Failed to link torch_library using cmake

[vsuryamurthy]

🐛 Bug

When I compile a simple package (a for instance) using cmake, the exported ${TORCH_LIBRARIES}$ is as follows,

torch;torch_library;/usr/lib/libc10.so;/opt/cuda/lib/stubs/libcuda.so;/opt/cuda/lib/libnvrtc.so;/opt/cuda/lib/libnvToolsExt.so;/opt/cuda/lib64/libcudart.so;/usr/lib/libc10_cuda.so

Package a compiles successfully even if the linker fails to link torch_library.

The actual problem arises when I have another package (b), dependent on the already created package a. When I build, it fails with error

CMake Error at /home/vsury/dev/ros/pytorch-example/devel_isolated/a/share/a/cmake/aConfig.cmake:150 (message):
  Project 'b' tried to find library '-Wl,--no-as-needed,$<TARGET_FILE:torch>
  -Wl,--as-needed'.  The library is neither a target nor built/installed
  properly.  Did you compile project 'a'? Did you find_package() it before
  the subdirectory containing its code is included?

The reason has to do with torch_library because there is no library such as libtorch_library.so.

Looking further, it seems like that ${TORCH_LIBRARIES} is linked to ${Caffe2_MAIN_LIBS},

https://github.com/pytorch/pytorch/blob/master/cmake/TorchConfig.cmake.in#L41

and ${Caffe2_MAIN_LIBS} is linked to torch_library,

https://github.com/pytorch/pytorch/blob/master/cmake/Caffe2Config.cmake.in#L121

I do not understand the need for torch_library and removing it from $TORCH_LIBRARIES$ fixes the entire problem.

To Reproduce

Steps to reproduce the behavior:

1. Create a package a with any script with torch functionalities (basically CMakeLists should contain find_package(Torch REQUIRED) and build target with torch libraries.
2. Create another package b and make it depend on a.
3. Compile package b to get the error.

Expected behavior

Successful build

Environment

Please copy and paste the output from our

• PyTorch Version (e.g., 1.0): 1.5.0
• OS (e.g., Linux): Archlinux
• How you installed PyTorch (conda, pip, source): pacman -S
• Build command you used (if compiling from source): cmake and make
• Python version:
• CUDA/cuDNN version:
• GPU models and configuration:
• Any other relevant information:

Additional context

cc @malfet @yf225 @glaringlee

[glaringlee]

@vsuryamurthy
Can you take a look at our installing instruction here?
https://pytorch.org/cppdocs/installing.html
There is a section which has the guide on what need to be added into CMakeLists and how to compile, and let me know if this works for you. thx

[vsuryamurthy]

@glaringlee Following the link, I get

torch;torch_library;/home/vsury/pytorch/libtorch/lib/libc10.so

when I print ${TORCH_LIBRARIES}.

I have the same problem of failing to link torch_library as there is no libtorch_library.so in libtorch/lib.

Can you please tell me what is the role of ${Caffe2_MAIN_LIBS} in
https://github.com/pytorch/pytorch/blob/master/cmake/TorchConfig.cmake.in#L41

[glaringlee]

@malfet Can you pls advise on this? Thanks.

[malfet]

@vsuryamurthy torch_library is interface defined in Caffe2Targets.cmake
But it looks like there are no reason why TORCH_LIBRARIES need to depend on Caffe2_MAIN_LIBS.
Let me figure out the best way to patch it.

[vsuryamurthy]

@malfet Precisely my point.

I have fixed it by removing ${Caffe2_MAIN_LIBS} from the line https://github.com/pytorch/pytorch/blob/master/cmake/TorchConfig.cmake.in#L41. This works for me but I am not sure if this is the way to go about it.

[vsuryamurthy]

@malfet any update?