Coding standards

In this project we are trying to adhere to the same coding convention as used in the Linux kernel (see CodingStyle). We achieve this by running checkpatch from Linux kernel. However there are a few exceptions that we had to make since the code also follows GlobalPlatform standards. The exceptions are as follows:

  1. CamelCase for GlobalPlatform types is allowed.

  2. We do not run checkpatch on third party code that we might use in this project, such as LibTomCrypt, MPA, newlib etc. The reason for that and not doing checkpatch fixes for third party code is because we would probably deviate too much from upstream and therefore it would be hard to rebase against those projects later on and we don’t expect that it is easy to convince other software projects to change coding style.

  3. All variables shall be initialized to a well known value in one or another way. The reason for that is that we have had potential security issues in the past that originated from not having variables initialized with a well defined value. We have also investigate various toolchain flags that are supposed to help out finding uninitialized variables. Unfortunately our conclusion is that you cannot trust the compilers here, since there are corner cases where compilers cannot reliably give a warning.

Variables are initialized according to these general guidelines:

  • Scalars (and types like time_t which are standardized as scalars) are initialized with 0, unless another value makes more sense.

  • For optee_client we need maximum portability. So use { 0 } for struct types where the first element is known to be a scalar and memset() otherwise unless there is a good reason not to do so.

  • For the rest of the gits we assume that a recent version of GCC or Clang is used so we initialize structs with { } in order to avoid the more clumsy memset() procedure. Types like pthread_t which can be a scalar or a composite type are initialized with memset() in order to minimize the amount of future headache. Arrays are initialized with { }, too.

Unsigned integer constants are defined using the U(), UL() or ULL() macros, depending on the required width. U() is a good choice for 32-bit values. Any of the minimum width cousins UINT{8,16,32,64}_C() are also accepted for compatibility. This makes the sign and size of the integer well defined instead of depend on how large the value is or which compiler is used. For example:


Running checkpatch

Regarding the checkpatch tool, it is not included directly into this project. Please use from the Linux kernel git in combination with the local checkpatch script. Environment variable CHECKPATCH is expected to provide the path to the Linux checkpatch script path, i.e.:

export CHECKPATCH=/path/to/linux/scripts/
./scripts/ HEAD
./scripts/ --diff github/master HEAD

There are also targets for common use cases in the Makefiles:

export CHECKPATCH=/path/to/linux/scripts/
make checkpatch         #check staging and working area
make checkpatch-staging #check staging area (added, but not committed files)
make checkpatch-working #check working area (modified, but not added files)