Understanding .PHONY Targets in Makefiles and the 'No Rule to Make Target' Error

When using .PHONY targets in a makefile without including actual output file names as prerequisites, you’ll encounter the “no rule to make target” error because make treats these targets as regular files rather than commands to execute. The .PHONY declaration tells make that these targets don’t represent actual files, but when you replace ‘.PHONY: foobuild barbuild all clean’ with ‘$(SOLIBNAME) $(BINNAME) all clean’, you’re explicitly listing the actual output files that make needs to generate, allowing make to understand which rules to execute and resolving the error.

Contents

• .PHONY Targets Explained
• The Build Process Without Output Files
• Understanding the “No Rule to Make Target” Error
• Resolving the Error with Output File Declarations
• Practical Examples
• Best Practices for Makefile Targets

.PHONY Targets Explained

The .PHONY target in a makefile serves a crucial purpose in defining commands that should run regardless of whether files with those names exist. According to the official GNU make documentation, “A phony target is one that is not really the name of a file; rather it is just a name for a recipe to be executed when you make an explicit request.”

When you declare .PHONY: foobuild barbuild all clean, you’re telling make that these names represent commands to be executed rather than files to be built. This is particularly useful for maintenance targets like clean, install, test, or all that don’t produce actual output files.

Without the .PHONY declaration, make would check if files named foobuild, barbuild, all, or clean exist in your directory. If they do, make would assume these files are up to date and wouldn’t execute their recipes, which could be problematic for maintenance commands.

The Build Process Without Output Files

When you use .PHONY targets without including actual output file names as prerequisites, the build process becomes problematic because make doesn’t know which files need to be generated. This is where the confusion begins for many makefile users.

The issue arises because make operates on a dependency graph. When you run make foobuild, make looks for:

1. A target named foobuild
2. Prerequisites for that target
3. Recipes to execute

If the foobuild target is declared as .PHONY but doesn’t list actual output files, make will execute the recipe but won’t know what files should be created as a result. This creates uncertainty in the build process.

From a practical standpoint, as explained in the community tutorial, “The .PHONY target overrides this last behaviour and let’s the make build execute no matter of the presence of a file named build. In the general case, assuming that there are no files called build in the project, when not using the .PHONY target, everytime the make build command is invoked it will execute the specified command.”

The problem occurs when the phony target doesn’t explicitly declare its output files, making it difficult for make to track dependencies and determine when the target needs to be rebuilt.

Understanding the “No Rule to Make Target” Error

The “no rule to make target” error is one of the most common makefile troubleshooting issues. This error occurs when make cannot find a rule to build a requested target. When you have .PHONY: foobuild barbuild all clean and try to run one of these commands, make will execute the recipe, but it won’t know what output files should be created.

The fundamental issue is that make uses timestamps to determine if a target needs rebuilding. Without explicit output file declarations, make has no way to track whether the target’s dependencies have changed since the last build.

As noted in the GNU make documentation, “There are two reasons to use a phony target: to avoid a conflict with a file of the same name, and to improve performance.” However, when phony targets don’t properly declare their outputs, they create confusion in the dependency graph.

The error manifests as:

make: *** No rule to make target 'foobuild'. Stop.

This happens because make treats foobuild as a regular file target rather than a command to execute, and since no recipe exists for creating a file named foobuild, it fails.

Resolving the Error with Output File Declarations

When you replace .PHONY: foobuild barbuild all clean with $(SOLIBNAME) $(BINNAME) all clean, you’re fundamentally changing how make interprets your build process. This solution works because you’re explicitly listing the actual output files that make needs to generate.

The key insight is that make needs to know which files are being produced by each target. By declaring $(SOLIBNAME) $(BINNAME) as targets (either explicitly or as prerequisites), you’re telling make:

1. These are the actual output files
2. These files should be created by their respective recipes
3. Make should track these files for dependency management

According to practical makefile examples in community tutorials, “Without it, implicit rules will try to build the executable ‘all’, since the prereqs are ‘.o’ files. .PHONY: all” - this illustrates the importance of properly declaring outputs versus phony targets.

The resolution works because:

1. $(SOLIBNAME) and $(BINNAME) represent actual output files (like libmyapp.so and myapp)
2. make knows these files should be generated by specific recipes
3. When you run make foobuild, make will execute the recipe for $(SOLIBNAME) and track it as the output
4. The all target now makes sense as a collection of outputs rather than a command

This approach creates a clear dependency graph where make understands which files depend on which sources and recipes.

Practical Examples

Let’s examine a concrete example of both problematic and corrected makefile structures:

Problematic makefile (causing “no rule to make target” error):

.PHONY: foobuild barbuild all clean

foobuild:
    $(CXX) -shared -o foobuild $(SRCS)

barbuild:
    $(CXX) -o barbuild $(SRCS)

all: foobuild barbuild

clean:
    rm -f foobuild barbuild

In this case, when you run make foobuild, it will execute the recipe but won’t properly track foobuild as an output file, potentially causing issues with dependency tracking.

Corrected makefile:

SOLIBNAME = libmyapp.so
BINNAME = myapp

$(SOLIBNAME): $(SRCS)
    $(CXX) -shared -o $(SOLIBNAME) $(SRCS)

$(BINNAME): $(SRCS)
    $(CXX) -o $(BINNAME) $(SRCS)

all: $(SOLIBNAME) $(BINNAME)

clean:
    rm -f $(SOLIBNAME) $(BINNAME)

The corrected version explicitly declares the output files, allowing make to:

1. Track dependencies properly
2. Determine when rebuilds are needed
3. Execute the correct recipes for each target

This approach eliminates the “no rule to make target” error and creates a more maintainable build system.

Best Practices for Makefile Targets

Based on the analysis of makefile behavior, here are some best practices for defining targets:

1. Separate phony targets from output files: Use .PHONY exclusively for maintenance targets like clean, install, test, and all. Declare actual output files as separate targets.

2. Use variables for output filenames: As shown in the corrected example, using variables like $(SOLIBNAME) and $(BINNAME) makes your makefile more maintainable.

3. Declare all output files explicitly: Make should always know which files are being produced by each target.

4. Use proper prerequisites: Each target should list its dependencies as prerequisites.

5. Avoid naming conflicts: Don’t name targets the same as existing files, as this can confuse make.

As noted in the GNU make documentation, the primary purposes of phony targets are “to avoid a conflict with a file of the same name, and to improve performance.”

By following these practices, you’ll create makefiles that are both efficient and easy to understand, eliminating the “no rule to make target” error and providing clear dependency tracking.

Sources

• Phony Targets (GNU make)
• The meaning of the ‘.PHONY’ target inside a Makefile
• Makefile Tutorial by Example

Conclusion

Understanding the distinction between .PHONY targets and actual output file declarations is crucial for creating effective makefiles. When you use .PHONY: foobuild barbuild all clean without including actual output files, make treats these as commands to execute rather than files to build, which can lead to the “no rule to make target” error. By replacing this with explicit output file declarations like $(SOLIBNAME) $(BINNAME) all clean, you’re creating a clear dependency graph that make can properly track and execute. The key insight is that make needs to know which files are being produced by each target to effectively manage the build process, resolve dependencies, and determine when rebuilds are necessary.