @samp{vFile:lstat}
+packets uses the following representation instead:
+
+@smallexample
+struct stat64 @{
+    unsigned long st_dev;      /* device */
+    unsigned long st_ino;      /* inode */
+    mode_t        st_mode;     /* protection */
+    unsigned long st_nlink;    /* number of hard links */
+    unsigned int  st_uid;      /* user ID of owner */
+    unsigned int  st_gid;      /* group ID of owner */
+    unsigned long st_rdev;     /* device type (if inode device) */
+    unsigned long st_size;     /* total size, in bytes */
+    unsigned long st_blksize;  /* blocksize for filesystem I/O */
+    unsigned long st_blocks;   /* number of blocks allocated */
+    unsigned long st_atime;    /* time of last access */
+    unsigned long st_mtime;    /* time of last modification */
+    unsigned long st_ctime;    /* time of last change */
+@};
+@end smallexample
+
+This structure is of size 92 bytes.  The fields have the same meanings
+as in @ref{struct stat}, but @code{st_dev}, @code{st_ino},
+@code{st_nlink}, @code{st_rdev} and the three timestamps are wide enough
+to hold the values found on a 64-bit host without truncation.
+
+This representation is only used by the @samp{vFile} packets; the
+File-I/O protocol always uses @ref{struct stat}.
+
 @node struct timeval
 @unnumberedsubsubsec struct timeval
 @cindex struct timeval, in file-i/o protocol
diff --git a/gdb/remote-fileio.c b/gdb/remote-fileio.c
index a151161371d..76deb80d10a 100644
--- a/gdb/remote-fileio.c
+++ b/gdb/remote-fileio.c
@@ -1220,7 +1220,40 @@ remote_fileio_to_host_stat (struct fio_stat *fst, struct stat *st)
   st->st_mtime = remote_fileio_to_host_time (fst->fst_mtime);
   st->st_ctime = remote_fileio_to_host_time (fst->fst_ctime);
 }
-\f
+
+/* Unpack an 8-byte protocol field.  */
+
+static ULONGEST
+remote_fileio_to_host_ulong8 (const char *fnum)
+{
+  return extract_unsigned_integer ((const gdb_byte *) fnum, 8,
+				   BFD_ENDIAN_BIG);
+}
+
+/* See remote-fileio.h.  */
+
+void
+remote_fileio_wide_to_host_stat (struct fio_stat_wide *fst, struct stat *st)
+{
+  memset (st, 0, sizeof (struct stat));
+  st->st_dev = remote_fileio_to_host_ulong8 (fst->fst_dev);
+  st->st_ino = remote_fileio_to_host_ulong8 (fst->fst_ino);
+  st->st_mode = remote_fileio_to_host_mode (fst->fst_mode);
+  st->st_nlink = remote_fileio_to_host_ulong8 (fst->fst_nlink);
+  st->st_uid = remote_fileio_to_host_uint (fst->fst_uid);
+  st->st_gid = remote_fileio_to_host_uint (fst->fst_gid);
+  st->st_rdev = remote_fileio_to_host_ulong8 (fst->fst_rdev);
+  st->st_size = remote_fileio_to_host_ulong8 (fst->fst_size);
+#ifdef HAVE_STRUCT_STAT_ST_BLKSIZE
+  st->st_blksize = remote_fileio_to_host_ulong8 (fst->fst_blksize);
+#endif
+#if HAVE_STRUCT_STAT_ST_BLOCKS
+  st->st_blocks = remote_fileio_to_host_ulong8 (fst->fst_blocks);
+#endif
+  st->st_atime = remote_fileio_to_host_ulong8 (fst->fst_atime);
+  st->st_mtime = remote_fileio_to_host_ulong8 (fst->fst_mtime);
+  st->st_ctime = remote_fileio_to_host_ulong8 (fst->fst_ctime);
+}
 
 static void
 set_system_call_allowed (const char *args, int from_tty)
diff --git a/gdb/remote-fileio.h b/gdb/remote-fileio.h
index d01b3df92ca..95fb042fc9d 100644
--- a/gdb/remote-fileio.h
+++ b/gdb/remote-fileio.h
@@ -44,4 +44,8 @@ extern void initialize_remote_fileio (
 extern void remote_fileio_to_host_stat (struct fio_stat *fst,
 					struct stat *st);
 
