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Sending Patches for GNU CC

If you would like to write bug fixes or improvements for the GNU C compiler, that is very helpful.

Send suggested fixes to the bug report mailing list: bug-gcc@prep.ai.mit.edu

Please follow these guidelines so we can study your patches efficiently. If you don’t follow these guidelines, your information might still be useful, but using it will take extra work. Maintaining GNU C is a lot of work in the best of circumstances, and we can’t keep up unless you do your best to help.

- Send an explanation with your changes of what problem they fix or what improvement they bring about. For a bug fix, just include a copy of the bug report, and explain why the change fixes the bug.
(Referring to a bug report is not as good as including it, because then we will have to look it up, and we have probably already deleted it if we’ve already fixed the bug.)
- Always include a proper bug report for the problem you think you have fixed. We need to convince ourselves that the change is right before installing it. Even if it is right, we might have trouble judging it if we don’t have a way to reproduce the problem.
- Include all the comments that are appropriate to help people reading the source in the future understand why this change was needed.
- Don’t mix together changes made for different reasons. Send them individually.
If you make two changes for separate reasons, then we might not want to install them both. We might want to install just one. If you send them all jumbled together in a single set of diffs, we have to do extra work to disentangle them—to figure out which parts of the change serve which purpose. If we don’t have time for this, we might have to ignore your changes entirely.
If you send each change as soon as you have written it, with its own explanation, then the two changes never get tangled up, and we can consider each one properly without any extra work to disentangle them. Ideally, each change you send should be impossible to subdivide into parts that we might want to consider separately, because each of its parts gets its motivation from the other parts.
- Send each change as soon as that change is finished. Sometimes people think they are helping us by accumulating many changes to send them all together. As explained above, this is absolutely the worst thing you could do.
Since you should send each change separately, you might as well send it right away. That gives us the option of installing it immediately if it is important.
- Use ‘diff -c’ to make your diffs. Diffs without context are hard for us to install reliably. More than that, they make it hard for us to study the diffs to decide whether we want to install them. Unidiff format is better than diffs without context, but not as easy to read as ‘-c’ format.
If you have GNU diff, use ‘diff -cp’, which shows the name of the function that each change occurs in.
- Write the change log entries for your changes. We get lots of changes, and we don’t have time to do all the change log writing ourselves.
Read the ‘ChangeLog’ file to see what sorts of information to put in, and to learn the style that we use. The purpose of the change log is to show people where to find what was changed. So you need to be specific about what functions you changed; in large functions, it’s often helpful to indicate where within the function the change was.
On the other hand, once you have shown people where to find the change, you need not explain its purpose. Thus, if you add a new function, all you need to say about it is that it is new. If you feel that the purpose needs explaining, it probably does—but the explanation will be much more useful if you put it in comments in the code.
If you would like your name to appear in the header line for who made the change, send us the header line.
- When you write the fix, keep in mind that we can’t install a change that would break other systems.
People often suggest fixing a problem by changing machine-independent files such as ‘toplev.c’ to do something special that a particular system needs. Sometimes it is totally obvious that such changes would break GNU CC for almost all users. We can’t possibly make a change like that. At best it might tell us how to write another patch that would solve the problem acceptably.
Sometimes people send fixes that might be an improvement in general—but it is hard to be sure of this. It’s hard to install such changes because we have to study them very carefully. Of course, a good explanation of the reasoning by which you concluded the change was correct can help convince us.
The safest changes are changes to the configuration files for a particular machine. These are safe because they can’t create new bugs on other machines.
Please help us keep up with the workload by designing the patch in a form that is good to install.