RTEMS GNU Tools On-Line Library

GDB/MI Draft Changes to Output Syntax

Debugging with GDB

19.15: GDB/MI Draft Changes to Output Syntax

One problem identified in the existing GDB/MI output syntax was the difficulty in differentiating between a tuple such as:

{number="1",type="breakpoint",disp="keep",enabled="y"}

where each value has a unique label, and a list such as:

{"1","2","4"}
{bp="1",bp="2",bp="4"}

where values are un-labeled or the label is duplicated.

What follows is a draft revision to the output specification that addresses this problem.

The output from GDB/MI consists of zero or more out-of-band records optionally followed by a single result record, the result record being for the most recent command input. The sequence is terminated by ``(gdb)''.

Asynchronous GDB/MI output is similar.

Each output record directly associated with an input command is prefixed by the input commands token.

output ==>: { out-of-band-record } [ result-record ] "(gdb)" nl
result-record ==>: [ token ] "^" result-class { "," result } nl
out-of-band-record ==>: async-record | stream-record
async-record ==>: exec-async-output | status-async-output | notify-async-output
exec-async-output ==>: [ token ] "*" async-output
status-async-output ==>: [ token ] "+" async-output
notify-async-output ==>: [ token ] "=" async-output
async-output ==>: async-class { "," result } nl
result-class ==>: "done" | "running" | "connected" | "error" | "exit"
async-class ==>: "stopped" | others depending on need as still in development
result ==>: string "=" value
value ==>: c-string | tupple | list
tupple ==>: "{}" | "{" result { "," result } "}"
list ==>: "[]" | "[" value { "," value } "]"
string ==>: [-A-Za-z\.0-9_]*
c-string ==>: See the input specification
stream-record ==>: console-stream-output | target-stream-output | log-stream-output
console-stream-output ==>: "~" c-string
target-stream-output ==>: "@" c-string
log-stream-output ==>: "&" c-string
nl ==>: CR | CR-LF
token ==>: "any sequence of digits"

In addition, the following are still being developed.

query: This action is currently undefined.

Notes:

All output sequences end in a single line containing a period.
The token is from the corresponding request. If an execution command is interrupted by the -exec-interrupt command, the token associated with the `*stopped' message is the one of the original execution command, not the one of the interrupt-command.
status-async-output contains on-going status information about the progress of a slow operation. It can be discarded. All status output is prefixed by the prefix `+'.
exec-async-output contains asynchronous state change on the target (stopped, started, disappeared). All async output is prefixed by the prefix `*'.
notify-async-output contains supplementary information that the client should handle (new breakpoint information). All notify output is prefixed by the prefix `='.
console-stream-output is output that should be displayed as is, in the console. It is the textual response to a CLI command. All the console output is prefixed by the prefix ``~''.
target-stream-output is the output produced by the target program. All the target output is prefixed by the prefix ``@''.
log-stream-output is output text coming from GDB's internals, for instance messages that should be displayed as part of an error log. All the log output is prefixed by the prefix ``&''.

Debugging with GDB