syscalls.md

List of supported Linux syscalls

Tilck supports both the int 0x80 syscall interface and the sysenter one. Here below there is an up-to-date table containing the status of each supported syscall at the moment. Because the list of the not-yet-supported syscalls is much longer than the list of supported ones, the table below mentions only the syscalls having some degree of support. The missing syscalls have to be considered as not implemented yet.

Syscall	Support level
sys_exit	full
sys_fork	full
sys_read	full
sys_write	full
sys_open	partial++ [1]
sys_close	full
sys_waitpid	full
sys_execve	full
sys_chdir	full
sys_getpid	full
sys_setuid16	limited [3]
sys_getuid16	limited [3]
sys_pause	minimal [2]
sys_access	partial
sys_brk	full
sys_setgid16	limited [3]
sys_getgid16	limited [3]
sys_seteuid16	limited [3]
sys_setegid16	limited [3]
sys_geteuid16	limited [3]
sys_getegid16	limited [3]
sys_ioctl	partial
sys_getppid	full
sys_gettimeofday	full
sys_munmap	full
sys_wait4	full
sys_newuname	full
sys_llseek	full
sys_readv	full
sys_writev	full
sys_nanosleep_time32	full
sys_prctl	stub
sys_getcwd	full
sys_mmap_pgoff	full
sys_stat64	full
sys_fstat64	full
sys_lstat64	partial
sys_getuid	limited [3]
sys_getgid	limited [3]
sys_geteuid	limited [3]
sys_getegid	limited [3]
sys_setuid	limited [3]
sys_setgid	limited [3]
sys_getdents64	full
sys_fcntl64	partial
sys_gettid	minimal [4]
sys_set_thread_area	full
sys_exit_group	minimal [5]
sys_set_tid_address	stub
sys_tkill	partial++ [6]
sys_tgkill	partial++ [6]
sys_kill	full
sys_setsid	full
sys_times	minimal [9]
sys_clock_gettime	compliant [10]
sys_clock_gettime32	compliant [10]
sys_clock_getres	compliant [10]
sys_clock_getres_time32	compliant [10]
sys_select	full
sys_poll	full
sys_readlink	full
sys_creat	full
sys_unlink	full
sys_symlink	full
sys_pread64	full
sys_pwrite64	full
sys_vfork	compliant [11]
sys_umask	full
sys_ia32_truncate64	full
sys_ia32_ftruncate64	full
sys_sync	full
sys_syncfs	full
sys_chown	limited [3]
sys_fchown	limited [3]
sys_lchown	limited [3]
sys_chmod	full
sys_fchmod	full
sys_rename	full
sys_link	full
sys_pipe	full
sys_pipe2	partial++ [13]
sys_sched_yield	full
sys_getsid	full
sys_setpgid	full
sys_getpgid	full
sys_getpgrp	full
sys_utime32	full
sys_utimes	full
sys_fsync	compliant
sys_fdatasync	compliant
sys_dup	full
sys_dup2	full
sys_reboot	full
sys_rt_sigprocmask	full
sys_rt_sigpending	full
sys_rt_sigreturn	partial [14]
sys_rt_sigaction	partial [14]
sys_rt_sigsuspend	partial [14]

Definitions:

Support level	Meaning
full	Syscall 100% supported.
partial	Syscall partially supported, work-in-progress
partial++	All of the really important flags and modes are supported
...	Most of the advanced stuff very likely is still not supported.
stub	The syscall does not return -ENOSYS, but it has actually a stub
...	implementation, at the moment.
minimal	Like partial, just even less features are supported
compliant	Syscall supported in a way compliant with a full
...	implementation, but actually it has several limitations due to
...	the different design of Tilck. Example: see the note [3].
limited	The syscall supports by design only a subset of the cases
...	supported by the Linux implementation.

Notes:

1. The syscall open() now supports read/write access, file creation, mode setting and flags like O_APPEND, O_CLOEXEC, O_EXCL, O_TRUNC. All the "advanced" flags like O_ASYNC are not supported yet.

2. Because custom signal handlers are not supported, pause() puts the process to sleep until a signal actually kills it.

3. Tilck does not support by design multiple users nor any form of authentication. Therefore, the following statement is always true: UID == GID == EUID == EGID == 0. All the calls like setuid(), seteuid(), setgid(), setegid(), chown() etc. succeed only when UID/GID == 0.

4. Because the lack of thread support, gettid() is the same as getpid()

5. Because the lack of thread support, exit_group() behaves as exit()

6. Because the lack of thread support, tgkill() works only when tgid == tid.

7. [Limitation removed]

8. [Limitation removed]

9. At the moment times() just updates tms_utime and tms_stime.

10. Only the clocks CLOCK_REALTIME and CLOCK_MONOTONIC are supported.

11. Behaves exactly as fork().

12. [Limitation removed]

13. The O_DIRECT mode is not supported.

14. Tilck has a partial support for POSIX signals. SIG_IGN and SIG_DFL are fully supported. Custom signal handlers are supported as well, but signal handlers (even of different type) cannot interrupt each other. In other words, nested custom signal handlers are not supported, yet. Also, even if the modern sys_rt_sigaction() interface is implemented, none of its flags like SA_NODEFER, SA_ONSTACK, SA_RESETHAND, SA_RESTART, SA_SIGINFO are supported, at the moment. The per-signal sa_mask is also fixed: while a custom handler is running, all the other signals having a custom handler are masked (terminating signals instead, can always we delieved). In addition, the order of delivery of all signals is unspecified and there is no distinction between regular signals and real-time ones. Also, at the moment, no syscall can be restarted if a signal interrupted it. The syscall sys_rt_sigsuspend() works as expected if we're not calling it from a signal handler otherwise, it returns -EPERM (not allowed according to POSIX).

    NOTE: while the just-described limited support for POSIX reliable signals might seem too limited, it's worth noting that it already opened a considerable amount of uses, like graceful process termination with SIGTERM.