Call a C function with arguments given as array (also known as fun.apply in JavaScript or PHP)

call-c-function-with-arguments-given-as-array.c

// Only works with System V AMD64 ABI (e.g. if you compile your code to 64-bit targetting Linux)

typedef uint64_t fun_arg_t;

/**
 * Call a function with given arguments.
 *
 * This requires System V AMD64 ABI compilation for this function as well as the called function.
 *
 * @param fun Pointer to the function
 * @param args The arguments, must be at most 6
 * @param arg_count The number of actual arguments (0 <= arg_count <= 6)
 * @return The return value of the called function. If the function had a void return type, it is unspecified what this function returns.
 */
static inline uint64_t call_function(void *fun, fun_arg_t *args, size_t arg_count) {
	// In the System V AMD64 ABI only the first 6 arguments will be passed via registers
	// And only for arguments passed via registers, it doesn't matter if we pretend the function pointer
	// to have fun_arg_t parameters or, say, uint8_t parameters! They will all be extended to
	// 64 bits.
	assert(arg_count <= 6);

	typedef uint64_t (*fun_ptr0)(void);
	typedef uint64_t (*fun_ptr1)(fun_arg_t);
	typedef uint64_t (*fun_ptr2)(fun_arg_t, fun_arg_t);
	typedef uint64_t (*fun_ptr3)(fun_arg_t, fun_arg_t, fun_arg_t);
	typedef uint64_t (*fun_ptr4)(fun_arg_t, fun_arg_t, fun_arg_t, fun_arg_t);
	typedef uint64_t (*fun_ptr5)(fun_arg_t, fun_arg_t, fun_arg_t, fun_arg_t, fun_arg_t);
	typedef uint64_t (*fun_ptr6)(fun_arg_t, fun_arg_t, fun_arg_t, fun_arg_t, fun_arg_t, fun_arg_t);

	#pragma GCC diagnostic push
	#pragma GCC diagnostic ignored "-Wpedantic"
	switch (arg_count) {
		case 0:
			return ((fun_ptr0) fun)();
		case 1:
			return ((fun_ptr1) fun)(args[0]);
		case 2:
			return ((fun_ptr2) fun)(args[0], args[1]);
		case 3:
			return ((fun_ptr3) fun)(args[0], args[1], args[2]);
		case 4:
			return ((fun_ptr4) fun)(args[0], args[1], args[2], args[3]);
		case 5:
			return ((fun_ptr5) fun)(args[0], args[1], args[2], args[3], args[4]);
		case 6:
			return ((fun_ptr6) fun)(args[0], args[1], args[2], args[3], args[4], args[5]);
		default:
			assert(0);
	}
	#pragma GCC diagnostic pop
}

Related code: https://github.com/kosh04/newlisp/blob/9eb8f27de842ebe96e8a6f8e631ffd3fa37d4611/nl-import.c#L248-L390