Consider the following Makefile:
MAKEFLAGS += --warn-undefined-variables
define foobar
echo "$(1)"
endef
.PHONY: all
all:
$(foobar)
Is there a way to have macros with default parameters without producing undefined variable warnings?
I mean: sometimes I call "foobar" with a parameter, but sometimes not. In the latter case I'd like to have a default value for $(1).
You can't set a default value in the macro but you can easily add one when the parameter is expanded:
1:=
define foobar
echo "$(if $1,$1,default)"
endef
all:
$(foobar)
$(call foobar,biz)
$ make
echo "default"
default
echo "biz"
biz
It's a bit annoying if you use the parameter lots of times because you have to use the if for each use.
The GNU make syntax is very limited; it's not a full blown programming language, so many things are missing, like default parameters in make macros.
But the shell is a programming language! Why not implement your requirements in the commands of a target? It may be possible to use something like this:
all:
if test "$(SOMECONDITION)"; then \
do_one_thing; \
else \
do_something_else; \
fi
There is a decent solution for GNU make. Not sure how portable it is.
Use a global variable that embodies the rather messy logic, using a naming convention to avoid conflicts:
# foo.mk
MAKEFLAGS += --warn-undefined-variables
foobar_p1_default = default parameter
foobar_p1 = $(if $(filter undefined,$(origin 1)),$(foobar_p1_default),$1)
define foobar
#echo $#: "$(foobar_p1)"
endef
.PHONY: all defaulted global local
all : defaulted global local
defaulted:
$(foobar)
variable = global value
global local:
$(call foobar,parameter was $(variable))
local: variable = target specific value
The results:
$ make -f foo.mk
defaulted: default parameter
global: parameter was global value
local: parameter was target specific value
Related
In GNU Make you can export a variable for a target:
foo: export X=42
foo:
echo $$X
# Call several more commands that use $X.
Is there a way to do this in portable POSIX Make? So far, I've found two ways. The first is to basically merge all commands into one:
foo:
export X=42; \
echo $$X; \
# Call several more commands that use $X.
This is bad because now everything is bundled together. The second is to call $(MAKE):
foo:
$(MAKE) foo_ X=42
foo_:
echo $$X
# Call several more commands that use $X.
But this has an extra call to make again. Is there a better way?
The simplest solution is probably to set the variable on the command line by invoking make with:
make X=42
This way:
The make X variable is defined and set to 42, even if it is set to another value in the Makefile.
The shell environment variable X is defined and set to 42 for all recipes.
If you cannot use this (for instance because it is make that computes the value) the recursive make solution is probably the best option:
ifeq ($(X),)
X := <some-make-magic>
all:
$(MAKE) X=$(X) all
else
all:
<recipe-that-uses-X-environment-variable>
endif
Note: This question was originally posted as a rant by a now-deleted user, but there was a valid question behind the rant; this is my attempt to provide an answer.
Given the Makefile:
ifeq "$(MAKELEVEL)" "0"
# Override the command-line specification of "foo".
override foo=replaced
export foo
all::
#echo outer: foo is "$(foo)"
#$(MAKE)
else
# Variable 'foo' was "exported" from the top-level Makefile.
all::
#echo inner: foo is "$(foo)"
endif
The expectation is that export foo will cause make to export the value defined in the override declaration. But it doesn't:
$ make -s foo=original
outer: foo is replaced
inner: foo is original
The expectation is probably reasonable, but it turns out that this is not the way Gnu make works. It could well be that the make documentation could be improved to clarify the process, but the hints all seem to be there.
How variables get their values
A variable can be set by the programmer in three ways:
On the command line with a var=value command-line argument
Explicitly in the make file
From the environment
The above list is the normal priority order; the first definition found in the list "wins". However, you can use the override directive to swap the priorities of the first two methods. (You can also use the -e flag to make to swap the priorities of the last two methods. The -e flag is required by Posix, but its use is discouraged and it does not interact will with override.)
How variables are passed to sub-makes
make is very similar to a shell in that the environment is used to pass variable values. If a variable is marked as exported, then its value is placed into the environment for any processes initiated by make, including sub-makes. As with the shell, a variable is marked as exported if its definition came from the environment or if it is explicitly marked as exported with the export directive. Variables are also exported if they were set on the command line.
