auto dependencies not working with eclipse CDT C++ project

Question

It seems the generated auto dependency rules in Eclipse CDT 8.1.0 are incorrect. To illustrate the problem I made an empty Executable project and added two files.

test.cpp:

    #include "SomeOtherHeader.h"
    int main(void){return 0;}

and SomeOtherHeader.h (which is empty)

Compiling this project causes Eclipse to generate the "Debug" folder in the project directory with the subdir.mk makefile include.

Contents of Debug/subdir.mk:

################################################################################
# Automatically-generated file. Do not edit!
################################################################################

# Add inputs and outputs from these tool invocations to the build variables 
CPP_SRCS += \
../test.cpp 

OBJS += \
./test.o 

CPP_DEPS += \
./test.d 


# Each subdirectory must supply rules for building sources it contributes
%.o: ../%.cpp
    @echo 'Building file: $<'
    @echo 'Invoking: GCC C++ Compiler'
    g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"$(@:%.o=%.d)" -MT"$(@:%.o=%.d)" -o "$@" "$<"
    @echo 'Finished building: $<'
    @echo ' '

Its the -MT"$(@:%.o=%.d)" line that concerns me because the MT option creates a nonsensical dependency in the file Debug/test.d

test.d: ../test.cpp ../SomeOtherHeader.h

../SomeOtherHeader.h:

Changing -MT"$(@:%.o=%.d)" to -MT"$@" in Debug/subdir.mk yields a more reasonable Debug/test.d:

test.o: ../test.cpp ../SomeOtherHeader.h

../SomeOtherHeader.h:

It looks like the "-MT" string is hard coded in the managedbuilder.core java code:

$ unzip -p /usr/lib64/eclipse/dropins/cdt/eclipse/plugins/org.eclipse.cdt.managedbuilder.core_8.1.0.201206111645.jar | strings | grep '\-MT'
-MT"
-MT"$(@:%.o=%.d)"
-MT"
-MT"$@"
-MT"$(@:%.d=%.o)"

It looks like the winning option -MT"$@" is in there, but how do I instruct the managedbuilder to use it? Does -MT"$(@:%.o=%.d)" serve any practical purpose?

Its my first time posting on this site so be easy on me :)

Answer 1

Add -MT"$@" to compiler flags in Project Properties->C/C++ Buid->Settings->GCC Compiler->Miscellaneous->Other flags. Eclipse will simply add this flag to compilation line inside makefile. Output inside test.d file should be something like:

test.o test.d: ../test.cpp ../SomeOtherHeader.h

../SomeOtherHeader.h: