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4.4 Your Program’s Environment
The environment consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start GDB over again.
Add directory to the front of the PATH environment variable (the search path for executables) that will be passed to your program. The value of PATH used by GDB does not change. You may specify several directory names, separated by whitespace or by a system-dependent separator character (‘ : ’ on Unix, ‘ ; ’ on MS-DOS and MS-Windows). If directory is already in the path, it is moved to the front, so it is searched sooner.
You can use the string ‘ $cwd ’ to refer to whatever is the current working directory at the time GDB searches the path. If you use ‘ . ’ instead, it refers to the directory where you executed the path command. GDB replaces ‘ . ’ in the directory argument (with the current path) before adding directory to the search path.
Display the list of search paths for executables (the PATH environment variable).
Print the value of environment variable varname to be given to your program when it starts. If you do not supply varname , print the names and values of all environment variables to be given to your program. You can abbreviate environment as env .
Set environment variable varname to value . The value changes for your program (and the shell GDB uses to launch it), not for GDB itself. The value may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The value parameter is optional; if it is eliminated, the variable is set to a null value.
For example, this command:
tells the debugged program, when subsequently run, that its user is named ‘ foo ’. (The spaces around ‘ = ’ are used for clarity here; they are not actually required.)
Note that on Unix systems, GDB runs your program via a shell, which also inherits the environment set with set environment . If necessary, you can avoid that by using the ‘ env ’ program as a wrapper instead of using set environment . See set exec-wrapper , for an example doing just that.
Environment variables that are set by the user are also transmitted to gdbserver to be used when starting the remote inferior. see QEnvironmentHexEncoded .
Remove variable varname from the environment to be passed to your program. This is different from ‘ set env varname = ’; unset environment removes the variable from the environment, rather than assigning it an empty value.
Environment variables that are unset by the user are also unset on gdbserver when starting the remote inferior. see QEnvironmentUnset .
Warning: On Unix systems, GDB runs your program using the shell indicated by your SHELL environment variable if it exists (or /bin/sh if not). If your SHELL variable names a shell that runs an initialization file when started non-interactively—such as .cshrc for C-shell, $ .zshenv for the Z shell, or the file specified in the BASH_ENV environment variable for BASH—any variables you set in that file affect your program. You may wish to move setting of environment variables to files that are only run when you sign on, such as .login or .profile .
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17.1 Assignment to Variables To alter the value of a variable, evaluate an assignment expression. See Expressions. For example, print x=4 stores the value 4 into the variable x, and then prints the value of the assignment expression (which is 4). See Using GDB with Different Languages, for more information on operators in supported languages.
You can create variables in the context of gdb for your convenience, like set $foo = ... and later reference $foo. Obviously such variables are in no way visible to the running code, however. - FatalError Apr 23, 2012 at 16:14
Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, GDB might not be able to display values for such local variables.
5 Google is your friend: For example, if your program has a variable width, you get an error if you try to set a new value with just `set width=13', because GDB has the command set width: (gdb) whatis width type = double (gdb) p width $4 = 13 (gdb) set width=47 Invalid syntax in expression. The invalid expression, of course, is `=47'.
GDB enable see impulses conversions include assignments than C; you can freely store and enumerable value into a display variable or vice versa, and you can konvertieren any structure up any other structure so is the same length or shorter.
Assignment to variables To switch the value of one variable, evaluate on subscription expression. See section Expressions. For example, print x=4 stores the value 4 into the variable scratch, and next prints the value of the assignment expression (which is 4).
You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value.
10.12 Convenience Variables. GDB provides convenience variables that to can make withinGDB to maintain on at a valued and refer to it later. ... Using a convenience variable forward the first set creates it, but its value remains void until you assign a new select. Thee can alter the value with another order at any time.
You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value. show convenience Print a list of convenience variables used so far, and their values.
The easiest is setting a program variable (see GDB: assignment ): (gdb) l 6 { 7 int i; 8 struct file *f, *ftmp; 9 (gdb) set variable i = 10 (gdb) p i $1 = 10 Or you can just update arbitrary (writable) location by address: (gdb) set {int}0x83040 = 4 There's more. Read the manual. Share Improve this answer Follow edited Sep 3, 2017 at 1:32
For example, here GDB shows that a variable ptt points at another variable t, defined in `hi2.c': (gdb) set print symbol-filename on (gdb) p/a ptt $4 = 0xe008 <t in hi2.c> ... You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience ...
Assignment to variables To alter the value of a variable, evaluate an assignment expression. See section Expressions. For example, print x=4 stores the value 4 into the variable x, and then prints the value of the assignment expression (which is 4).
1 Answer Sorted by: 8 eval does a printf of its arguments and then runs it as a command. So you can take your printf argument list, insert set $MyVar = at the beginning, and eval it. (gdb) eval "set $MyVar = \"Hello %d\"", 7 (gdb) print $MyVar $2 = "Hello 7" Share Improve this answer Follow edited Aug 22, 2014 at 15:06
A user-defined command is a sequence of GDB commands to which you assign a new name as a command. This is done with the define command. User commands may accept an unlimited number of arguments separated by whitespace. Arguments are accessed within the user command via $arg0…$argN. A trivial example: define adder print $arg0 + $arg1 + $arg2 end
Debugging with GDB - Variables. , , table of contents . The most common kind of expression to use is the name of a variable in your program. Variables in expressions are understood in the selected stack frame (see section Selecting a frame ); they must be either: global (or file-static) visible according to the scope rules of the programming ...
We can also add and remove environment variables within gdb, but these changes won't update the environment once we exit gdb. All environment variables are simple strings. We can define a variable: (gdb) set env VAR_NAME_1 = var_name_value. (gdb) show env VAR_NAME_1. VAR_NAME_1 = var_name_value.
Ask Question Asked 9 years, 8 months ago Modified 9 years, 8 months ago Viewed 3k times 3 So I have this code for homework that I must debug with gdb. I have found the problem but don't know how to use gdb to change it #define ARRAYSIZE 12 for (i = ARRAYSIZE - 2; i > 0; i--) { for (j = i; j < ARRAYSIZE - 1; j++) {
27.15 GDB/MI Variable Objects Introduction to Variable Objects. Variable objects are "object-oriented" MI interface for examining and changing values of expressions. Unlike some other MI interfaces that work with expressions, variable objects are specifically designed for simple and efficient presentation in the frontend.
By assigning the weight of the k-th window to the combined model at time t k + V − 1, we calculated the predictions of the variable-weight combined model. Taking the Usher-Weibull combined model as an example, this paper provided the coefficient of variation and weights for the three distinct weighting methods, as shown in Table 3 .
1 You don't mention why you can't use a Python function. That's by far the simplest way to program gdb. However, if you really must do it, and really must avoid Python, there is a way. It's gross! But it does work. It's like this: Use the various set logging commands to redirect output to a temporary file. Invoke the command you want.
The value changes for your program (and the shell GDB uses to launch it), not for GDB itself. The value may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The value parameter is optional; if it is eliminated, the variable is set to a null value. For example, this ...
When starting gdb from shell command-line, you can specify which program to run, with which arguments (with --args), and even modify the environment of the program with the help of env! I just did it successfully like this: gdb --ex=run --args env LD_BIND_NOW=1 LD_DEBUG=libs \ apt-get install --yes $(cat pkgs-to-install-to-crash-apt)