byrum@sleet.cs.odu.edu (06/22/88)
I am conducting some research in software transformation. One problem area involves source-to-source changes in which the new piece of code does not perform as the original. The source-to-source modifications are assumed to be "semantically correct." These may be errors induced either by mistakes in the original code or by the programmer's taking advantage of the compiler's characteristics. Could all you people in net land send me some of your horror stories and/or problems encountered during development and/or maintenance? Examples in any language are welcome. I thought of some interesting problems with source-to-source transformations on C code. Below is the example. The problem is due to several library functions that work with strings. Consider: >> #include <stdio.h> >> >> #define LONGSTRING "1234567890123" >> >> main() >> { >> extern char *strcpy(); >> >> char string[10], a, b, c; >> >> strcpy( string, LONGSTRING); >> printf( "the string is {%s}\n", string); >> a = 'A'; >> b = 'B'; >> c = 'C'; >> printf( "a = {%c} b = {%c} c = {%c}\n", a, b, c); >> } Notice that the programmer takes advantage of string and the variable space behind it. LONGSTRING consist of 13 characters and string has only 10 allocated spaces in the array. OUTPUT: >> the string is {1234567890123} >> a = {A} b = {B} c = {C} Now consider: >> #include <stdio.h> >> >> #define LONGSTRING "1234567890123" >> >> main() >> { >> extern char *strcpy(); >> >> char string[10], a = 'A', b = 'B', c = 'C'; >> >> strcpy( string, LONGSTRING); >> printf( "the string is {%s}\n", string); >> printf( "a = {%c} b = {%c} c = {%c}\n", a, b, c); >> } Notice, that the assignments of a, b, and c have been moved to the declaration. Since a, b, and c have no other dependencies in the program, this is a legal source-to-source transformation. OUTPUT >> the string is {1234567890123} >> a = {1} b = {2} c = {3} I have found that through carelessness this type of problem may occur often. (I realize that the programmer should be responsible for checking the array bounds!) This is just an example of a piece of code that works before transformation and not after. If people are interested I will compile the best examples and repost them. Any help is appreciated. Direct flames to /dev/null. Respond by email, not posting. If I get enough responses, I will summarize. | Terry Franklin (Frank) Byrum | Old Universion University ___ | INET: byrum@cs.odu.edu /__ _. __. _ _ /_ | UUCP: ...!uunet!xanth!brooks!byrum / _/ \_(_/|_|\|_/ \ | DISCLAIMER: No one listens anyway! -- Send compilers articles to ima!compilers or, in a pinch, to Levine@YALE.EDU Plausible paths are { ihnp4 | decvax | cbosgd | harvard | yale | bbn}!ima Please send responses to the originator of the message -- I cannot forward mail accidentally sent back to compilers. Meta-mail to ima!compilers-request