Fixing Your Program

You can use the fix command to relink source files after you make changes, without recompiling the entire program. You can then continue execution of the program.

To Fix Your File

1. Save the changes to your source.
2. Type fix at the dbx prompt.

   Although you can do an unlimited number of fixes, if you have done several fixes in a row, consider rebuilding your program. The fix command changes the program image in memory, but not on the disk. As you do more fixes, the memory image gets out of sync with what is on the disk.

   The fix command does not make the changes within your executable file, but only changes the .o files and the memory image. Once you have finished debugging a program, you must rebuild your program to merge the changes into the executable. When you quit debugging, a message reminds you to rebuild your program.

   If you invoke the fix command with an option other than -a and without a file name argument, only the current modified source file is fixed.

   When fix is invoked, the current working directory of the file that was current at the time of compilation is searched before executing the compilation line. There might be problems locating the correct directory due to a change in the file system structure from compilation time to debugging time. To avoid this problem, use the command pathmap, which creates a mapping from one path name to another. Mapping is applied to source paths and object file paths.

Continuing After Fixing

You can continue executing using the cont command (see cont Command).

Before resuming program execution, be aware of the following conditions that determine the effect of your changes.

Changing an Executed Function

If you made changes in a function that has already executed, the changes have no effect until:

• You run the program again

• That function is called the next time

If your modifications involve more than simple changes to variables, use the fix command, then the run command. Using the run command is faster because it does not relink the program.

Changing a Function Not Yet Called

If you have made changes in a function not yet called, the changes will be in effect when that function is called.

Changing a Function Currently Being Executed

If you have made changes to the function currently being executed, the impact of the fix command depends on where the change is relative to the stopped in function:

• If the change is in code that has already been executed, the code is not re-executed. Execute the code by popping the current function off the stack (see pop Command) and continuing from where the changed function is called. You need to know your code well enough to determine whether the function has side effects that can’t be undone (for example, opening a file).

• If the change is in code that is yet to be executed, the new code is run.

Changing a Function Presently on the Stack

If you have made changes to a function presently on the stack, but not to the stopped in function, the changed code is not used for the present call of that function. When the stopped in function returns, the old versions of the function on the stack are executed.

There are several ways to solve this problem:

• Use the pop command to pop the stack until all changed functions are removed from the stack. You need to know your code to be sure that no problems are created.

• Use the cont at line_number command to continue from another line.

• Manually repair data structures (use the assign command) before continuing.

• Rerun the program using the run command.

If there are breakpoints in modified functions on the stack, the breakpoints are moved to the new versions of the functions. If the old versions are executed, the program does not stop in those functions.