+/* Unpack a struct fio_stat_wide.  */
+extern void remote_fileio_wide_to_host_stat (struct fio_stat_wide *fst,
+					     struct stat *st);
+
 #endif /* GDB_REMOTE_FILEIO_H */
diff --git a/gdb/remote.c b/gdb/remote.c
index 76cf6b5234f..03cb8a074b7 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -389,6 +389,8 @@ enum {
      packets and the tag violation stop replies.  */
   PACKET_memory_tagging_feature,
 
+  PACKET_stat64_feature,
+
   /* Support for the qIsAddressTagged packet.  */
   PACKET_qIsAddressTagged,
 
@@ -844,6 +846,9 @@ struct remote_features
   bool remote_memory_tagging_p () const
   { return packet_support (PACKET_memory_tagging_feature) == PACKET_ENABLE; }
 
+  bool stat64_feature () const
+  { return packet_support (PACKET_stat64_feature) == PACKET_ENABLE; }
+
   /* Returns true if there is support for sending vRun inferior arguments
      as a single string.  */
   bool remote_vrun_single_arg_p () const
@@ -6199,6 +6204,8 @@ static const struct protocol_feature remote_protocol_features[] = {
   { "no-resumed", PACKET_DISABLE, remote_supported_packet, PACKET_no_resumed },
   { "memory-tagging", PACKET_DISABLE, remote_supported_packet,
     PACKET_memory_tagging_feature },
+  { "stat64", PACKET_DISABLE, remote_supported_packet,
+    PACKET_stat64_feature },
   { "error-message", PACKET_ENABLE, remote_supported_packet,
     PACKET_accept_error_message },
   { "binary-upload", PACKET_DISABLE, remote_supported_packet, PACKET_x },
@@ -6309,6 +6316,10 @@ remote_target::remote_query_supported ()
 	  != AUTO_BOOLEAN_FALSE)
 	remote_query_supported_append (&q, "QThreadOptions+");
 
+      if (m_features.packet_set_cmd_state (PACKET_stat64_feature)
+	  != AUTO_BOOLEAN_FALSE)
+	remote_query_supported_append (&q, "stat64+");
+
       if (m_features.packet_set_cmd_state (PACKET_no_resumed)
 	  != AUTO_BOOLEAN_FALSE)
 	remote_query_supported_append (&q, "no-resumed+");
@@ -13663,29 +13674,35 @@ remote_target::fileio_readlink (struct inferior *inf, const char *filename,
    remote syscall reply.  EXPECTED_LEN is the length returned from the
    fstat or stat call, this the length of the returned data (in ATTACHMENT)
    once it has been decoded.  The fstat/stat result (from the ATTACHMENT
-   data) is to be placed in ST.  */
+   data) is to be placed in ST.
 
+   The reply holds either a struct fio_stat or, if the stat64 feature was
+   negotiated, the wider struct fio_stat_wide; the two are distinguished
+   by their length.  */
 static int
 fileio_process_fstat_and_lstat_reply (const char *attachment,
 				      int attachment_len,
 				      int expected_len,
 				      struct stat *st)
 {
-  struct fio_stat fst;
+  gdb_byte buf[sizeof (struct fio_stat_wide)];
 
   int read_len
     = remote_unescape_input ((gdb_byte *) attachment, attachment_len,
-			     (gdb_byte *) &fst, sizeof (fst));
+			     buf, sizeof (buf));
 
   if (read_len != expected_len)
     error (_("vFile:fstat returned %d, but %d bytes."),
 	   expected_len, 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);
+  if (read_len == sizeof (struct fio_stat_wide))
+    remote_fileio_wide_to_host_stat ((struct fio_stat_wide *) buf, st);
+  else if (read_len == sizeof (struct fio_stat))
+    remote_fileio_to_host_stat ((struct fio_stat *) buf, st);
+  else
+    error (_("vFile:fstat returned %d bytes, but expecting %d or %d."),
+	   read_len, (int) sizeof (struct fio_stat),
+	   (int) sizeof (struct fio_stat_wide));
 
   return 0;
 }
@@ -17039,6 +17056,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (PACKET_memory_tagging_feature,
 			 "memory-tagging-feature", "memory-tagging-feature", 0);
 
