The Real Curriculum

You have done the workshop loop. The five tools are not abstract any more. You know what each one is for, when it speaks up, and what it prints when it does.

Tool	What it caught
`gcc -Wall -Wextra -g`	Nothing this round — but it can.
`gdb` (`run`, `bt`)	A segfault, with the file and line.
`valgrind`	A memory leak, with the allocation site.
`-fsanitize=address`	A heap buffer overflow, with both stacks.
`-fsanitize=undefined`	Standing by for signed overflows and friends.

You also wrote a Makefile, split a single file into a real project, and made make recompile only what changed.

This is what building C means.

Reading Doom's Makefile

You earned the right to clone the Doom source and read its build file. Do it now:

git clone https://github.com/id-Software/DOOM.git
cd DOOM/linuxdoom-1.10
less Makefile

The first lines look familiar:

CC=  gcc  # gcc or g++
 
CFLAGS=-g -Wall -DNORMALUNIX -DLINUX # -DUSEASM
LDFLAGS=-L/usr/X11R6/lib
LIBS=-lXext -lX11 -lnsl -lm

Same CC, same CFLAGS, same -g and -Wall you have been using. -DNORMALUNIX and -DLINUX define preprocessor symbols so the C code can #ifdef LINUX for platform-specific paths; -DUSEASM is commented out — a switch the original developers used to toggle hand-written assembly paths in or out. LDFLAGS=-L/usr/X11R6/lib is the -L flag from earlier in this chapter — it adds X11's library directory to the linker search path. LIBS=-lXext -lX11 -lnsl -lm is -l four times — link against libXext, libX11, libnsl, and libm (the math library). The full toolchain you used for sort, written by id Software for a 1995 game, with two more libraries in the link line.

The recipe section, further down, has the same shape as yours:

$(O)/linuxxdoom:	$(OBJS) $(O)/i_main.o
	$(CC) $(CFLAGS) $(LDFLAGS) $(OBJS) $(O)/i_main.o \
	-o $(O)/linuxxdoom $(LIBS)

$(OBJS) is a long list of .o files, one per source — the same shape as your OBJS = $(SRCS:.c=.o). The link command takes them all, names the output, and links against the libraries.

Doom is bigger than sort. The Makefile is longer. The pieces are the same.

What is next

You have a working C development environment. The c-tier starts right after this page. The first chapter — c01 — is libtci: you will spend it building a small standard-library replacement, function by function, starting with tci_strlen and ending with tci_atoi.

Every line of code you write in c01 will be compiled with -Wall -Wextra -g, built with a Makefile, debugged with gdb when it crashes, checked with valgrind when it leaks, and hardened with the sanitisers when it does something weird.

The workshop is yours. The real curriculum starts now.

Reading Doom's Makefile

What is next

The Toolkit