However, there is another mechanism by which variables on the command-line are passed to subprocesses: the MAKEFLAGS exported variable.. MAKEFLAGS contains (most) command-line options as well as all of the command-line variable overrides. If make finds MAKEFLAGS in the environment, it merges the settings in that variable with the ones actually specified on its command line. That means that command-line variable settings in a make will also take priority in a sub-make.
Since command-line variable settings are passed through the MAKEFLAGS variable, they are not subject to any changes in the makefile. A makefile can unexport or override a variable set on the command-line, but that will only affect the value (or presence) of the variable in the environment; it does not remove or change the value from MAKEFLAGS.
Resolution
So if the intent is to override (or modify) a command-line variable both in the make itself and in the environment of sub-makes, it is necessary to use both an override and an explicit modification of MAKEFLAGS. (As explained in the make manual, MAKEFLAGS is actually recursively composed using the MAKEOVERRIDES variable, so we actually modify that variable.)
ifeq "$(MAKELEVEL)" "0"
# Override the command-line specification of "foo".
override foo=replaced
MAKEOVERRIDES += foo=replaced
all::
#echo outer: foo is "$(foo)"
#$(MAKE) -s
else
# Variable 'foo' was "exported" from the top-level Makefile.
all::
#echo inner: foo is "$(foo)"
endif
And now we get the expected result:
$ make -s foo=original
outer: foo is replaced
inner: foo is replaced
Real-life application: dealing with whitespace
The primary intention of overrides is to allow the makefile to append words to a variable possibly provided on the command line. The example provided in the gnu make manual is insisting that CFLAGS always includes the -g flag, even if it were specified on the make command line:
override CFLAGS += -g
Passing the append through to a sub-make needs a little caution; in particular, the obvious:
MAKEOVERRIDES += CFLAGS=$(CFLAGS) # Don't do this
won't work because the whitespace inside the CFLAGS variable will not be escaped when it is added to MAKEFLAGS; the result will be that MAKEFLAGS will look something like this:
-- CFLAGS=-O3 CFLAGS=-O3 -g
instead of the desired
-- CFLAGS=-O3 CFLAGS=-O3\ -g
If the value assigned to CFLAGS on the command line included whitespace, the whitespace is escaped in MAKEFLAGS. The particular escaping mechanism used is not documented, and Posix only requires that there be some mechanism; apparently, Gnu make uses backslash. It would be possible to manually backslash escape the whitespace, resulting in something like this:
# Don't do this either
MAKEOVERRIDES += CFLAGS=$(subst $(space),\ ,$(CFLAGS))
(The definition and use of space is based on an example in the gnu make manual.)
But it is actually easier to just use an append assignment in MAKEOVERRIDES, which is undocumented but appears to work. It works on the command line, too.
override CFLAGS+=-g
MAKEOVERRIDES += CFLAGS+=-g
Important Note as of make v4.1: A bit of testing revealed that the above stanza will only work if CFLAGS (or some other variable) is actually set on the command-line. I reported this bug as Savannah issue 46013, with a very simple fix in the bug report. In the meantime, if you really want to do this, use the following workaround:
override CFLAGS+=-g
MAKEOVERRIDES += CFLAGS+=-g
# This line is necessary in case there were no command-line overrides.
# In effect, it produces a command-line override, although that value
# will not be passed on to sub-makes.
MAKEFLAGS += dummy=dummy
Update May 19, 2019: Today I was informed that a fix for the bug referenced above has been committed, so it should be fixed in the next gmake release.
First of all, I want to point out that your suggestion to add to MAKEOVERRIDES, is dangerous!
And SHOULD NEVER BE DONE!!
You simply turn a recursive variable into a simple one, you will always get false results, if recursive expansion is done.
I can not believe that you got up-voted for this clearly wrong "suggestion".
And note this:
You can not even fix it with a quoted assignment, like MAKEOVERRIDES += foo=$$(bar)!!!
But, let me return to the main point of your post.
And, with which, I couldn't disagree more.
One simple example would be, if you run the very same makefile, that you have:
This one is copied verbatim, from your post:
ifeq "$(MAKELEVEL)" "0"
# Override the command-line specification of "foo".
override foo=replaced
export foo
all::
#echo outer: foo is "$(foo)"
#$(MAKE) -s
else
# Variable 'foo' was "exported" from the top-level Makefile.
all::
#echo inner: foo is "$(foo)"
endif
And running in any modern version, 4.0 and up:
# Sub-make does NOT get the value from the root-Make's command-line.
# Instead, it "inherits" the value from the root-Make's definition in the Makefile.
$ make -s foo=original -e
outer: foo is replaced
inner: foo is replaced
Now, given your assertion above:
However, there is another mechanism by which variables on the command-line are passed to subprocesses: the [MAKEFLAGS exported variable.][3]. MAKEFLAGS contains (most) command-line options as well as all of the command-line variable overrides. If make finds MAKEFLAGS in the environment, it merges the settings in that variable with the ones actually specified on its command line. That means that command-line variable settings in a make will also take priority in a sub-make.
