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procenv drivers

1   Overview

procenv now supports platform drivers. These are simply translation units that are compiled only for a particular platform. They were introduced to combat the "#ifdef hell" of previous releases.

2   Build Stategy


Used to identify the platform the build is run on, exporting "PROCENV_PLATFORM_<name>" and $procenv_platform" to "src/".

2.2   src/

  • Defines "PROCENV_PLATFORM_<name>" as a symbol to the compiler.
  • Adds platform driver (platform-specific) source files to the list of files to be built.

To simplify the include policy, all platform-specific headers are added to the appropriate section in platform-headers.h.

Additionally, one other object get built on all platforms:

  • platform-generic

    Provides generic Unix/Linux implementations of particular methods.

Drivers are free to reference the functions from this translation unit. See below for details.

The build uses some magic options so that although all possible implementations get built, only those symbols actually referenced become part of the final binary (meaning you don't end up with lots of generic functions linked into your binary if your driver doesn't use them :-)

3   Implementing a new driver

    • Update the $target_to_consider case logic for your platform.
  • Create src/platform/${platform}/platform.c with an implementation of the global "struct procenv_ops platform_ops".

    For each struct procenv_ops function pointer,

    • If it doesn't make sense to define a particular function for the platform, simply omit specifying a function pointer.

      (Note that you could set the function pointer to NULL, but that isn't necessary given that the platform_ops symbol is global, and thus effectively all pointers not specified are already implicitly set to NULL).

    • If one of the generic implementations is suitable, set the function pointer to the corresponding *_generic() function in platform-generic.c.

    • If neither of the above options is suitable, define a static implementation in your platform.c (with the function name *_<platform>) file and set the corresponding function pointer to that function.

  • Create src/platform/${platform}/platform-${platform}.h.