Here is a brief overview of the packets that an lldb platform server
needs to implement for the lldb testsuite to be run on a remote
target device/system.

These are almost all lldb extensions to the gdb-remote serial
protocol.  Many of the vFile: packets are described to the "Host
I/O Packets" detailed in the gdb-remote protocol documentation,
although the lldb platform extensions include packets that are not
defined there (vFile:size:, vFile:mode:, vFile:symlink, vFile:chmod:).
Most importantly, the flags that lldb passes to vFile:open: are 
incompatible with the flags that gdb specifies.


//----------------------------------------------------------------------
// QStartNoAckMode
//
// BRIEF
//   A request to stop sending ACK packets for each properly formatted packet.
//
// EXAMPLE 
//   A platform session will typically start like this:
//
//   receive: +$QStartNoAckMode#b0
//   send:    +       <-- ACKing the properly formatted QStartNoAckMode packet
//   send:    $OK#9a
//   receive: +       <-- Our OK packet getting ACKed
//
//   ACK mode is now disabled.

//----------------------------------------------------------------------
// qHostInfo
//
// BRIEF
//   Describe the hardware and OS of the target system
//
// EXAMPLE
//
//  receive: qHostInfo
//  send:    cputype:16777228;cpusubtype:1;ostype:ios;watchpoint_exceptions_received:before;os_version:12.1;vendor:apple;default_packet_timeout:5;
//
//  All numbers are base 10, os_version is a string that will be parsed as major.minor.patch.

//----------------------------------------------------------------------
// qModuleInfo
//
// BRIEF
//   Report information about a binary on the target system
//
// EXAMPLE
//  receive: qModuleInfo:2f62696e2f6c73;
//
// FIXME finish this packet description, v. GDBRemoteCommunicationServerCommon::Handle_qModuleInfo


//----------------------------------------------------------------------
// qGetWorkingDir
//
// BRIEF
//   Get the current working directory of the platform stub in
//   ASCII hex encoding.
//
// EXAMPLE
// 
//  receive: qGetWorkingDir
//  send:    2f4170706c65496e7465726e616c2f6c6c64622f73657474696e67732f342f5465737453657474696e67732e746573745f646973617373656d626c65725f73657474696e6773 


//----------------------------------------------------------------------
// QSetWorkingDir:
//
// BRIEF
//   Set the current working directory of the platform stub in
//   ASCII hex encoding.
//
// EXAMPLE
// 
//  receive: QSetWorkingDir:2f4170706c65496e7465726e616c2f6c6c64622f73657474696e67732f342f5465737453657474696e67732e746573745f646973617373656d626c65725f73657474696e6773 
//  send:    OK

//----------------------------------------------------------------------
// qPlatform_mkdir:
//
// BRIEF
//   Create a directory on the target system.
//
// EXAMPLE
// 
//  receive: qPlatform_mkdir:000001fd,2f746d702f6131
//  send:    F0
//
//  request packet has the fields:
//     1. mode bits in base 16
//     2. file path in ascii-hex encoding
//
//  response is F followed by the return value of the mkdir() call,
//  base 10 encoded.

//----------------------------------------------------------------------
// qPlatform_shell:
//
// BRIEF
//   Run a shell command on the target system, return the output.
//
// EXAMPLE
// 
//  receive: qPlatform_shell:6c73202f746d702f,0000000a
//  send:    F,0,0,<OUTPUT>
//
//  request packet has the fields:
//     1. shell command ascii-hex encoded
//     2. timeout 
//     3. {optional} working directory ascii-hex encoded
//
//  Response is F followed by the return value of the command (base 16),
//  followed by another number, followed by the output of the command
/   in binary-escaped-data encoding.

//----------------------------------------------------------------------
// qLaunchGDBServer
//
// BRIEF
//   Start a gdbserver process (gdbserver, debugserver, lldb-server)
//   on the target system.
//
// EXAMPLE
// 
//  receive: qLaunchGDBServer;host:<HOSTNAME_LLDB_IS_ON>;
//  send:    pid:1337;port:43001;
//
//  request packet hostname field is not ascii-hex encoded. Hostnames 
//  don't have $ or # characters in them.
//
//  response to the packet is the pid of the newly launched gdbserver,
//  and the port it is listening for a connection on.
//
//  When the testsuite is running, lldb may use the pid to kill off a 
//  debugserver that doesn't seem to be responding, etc.

//----------------------------------------------------------------------
// qKillSpawnedProcess:
//
// BRIEF
//   Kill a process running on the target system.
//
// EXAMPLE
// 
//  receive: qKillSpawnedProcess:1337
//  send:    OK
//
//  The request packet has the process ID in base 10.