+  add_packet_config_cmd (PACKET_stat64_feature,
+			 "stat64-feature", "stat64-feature", 0);
+
   add_packet_config_cmd (PACKET_qIsAddressTagged,
 			 "qIsAddressTagged", "memory-tagging-address-check", 0);
 
diff --git a/gdb/testsuite/gdb.server/fileio-packets.py b/gdb/testsuite/gdb.server/fileio-packets.py
index 54ae56fa68a..2d06edcdbf7 100644
--- a/gdb/testsuite/gdb.server/fileio-packets.py
+++ b/gdb/testsuite/gdb.server/fileio-packets.py
@@ -57,33 +57,48 @@ def decode_stat_reply(buf, byteorder="big"):
 
     buf = unescape_remote_data(buf)
 
-    if (
-        buf[0] != ord("F")
-        or buf[1] != ord("4")
-        or buf[2] != ord("0")
-        or buf[3] != ord(";")
-        or len(buf) != 68
-    ):
+    if buf[0:4] == b"F40;" and len(buf) == 68:
+        wide = False
+    elif buf[0:4] == b"F5c;" and len(buf) == 96:
+        wide = True
+    else:
         print(f"decode_stat_reply failed: {buf}\t(length = {len(buf)})")
         return None
 
-    # Discard the 'F40;' prefix.  The rest is the 64 bytes of data to
-    # be decoded.
+    # Discard the 'FNN;' prefix.
     buf = buf[4:]
 
-    st_dev = int.from_bytes(buf[0:4], byteorder=byteorder)
-    st_ino = int.from_bytes(buf[4:8], byteorder=byteorder)
-    st_mode = int.from_bytes(buf[8:12], byteorder=byteorder)
-    st_nlink = int.from_bytes(buf[12:16], byteorder=byteorder)
-    st_uid = int.from_bytes(buf[16:20], byteorder=byteorder)
-    st_gid = int.from_bytes(buf[20:24], byteorder=byteorder)
-    st_rdev = int.from_bytes(buf[24:28], byteorder=byteorder)
-    st_size = int.from_bytes(buf[28:36], byteorder=byteorder)
-    st_blksize = int.from_bytes(buf[36:44], byteorder=byteorder)
-    st_blocks = int.from_bytes(buf[44:52], byteorder=byteorder)
-    st_atime = int.from_bytes(buf[52:56], byteorder=byteorder)
-    st_mtime = int.from_bytes(buf[56:60], byteorder=byteorder)
-    st_ctime = int.from_bytes(buf[60:64], byteorder=byteorder)
+    def field(off, size):
+        return int.from_bytes(buf[off : off + size], byteorder=byteorder)
+
+    if wide:
+        st_dev     = field(0, 8)
+        st_ino     = field(8, 8)
+        st_mode    = field(16, 4)
+        st_nlink   = field(20, 8)
+        st_uid     = field(28, 4)
+        st_gid     = field(32, 4)
+        st_rdev    = field(36, 8)
+        st_size    = field(44, 8)
+        st_blksize = field(52, 8)
+        st_blocks  = field(60, 8)
+        st_atime   = field(68, 8)
+        st_mtime   = field(76, 8)
+        st_ctime   = field(84, 8)
+    else:
+        st_dev     = field(0, 4)
+        st_ino     = field(4, 4)
+        st_mode    = field(8, 4)
+        st_nlink   = field(12, 4)
+        st_uid     = field(16, 4)
+        st_gid     = field(20, 4)
+        st_rdev    = field(24, 4)
+        st_size    = field(28, 8)
+        st_blksize = field(36, 8)
+        st_blocks  = field(44, 8)
+        st_atime   = field(52, 4)
+        st_mtime   = field(56, 4)
+        st_ctime   = field(60, 4)
 
