Makefile 自动依赖不适用于 GNU Make 4.0 或更高版本

Question

我参考this site 创建了以下makefile 来尝试自动生成依赖项。当我使用 GNU Make 3.81（macOS 附带的那个）运行它时，我的 makefile 工作正常。但是，如果我使用较新版本的 GNU Make（4.3，通过 Homebrew 安装）运行它，则每次运行 make 时都会重新创建所有对象和依赖文件，即使源文件没有变化。

CXX          := clang++
CXXFLAGS     := -Wall -Werror -std=c++11
ICUROOT      := ${HOME}/opt/icu4c
XERCESCROOT  := ${HOME}/opt/xercesc
CPPFLAGS     := -I$(ICUROOT)/include -I$(XERCESCROOT)/include
LDFLAGS      := -lxerces-c -licuuc
LDLIBS       := -L$(ICUROOT)/lib -L$(XERCESCROOT)/lib
OBJDIR       := obj
DEPDIR       := $(OBJDIR)/.deps
DEPFLAGS      = -MT $@ -MMD -MP -MF $(DEPDIR)/$*.d

SRCS = $(wildcard *.cpp)


.PHONY: all
all: DOMPrint

COMPILE.cc = $(CXX) $(DEPFLAGS) $(CXXFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c

$(OBJDIR)/%.o: %.cpp
$(OBJDIR)/%.o: %.cpp $(DEPDIR)/%.d | $(DEPDIR)
    $(COMPILE.cc) $(OUTPUT_OPTION) $<

$(DEPDIR): ; @mkdir -p $@

DEPFILES := $(SRCS:%.cpp=$(DEPDIR)/%.d)
$(DEPFILES): ;

DOMPrint: $(addprefix $(OBJDIR)/,DOMPrint.o DOMPrintFilter.o DOMPrintErrorHandler.o DOMTreeErrorReporter.o)
    $(CXX) $(CXXFLAGS) $(LDLIBS) $(LDFLAGS) -o $@ $^


-include $(wildcard $(DEPFILES))

从make --debug(partial)打印的调试信息，显示依赖文件比目标文件新，重建目标文件：

GNU Make 4.3
Built for arm-apple-darwin21.1.0
Copyright (C) 1988-2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Reading makefiles...
Updating makefiles....
Updating goal targets....
 File 'all' does not exist.
     Prerequisite 'obj/.deps/DOMPrintErrorHandler.d' is newer than target 'obj/DOMPrintErrorHandler.o'.
    Must remake target 'obj/DOMPrintErrorHandler.o'.
clang++ -MT obj/DOMPrintErrorHandler.o -MMD -MP -MF obj/.deps/DOMPrintErrorHandler.d -Wall -Werror -std=c++11 -I/Users/chunwaichan/opt/icu4c/include -I/Users/chunwaichan/opt/xercesc/include  -c -o obj/DOMPrintErrorHandler.o DOMPrintErrorHandler.cpp
    Successfully remade target file 'obj/DOMPrintErrorHandler.o'.
...

但是，查看下面（部分）make -p 输出中的最后修改时间，依赖文件并不比目标文件更新，但自动变量 ? 确实表明它更新。

obj/DOMPrintErrorHandler.o: DOMPrintErrorHandler.cpp obj/.deps/DOMPrintErrorHandler.d ...
#  Implicit rule search has been done.
#  Implicit/static pattern stem: 'DOMPrintErrorHandler'
#  Last modified 2022-01-08 10:50:25.517904773
#  File has been updated.
#  Successfully updated.
# automatic
# ? := obj/.deps/DOMPrintErrorHandler.d

obj/.deps/DOMPrintErrorHandler.d:
#  Implicit rule search has not been done.
#  Last modified 2022-01-08 09:45:13.890973263
#  File has been updated.
#  Successfully updated.
#  recipe to execute (from 'Makefile', line 32):

我已经用 GNU Make 3.81 到 4.3 测试了这个 makefile，从 4.0 版开始，这个问题发生了。我想知道较新版本的 GNU Make 中的哪些更改/增强功能导致了此问题，以及如何修复我的 makefile 以使其兼容。

Answer 1

我无法在我的 GNU/Linux 系统上重现您使用标准版 GNU make 看到的行为。这是我使用的完整复制案例：

$ cat main.h
#define RET 0

$ cat main.cpp
#include "main.h"
int main() { return RET; }

$ cat Makefile
CXX          := g++
CXXFLAGS     := -Wall -Werror -std=c++11
CPPFLAGS     := -I.
OBJDIR       := obj
DEPDIR       := $(OBJDIR)/.deps
DEPFLAGS      = -MT $@ -MMD -MP -MF $(DEPDIR)/$*.d

COMPILE.cc = $(CXX) $(DEPFLAGS) $(CXXFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c

SRCS = $(wildcard *.cpp)
OBJS = $(SRCS:%.cpp=$(OBJDIR)/%.o)
DEPS = $(SRCS:%.cpp=$(DEPDIR)/%.d)

all: main

$(OBJDIR)/%.o: %.cpp
$(OBJDIR)/%.o: %.cpp $(DEPDIR)/%.d | $(DEPDIR) ; $(COMPILE.cc) $(OUTPUT_OPTION) $<

$(DEPDIR): ; @mkdir -p $@

$(DEPS): ;

main: $(OBJS) ; $(CXX) $(CXXFLAGS) $(LDLIBS) $(LDFLAGS) -o $@ $^

clean: ; rm -rf obj main

-include $(wildcard $(DEPS))

$ make
g++ -MT obj/main.o -MMD -MP -MF obj/.deps/foo.d -Wall -Werror -std=c++11 -I.  -c -o obj/main.o main.cpp
g++ -Wall -Werror -std=c++11   -o main obj/main.o

$ make
make: Nothing to be done for 'all'.

还有点奇怪：我的make -p 的输出没有显示任何自动变量，如您的示例所示：

obj/main.o: main.cpp obj/.deps/main.d main.cpp main.h | obj/.deps
#  Implicit rule search has been done.
#  Implicit/static pattern stem: 'main'
#  Last modified 2022-01-08 14:18:05.5745307
#  File has been updated.
#  Successfully updated.
#  recipe to execute (from 'Makefile', line 19):
    $(COMPILE.cc) $(OUTPUT_OPTION) $<

也许您使用的 GNU 版本有一些本地更改？

如果你从 https://ftp.gnu.org/gnu/make/ 下载 vanilla GNU make 源代码并编译它是否可以正常工作？