Merging archives / GCC link issue / access bazel-generated path when using cc_library.

[Jiayuan Meng]

I'm trying to merge some .c files with .a archives into a shared library, so that it can be imported from a Swig-generated python module. However, I'm stuck and needs some help..

Here is what I've tried:

----------------------

1. I can create a rule implementation where I define the gcc commandline:

"g++ -shared -o %s -Wl,--whole-archive %s -Wl,--no-whole-archive" % (my_lib.path, archive.path)

When I try to run the plain command manually in the terminal, it works. However, Bazel returns:

g++: fatal error: -fuse-linker-plugin, but liblto_plugin.so not found

But liblto_plugin exists at /usr/lib/gcc/x86_64-linux-gnu/4.8. However, even if I pass the path to the library as below, it still results in the same error. I tried setting LD_LIBRARY_PATH as environment variable, and it didn't work either.

"g++ -shared -o %s -lm -B/usr/bin/ -lstdc++ -Wl,-S -Wl,-L/usr/lib/gcc/x86_64-linux-gnu/4.8 -Wl,--whole-archive %s -Wl,--no-whole-archive" % (my_lib.path, archive.path)

------------------------

2. I can reuse cc_library without manually invoking gcc/g++. However, cc_library doesn't seem to merge the archives, even if I pass the rules producing the archives in "deps". I also tried to manually specify the library to merge using linkopts, as the following shows (libutil.a). However, I have to pass the absolute path to make it work, and the absolute path is bazel generated (e.g. .cache/bazel/adbcd123../...), and I can't access the bazel generated path as I can when defining a rule implementation.

# swig_rules.bzl

def merge_libs(name, hdrs=[], srcs=[], deps=[], copts=[], linkopts=[],                              

              defines=[], data=[], includes=[], input_libs=[]):  

  native.cc_library(                                                                                

      name = name,                                                                                  

      srcs = srcs + input_libs,                                                                     

      deps = deps,                                                                                  

      linkopts = ['-shared', "-Wl,--whole-archive /path/to/libutil.a", "-Wl,--no-whole-archive"],            

      copts = ['-fpic'],                                                                            

      includes = includes,                                                                          

  )

# BUILD

merge_libs(                                                                                         

    name = "merge",                                                                                 

    srcs = ["lab_wrap.cc", "lab.cc"],                                                               

    input_libs = ["libutil.a"],                                                                     

    includes=["python2.7"],                                                                         

    deps = [                                                                                        

        ":util",                                                                                    

    ]                                                                                               

)

Any suggestions would be very helpful!

Thanks,

Jiayuan

[Han-Wen Nienhuys]

cc_library just compiles and puts together the .c files mentioned in its srcs

I guess you want to generate a self-contained .so that can be loaded
as a plugin? In that case, you should create a cc_binary, setting
linkshared = 1.

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--
Han-Wen Nienhuys
Google Munich
han...@google.com

[Jiayuan Meng]

Works like a charm. Thanks, Han-Wen!!