     return {
         "st_dev": st_dev,
diff --git a/gdbserver/hostio.cc b/gdbserver/hostio.cc
index b9ca27c2ff4..34def5d22da 100644
--- a/gdbserver/hostio.cc
+++ b/gdbserver/hostio.cc
@@ -26,7 +26,6 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#include "gdbsupport/fileio.h"
 
 struct fd_list
 {
@@ -465,7 +464,7 @@ handle_fstat (char *own_buf, int *new_packet_len)
   int fd, bytes_sent;
   char *p;
   struct stat st;
-  struct fio_stat fst;
+  client_state &cs = get_client_state ();
 
   p = own_buf + strlen ("vFile:fstat:");
 
@@ -483,16 +482,31 @@ handle_fstat (char *own_buf, int *new_packet_len)
       return;
     }
 
-  host_to_fileio_stat (&st, &fst);
-
-  bytes_sent = hostio_reply_with_data (own_buf,
-				       (char *) &fst, sizeof (fst),
-				       new_packet_len);
+  struct fio_stat_wide wide;
+  host_to_fileio_stat_wide (&st, &wide);
 
-  /* If the response does not fit into a single packet, do not attempt
-     to return a partial response, but simply fail.  */
-  if (bytes_sent < sizeof (fst))
-    write_enn (own_buf);
+  /* Send the wide form if GDB understands it, otherwise narrow the
+     result first.  */
+  if (cs.stat64_feature)
+    {
+      bytes_sent = hostio_reply_with_data (own_buf, (char *) &wide,
+					   sizeof (wide), new_packet_len);
+      /* If the response does not fit into a single packet, do not attempt
+	 to return a partial response, but simply fail.  */
+      if (bytes_sent < sizeof (wide))
+	write_enn (own_buf);
+    }
+  else
+    {
+      struct fio_stat narrow;
+      fileio_stat_wide_to_narrow (&wide, &narrow);
+      bytes_sent = hostio_reply_with_data (own_buf, (char *) &narrow,
+					   sizeof (narrow), new_packet_len);
+      /* If the response does not fit into a single packet, do not attempt
+	 to return a partial response, but simply fail.  */
+      if (bytes_sent < sizeof (narrow))
+	write_enn (own_buf);
+    }
 }
 
 static void
@@ -501,8 +515,8 @@ handle_stat (char *own_buf, int *new_packet_len)
   int bytes_sent;
   char *p;
   struct stat st;
-  struct fio_stat fst;
   char filename[HOSTIO_PATH_MAX];
+  client_state &cs = get_client_state ();
 
   p = own_buf + strlen ("vFile:stat:");
 
@@ -519,16 +533,31 @@ handle_stat (char *own_buf, int *new_packet_len)
       return;
     }
 
-  host_to_fileio_stat (&st, &fst);
-
-  bytes_sent = hostio_reply_with_data (own_buf,
-				       (char *) &fst, sizeof (fst),
-				       new_packet_len);
+  struct fio_stat_wide wide;
+  host_to_fileio_stat_wide (&st, &wide);
 
-  /* If the response does not fit into a single packet, do not attempt
-     to return a partial response, but simply fail.  */
-  if (bytes_sent < sizeof (fst))
-    write_enn (own_buf);
+  /* Send the wide form if GDB understands it, otherwise narrow the
+     result first.  */
+  if (cs.stat64_feature)
+    {
+      bytes_sent = hostio_reply_with_data (own_buf, (char *) &wide,
+					   sizeof (wide), new_packet_len);
+      /* If the response does not fit into a single packet, do not attempt
+	 to return a partial response, but simply fail.  */
+      if (bytes_sent < sizeof (wide))
+	write_enn (own_buf);
+    }
+  else
+    {
+      struct fio_stat narrow;
+      fileio_stat_wide_to_narrow (&wide, &narrow);
+      bytes_sent = hostio_reply_with_data (own_buf, (char *) &narrow,
+					   sizeof (narrow), new_packet_len);
+      /* If the response does not fit into a single packet, do not attempt
+	 to return a partial response, but simply fail.  */
+      if (bytes_sent < sizeof (narrow))
+	write_enn (own_buf);
+    }
 }
 
