[Bug server/34567] New: remote fileio: st_ino truncated to 32 bits in vFile:stat/lstat reply

https://sourceware.org/bugzilla/show_bug.cgi?id=34567

            Bug ID: 34567
           Summary: remote fileio: st_ino truncated to 32 bits in
                    vFile:stat/lstat reply
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: server
          Assignee: unassigned at sourceware dot org
          Reporter: abhay at sourceware dot org
  Target Milestone: ---

gdb.server/fileio-packets.exp fails on filesystems whose inode numbers
exceed 2^32.  The st_ino value returned by vFile:stat and vFile:lstat is
truncated to 32 bits and no longer matches the value the same file
reports locally.

  FAIL: gdb.server/fileio-packets.exp: check remote lstat works on a normal
file
  FAIL: gdb.server/fileio-packets.exp: check remote lstat works on a symbolic
link
  FAIL: gdb.server/fileio-packets.exp: check remote stat works on a normal file
  FAIL: gdb.server/fileio-packets.exp: check remote stat works on a symbolic
link

Every field matches except st_ino:

  remote = {'st_dev': 2304, 'st_ino': 2161233200, 'st_mode': 33188, 'st_nlink':
1, 'st_uid': 1023, 'st_gid': 1023, 'st_rdev': 0, 'st_size': 0, 'st_blksize':
65536, 'st_blocks': 0, 'st_atime': 1787650798, 'st_mtime': 1787650798,
'st_ctime': 1787650798}
  local  = {'st_dev': 2304, 'st_ino': 122420317488, 'st_mode': 33188,
'st_nlink': 1, 'st_uid': 1023, 'st_gid': 1023, 'st_rdev': 0, 'st_size': 0,
'st_blksize': 65536, 'st_blocks': 0, 'st_atime': 1787650798, 'st_mtime':
1787650798, 'st_ctime': 1787650798}

  122420317488 = 0x1C80CE9BB0
   2161233200  =   0x80CE9BB0

The low 32 bits are identical; the high bits are dropped.

The protocol struct declares the field as 4 bytes, while st_ino is 64-bit
on Linux:

  gdbsupport/fileio.h:130     fio_uint_t  fst_ino;
  gdbsupport/fileio.cc:281    host_to_fileio_uint ((long) st->st_ino,
fst->fst_ino);
  gdb/remote-fileio.c:1206    st->st_ino = remote_fileio_to_host_uint
(fst->fst_ino);

fst_size, fst_blksize and fst_blocks in the same struct already use the
8-byte fio_ulong_t, so the wide type exists; fst_ino simply does not use
it.

Whether the truncation is visible depends on the filesystem:

  ext4 on 2 TB    largest inode under /home:        132907009    PASS
  xfs  on 86 TB   largest inode under /home:     171801755018    FAIL

On the xfs volume essentially every file exceeds 2^32, so the failure is
not intermittent.  Both hosts are powerpc64le-unknown-linux-gnu running
GDB 19.0.50.20260825-git against a local gdbserver; the failing host is
the xfs one.

Note that struct fio_stat is shared between the vFile packets and the
older F-packet file-I/O protocol, so widening fst_ino changes the wire
layout for both.  Possible approaches: widen the shared field; add a
separate wider struct used only by the vFile packets (which were added
in GDB 16); or negotiate the wider format via qSupported.

Related, not covered by this report: fst_dev and fst_rdev are also
fio_uint_t although dev_t is 64-bit, and fst_atime/fst_mtime/fst_ctime
are 4 bytes, which is a year-2038 problem.

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