//----------------------------------------------------------------------
// qProcessInfoPID:
//
// BRIEF
//   Gather information about a process running on the target
//
// EXAMPLE
// 
//  receive: qProcessInfoPID:71964
//  send:    pid:71964;name:612e6f7574;
//
//  The request packet has the pid encoded in base 10.
//
//  The reply has semicolon-separated name:value fields, two are
//  shown here.  pid is base 10 encoded.  name is ascii hex encoded.
//  lldb-server can reply with many additional fields, but I think
//  this is enough for the testsuite.

//----------------------------------------------------------------------
// qfProcessInfo:
//
// BRIEF
//   Search the process table for processes matching criteria, 
//   respond with them in multiple packets.
//
// EXAMPLE
// 
//  receive: qfProcessInfo:name_match:equals;name:6e6f70726f6365737365786973747377697468746869736e616d65;
//  send:    pid:3500;name:612e6f7574;
//
//  The request packet has a criteria to search for, followed by
//  a specific name.  
//
//  KEY           VALUE     DESCRIPTION
//  ===========   ========  ================================================
//  "name"        ascii-hex An ASCII hex string that contains the name of 
//                          the process that will be matched.
//  "name_match"  enum      One of: "equals", "starts_with", "ends_with", 
//                          "contains" or "regex"
//  "pid"         integer   A string value containing the decimal process ID
//  "parent_pid"  integer   A string value containing the decimal parent 
//                          process ID
//  "uid"         integer   A string value containing the decimal user ID
//  "gid"         integer   A string value containing the decimal group ID
//  "euid"        integer   A string value containing the decimal effective user ID
//  "egid"        integer   A string value containing the decimal effective group ID
//  "all_users"   bool      A boolean value that specifies if processes should
//                          be listed for all users, not just the user that the 
//                          platform is running as
//  "triple"      ascii-hex An ASCII hex target triple string ("x86_64", 
//                          "x86_64-apple-macosx", "armv7-apple-ios")
//
//  If no criteria is given, qfProcessInfo will request a list of every process.
//
//  The lldb testsuite currently only uses name_match:equals and the
//  no-criteria mode to list every process.
//
//  The response should include any information about the process that
//  can be retrieved in semicolon-separated name:value fields.
//  In this example, pid is base 10, name is ascii-hex encoded.
//  The testsuite seems to only require these two.
//
//  This packet only responds with one process.  To get further matches to
//  the search, qsProcessInfo should be sent.
//
//  If no process match is found, Exx should be returned.
//
//  Sample packet/response:
//  send packet: $qfProcessInfo#00
//  read packet: $pid:60001;ppid:59948;uid:7746;gid:11;euid:7746;egid:11;name:6c6c6462;triple:7838365f36342d6170706c652d6d61636f7378;#00
//  send packet: $qsProcessInfo#00
//  read packet: $pid:59992;ppid:192;uid:7746;gid:11;euid:7746;egid:11;name:6d64776f726b6572;triple:7838365f36342d6170706c652d6d61636f7378;#00
//  send packet: $qsProcessInfo#00
//  read packet: $E04#00

//----------------------------------------------------------------------
// qsProcessInfo
//
// BRIEF
//   Return the next process info found by the most recent qfProcessInfo:
//   packet.
//
// EXAMPLE
// 
//  Continues to return the results of the qfProcessInfo.  Once all matches
//  have been sent, Exx is returned to indicate end of matches.

//----------------------------------------------------------------------
// qPathComplete
//
// BRIEF
//   Get a list of matched disk files/directories by passing a boolean flag
//   and a partial path.
//
// EXAMPLE
//
//   receive: qPathComplete:0,6d61696e
//   send:    M6d61696e2e637070
//   receive: qPathComplete:1,746573
//   send:    M746573742f,74657374732f
//
//   If the first argument is zero, the result should contain all
//   files (including directories) starting with the given path. If the
//   argument is one, the result should contain only directories.
//
//   The result should be a comma-separated list of hex-encoded paths.
//   Paths denoting a directory should end with a directory separator ('/' or '\').

//----------------------------------------------------------------------
// vFile:size:
//
// BRIEF
//   Get the size of a file on the target system, filename in ASCII hex.
//
// EXAMPLE
// 
//  receive: vFile:size:2f746d702f61
//  send:    Fc008
//
//  response is "F" followed by the file size in base 16.
//  "F-1,errno" with the errno if an error occurs.