 static void
@@ -537,8 +566,8 @@ handle_lstat (char *own_buf, int *new_packet_len)
   int ret, bytes_sent;
   char *p;
   struct stat st;
-  struct fio_stat fst;
   char filename[HOSTIO_PATH_MAX];
+  client_state &cs = get_client_state ();
 
   p = own_buf + strlen ("vFile:lstat:");
 
@@ -560,16 +589,31 @@ handle_lstat (char *own_buf, int *new_packet_len)
       return;
     }
 
-  host_to_fileio_stat (&st, &fst);
-
-  bytes_sent = hostio_reply_with_data (own_buf,
-				       (char *) &fst, sizeof (fst),
-				       new_packet_len);
+  struct fio_stat_wide wide;
+  host_to_fileio_stat_wide (&st, &wide);
 
-  /* If the response does not fit into a single packet, do not attempt
-     to return a partial response, but simply fail.  */
-  if (bytes_sent < sizeof (fst))
-    write_enn (own_buf);
+  /* Send the wide form if GDB understands it, otherwise narrow the
+     result first.  */
+  if (cs.stat64_feature)
+    {
+      bytes_sent = hostio_reply_with_data (own_buf, (char *) &wide,
+					   sizeof (wide), new_packet_len);
+      /* If the response does not fit into a single packet, do not attempt
+	 to return a partial response, but simply fail.  */
+      if (bytes_sent < sizeof (wide))
+	write_enn (own_buf);
+    }
+  else
+    {
+      struct fio_stat narrow;
+      fileio_stat_wide_to_narrow (&wide, &narrow);
+      bytes_sent = hostio_reply_with_data (own_buf, (char *) &narrow,
+					   sizeof (narrow), new_packet_len);
+      /* If the response does not fit into a single packet, do not attempt
+	 to return a partial response, but simply fail.  */
+      if (bytes_sent < sizeof (narrow))
+	write_enn (own_buf);
+    }
 }
 
 static void
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index a208e24d09f..dfa24617847 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -2746,6 +2746,8 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 		cs.single_inferior_argument = true;
 	      else if (feature == "multi-wp-addr+")
 		cs.multiple_wp_addr_feature = true;
+	      else if (feature == "stat64+")
+		cs.stat64_feature = true;
 	      else
 		{
 		  /* Move the unknown features all together.  */
@@ -2762,7 +2764,7 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 	       "PacketSize=%x;QPassSignals+;QProgramSignals+;"
 	       "QStartupWithShell+;QEnvironmentHexEncoded+;"
 	       "QEnvironmentReset+;QEnvironmentUnset+;"
-	       "QSetWorkingDir+;binary-upload+",
+	       "QSetWorkingDir+;binary-upload+;stat64+",
 	       PBUFSIZ - 1);
 
       if (target_supports_catch_syscall ())
diff --git a/gdbserver/server.h b/gdbserver/server.h
index bbba3650de7..cf811f228fa 100644
--- a/gdbserver/server.h
+++ b/gdbserver/server.h
@@ -192,6 +192,11 @@ struct client_state
   /* If true, memory tagging features are supported.  */
   bool memory_tagging_feature = false;
 
