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gccmakefilebuild-automation
anton_rh
anton_rh

Reputation: 9175

How to generate dependency file for executable (during linking) with gcc

gcc has -M-class options (-MMD, -MF, etc.) that allows to generate dependency file during compiling source file. The dependency file contains Makefile rules describing on which source files and headers the generated object file depends on. The dependency file may be included into Makefile and then make will automatically recompile source file when headers are changed.

I need a similar option but for generating dependency file during linking an executable. The dependency file should contain list of libraries used for linking an executable, so if any of libraries is updated, make will re-execute linking of the executable automatically.

I tried to use the same flags (-MMD, -MF), but they doesn't work for linking. It seems they are only for generating dependency files during compiling.

Is there any other flags or means for generating dependency file for executable?

Upvotes: 2

Views: 9074

Answers (1)

anton_rh
anton_rh

Reputation: 9175

So far I have not found dedicated gcc options for generating dependency file for executable, but found the --trace option (-Wl,--trace when used with gcc). This option generates list of libraries used during linking. Its output has the next format:

gcc -Wl,--trace myprog.c -o myprog -L. -lmylib
-lmylib (./libmylib.a)
-lgcc_s (/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/libgcc_s.so)
...

The list of libraries then may be converted to Makefile rules using sed:

echo "myprog: " > myprog.dep
gcc -Wl,--trace myprog.c -o myprog -L. -lmylib \
    | sed -n 's/.*(\(.*\)).*/\1 \\/p' >> myprog.dep

So myprog.dep will have the following content:

myprog: \
./libmylib.a \
/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.5.2/libgcc_s.so \
...

This dependency file may be included to Makefile and make will relink myprog if any of libraries are updated.

The dependency file doesn't contain list of object files, but the object files are usually known inside Makefile-script without help of compiler:

myprog: $(OBJS)
    gcc -Wl,--trace $^ -o myprog -L. -lmylib | sed -n 's/.*(\(.*\)).*/\1 \\/p' >> myprog.dep

Upvotes: 1

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