Introduction to Software Development Tooling

Homework 5: BLD, Investigative

For this assignment, you’ll explore the Makefile of scdoc. scdoc is an open-source project used to generate man pages—which have a notoriously ugly formatting language—from a more friendly, Markdown-like language. The scdoc source repository is located here¹. You can click “tree” to see a web listing of the repository’s files, or you can clone it and browse around using the CLI. You’ll eventually need to clone it to answer some questions.

Navigate to the tree at commit 5ea8873e, open up the Makefile for the “scdoc” project, and answer the following questions. Please provide both the answer and how you arrived at that answer (show your work or cite your sources, as appropriate):

1. In general, how does Make determine which target to build if you run it with no arguments?
2. For scdoc specifically, which target does make build if you run it with no arguments? Assume GNU Make.
3. The command on line 30 of the Makefile, used to link the final scdoc binary, includes a number of Make variable expansions (the words starting with $).
   1. What is an automatic variable? How does the visible behavior of automatic variables differ from that of other kinds of variables? Please provide at least two examples.
   2. Which of the variables used in the command on line 30 are automatic variables? For each one, what is the meaning?
   3. The Makefile does not explicitly define some variables it uses, such as LDFLAGS. What three places can these values come from?
   4. What does the entire line expand to when Make runs it? Explain where the value of each variable came from. Assume that no variables are overridden by the outside environment.
4. If you run make scdoc from a clean directory (i.e. after initial checkout or running “make clean”), you will see 10 commands that get run. Please do this and tell us the commands. Annotate each command with the line number of the Makefile that generated the command. Many of these will share a line number—that’s okay.
5. Are any additional commands run by make scdoc beyond the ones you annotated in the previous question? If so, what are they and why were they not included in the output?
6. Pretend you are the Make program. What does Make do when you run make .build/main.o? Be specific and do not assume anything about the state of the .build/ directory.
7. The install rule copies the resulting binary and documentation to various special system directories so that you can use the program from anywhere on your system. To do this, it runs the install command. What does the install program do? Why might you use it instead of cp?
8. Line 62 looks different from most other lines. It starts with .PHONY and lists a number of targets. What is the purpose of this line? What could happen if it were not present?

Submitting your work

Write your answers in a text file, answers.txt. Submit this file on Gradescope.

1. You may notice that, unlike many of the other projects you’ve encountered, scdoc is hosted on SourceHut and not GitHub. SourceHut and GitHub are just two examples of Git hosting platforms; GitLab is another. Regardless of what hosting platform a project’s main repository uses, the repository itself is still plain Git. That means you can clone it, make local commits, and even push your own copy (or fork) to a different hosting provider! This illustrates the distributed nature of Git—your local clone contains the entire repository and all metadata needed to reconstruct it elsewhere. ↩

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