make

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Translated

GNU Make skill for C/C++ build systems. Use when writing or debugging Makefiles, understanding pattern rules and automatic dependency generation, managing CFLAGS/LDFLAGS, converting ad-hoc compile commands into maintainable Makefiles, or diagnosing incremental build issues. Activates on queries about Makefiles, make targets, pattern rules, phony targets, dependency tracking, recursive make, or make errors.

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gnu-makec-cpp-build-systemsmakefile-developmentbuild-automationdependency-tracking

SKILL.md Content

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GNU Make

Purpose

Guide agents through idiomatic Makefile patterns for C/C++ projects: phony targets, pattern rules, automatic dependency generation, and common build idioms.

Triggers

  • "How do I write a Makefile for my C project?"
  • "My Makefile rebuilds everything every time"
  • "How do I add dependency tracking to Make?"
  • "What does 
    $@
    , 
    $<
    , 
    $^
    mean?"
  • "I'm getting 'make: Nothing to be done for all'"
  • "How do I convert my shell compile script to a Makefile?"

Workflow

1. Minimal correct Makefile for C

makefile
CC      := gcc
CFLAGS  := -std=c11 -Wall -Wextra -g -O2
LDFLAGS :=
LDLIBS  :=

SRCS    := $(wildcard src/*.c)
OBJS    := $(SRCS:src/%.c=build/%.o)
TARGET  := build/prog

.PHONY: all clean

all: $(TARGET)

$(TARGET): $(OBJS)
	$(CC) $(LDFLAGS) -o $@ $^ $(LDLIBS)

build/%.o: src/%.c | build
	$(CC) $(CFLAGS) -c -o $@ $<

build:
	mkdir -p build

clean:
	rm -rf build
Automatic variables:
  • $@
    — target name
  • $<
    — first prerequisite
  • $^
    — all prerequisites (deduplicated)
  • $*
    — stem (the 
    %
    part in a pattern rule)
  • $(@D)
    — directory part of 
    $@

2. Automatic dependency generation

Without this, changing a header doesn't trigger a rebuild of 
.c
files that include it.
makefile
CC      := gcc
CFLAGS  := -std=c11 -Wall -Wextra -g -O2
DEPFLAGS = -MMD -MP            # -MMD: generate .d file; -MP: phony targets for headers

SRCS    := $(wildcard src/*.c)
OBJS    := $(SRCS:src/%.c=build/%.o)
DEPS    := $(OBJS:.o=.d)
TARGET  := build/prog

.PHONY: all clean

all: $(TARGET)

$(TARGET): $(OBJS)
	$(CC) $(LDFLAGS) -o $@ $^ $(LDLIBS)

build/%.o: src/%.c | build
	$(CC) $(CFLAGS) $(DEPFLAGS) -MF $(@:.o=.d) -c -o $@ $<

-include $(DEPS)    # '-' ignores errors on first build (no .d files yet)

build:
	mkdir -p build

clean:
	rm -rf build

3. Pattern rules cheatsheet

makefile
# Compile C
%.o: %.c
	$(CC) $(CFLAGS) -c -o $@ $<

# Compile C++
%.o: %.cpp
	$(CXX) $(CXXFLAGS) -c -o $@ $<

# Generate assembly
%.s: %.c
	$(CC) $(CFLAGS) -S -o $@ $<

# Run a tool on each file
build/%.processed: src/%.raw | build
	mytool $< > $@

4. Common Make patterns

Debug and release builds

makefile
BUILD ?= release

ifeq ($(BUILD),debug)
  CFLAGS += -g -Og -DDEBUG
else
  CFLAGS += -O2 -DNDEBUG
endif
Usage: 
make BUILD=debug

Parallel builds

bash
make -j$(nproc)     # use all CPUs
make -j4            # exactly 4 jobs
Add 
-Otarget
(or 
-O
) for ordered output: 
make -j$(nproc) -O

Verbose output

makefile
# In Makefile: suppress with @
build/%.o: src/%.c | build
	@echo "  CC  $<"
	@$(CC) $(CFLAGS) -c -o $@ $<
Override silence: 
make V=1
if you guard with 
$(V)
:
makefile
Q := $(if $(V),,@)
build/%.o: src/%.c
	$(Q)$(CC) $(CFLAGS) -c -o $@ $<

Installing

makefile
PREFIX ?= /usr/local

install: $(TARGET)
	install -d $(DESTDIR)$(PREFIX)/bin
	install -m 0755 $(TARGET) $(DESTDIR)$(PREFIX)/bin/

5. Multi-directory projects

For medium projects, avoid recursive make (fragile, slow). Use a flat Makefile that includes sub-makefiles:
makefile
# project/Makefile
include lib/module.mk
include src/app.mk
makefile
# lib/module.mk
LIB_SRCS := $(wildcard lib/*.c)
LIB_OBJS := $(LIB_SRCS:lib/%.c=build/lib_%.o)
OBJS      += $(LIB_OBJS)

build/lib_%.o: lib/%.c
	$(CC) $(CFLAGS) -c -o $@ $<

6. Common errors

ErrorCauseFix
No rule to make target 'foo.o'
Missing source or ruleCheck source path and pattern rule
Nothing to be done for 'all'
Targets up to dateTouch a source file or run 
make clean
Circular dependency dropped
Target depends on itselfCheck dependency chain
missing separator
Tab vs spacesRecipes must use a tab, not spaces
*** multiple target patterns
Pattern rule syntax errorCheck 
%
placement
Rebuilds everything every timeTimestamps wrong, or PHONY missingCheck 
date
; ensure 
all
is 
.PHONY
Header change not detectedNo dep trackingAdd 
-MMD -MP
and 
-include $(DEPS)
For a full variable and function reference, see references/cheatsheet.md.

Related skills

  • Use 
    skills/build-systems/cmake
    for CMake-based projects
  • Use 
    skills/build-systems/ninja
    for Ninja as a make backend
  • Use 
    skills/compilers/gcc
    for CFLAGS details