Since command-line variable settings are passed through the MAKEFLAGS variable, they are not subject to any changes in the makefile. A makefile can unexport or override a variable set on the command-line, but that will only affect the value (or presence) of the variable in the environment; it does not remove or change the value from MAKEFLAGS.
You should get:
outer: foo is replaced
inner: foo is original
In other words, we should get for the sub-make, the value defined on the command-line (original)!
Because, you said yourself:
A makefile can't unexport or override a variable set on the command-line.
So, here, when we empower the environment over the makefile, which means that the makefile has less "power" in the total scheme of things. Right?
Sure, for such a case, you assertion will hold even stronger.
I'm trying to debug makefiles for a large project and I'm struggling define TEMPLATE/endef and foreach/eval/call constructs. In particular I think I'm having a hard time figuring out which variables I need to reference with $ and which I need to reference with $$.
I think would be easier for me to debug if I could see the actual results of the the eval/call expansion, before variable expansion.
For instance if we use the example in the eval documentation for gnu-make, we have the following makefile-fragment:
PROGRAMS = server client
server_OBJS = server.o server_priv.o server_access.o
server_LIBS = priv protocol
client_OBJS = client.o client_api.o client_mem.o
client_LIBS = protocol
...
define PROGRAM_template =
$(1): $$($(1)_OBJS) $$($(1)_LIBS:%=-l%)
ALL_OBJS += $$($(1)_OBJS)
endef
$(foreach prog,$(PROGRAMS),$(eval $(call PROGRAM_template,$(prog))))
I think this foreach should effectively expand to the following, before variable expansion:
server: $(server_OBJS) $(server_LIBS:%=-l%)
ALL_OBJS += $(server_OBJS)
client: $(client_OBJS) $(client_LIBS:%=-l%)
ALL_OBJS += $(client_OBJS)
I figured out the above expansion by hand (corrections welcome), but I'm looking for a general method to display this expansion for more complex examples. Does such a method exist?
I have looked into make -d and make -pn options, and as far as I can tell, I don't think either of these will provide this particular output.
I'm using make-3.81.
Replace all your $(eval ...) calls with $(info ...). Actually if you're stuck with 3.81 you may have to use $(warning ...) and ignore the extra output, because I think $(info ...) might not have existed until version 3.82.
Anyway, writing:
$(foreach prog,$(PROGRAMS),$(info $(call PROGRAM_template,$(prog))))
(or warning) you'll see what make is parsing.
I've written a macro to help with seeing the results of $(eval ...):
# This version prints out rules for debugging
#c = $(eval $(call $(strip $1),$(strip $2),$(strip $3),$(strip $4),$(strip $5),$(strip $6),$(strip $7),$(strip $8),$(strip $9))) $(info $(call $(strip $1),$(strip $2),$(strip $3),$(strip $4),$(strip $5),$(strip $6),$(strip $7),$(strip $8),$(strip $9)))
# This version is the production version
c = $(eval $(call $(strip $1),$(strip $2),$(strip $3),$(strip $4),$(strip $5),$(strip $6),$(strip $7),$(strip $8),$(strip $9)))
Use it like this:
$(call c,function,arg1,arg2,...)
To see what is being generated by eval, simply use the debugging version. I needed this instead of simply replacing $(eval ...) by $(info ...) because functionality later in the makefile depended on the results of the $(eval ...)
Alright I am stuck on this and I have no idea what I am doing wrong. Everything was going great working on a more complicated makefile but then all of a sudden I got the "Missing separator" error. I was able to isolate it down to a very simple scenario:
test.mk
define push_dir
$(info ${1})
endef
define pop_dir
$(info ${1})
endef
define include_submake
$(call push_dir,${1})
$(call pop_dir,${1})
endef
Simple
include test.mk
INITIAL_SUBMAKE:= includeme.mk
$(call include_submake,${INITIAL_SUBMAKE})
process:
#echo Processed...
