1 /* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */ 2 #ifndef PLDM_COMPILER_H 3 #define PLDM_COMPILER_H 4 5 // NOLINTBEGIN(bugprone-macro-parentheses) 6 /** 7 * Require that the given object is of the specified type. 8 * 9 * If the object is not of the required type then a diagnostic will be emitted. 10 * 11 * If you are reading this documentation due to hitting a compilation error 12 * passing through the macro, then you have a type error in your code that must 13 * be fixed. Despite the compiler output, the error is _not_ that some array 14 * is negatively sized, the array is negatively sized _because_ you have a type 15 * error. 16 * 17 * How this works: 18 * 19 * If the type of @p obj is not equivalent to the provided type @p type then 20 * we force the compiler to evaluate sizeof on a negatively-sized array. The 21 * C standard requires that the integer constant expression that specifies 22 * the array length must be greater than zero. Failure to meet this constraint 23 * generally terminates compilation of the translation unit as any other result 24 * cannot be handled in a sensible way. The array size is derived to an integer 25 * constant expression from a type eqivalence evaluated using _Generic() 26 * allowing us to stay within the language standard. The default generic 27 * association, representing a type mismatch, yields -1. 28 * 29 * pldm_require_obj_type() was introduced into the libpldm implementation to 30 * enable use of the pldm_msgbuf_extract*() APIs for objects that may or may not 31 * reside in a packed struct. See src/msgbuf.h for more details. 32 * 33 * @param obj The name of the object to evaluate 34 * @param type The required type of @p obj 35 * 36 * @return The expression either yields 1, or compilation is terminated 37 */ 38 #define pldm_require_obj_type(obj, type) \ 39 ((void)(sizeof( \ 40 struct { char buf[_Generic((obj), type: 1, default: -1)]; }))) 41 // NOLINTEND(bugprone-macro-parentheses) 42 43 #endif 44