Signals

This document describes the signal handling implementation in the Kyronix kernel. It is the child of Process Management.

Source

kernel/proc/signal.c, kernel/proc/signal.h

Overview

The Kyronix kernel implements POSIX-compatible signal handling with Linux ABI compatibility. Signals are delivered by constructing an rt_sigframe on the user stack and redirecting execution to the signal handler.

Supported Signals

Signal Delivery

signal_check(f)

Called on every syscall entry/exit and timer interrupt:

1. Check terminal-driven signals via tty_check_signals()
2. Load pending signals masked by complement of sig_mask
3. Find lowest-numbered unmasked signal via __builtin_ctzll
4. Clear from pending_sigs
5. If ptrace-traced, call proc_ptrace_stop()
6. Otherwise call deliver_signal()

deliver_signal(p, sig, frame)

• SIGSTOP/SIGTSTP (default): Enter job-control stop
• SIG_IGN: No action
• SIG_DFL: If fatal, call proc_do_exit(-sig)
• Custom handler: Build signal frame and redirect execution

setup_sigframe(p, sig, frame)

1. Check for alternate signal stack (SA_ONSTACK)
2. Allocate rt_sigframe_t (440 bytes) below user RSP
3. Populate with register snapshot, signal info, ucontext
4. Update signal mask (add signal bit + sa_mask)
5. Redirect: rcx = handler, rdi = signal number, rsi = siginfo, rdx = ucontext

Signal Action Flags

Alternate Signal Stack

Each process can have an alternate stack configured via sigaltstack(). The frame is placed at the top of the alternate stack when SA_ONSTACK is set.

Last reviewed: 2026-07-22