musl/arch/i386/bits/stdarg.h

#define __VA_ALIGNED_SIZE(x) ((sizeof(x) + sizeof(int) - 1) & ~(sizeof(int) - 1))

#define va_start(ap, last) ((ap) = (void *)(((char *)&(last)) + __VA_ALIGNED_SIZE(last)))
#define va_end(ap) ((void)0)
#define va_copy(dest, src) ((dest) = (src))

#define va_arg(ap, type) \
	( ((ap) = (va_list)((char *)(ap) + __VA_ALIGNED_SIZE(type))), \
	*(type *)(void *)((char *)(ap) - __VA_ALIGNED_SIZE(type)) )