With p4c from today (11/29/2018) flexsai fails to build

[hesingh]

I used the steps to build from https://github.com/opencomputeproject/SAI/tree/master/flexsai/p4/README.md.

The p4c used is from today. I see the following error on invoking 'make -j3' in p4c/build/

/home/hemant/bak/p4c/extensions/sai/json_stage/sai.cpp: In function ‘int main_wrapper(int, char* const*)’:
/home/hemant/bak/p4c/extensions/sai/json_stage/sai.cpp:128:18: error: ‘Py_DecodeLocale’ was not declared in this scope
py_argv[0] = Py_DecodeLocale("P4_compiler.py", NULL);
^~~~~~~~~~~~~~~
/home/hemant/bak/p4c/extensions/sai/json_stage/sai.cpp:128:18: note: suggested alternative: ‘PyEval_GetLocals’
py_argv[0] = Py_DecodeLocale("P4_compiler.py", NULL);
^~~~~~~~~~~~~~~
PyEval_GetLocals
/home/hemant/bak/p4c/extensions/sai/json_stage/sai.cpp:141:35: error: cannot convert ‘wchar_t**’ to ‘char**’ for argument ‘2’ to ‘void PySys_SetArgv(int, char**)’
PySys_SetArgv(py_argc, py_argv);
^
extensions/sai/CMakeFiles/p4c-sai.dir/build.make:62: recipe for target 'extensions/sai/CMakeFiles/p4c-sai.dir/json_stage/sai.cpp.o' failed
make[2]: *** [extensions/sai/CMakeFiles/p4c-sai.dir/json_stage/sai.cpp.o] Error 1
CMakeFiles/Makefile2:734: recipe for target 'extensions/sai/CMakeFiles/p4c-sai.dir/all' failed
make[1]: *** [extensions/sai/CMakeFiles/p4c-sai.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[ 98%] Linking CXX executable gtestp4c
[ 98%] Built target gtestp4c
Makefile:140: recipe for target 'all' failed
make: *** [all] Error 2
hemant@ubuntu:~/bak/p4c/build$

[hesingh]

The problem is that if one has python2.7 and also python 3.6m installed on their build machine, the flexsai cmake loses its brain. I had to force specific python3 path in flexsai/p4/backend/CMakeLists.txt and then compiling and linking passed. I also made one change to sai.cpp to fix compiling. Diffs are included as attached file.

diffs.txt

[hesingh]

It also makes sense to remove all Python code from sai.cpp and just use C/C++ code. p4c code has long back changed to parsing options using p4c/frontend/common/options.cpp. Time permitting, I can make the code change. If anyone has cycles, please make the code change.

[hesingh]

Maybe, more cleanup is needed.
Why does flexsai/p4 need this step before the build?

git checkout 6d265b2d15b927db522c08f36a60fe23784e8357

The commit is related to this PR: p4lang/p4c#1219