//----------------------------------------------------------------------
// vFile:mode:
//
// BRIEF
//   Get the mode bits of a file on the target system, filename in ASCII hex.
//
// EXAMPLE
// 
//  receive: vFile:mode:2f746d702f61
//  send:    F1ed
//
//  response is "F" followed by the mode bits in base 16, this 0x1ed would 
//  correspond to 0755 in octal.  
//  "F-1,errno" with the errno if an error occurs.

//----------------------------------------------------------------------
// vFile:unlink:
//
// BRIEF
//   Remove a file on the target system.
//
// EXAMPLE
// 
//  receive: vFile:unlink:2f746d702f61
//  send:    F0
//
//  Argument is a file path in ascii-hex encoding.
//  Response is "F" plus the return value of unlink(), base 10 encoding.

//----------------------------------------------------------------------
// vFile:symlink:
//
// BRIEF
//   Create a symbolic link (symlink, soft-link) on the target system.
//
// EXAMPLE
// 
//  receive: vFile:symlink:<SRC-FILE>,<DST-NAME>
//  send:    F0,0
//
//  Argument file paths are in ascii-hex encoding.
//  Response is "F" plus the return value of symlink(), base 10 encoding, twice.

//----------------------------------------------------------------------
// vFile:chmod:
// qPlatform_chmod:
//
// BRIEF
//   Change the permission mode bits on a file on the target
//
// EXAMPLE
// 
//  receive: vFile:chmod:180,2f746d702f61
//  send:    F0
//
//  Arguments are the mode bits to set, base 16, and a file path in 
//  ascii-hex encoding.
//  Response is "F" plus the return value of chmod(), base 10 encoding.
//
//  I don't know why there are two packets for the same thing, v.
//  vFile:chmod:.

//----------------------------------------------------------------------
// vFile:chmod:
//
// BRIEF
//   Change the permission mode bits on a file on the target
//
// EXAMPLE
// 
//  receive: vFile:chmod:180,2f746d702f61
//  send:    F0
//
//  Arguments are the mode bits to set, base 16, and a file path in 
//  ascii-hex encoding.
//  Response is "F" plus the return value of chmod(), base 10 encoding.


//----------------------------------------------------------------------
// vFile:open:
//
// BRIEF
//   Open a file on the remote system and return the file descriptor of it.
//
// EXAMPLE
// 
//  receive: vFile:open:2f746d702f61,00000001,00000180
//  send:    F8
//
//  request packet has the fields:
//     1. ASCII hex encoded filename
//     2. flags passed to the open call, base 16.
//        Note that these are not the oflags that open(2) takes, but
//        are the constant values in enum OpenOptions from lldb's File.h
//     3. mode bits, base 16
//  
//  response is F followed by the opened file descriptor in base 16.
//  "F-1,errno" with the errno if an error occurs.
//
//----------------------------------------------------------------------
// vFile:close:
//
// BRIEF
//   Close a previously opened file descriptor.
//
// EXAMPLE
// 
//  receive: vFile:close:7
//  send:    F0
//
//  File descriptor is in base 16.
//  "F-1,errno" with the errno if an error occurs.


//----------------------------------------------------------------------
// vFile:pread:
//
// BRIEF
//   Read data from an opened file descriptor.
//
// EXAMPLE
// 
//  receive: vFile:pread:7,1024,0
//  send:    F4;a'b\00
//
//  request packet has the fields:
//     1. file descriptor, base 16
//     2. number of bytes to be read, base 16
//     3. offset into file to start from, base 16
//
//  Response is F, followed by the number of bytes read (base 16), a
//  semicolon, followed by the data in the binary-escaped-data encoding.


//----------------------------------------------------------------------
// vFile:pwrite:
//
// BRIEF
//   Write data to a previously opened file descriptor.
//
// EXAMPLE
// 
//  receive: vFile:pwrite:8,0,\cf\fa\ed\fe\0c\00\00
//  send:    F1024
//
//  request packet has the fields:
//     1. file descriptor, base 16
//     2. offset into file to start from, base 16
//     3. binary-escaped-data to be written
//
//  Response is F, followed by the number of bytes written (base 16)


Finally, the platform must be able to launch processes so that debugserver
can attach to them.  To do this, the following packets should be handled:

QSetDisableASLR
QSetDetachOnError
QSetSTDOUT
QSetSTDERR
QSetSTDIN
QEnvironment
QEnvironmentHexEncoded
A
qLaunchSuccess
qProcessInfo

Most of these are documented in the standard gdb-remote protocol
and/or the lldb-gdb-remote.txt documentation.