roniovine / gdbhooks

A small package to show gdb hooks for breakpoint safe system time based service access

gdbHooks

A small package to show gdb hooks for breakpoint safe system time based service access

Overview
Building
Setup
CLI Mode
Emacs Mode

Overview

This package contians code and examples for building a timer based process with the capability to be run withing GDB and still maintain all its original timing characteristics. It includes a simple module, TimerWrapper.h/cc, that will encapsulate all access to the system get time functions and will adjust the value returned for any time spent stopped at a GDB breakpoint. This module should be built/linked with an application. All calls to get the system time from the process must be done via these functions.

There is a demo program provided that can be run to show the functionality of this package. This demo program has a simple infinite loop with a call to a function, foo, that will print out the actual system time and the adusted time, and then sleep for 1 second.

Building

To build the demo program, from this directory run:

$ g++ -g TimerWrapper.cc gdbHooksDemo.cc -o gdbHooksDemo

Setup

To setup for emacs use, copy the included .emacs file to your home directory and edit the file per the instructions in the comments. Also, place the shell scripts gdbCli and gdbEmacs and the timerHooks file in other locations as necessary and edit the gdbCli and gdbEmacs files and change the location of the timerHooks file as necessary. When using emacs for the graphical GDB front end, it is recommended to use emacs23, the reasons are described below in the Emacs Mode section. If emacs23 is not available on your host, it should be installed as follows, ex for Ubuntu:

$ sudo apt-get install emacs23

CLI Mode

This section describes running the demo program in command line mode. There is a simple shell script wrapper around the 'gdb' command line program.

Run the program from within gdb in CLI mode as follows:

$ gdbCli gdbHooksDemo

Once within the gdb prompt, set a breakpoint at the function 'foo' as follows:

(gdb) break foo

Once the breakpoint is set, you can just successively run continue as follows to see the actual time, and the adjusted time based on the time spent at a breakpoint/stopped state as shown below. As can be seen by comparing the actual and adjusted times, regardless of how much time is spent at a breakpoint, the adjusted time will only reflect the actual process run time.

(gdb) continue
Actual Elapsed Time: 133324184 usec, Adjusted Elapsed Time: 11112 usec
Actual Elapsed Time: 133324 msec, Adjusted Elapsed Time: 11 msec
Actual Elapsed Time: 133 sec, Adjusted Elapsed Time: 0 sec
Actual Time Of Day: 12-22-2019 13:22:29.428603, Adjusted Time Of Day: 12-22-2019 13:20:16.115524

(gdb) continue
Actual Elapsed Time: 135933179 usec, Adjusted Elapsed Time: 1022161 usec
Actual Elapsed Time: 135933 msec, Adjusted Elapsed Time: 1022 msec
Actual Elapsed Time: 135 sec, Adjusted Elapsed Time: 1 sec
Actual Time Of Day: 12-22-2019 13:22:32.037598, Adjusted Time Of Day: 12-22-2019 13:20:17.126578

(gdb) continue
Actual Elapsed Time: 141762466 usec, Adjusted Elapsed Time: 2032749 usec
Actual Elapsed Time: 141762 msec, Adjusted Elapsed Time: 2032 msec
Actual Elapsed Time: 141 sec, Adjusted Elapsed Time: 2 sec
Actual Time Of Day: 12-22-2019 13:22:37.866885, Adjusted Time Of Day: 12-22-2019 13:20:18.137166

(gdb) continue
Actual Elapsed Time: 202398215 usec, Adjusted Elapsed Time: 3046006 usec
Actual Elapsed Time: 202398 msec, Adjusted Elapsed Time: 3046 msec
Actual Elapsed Time: 202 sec, Adjusted Elapsed Time: 3 sec
Actual Time Of Day: 12-22-2019 13:23:38.502634, Adjusted Time Of Day: 12-22-2019 13:20:19.150423

(gdb) continue
Actual Elapsed Time: 226610267 usec, Adjusted Elapsed Time: 4057473 usec
Actual Elapsed Time: 226610 msec, Adjusted Elapsed Time: 4057 msec
Actual Elapsed Time: 226 sec, Adjusted Elapsed Time: 4 sec
Actual Time Of Day: 12-22-2019 13:24:02.714686, Adjusted Time Of Day: 12-22-2019 13:20:20.161889

(gdb) continue
Actual Elapsed Time: 369408255 usec, Adjusted Elapsed Time: 5068584 usec
Actual Elapsed Time: 369408 msec, Adjusted Elapsed Time: 5068 msec
Actual Elapsed Time: 369 sec, Adjusted Elapsed Time: 5 sec
Actual Time Of Day: 12-22-2019 13:26:25.512674, Adjusted Time Of Day: 12-22-2019 13:20:21.173001

Emacs Mode

This section describes running programs via the Emacs/GUD GDB graphical front end.

This has been tested with the following versions of emacs and gdb:

GNU Emacs 24.3.1
GNU Emacs 23.4.1
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.3) 7.7.1

It is recommended to use emacs23 for the emacs GUI front end. This version of emacs does not need the -i=mi option and will use the native GDB console based commands for it's GUI based control. This will allow all timer hooks to work correctly with the GUI based program control. If emacs23 is not available, the gdbEmacs shell script will detect that and run the standard installed emacs instead.

IMPORTANT NOTE: When running with a non-emacs23 version of emacs or later, DO NOT use any of the graphical buttons (i.e. run, continue etc) for program control and execution. This is because with the latest Emacs/GUD/GDB intgegration, it uses the gud-mi based interface for the graphical commands, so all of the gdb commands are preceeded with the -exec- prefix, i.e. -exec-continue as opposed to just continue etc. I have not found a way to add gdb callback hooks for any of the -exec- based command formats. If anyone knows of a way to do this, I would greatly appreciate any info on this. For an emacs version other that emacs23, all program control should be done via the gdb command line prompt sub-window and enter the same commands as the above CLI based example.

There is a simple shell script wrapper around the gdb command line program.

Run the program from within gdb with Emacs/GUD mode as the graphical front end as follows and then control the program either from the GUI or the GDB command line sub-window based on the emacs version described above.

$ gdbEmacs gdbHooksDemo