+  /* True if GDB supports the wide form of struct stat in the vFile
+     fstat, stat and lstat replies.  When false, gdbserver narrows the
+     result to struct fio_stat before sending it.  */
+  bool stat64_feature = false;
+
   /* If true then E.errtext style errors are supported everywhere,
      including for the qRcmd and m packet.  When false E.errtext errors
      are not supported with qRcmd and m packets, but are still supported
diff --git a/gdbsupport/fileio.cc b/gdbsupport/fileio.cc
index 6d2ffb14544..bab2c4c8efe 100644
--- a/gdbsupport/fileio.cc
+++ b/gdbsupport/fileio.cc
@@ -20,6 +20,7 @@
 #include "fileio.h"
 #include <sys/stat.h>
 #include <fcntl.h>
+#include "gdbsupport/errors.h"
 
 /* See fileio.h.  */
 
@@ -305,3 +306,72 @@ host_to_fileio_stat (struct stat *st, struct fio_stat *fst)
   host_to_fileio_time (st->st_mtime, fst->fst_mtime);
   host_to_fileio_time (st->st_ctime, fst->fst_ctime);
 }
+
+/* See fileio.h.  */
+
+void
+host_to_fileio_stat_wide (struct stat *st, struct fio_stat_wide *fst)
+{
+  LONGEST blksize;
+
+  host_to_bigendian ((LONGEST) st->st_dev, (char *) fst->fst_dev, 8);
+  host_to_bigendian ((LONGEST) st->st_ino, (char *) fst->fst_ino, 8);
+  host_to_fileio_mode (st->st_mode, fst->fst_mode);
+  host_to_bigendian ((LONGEST) st->st_nlink, (char *) fst->fst_nlink, 8);
+  host_to_fileio_uint ((long) st->st_uid, fst->fst_uid);
+  host_to_fileio_uint ((long) st->st_gid, fst->fst_gid);
+  host_to_bigendian ((LONGEST) st->st_rdev, (char *) fst->fst_rdev, 8);
+  host_to_bigendian ((LONGEST) st->st_size, (char *) fst->fst_size, 8);
+#ifdef HAVE_STRUCT_STAT_ST_BLKSIZE
+  blksize = st->st_blksize;
+#else
+  blksize = 512;
+#endif
+  host_to_bigendian (blksize, (char *) fst->fst_blksize, 8);
+#if HAVE_STRUCT_STAT_ST_BLOCKS
+  host_to_bigendian ((LONGEST) st->st_blocks, (char *) fst->fst_blocks, 8);
+#else
+  host_to_bigendian (((LONGEST) st->st_size + blksize - 1) / blksize,
+		     (char *) fst->fst_blocks, 8);
+#endif
+  host_to_bigendian ((LONGEST) st->st_atime, (char *) fst->fst_atime, 8);
+  host_to_bigendian ((LONGEST) st->st_mtime, (char *) fst->fst_mtime, 8);
+  host_to_bigendian ((LONGEST) st->st_ctime, (char *) fst->fst_ctime, 8);
+}
+
+/* Copy the 8-byte value in FROM into the 4-byte field TO, warning if
+   the value does not fit.  WHAT names the field, for the warning.  */
+
+static void
+narrow_field (const char *from, char *to, const char *what)
+{
+  ULONGEST num = bigendian_to_host (from, 8);
+
+  if (num != (ULONGEST) (uint32_t) num)
+    warning (_("file-i/o: %s value %s does not fit in 32 bits; "
+	       "the value seen by the peer will be truncated"),
+	     what, pulongest (num));
+
+  host_to_bigendian ((LONGEST) num, to, 4);
+}
+
+/* See fileio.h.  */
+
+void
+fileio_stat_wide_to_narrow (const struct fio_stat_wide *wide,
+			    struct fio_stat *narrow)
+{
+  narrow_field (wide->fst_dev, narrow->fst_dev, "st_dev");
+  narrow_field (wide->fst_ino, narrow->fst_ino, "st_ino");
+  memcpy (narrow->fst_mode, wide->fst_mode, 4);
+  narrow_field (wide->fst_nlink, narrow->fst_nlink, "st_nlink");
+  memcpy (narrow->fst_uid, wide->fst_uid, 4);
+  memcpy (narrow->fst_gid, wide->fst_gid, 4);
+  narrow_field (wide->fst_rdev, narrow->fst_rdev, "st_rdev");
+  memcpy (narrow->fst_size, wide->fst_size, 8);
+  memcpy (narrow->fst_blksize, wide->fst_blksize, 8);
+  memcpy (narrow->fst_blocks, wide->fst_blocks, 8);
+  narrow_field (wide->fst_atime, narrow->fst_atime, "st_atime");
+  narrow_field (wide->fst_mtime, narrow->fst_mtime, "st_mtime");
+  narrow_field (wide->fst_ctime, narrow->fst_ctime, "st_ctime");
+}
diff --git a/gdbsupport/fileio.h b/gdbsupport/fileio.h
index c2592cf8c15..fa5de54dd40 100644
--- a/gdbsupport/fileio.h
+++ b/gdbsupport/fileio.h
@@ -120,9 +120,11 @@ using fio_time_t = char[FIO_TIME_LEN];
 using fio_long_t = char[FIO_LONG_LEN];
 using fio_ulong_t = char[FIO_ULONG_LEN];
 