And the output:
C:\project>make -f Simple process
includeme.mk
includeme.mk
Simple:4: *** missing separator. Stop.
includeme.mk does not actually exist. I have no idea what is going wrong here I have tried a multitude of things. If I surround the call to include_submake in info like so:
$(info $(call include_submake,${INITIAL_SUBMAKE}))
The missing separator error goes away. Also If in the include_submake define I only call one of the functions it works fine. Additionally if I directly call the functions instead of calling them include_submake it works as well:
include test.mk
INITIAL_SUBMAKE:= includeme.mk
$(call push_dir,${INITIAL_SUBMAKE})
$(call pop_dir,${INITIAL_SUBMAKE})
process:
#echo Processed...
C:\project>make -f Simple process
includeme.mk
includeme.mk
Processed...
I feel like I'm overlooking something fundamental here. Thanks for your help.
The missing separator error happens because of a non-empty return value of include_submake, which is a single line feed character in your case. Make only permits whitespace characters (that is, a space or tab) to occur in an expression which is not assumed to be a part of some rule or another directive.
Rewrite your functions using plain-old Make variable assignment and the error should go away:
push_dir = \
$(info $1)
pop_dir = \
$(info $1)
include_submake = \
$(call push_dir,$1) \
$(call pop_dir,$1)
UPD.: define vs plain old variable assignment
Answering to a question from the first comment. Personally I would prefer using define directive in several cases.
Using with eval function
As the GNU Make manual suggests, define directive is very useful in conjunction with the eval function. Example from the manual (emphasis is mine):
PROGRAMS = server client
server_OBJS = server.o server_priv.o server_access.o
server_LIBS = priv protocol
client_OBJS = client.o client_api.o client_mem.o
client_LIBS = protocol
# Everything after this is generic
.PHONY: all
all: $(PROGRAMS)
define PROGRAM_template
$(1): $$($(1)_OBJS) $$($(1)_LIBS:%=-l%)
ALL_OBJS += $$($(1)_OBJS)
endef
$(foreach prog,$(PROGRAMS),$(eval $(call PROGRAM_template,$(prog))))
$(PROGRAMS):
$(LINK.o) $^ $(LDLIBS) -o $#
clean:
rm -f $(ALL_OBJS) $(PROGRAMS)
Generator templates
Verbatim variables fit perfectly for cases when you want to generate a file from GNU Make. For example, consider generating a header file based on some information from Makefile.
# Args:
# 1. Header identifier.
define header_template
/* This file is generated by GNU Make $(MAKE_VERSION). */
#ifndef $(inclusion_guard)
#define $(inclusion_guard)
$(foreach inc,$($1.includes),
#include <$(inc).h>)
/* Something else... */
#endif /* $(inclusion_guard) */
endef
# 1. Unique header identifier.
inclusion_guard = \
__GEN_$1_H
# Shell escape.
sh_quote = \
'$(subst ','"'"',$1)'
foo.includes := bar baz
HEADERS := foo.h
$(HEADERS) : %.h :
#printf "%s" $(call sh_quote,$(call header_template,$(*F)))> $#
Extended Make syntax
In our project we use our own build system called Mybuild, and it is implemented entirely on top of GNU Make. As one of low-level hacks that we used to improve the poor syntax of the builtin language of Make, we have developed a special script which allows one to use extended syntax for function definitions. The script itself is written in Make too, so it is a sort of meta-programming in Make.
In particular, one can use such features as:
Defining multiline functions without the need to use backslash
Using comments inside functions (in plain-old Make comments can only occur outside variable assignment directives)
Defining custom macros like $(assert ...) or $(lambda ...)
Inlining simple functions like $(eq s1,s2) (string equality check)
This is an example of how a function can be written using the extended syntax. Note that it becomes a valid Make function and can be called as usual after a call to $(def_all).
# Reverses the specified list.
# 1. The list
# Return:
# The list with its elements in reverse order.
define reverse
# Start from the empty list.
$(fold ,$1,
# Prepend each new element ($2) to
# the result of previous computations.
$(lambda $2 $1))
endef
$(def_all)
Using these new features we were able to implement some really cool things (well, at least for Make :-) ) including:
Object-Oriented layer with dynamic object allocation, class inheritance, method invocations and so on
LALR parser runtime engine for parsers generated by GOLD Parser Builder
Modelling library with runtime support for models generated with EMF
Feel free to use any part of the code in your own projects!
