Summary
=======

This document descripts MI extension to support debugging several executables.

Design
======

The local thread groups of type 'process' are redefined to mean inferior. In
particular:

   - They may exist when the process does not exist. 
   - They might not have any contained threads.
   - The following notifications are added:
       - 'thread-group-added'
       - 'thread-group-removed'
     Those are emitted when an inferior is added or removed to the inferior
     list, as output by 'info inferior'.
   - The following notifcation is also added:
       - 'thread-group-started'
     This is emitted when a thread group is connected to something really
     running.
   - The existing notification:
       - 'thread-group-created'
     is removed. If we retain the current meaning of 'process was created'
     it will be extra confusing, given that no new thread group
     is actually created, but rather an existing thread group gets a live
     process. It is believed that those notifications were only used for DICOS
     multiprocess implementation, and IDE for DICOS can be easily modified to
     handle both old and new notifications.
   - a new field, 'executable' is added to report the executable that is being
     debugged. Note: executable, not symbol files. There can be several symbol
     files, and queried via separate command.

[Note: this means that if '-list-thread-groups --available' reports a thread
group 345 and we attach to it, we don't get a thread group with id of 345.
Rather, whatever thread group we attached is associated to that pid]

Two additional commands will be required -- '-add-inferior' and
'-remove-inferior'. The CLI 'clone-inferior' is more like a convenience
for a human being, and will not get a MI counterpart.

Changes to existing commands
============================

Global changes.

    New option --thread-group will be introduced. Current, this option is
    available for a couple of commands only.

Breakpoint commands

    break-after
    break-condition
    break-commands
    break-delete
    break-disable
    break-enable
    break-info
    break-insert
    break-list
    break-watch
    The changes outlined above don't require any command changes. 

Data commands.

    data-disassemble
    data-evaluate-expression
    data-list-changed-registers
    data-list-register-names
    data-list-register-values
    data-read-memory
    data-write-memory
    data-write-register-values
    These operate on the current thread. No change at all.

Program context commands. 

    environment-cd
    environment-directory
    environment-path
    environment-pwd
    Will be made per-inferior. Not planned originally, but already requested
    by Pedro.
    
    inferior-tty-set
    inferior-tty-show
    exec-arguments
    Made to be per-inferior.

Execution commands

    exec-finish
    exec-jump
    exec-next
    exec-next-instruction
    exec-return
    exec-step
    exec-step-instruction
    exec-until
    These all operate on specific thread. No change needed.

    exec-continue. 
    Need to make --all option resume all inferiors, and special-case explicit
    --thread-group to resume all threads in the specified inferior.

    exec-interrupt.
    Need to make --all and --thread-group option behave similarly to 
    exec-continue.

    exec-run. 
    This is directly routed to CLI, so MI wrapper should be introduced.
    Support for --all should be added.

    
File commands

     file-exec-and-symbols
     file-exec-file
     file-symbol-file
     file-list-exec-source-file
     file-list-exec-source-files
     symbol-list-lines.

     These operate on inferior, and are typically used when there are no
     threads. Generic --thread-group option will handle them fine.

Stack commands

    stack-info-depth
    stack-info-frame
    stack-list-arguments
    stack-list-frames
    stack-list-locals
    stack-list-variables
    stack-select-frame

    These always operate on specific thread. No change needed.

Target commands

    target-attach
    target-detach
    Should be per-inferior.

    target-disconnect
    This, in theory, should be just like target-detach. In practice, it
    pops the target and therefore need not care about inferiors.

    target-download
    target-file-delete
    target-file-get
    target-file-put
    target-select
    At present, all inferiors should use the same target, so these commands
    are 'global'.

    
Thread commands

    thread-info
    thread-list-ids
    thread-select

    Except for the fact that thread group may now be empty, no change.

Variable objects

    var-assign
    var-create
    var-delete
    var-evaluate-expression
    var-info-path-expression
    var-info-expression
    var-info-num-children
    var-info-type
    var-list-children
    var-set-format
    var-set-frozen
    var-set-update-range
    var-set-visualizer
    var-show-attributes
    var-show-format
    var-update
    These operate on specific thread. No change needed.

Misc.

    enable-timings
    enable-pretty-printing
    gdb-exit
    gdb-set
    gdb-show
    gdb-version
    interpreter-exec
    list-features
    list-thread-groups
    Nothing to change.

    list-target-features
    Will have to handle --thread-group when/if inferiors have different
    targets with different feature. I imagine that mixing sync and async
    targets will be just impossible.