Reversible load-time dynamic linking

A method for reversibly linking an application to a selected library and one or more external libraries, wherein the application comprises object code, wherein a pointer references a list of libraries, wherein the pointer initially references a list of the external libraries, the method comprising:

• archiving the state of the pointer;
• selecting a library;
• associating the selected library with the one or more external libraries, wherein the associating changes which libraries are linked to the application, the associating comprising:
• prepending to the list of the external libraries a reference to the selected library;
• and
• changing the state of the pointer to reference the prepended list;
• and
• loading the application and the selected library.

A method for reversibly linking an application to a selected library, wherein an executable file for the application comprises a header, a data section, and an imports section, wherein the header comprises a pointer to the imports section, wherein the data section comprises object code and one or more function calls, and wherein the imports section comprises a list of one or more names of libraries and a list for each library of the functions of the library, the method comprising:

• creating an interim imports section;
• selecting a library to link to the application;
• adding to the interim imports section a reference to the selected library;
• copying the imports section of the executable file;
• adding to the interim imports section the copy of the imports section of the executable file after the added reference to the selected library;
• changing the header pointer to reference the interim imports section, wherein the changing the header pointer changes which libraries are linked to the application;
• and
• loading the application and at least one of the one or more libraries of the interim imports section.

A computer-readable medium having stored thereon a data structure, comprising:

• a first data field containing data representing a header for an application, the header comprising a pointer to a list of libraries linked to the application during linking;
• a second data field containing data representing object code for the application and one or more references to external functions, wherein a reference to an external function is replaced with a reference to a library and function within that library during linking;
• a third data field containing data representing the list of libraries and functions referenced within the object code for the application;
• a fourth data field derived from the first data field, the fourth data field containing data representing an initial state of the first data field;
• and
• a fifth data field derived from the third data field, the fifth data field containing data representing a reference to an additional library comprising plural functions, and further containing the data of the third data field, wherein the pointer of the first data field references the fifth data field to change which libraries are loaded for the application.

A method for reversibly linking an application to a selected library and one or more external libraries, wherein the application comprises object code, the method comprising:

• selecting a library;
• associating the selected library with the one or more external libraries;
• creating a data record;
• storing configuration information in the data record, wherein the application comprises plural units, and wherein the configuration information comprises a distribution scheme for the plural units in a distributed computing environment;
• and
• loading the application and the selected library.

A method for reversibly linking an application to a selected library and one or more external libraries, wherein the application comprises object code, wherein an operating system comprises plural functions for servicing the application, wherein the selected library comprises an entry point function, the method comprising:

• selecting a library;
• associating the selected library with the one or more external libraries;
• loading the application and the selected library, wherein the loading comprises:
• loading the selected library;
• rewriting an operating system function using the entry point function of the selected library;
• and
• loading the application.

A computer readable medium storing computer executable instructions for causing a computer programmed thereby to perform a method of reversibly linking an application to an external library, the method comprising:

• archiving original linking information associated with an application, the archived original linking information referencing a set of one or more external libraries for loading with the application;
• and
• modifying the original linking information to reference the set of one or more external libraries and an additional external library, wherein the modifying causes loading of the additional external library with the application;
• wherein the archiving facilitates reversal of the modifying to thereby disable the loading of the additional external library with the application.

A utility program operable to reversibly install an instrumentation package on an application, the utility program comprising:

• code for archiving original linking information associated with the application, the archived original linking information referencing a set of one or more external libraries;
• and
• code for modifying the original linking information to reference the set of one or more external libraries and an additional external library;
• wherein the modifying causes loading of the additional external library with the application, and wherein the archiving facilitates reversal of the modifying.

A computer-readable medium storing computer-executable instructions for causing a computer programmed thereby to perform a method of reversibly modifying a computer program the method comprising:

• determining original state of first information in an original object file for a computer program;
• modifying the first information in the original object file for the computer program, thereby creating a modified object file for the computer program;
• and
• storing the original state of the first information in the modified object file for the computer program, the stored original state of the first information for reversing the modifying to restore the original object file the computer program.