[llvm-dev] Android kernel PGO with LLVM

[Yi Ma via llvm-dev]

Hello, 

I'm working on Android kernel profile-guided optimization to figure out 
whether pgo can improve the performance of Android kernel. I have tried 
to added '-fprofile-generate' option to build Android kernel(msm-4.19). 
But error occurs during building: "undefined reference to 
'__llvm_profile_instrument_target'". 
I have tried to add libclang_rt.profile-aarch64-android.a as a library 
when building Android kernel, but the error still shows up. I think the 
kernel may not be able to call libraries outside the kernel source tree, 
so I was porting pgo-related files(compiler-rt/lib/profile/) from 
compiler-rt to Android kernel source tree. 

Do you know why did this error occurs? And am I doing the right thing? 
Is it possible to improve the performance of Android kernel with llvm 
pgo mechanism?

Thanks,
Yi Ma