Evaluate a body of code and return its size

asm_sizeof.c

// Works in GCC and clang, produces correct results at all optimization levels

// returns the contents of the instruction pointer
#define get_pc() ({                      \
	register void *temp;             \
	asm volatile("call	.+5\n\t" \
	             "pop	%0"      \
		    :"=r"(temp)          \
	);                               \
	temp;                            \
})

// returns the size of a block of code
#ifdef __OPTIMIZE__
#define ASM_SIZEOF_OVERHEAD 6
#else
#define ASM_SIZEOF_OVERHEAD 16
#endif
#define asm_sizeof(body) ({                                                       \
	void *_asm_sizeof_first = get_pc();                                       \
	body;                                                                     \
	void *_asm_sizeof_second = get_pc();                                      \
	(size_t)(_asm_sizeof_second - (_asm_sizeof_first + ASM_SIZEOF_OVERHEAD)); \
})

int main(){
	printf("%zu\n", asm_sizeof(puts("Hello, World!")));
}