[原创] 在树莓派3上跑ELL的demo报错：ImportError: build/_darknetReference.so: undefined symbol: cblas_sgemm

[root@alarmpi ~]# pacman -Ss blas
extra/blas 3.7.1-1
    Basic Linear Algebra Subprograms
extra/cblas 3.7.1-1
    C interface to BLAS
extra/liblastfm 1.0.9-2
    A Qt4 C++ library for the Last.fm webservices

我试验过，无论是单独安装 blas，还是安装 cblas，或者是两个一起装，最终都不能解决问题。
下面的这段message，就是在我同时安装了 blas 和 cblas 之后，编译_darknetReference.so过程中的 cmake 输出：

[root@alarmpi build]# cmake ..

-- The C compiler identification is GNU 7.1.1

-- The CXX compiler identification is GNU 7.1.1

-- Check for working C compiler: /usr/bin/cc

-- Check for working C compiler: /usr/bin/cc -- works

-- Detecting C compiler ABI info

-- Detecting C compiler ABI info - done

-- Detecting C compile features

-- Detecting C compile features - done

-- Check for working CXX compiler: /usr/bin/c++

-- Check for working CXX compiler: /usr/bin/c++ -- works

-- Detecting CXX compiler ABI info

-- Detecting CXX compiler ABI info - done

-- Detecting CXX compile features

-- Detecting CXX compile features - done

-- Looking for pthread.h

-- Looking for pthread.h - found

-- Looking for pthread_create

-- Looking for pthread_create - not found

-- Looking for pthread_create in pthreads

-- Looking for pthread_create in pthreads - not found

-- Looking for pthread_create in pthread

-- Looking for pthread_create in pthread - found

-- Found Threads: TRUE  

-- Blas libraries: /usr/lib/libblas.so

-- Blas linker flags: 

-- Blas include directories: 

-- Using BLAS include path: /usr/include

-- Using BLAS library: /usr/lib/libblas.so

-- Using BLAS DLLs: 

-- Found PythonInterp: /usr/bin/python3 (found suitable version "3.6.2", minimum required is "3.4") 

-- Found PythonLibs: /usr/lib/libpython3.6m.so (found suitable version "3.6.2", minimum required is "3.4") 

-- Configuring done

-- Generating done

-- Build files have been written to: /root/raspberry-pi/ai/ell-related/compiled_darknetReference_pi3/build

经历了以上失败的过程，我一度很困惑，经过一番探索，最终找到了可行的解决方案：自己编译安装OpenBLAS，并且在编译ELL的Python module的时候对编译过程略作修改，从而让编译脚本找到正确的blas库。
文章来源：https://www.codelast.com/
二话不说我们马上开始干活：

• 下载OpenBLAS源码 & 编译

git clone https://github.com/xianyi/OpenBLAS
cd OpenBLAS
make

最后一段输出信息如下：

......

make[1]: Leaving directory '/root/resource/OpenBLAS/exports'

 

 OpenBLAS build complete. (BLAS CBLAS) 

 

  OS               ... Linux                                                  

  Architecture     ... arm                                                    

  BINARY           ... 32bit                                                  

  C compiler       ... GCC  (command line : gcc)                              

  Library Name     ... libopenblas_armv7p-r0.3.0.dev.a (Multi threaded; Max num-threads is 4)

 

To install the library, you can run "make PREFIX=/path/to/your/installation install".

最后一句提示我们，可以通过 make PREFIX=路径 install 的方式，把编译好的OpenBLAS安装到指定的路径下。

pacman -R blas cblas

[root@alarmpi build]# export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib/openblas/lib