Keep in mind that fallthrough is an official attribute in C23. Not a reserved word but in attribute context it is claimed by the standard. #defining fallthrough to something not compatible with attribute context is bad.

From: Jens Wiklander jens.wiklander@linaro.org Date: Thursday, 3 April 2025 at 10:26 To: Jacob Kroon Jacob.Kroon@axis.com Cc: op-tee@lists.trustedfirmware.org op-tee@lists.trustedfirmware.org Subject: Re: Conflict with "fallthrough" define Hi,

On Wed, Apr 2, 2025 at 8:21 PM Jacob Kroon Jacob.Kroon@axis.com wrote:

Hi,

We are using OP-TEE together with a library that provides its own "fallthrough" define, similar to what OP-TEE does in lib/libutils/ext/include/compiler.h:

#define fallthrough __attribute__((__fallthrough__))

However, this other library checks for fallthrough attribute support by first doing:

#if __has_cpp_attribute(fallthrough) ... #endif

which fails to compile due to the OP-TEE define.

Would OP-TEE accept a patch to rename the "fallthrough" define to something like "optee_fallthrough", "FALLTHROUGH", <other suggestion> ?

No, the name should stay "fallthrough". We may accept an extra check to see how and if it should be defined, but the result should be a usable "fallthrough" macro after <compiler.h> has been included.

Or should we upstream a patch to the library to do:

#if __has_cpp_attribute(__fallthrough__) ... #endif

It seems like at least some change will be needed in that library.

Cheers, Jens

(which is what OP-TEE currently does)

Regards Jacob