http://stackoverflow.com/questions/12372500/how-to-run-custom-rule-in-android-mk-before-compilation

How to run custom rule in Android.mk before compilation?

In Android NDK, I build JNI files generated automatically by SWIG. callmanager_wrap.cpp is part of a shared library:

LOCAL_SRC_FILES += callmanager_wrap.cpp
include $(BUILD_SHARED_LIBRARY)

But I would like to append/edit callmanager_wrap.cpp before compiling. To be more explicit:

cat jnistuff.txt >> callmanager_wrap.cpp

Content I need to add is known in advance but callmanager_wrap.cpp is not. It is generated by SWIG. Ultimately, my custom rule will have to run following command to generate callmanager_wrap.cpp:

swig -c++ -java -package com.package.my -o callmanager_wrap.cpp callmanager.i

According to this post, it is not possible to add custom rules to Android.mk. But in Android sources, I believe there are some Android.mk handling steps after BUILT or INSTALLED. I tried the following:

MY_JNI_WRAP=callmanager_wrap.cpp

include $(CLEAR_VARS)

LOCAL_SRC_FILES += callmanager_wrap.cpp

LOCAL_INTERMEDIATE_TARGETS += myjni
myjni:
    echo "in myjni target"
    swig -c++ -java -package com.package.my -o $(MY_JNI_WRAP) callmanager.i
    cat jnistuff.txt >> $(MY_JNI_WRAP)

include $(BUILD_SHARED_LIBRARY)

But myjni target is never called.

What is LOCAL_INTERMEDIATE_TARGETS used for?
Can I possibly achieve what I want to do here without writing an external script or makefile?

edited Sep 11 '12 at 15:12

asked Sep 11 '12 at 14:51

m-ric

2,20432139

can you clarify this sentence "I would like to append callmanager_wrap.cpp before compiling"? I can help you if you clear that up a bit. – Infinity Sep 11 '12 at 14:54

Do you really need to run swig on every single build? – Seva Alekseyev Sep 11 '12 at 19:37

On one hand, it is cleaner and prevent from versioning generated files. On the other hand, not versioning these files can break the build if developer does not make clean after a git rebase. But that's a developer's problem. Isn't it possible to custom android makefiles to that extent? I won't hide that I am considering writing a top-script to do just that but I remain curious about this android limitation. – m-ric Sep 11 '12 at 20:40

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2 Answers

active oldest votes

up vote 8 down vote accepted

I would suggest the following:

include $(CLEAR_VARS)

LOCAL_SRC_FILES += callmanager_wrap.cpp
MY_JNI_WRAP := $(LOCAL_PATH)/callmanager_wrap.cpp

$(MY_JNI_WRAP):
    echo "in myjni target"
    swig -c++ -java -package com.package.my -o $(MY_JNI_WRAP) callmanager.i
    cat jnistuff.txt >> $(MY_JNI_WRAP)
.PHONY: $(MY_JNI_WRAP)

include $(BUILD_SHARED_LIBRARY)

That's it.

I probably owe you some explanations. So here we go:

$(LOCAL_SRC_FILES) is a list of file names relative to $(LOCAL_PATH), so to address a file from outside the standard NDK actions, you need the full path for your file, which is $(LOCAL_PATH)/callmanager_wrap.cpp.
We specify the file as .PHONY to guarantee that the custom action is executed every time you run ndk-build. But if you know which are actual dependencies of callmanager_wrap.cpp, you can specify them instead, like

$(MY_JNI_WRAP): callmanager.i jnistuff.txt $(LOCAL_PATH)/../src/com/package/my/Something.java

In this case, you will not need the .PHONY line.
If you want your source directory to remain clean, you can declare the wrapper file as .INTERMEDIATE like this:

.INTERMEDIATE: $(MY_JNI_WRAP)

Now make will delete the wrapper file after build, if it did not exist before the build.

answered Sep 12 '12 at 7:28

Alex Cohn

25.5k43493

I've tried your proposal with something like:

MY_JNI_WRAP:=bus/callmanager_wrap.cpp LOCAL_SRC_FILES += $(MY_JNI_WRAP) $(MY_JNI_WRAP): echo "in myjni target" touch mememe .PHONY: $(MY_JNI_WRAP)

But after I ran rm -rf obj/local/ libs/armeabi && ndk-build -j5, find -name mememe never returns something. Are you sure .PHONY is recognized by ndk-build? – m-ric Sep 12 '12 at 14:52

In my example above, the phony target was not the same string as what I added to LOCAL_SRC_FILES. The trick is that LOCAL_SRC_FILES is relative tothe Android.mk but the make itself and its targets are relative to the current dir. tl;nr use $(LOCAL_PATH)/$(MY_JNI_WRAP) everywhere except the LOCAL_SRC_FILES line. – Alex Cohn Sep 12 '12 at 17:28

Wow, you made my day Alex! Thanks heaps – m-ric Sep 12 '12 at 18:15

Using all: $(MY_JNI_WRAP) instead of .PHONY: $(MY_JNI_WRAP) worked for me. – Juozas Kontvainis Jul 26 '13 at 13:24

@juozas-kontvainis: you mean, .PHONEY didn't work? – Alex Cohn Jul 26 '13 at 18:48

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up vote 0 down vote

I have done it this way: let's say I need to create .s file from .ll file

# custom build
source_ll_files := $(wildcard *.ll)
%.s:
    llc -o $@ $(patsubst %.s,%.ll,$@)

LOCAL_SRC_FILES += $(patsubst %.ll,%.s,$(source_ll_files))
# end