Raion at 23:56, 9 January 2026

2026-01-09T23:56:07Z

← Older revision		Revision as of 23:56, 9 January 2026
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	Differences: BSD simpler — no queued signals, weaker real-time, different threading model.		Differences: BSD simpler — no queued signals, weaker real-time, different threading model.
	Overall, IRIX signal system is SVR4/POSIX compliant with strong multi-threading and queued signal support. illumos closest modern analog; BSD covers basics but lacks queued delivery and per-thread complexity. For replication: preserve dual process/thread model, queued siginfo handling, and careful ut_lock/sigvec coordination.		Overall, IRIX signal system is SVR4/POSIX compliant with strong multi-threading and queued signal support. illumos closest modern analog; BSD covers basics but lacks queued delivery and per-thread complexity. For replication: preserve dual process/thread model, queued siginfo handling, and careful ut_lock/sigvec coordination.

			[[Category: Kernel Documentation]]

Raion: Created page with "== Overview == The IRIX kernel signal infrastructure provides a comprehensive, POSIX-compliant signal delivery system with extensions for real-time, debugging, and multi-threaded processes. Signals are managed at both process (sigvec_t in proc_t) and thread (ut_sig, ut_sighold in uthread_t) levels, allowing per-thread signal masks and delivery while maintaining process-wide consistency. Key features: Queued signals (sigqueue_t) for POSIX sigqueue and siginfo delivery. P..."

2026-01-04T03:52:14Z

Created page with "== Overview == The IRIX kernel signal infrastructure provides a comprehensive, POSIX-compliant signal delivery system with extensions for real-time, debugging, and multi-threaded processes. Signals are managed at both process (sigvec_t in proc_t) and thread (ut_sig, ut_sighold in uthread_t) levels, allowing per-thread signal masks and delivery while maintaining process-wide consistency. Key features: Queued signals (sigqueue_t) for POSIX sigqueue and siginfo delivery. P..."

New page

== Overview ==
The IRIX kernel signal infrastructure provides a comprehensive, POSIX-compliant signal delivery system with extensions for real-time, debugging, and multi-threaded processes. Signals are managed at both process (sigvec_t in proc_t) and thread (ut_sig, ut_sighold in uthread_t) levels, allowing per-thread signal masks and delivery while maintaining process-wide consistency.
Key features:

Queued signals (sigqueue_t) for POSIX sigqueue and siginfo delivery.
Priority-based delivery with job control stops handled specially.
Alternate signal stacks (sigaltstack, legacy sigstack).
Signal contexts (ucontext_t, sigcontext) for setcontext/getcontext and signal handlers.
Debugging integration (/proc, ptrace).
Multi-threaded awareness — signals can target specific uthreads or the process.
Async signal delivery via async_vec_t for non-sleepable contexts.

The system carefully handles races between signal posting, masking, and delivery using spinlocks and atomic operations.
== Key Functions ==
Signal Posting

sigtopid: Send signal to process by PID (handles async via async_call if SIG_NOSLEEP).
sigtouthread / sigtouthread_common: Deliver to specific uthread.
sigaddq / sigdeq / sigdelq: Manage queued siginfo structures.
sigqueue_alloc / sigqueue_free: Zone-based allocation.

Signal Delivery

issig: Check for pending unmasked signals (returns signal number).
fsig: Find first unheld signal.
psig: Process current signal — installs handler or takes default action.
sendsig: Set up user context and registers for handler entry.
stop / unstop: Job control and debugger stops.

Context Management

save/restore context functions for ucontext_t and legacy sigcontext.
irix5_*_savecontext / restorecontext: ABI-specific versions.

Signal Waiting

sigpending: Return pending signal set.
sigsuspend: Swap mask and sleep.
sigprocmask: Modify signal mask.
sigpoll / sigtimedwait: Wait for specific signals (POSIX sigwait family).

Special Interfaces

ptrace: Classic debugging interface.
sigaltstack / sigstack: Alternate signal stack control.
core: Generate core dump on fatal signals.

== Undocumented or IRIX-Specific Interfaces and Behaviors ==
Structures

sigvec_t (process-wide):
sv_sig, sv_sigign, sv_sigcatch: Pending, ignored, caught signals.
sv_hndlr[NSIG_HNDLRS]: Handler array.
sv_sigmasks, sv_signodefer, sv_sigrestart, sv_sigresethand: Per-signal flags.
sv_sigqueue: Head of queued siginfo list.
sv_pending: Count of queued signals.

uthread_t signal fields:
ut_sig: Thread-private pending signals.
ut_sighold: Thread-private blocked mask.
ut_sigwait: Signals being waited on.
ut_cursig, ut_curinfo: Current signal and siginfo.
ut_suspmask: Saved mask during sigsuspend.

sigqueue_t: Queued siginfo with chaining.

Dual Delivery Model

Signals can be process-directed (posted to sigvec_t) or thread-directed (sigtouthread).
VPROC_SENDSIG virtualizes delivery across threads.
Async delivery queue for non-sleepable contexts.

Job Control Special Cases

SIGCONT cancels pending stop signals.
Stop signals ignored if no handler and process orphaned (except SIGSTOP).

Queued Signals

sigqueue() delivers siginfo_t with value.
Multiple same-signal infos preserved only if SI_QUEUE, SI_ASYNCIO, etc.

Alternate Stack

prxy_sigsp, prxy_spsize, prxy_siglb: Track alternate stack base/size/low bound.
SS_ONSTACK flag managed carefully.

== Similarities to illumos and BSD Kernel Implementations ==
illumos (Solaris-derived)
Strong similarity:

sigqueue(), queued signals, siginfo_t.
sigprocmask, sigsuspend, sigaction semantics.
Alternate stack via sigaltstack.
Process + thread signal masks.

Differences: illumos uses turnstiles; IRIX uses explicit queues and sv_t.
BSD (FreeBSD, etc.)
Moderate similarity:

sigaction, sigprocmask, kill, sigaltstack.
Signal contexts for longjmp-style handlers.

Differences: BSD simpler — no queued signals, weaker real-time, different threading model.
Overall, IRIX signal system is SVR4/POSIX compliant with strong multi-threading and queued signal support. illumos closest modern analog; BSD covers basics but lacks queued delivery and per-thread complexity. For replication: preserve dual process/thread model, queued siginfo handling, and careful ut_lock/sigvec coordination.

Kernel: Signal Infrastructure - Revision history

Raion at 23:56, 9 January 2026