[LLVMdev] Running an LLVM pass during an android compile

[Joshua Tuttle]

We have developed and tested an optimization pass using LLVM, and have been able to build other software such as gzip while running our pass by passing "clang" and "-Xclang -load -Xclang <path to .so>" as configure options. Now we would like to try and build android while running our pass only on certain files. It seems that android has its own version of LLVM built into it, and we haven't been successful with the aforementioned parameters working in the android makefiles. Does anyone know what is necessary to get the android version of LLVM to run our pass?

Thanks,

Josh

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[Tom Roeder]

In Android.mk, have you tried the following options?

LOCAL_CLANG := true

LOCAL_CFLAGS := <some flags here for clang, e.g., -flto>

LOCAL_LDFLAGS := <some flags for clang at link time, e.g., -flto -Wl,--plugin-opt=-mattr=+aes>

If these don't work, could you be more specific about the errors that you get?

Thanks,

Tom

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[Joshua Tuttle]

Tom,

Thanks for the reply.

I have tried the following options in Android.mk

LOCAL_CLANG := true

LOCAL_CFLAGS := -Xclang -load -Xclang /home/josh/llvm.tan/lib/LLVMHello.so (I'm using this pass just to see if it will run through)

The error I get when tying to compile is as follows:

target thumb C++: keystore <= system/security/keystore/keystore.cpp
target thumb C++: keystore <= system/security/keystore/keyblob_utils.cpp
error: unable to load plugin '/home/josh/llvm.tan/lib/LLVMHello.so': '/home/josh/llvm.tan/lib/LLVMHello.so: undefined symbol: _ZNK4llvm4Pass11getPassNameEv'
make: *** [out/target/product/nitrogen6x/obj/EXECUTABLES/keystore_intermediates/keystore.o] Error 1
make: *** Waiting for unfinished jobs....

error: unable to load plugin '/home/josh/llvm.tan/lib/LLVMHello.so': '/home/josh/llvm.tan/lib/LLVMHello.so: undefined symbol: _ZNK4llvm4Pass11getPassNameEv'
make: *** [out/target/product/nitrogen6x/obj/EXECUTABLES/keystore_intermediates/keyblob_utils.o] Error 1

I'm assuming this error message is related to some kind of linker problem, but I am not sure why, considering this pass does nothing more than print out function names to the terminal. If I run the compile with out the CFLAGS, it works fine.

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From: Tom Roeder <tmro...@google.com>
Sent: Friday, July 18, 2014 5:45 PM
To: Joshua Tuttle
Cc: llv...@cs.uiuc.edu
Subject: Re: [LLVMdev] Running an LLVM pass during an android compile

 

[Tom Roeder]

Yeah, that is likely due to a difference between the version of LLVM you built LLVMHello.so with and the version used in Android.

IIRC, the version used in the toolchain is at prebuilts/clang/linux-x86/host/3.5/bin/clang in the latest version of the Android tree, and it's built from the code in external/clang and external/llvm. The first thing I'd try to do in your case is to build LLVMHello.so from those sources and see if you can get it to run using the toolchain version of clang directly. If you can, then you can port your optimization pass into external/llvm and build it there.