https://elixir.bootlin.com/linux/v5.14.21/source/fs/open.c#L1228

do_sys_open.h

/* arm64/include/asm/unistd32.h::__SYSCALL */
#undef __SYSCALL
#define __SYSCALL(nr, sym)	asmlinkage long __arm64_##sym(const struct pt_regs *);
#include <asm/unistd.h>

#undef __SYSCALL
#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,

/* arch/arm64/include/asm/unistd32.h::__NR_open */
#define __NR_open 5
__SYSCALL(__NR_open, compat_sys_open)
	
/* include/linux/compat.h::compat_sys_open */
asmlinkage long compat_sys_open(const char __user *filename, int flags,
				umode_t mode);

/* arch/arm64/include/asm/syscall_wrapper.h */
#define __SYSCALL_DEFINEx(x, name, ...)						\
	asmlinkage long __arm64_sys##name(const struct pt_regs *regs);		\
	ALLOW_ERROR_INJECTION(__arm64_sys##name, ERRNO);			\
	static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__));		\
	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
	asmlinkage long __arm64_sys##name(const struct pt_regs *regs)		\
	{									\
		return __se_sys##name(SC_ARM64_REGS_TO_ARGS(x,__VA_ARGS__));	\
	}									\
	static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__))		\
	{									\
		long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));	\
		__MAP(x,__SC_TEST,__VA_ARGS__);					\
		__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__));		\
		return ret;							\
	}									\
	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))

/* include/linux/syscalls.h */
/*
 * __MAP - apply a macro to syscall arguments
 * __MAP(n, m, t1, a1, t2, a2, ..., tn, an) will expand to
 *    m(t1, a1), m(t2, a2), ..., m(tn, an)
 * The first argument must be equal to the amount of type/name
 * pairs given.  Note that this list of pairs (i.e. the arguments
 * of __MAP starting at the third one) is in the same format as
 * for SYSCALL_DEFINE<n>/COMPAT_SYSCALL_DEFINE<n>
 */
#define __MAP0(m,...)
#define __MAP1(m,t,a,...) m(t,a)
#define __MAP2(m,t,a,...) m(t,a), __MAP1(m,__VA_ARGS__)
#define __MAP3(m,t,a,...) m(t,a), __MAP2(m,__VA_ARGS__)
#define __MAP4(m,t,a,...) m(t,a), __MAP3(m,__VA_ARGS__)
#define __MAP5(m,t,a,...) m(t,a), __MAP4(m,__VA_ARGS__)
#define __MAP6(m,t,a,...) m(t,a), __MAP5(m,__VA_ARGS__)
#define __MAP(n,...) __MAP##n(__VA_ARGS__)

/* https://elixir.bootlin.com/linux/v5.14.21/source/fs/open.c#L1228 */
/* fs/open.c::do_sys_open() */
long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
{
	struct open_how how = build_open_how(flags, mode);
	return do_sys_openat2(dfd, filename, &how);
}

/* fs/open.c::do_sys_openat2() */
static long do_sys_openat2(int dfd, const char __user *filename,
			   struct open_how *how)
{
	struct open_flags op;
	int fd = build_open_flags(how, &op);
	struct filename *tmp;

	if (fd)
		return fd;

	tmp = getname(filename);
	if (IS_ERR(tmp))
		return PTR_ERR(tmp);

	fd = get_unused_fd_flags(how->flags);
	if (fd >= 0) {
		struct file *f = do_filp_open(dfd, tmp, &op);
		if (IS_ERR(f)) {
			put_unused_fd(fd);
			fd = PTR_ERR(f);
		} else {
			fsnotify_open(f);
			fd_install(fd, f);
		}
	}
	putname(tmp);
	return fd;
}

/* fs/namei.c::do_o_path() */
static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file)
{
	struct path path;
	int error = path_lookupat(nd, flags, &path);
	if (!error) {
		audit_inode(nd->name, path.dentry, 0);
		error = vfs_open(&path, file);
		path_put(&path);
	}
	return error;
}
/** 
 * fs/open.c::vfs_open()
 *   -> fs/open.c::do_dentry_open() 
 *     => each handle for FMODE_XXXXX 
 */