https://elixir.bootlin.com/linux/latest/source/tools/include/nolibc/nolibc.h#L2114

nolibc-open.h

/* https://elixir.bootlin.com/linux/latest/source/tools/include/nolibc/nolibc.h#L2114 */
/* nolibc.h::open() */
static __attribute__((unused))
int open(const char *path, int flags, mode_t mode)
{
    int ret = sys_open(path, flags, mode);
    if (ret < 0) {
        SET_ERRNO(-ret);
        ret = -1;
    }
    return ret;
}

/* arch/arm64/include/asm/unistd32.h::__NR_open */
#define __NR_open 5

/* https://elixir.bootlin.com/linux/latest/source/tools/include/nolibc/nolibc.h#L1625 */
/* nolibc.h::sys_open() */
static __attribute__((unused))
int sys_open(const char *path, int flags, mode_t mode)
{
#ifdef __NR_openat
    return my_syscall4(__NR_openat, AT_FDCWD, path, flags, mode);
#elif defined(__NR_open)
    return my_syscall3(__NR_open, path, flags, mode);
#else
#error Neither __NR_openat nor __NR_open defined, cannot implement sys_open()
#endif
}