Process Control

This document describes the process control system calls (syscalls) in the Kyronix kernel. It is the child of Syscalls.

Syscall Table

• 56 clone - Create a new process/thread

• 57 fork - Create a child process

• 58 vfork - Create a child process (treated as fork)

• 59 execve - Execute a program

• 60 exit - Terminate a process

• 61 wait4 - Wait for a process to change state

• 231 exit_group - Terminate all threads in a process

• 247 waitid - Wait for a specific process state change

• 39 getpid - Get process id (PID)

• 110 getppid - Get parent PID

• 186 gettid - Get thread id (TID)

• 102 getuid - Get real user id (UID)

• 104 getgid - Get real group id (GID)

• 107 geteuid - Get effective UID

• 108 getegid - Get effective GID

• 105 setuid - Set real UID

• 106 setgid - Set real GID

• 109 setpgid - Set process group id (PGID)

• 112 setsid - Create a session and set session id (SID)

• 113 setreuid - Set real and effective UID

• 114 setregid - Set real and effective GID

• 115 getgroups - Get supplementary group list

• 116 setgroups - Set supplementary group list

• 117 setresuid - Set real, effective, and saved UID

• 118 getresuid - Get real, effective, and saved UID

• 119 setresgid - Set real, effective, and saved GID

• 120 getresgid - Get real, effective, and saved GID

• 121 getpgid - Get PGID

• 122 setfsuid - Set filesystem UID

• 123 setfsgid - Set filesystem GID

• 124 getsid - Get session ID

• 158 arch_prctl - Architecture-specific process register (ARCH_SET_FS, ARCH_SET_GS, ARCH_GET_FS, ARCH_GET_GS)

clone Flags

The clone syscall accepts flags to control process/thread creation behavior:

• CLONE_VM - Share memory with parent process
• CLONE_FILES - Share file descriptor table with parent
• CLONE_THREAD - Create a thread (shared address space)
• CLONE_SETTLS - Set thread-local storage (TLS)
• CLONE_PARENT_SETTID - Store child TID at parent-provided address
• CLONE_CHILD_CLEARTID - Clear child TID at exit and wake waiters
• CLONE_CHILD_SETTID - Store child TID at child-provided address

execve Details

The execve syscall performs the following operations:

1. Reads the shebang line (#!) if present and interprets the interpreter path
2. Loads the executable binary (Executable and Linkable Format (ELF))
3. For dynamically linked executables, sets up the dynamic linker via PT_INTERP segment at virtual address 0x7f0000000000
4. Sets Position Independent Executable (PIE) base address at 0x400000
5. Sets up the user stack with argc, argv, envp, and auxiliary vector (auxv)
6. Initializes Address Space Layout Randomization (ASLR) for the memory map bump allocator (mmap_bump)

fork Details

The fork syscall performs the following operations:

1. Deep-copies the address space via vmm_fork_user()
2. Copies the file descriptor table
3. Creates a new kernel stack for the child process
4. The child process returns with rax set to 0

clone Thread Support

The clone syscall with CLONE_THREAD flag creates a thread that shares:

• The address space (via CLONE_VM)
• The file descriptor table (via CLONE_FILES)

wait4 Details

The wait4 syscall supports the following features:

• Zombie reaping of terminated children
• Handling of ptrace-stopped tracees
• Job-stopped children
• Non-blocking operation via WNOHANG flag

proc_do_exit

The proc_do_exit function performs the following cleanup operations:

1. Cleans up System V Shared Memory (SHM)
2. Unreferences the jail
3. Releases the file descriptor table
4. Reparents children to PID 1 (init process)
5. Delivers SIGCHLD signal to the parent process

Last reviewed: 2026-07-22