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Full Discussion: Knowing the size and location of variables in a C program
Special Forums UNIX Desktop Questions & Answers Knowing the size and location of variables in a C program Post 302833697 by Corona688 on Wednesday 17th of July 2013 04:30:15 PM
Old 07-17-2013
Quote:
Originally Posted by Cambria
So I need some help with this. Pardon me if I'm posting in the wrong forum, after some googling for my answer and finding nothing I found this forum. It seemed appropriate for what I was seeking. I just didnt find a forum that concerned the use of GDB. I'm learning to use the C language and GDB. What I don't understand is how the computer knows how big each piece of a program is in memory, and how I could find my variable's in memory using GDB.
To get nice debugging information like that, you have to build the executable with debugging information(i.e. -ggdb). This embeds lots of offsets and labels inside the program file for gdb's convenience.

This is also why gdb has trouble when it steps into code outside your program, like libc... Libraries are probably not built with debugging information, so details about their insides will be very limited.

Quote:
I mean if all memory is numbered how can anyone including the CPU know where a word or giant or w/e starts and ends?
To put it bluntly -- it doesn't. They all become hardcoded segment offsets, in the end. Without debugging information, you're left with detective work.

Quote:
If I wanted to find my variable in memory after setting a break point in it and accessing the $esp register how would I know where my variables began and ended?
If your executable wasn't built with debugging info, that'd mean detective work.
Last edited by Corona688; 07-17-2013 at 05:38 PM..
 

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LEARN ABOUT PLAN9

cas

CAS(1)                                                            aMule utilities                                                           CAS(1)

NAME

       cas - c aMule statistics

SYNOPSIS

       cas [-o] [-p] [-c <path>]

       cas [-h]

DESCRIPTION

       cas  is  a program for displaying the contents of your aMule online signature file to console (in a human readable form). For this to work,
       you must enable the "Online Signature" option in aMule's preferences.

       [ -o, --picture, -P ]
              Writes the online signature picture.  You can optionally append =<PATH> to this option, to specify the location it should be written
              to.

       [ -p, --html, -H ]
              HTML  page  with  stats and picture.  You can optionally append =<PATH> to this option, to specify the location it should be written
              to.

       [ -c <path>, --config-dir=<path> ]
              Read config from <path> instead of home

       [ -h, --help ]
              Prints a short usage description.

       Without any options, it prints online signature data to stdout.

       cas was written by Pedro de Oliveira <falso@rdk.homeip.net>

FILES

       ~/.aMule/casrc
       stat.png
       tmp.html

REPORTING BUGS

       Please report bugs either on our forum (http://forum.amule.org/), or in our bugtracker (http://bugs.amule.org/).  Please do not report bugs
       in e-mail, neither to our mailing list nor directly to any team member.

COPYRIGHT

       aMule and all of its related utilities are distributed under the GNU General Public License.

SEE ALSO

       amule(1), wxcas(1)

AUTHOR

       This manpage was written by Vollstrecker <amule@vollstreckernet.de>

cas v0.8                                                           November 2011                                                            CAS(1)
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