-/* Struct stat as used in protocol.  For complete independence
-   of host/target systems, it's defined as an array with offsets
-   to the members. */
+/* Struct stat as used in the protocol.  This is the format used by the
+   F-packet file-i/o protocol, and by the vFile stat packets when the
+   stat64 feature has not been negotiated.  Several fields are too narrow
+   to hold the corresponding struct stat member on a 64-bit host; see
+   struct fio_stat_wide.  */
 
 struct fio_stat
 {
@@ -141,6 +143,29 @@ struct fio_stat
   fio_time_t  fst_ctime;
 };
 
+/* Struct stat as used in the wide form of the protocol.  The fields
+   which cannot hold the corresponding struct stat member on a 64-bit
+   host are widened to 8 bytes.  This layout is only used by the vFile
+   stat packets, and only when the stat64 feature has been negotiated
+   with the peer.  */
+
+struct fio_stat_wide
+{
+  fio_ulong_t fst_dev;
+  fio_ulong_t fst_ino;
+  fio_mode_t  fst_mode;
+  fio_ulong_t fst_nlink;
+  fio_uint_t  fst_uid;
+  fio_uint_t  fst_gid;
+  fio_ulong_t fst_rdev;
+  fio_ulong_t fst_size;
+  fio_ulong_t fst_blksize;
+  fio_ulong_t fst_blocks;
+  fio_ulong_t fst_atime;
+  fio_ulong_t fst_mtime;
+  fio_ulong_t fst_ctime;
+};
+
 struct fio_timeval
 {
   fio_time_t  ftv_sec;
@@ -179,6 +204,20 @@ host_to_bigendian (LONGEST num, char *buf, int bytes)
     buf[i] = (num >> (8 * (bytes - i - 1))) & 0xff;
 }
 
+/* Unpack an integer of BYTES bytes from BUF, which holds it in
+   big-endian, protocol format.  */
+
+static inline ULONGEST
+bigendian_to_host (const char *buf, int bytes)
+{
+  ULONGEST num = 0;
+  int i;
+
+  for (i = 0; i < bytes; ++i)
+    num = (num << 8) | (unsigned char) buf[i];
+  return num;
+}
+
 /* Pack a host-format integer into an fio_uint_t.  */
 
 static inline void
@@ -199,4 +238,13 @@ host_to_fileio_time (time_t num, fio_time_t fnum)
 
 extern void host_to_fileio_stat (struct stat *st, struct fio_stat *fst);
 
+/* Pack a host-format struct stat into a struct fio_stat_wide.  */
+extern void host_to_fileio_stat_wide (struct stat *st,
+				      struct fio_stat_wide *fst);
+
+/* Narrow a struct fio_stat_wide into a struct fio_stat, warning if any
+   value does not fit.  */
+extern void fileio_stat_wide_to_narrow (const struct fio_stat_wide *wide,
+					struct fio_stat *narrow);
+
 #endif /* GDBSUPPORT_FILEIO_H */
-- 
2.52.0