I ran into the same problem. I inserted 'tab', deleted 'tab', reinserted to be sure. Same error message.
But, I did all of this inside of XCodem which to my surprise inserted white spaces, not '\t'. Once I used different editor these 'phantom' errors went away.
HTH...
Can I pass variables to a GNU Makefile as command line arguments? In other words, I want to pass some arguments which will eventually become variables in the Makefile.
You have several options to set up variables from outside your makefile:
From environment - each environment variable is transformed into a makefile variable with the same name and value.
You may also want to set -e option (aka --environments-override) on, and your environment variables will override assignments made into makefile (unless these assignments themselves use the override directive . However, it's not recommended, and it's much better and flexible to use ?= assignment (the conditional variable assignment operator, it only has an effect if the variable is not yet defined):
FOO?=default_value_if_not_set_in_environment
Note that certain variables are not inherited from environment:
MAKE is gotten from name of the script
SHELL is either set within a makefile, or defaults to /bin/sh (rationale: commands are specified within the makefile, and they're shell-specific).
From command line - make can take variable assignments as part of his command line, mingled with targets:
make target FOO=bar
But then all assignments to FOO variable within the makefile will be ignored unless you use the override directive in assignment. (The effect is the same as with -e option for environment variables).
Exporting from the parent Make - if you call Make from a Makefile, you usually shouldn't explicitly write variable assignments like this:
# Don't do this!
target:
$(MAKE) -C target CC=$(CC) CFLAGS=$(CFLAGS)
Instead, better solution might be to export these variables. Exporting a variable makes it into the environment of every shell invocation, and Make calls from these commands pick these environment variable as specified above.
# Do like this
CFLAGS=-g
export CFLAGS
target:
$(MAKE) -C target
You can also export all variables by using export without arguments.
The simplest way is:
make foo=bar target
Then in your makefile you can refer to $(foo). Note that this won't propagate to sub-makes automatically.
If you are using sub-makes, see this article: Communicating Variables to a Sub-make
Say you have a makefile like this:
action:
echo argument is $(argument)
You would then call it make action argument=something
From the manual:
Variables in make can come from the environment in which make is run. Every environment variable that make sees when it starts up is transformed into a make variable with the same name and value. However, an explicit assignment in the makefile, or with a command argument, overrides the environment.
So you can do (from bash):
FOOBAR=1 make
resulting in a variable FOOBAR in your Makefile.
It seems command args overwrite environment variable.
Makefile:
send:
echo $(MESSAGE1) $(MESSAGE2)
Example run:
$ MESSAGE1=YES MESSAGE2=NG make send MESSAGE2=OK
echo YES OK
YES OK
There's another option not cited here which is included in the GNU Make book by Stallman and McGrath (see http://www.chemie.fu-berlin.de/chemnet/use/info/make/make_7.html). It provides the example:
archive.a: ...
ifneq (,$(findstring t,$(MAKEFLAGS)))
+touch archive.a
+ranlib -t archive.a
else
ranlib archive.a
endif
It involves verifying if a given parameter appears in MAKEFLAGS. For example .. suppose that you're studying about threads in c++11 and you've divided your study across multiple files (class01, ... , classNM) and you want to: compile then all and run individually or compile one at a time and run it if a flag is specified (-r, for instance). So, you could come up with the following Makefile:
CXX=clang++-3.5
CXXFLAGS = -Wall -Werror -std=c++11
LDLIBS = -lpthread
SOURCES = class01 class02 class03
%: %.cxx
$(CXX) $(CXXFLAGS) -o $#.out $^ $(LDLIBS)
ifneq (,$(findstring r, $(MAKEFLAGS)))
./$#.out
endif
all: $(SOURCES)
.PHONY: clean
clean:
find . -name "*.out" -delete
Having that, you'd:
build and run a file w/ make -r class02;
build all w/ make or make all;
build and run all w/ make -r (suppose that all of them contain some certain kind of assert stuff and you just want to test them all)
If you make a file called Makefile and add a variable like this $(unittest)
then you will be able to use this variable inside the Makefile even with wildcards
example :
make unittest=*
I use BOOST_TEST and by giving a wildcard to parameter --run_test=$(unittest)
then I will be able to use regular expression to filter out the test I want my Makefile
to run
export ROOT_DIR=<path/value>
Then use the variable, $(ROOT_DIR) in the Makefile.