In the case of CONFIG_MODVERSIONING, the build step will only
generate preliminary <module>.o objects, and an additional
postprocessing step is necessary to record the versions of the unresolved
symbols and add them into the final <module>.ko
  
The version information for unresolved symbols is again recorded into
a special section, "__versions", which contains an array of symbol
name strings and checksum (struct modversion_info). Size is here not
an issue, since this section will not be stored permanently in kernel
memory.
  
Makefile.modver takes care of the following steps:
o Collect the version information for all exported symbols from vmlinux
  and all modules which export symbols.
o For each module, generate a C file which contains the modversion
  information for all unresolved symbols in that module.
o For each module, compile that C file to an object file
o Finally, link the <module>.ko using the preliminary <module.o> + the
  version information above.
  
The first two steps are currently done by not very efficient scripting,
so there's room for performance improvement using some helper C code.