BSD syscalls: Signals and thread control

Dispatch and catalog guide · Every number and configuration alternative

This page is generated from syscalls.master and authored descriptions.json. The signature is the master declaration, not the internal handler's (proc, args, retval) ABI. Descriptions identify selected local mechanisms; they do not claim every branch was audited.

37: kill

int kill(int pid, int signum, int posix) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_KILL.

Send a signal to a selected process or process group.

Implementation: kill. Finds/refers to the target, applies cansignal, and calls psignal or killpg1; posting selects pending/action state and is separate from building a user signal frame.

46: sigaction

int sigaction(int signum, struct __sigaction *nsa, struct sigaction *osa) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGACTION.

Query or replace a process signal disposition.

Implementation: sigaction. Imports/converts the caller ABI, validates signal/restriction flags, copies old state out and updates handler/mask/action state used by posting and delivery.

48: sigprocmask

int sigprocmask(int how, user_addr_t mask, user_addr_t omask);

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGPROCMASK.

Change the calling thread's blocked-signal mask and optionally return the previous mask.

Implementation: sigprocmask. Imports the mask, uses block/unblock/set helpers, requests an AST when newly deliverable work appears, and copies old mask state out.

52: sigpending

int sigpending(struct sigvec *osv);

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGPENDING.

Read the calling thread's pending-signal set.

Implementation: sigpending. Copies the maintained uthread pending-signal mask to the supplied user address; it does not deliver or consume those signals.

53: sigaltstack

int sigaltstack(struct sigaltstack *nss, struct sigaltstack *oss) NO_SYSCALL_STUB ;

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGALTSTACK.

Query or change the calling thread's alternate signal-stack configuration.

Implementation: sigaltstack. Converts 32/64-bit stack descriptors, validates current/on-stack restrictions and updates uthread state used by later signal delivery.

111: sigsuspend

int sigsuspend(sigset_t mask) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_NULL.

Temporarily replace the signal mask and sleep for signal handling.

Implementation: sigsuspend. The nocancel body records restoration state and enters interruptible tsleep0; signal delivery/return restores the appropriate mask. The ordinary entry first tests cancellation.

184: sigreturn

int sigreturn(struct ucontext *uctx, int infostyle, user_addr_t token) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGRETURN.

Restore user execution and signal-mask/alternate-stack state after a handler.

Implementation: sigreturn, sigreturn. Architecture-specific ARM and x86 bodies import the user context, validate tokens/machine state and install the saved state, using EJUSTRETURN so normal syscall result encoding does not overwrite it. Failure ordering is not an all-or-nothing memory transaction.

328: __pthread_kill

int __pthread_kill(int thread_port, int sig);

Declaration: syscalls.master · Condition: always · Audit event: AUE_PTHREADKILL.

Send a signal to a pthread identified by a Mach thread port name.

Implementation: __pthread_kill. Converts the port to a referenced thread, checks pthread/task association and posts through psignal_uthread, then drops the thread reference.

329: __pthread_sigmask

int __pthread_sigmask(int how, user_addr_t set, user_addr_t oset);

Declaration: syscalls.master · Condition: always · Audit event: AUE_PTHREADSIGMASK.

Change/query the current pthread's signal mask.

Implementation: __pthread_sigmask. Operates on uthread mask state after user copyin, requests a signal AST as appropriate and copies the previous mask out; it bypasses process-wide disposition changes.

330: __sigwait

int __sigwait(user_addr_t set, user_addr_t sig);

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGWAIT.

Synchronously wait for and consume a signal from a supplied set.

Implementation: __sigwait. The common body coordinates process signal state, waits when no matching pending bit exists and copies the selected signal number out. The ordinary entry first tests cancellation.

331: __disable_threadsignal

int __disable_threadsignal(int value);

Declaration: syscalls.master · Condition: always · Audit event: AUE_NULL.

Mark the current thread as excluded from ordinary process-directed signal selection.

Implementation: __disable_threadsignal. Sets UT_NO_SIGMASK | UT_CANCELDISABLE in the current uthread, excluding ordinary signal selection and disabling cancellation handling. It does not alter every process signal disposition or the hardware interrupt mask.

332: __pthread_markcancel

int __pthread_markcancel(int thread_port);

Declaration: syscalls.master · Condition: always · Audit event: AUE_NULL.

Mark a target pthread as having cancellation pending.

Implementation: __pthread_markcancel. Converts and checks the thread port, updates uthread cancellation flags and calls thread_abort_safely when the current cancellation state permits interruption, then releases the thread reference.

333: __pthread_canceled

int __pthread_canceled(int action);

Declaration: syscalls.master · Condition: always · Audit event: AUE_NULL.

Query or modify the current pthread's kernel cancellation bookkeeping.

Implementation: __pthread_canceled. Dispatches actions over uthread flags/state used by cancellation-point checks; userspace pthread cleanup handlers are not implemented by this syscall body.

334: __semwait_signal

int __semwait_signal(int cond_sem, int mutex_sem, int timeout, int relative, int64_t tv_sec, int32_t tv_nsec);

Declaration: syscalls.master · Condition: always · Audit event: AUE_SEMWAITSIGNAL.

Wait on a Mach semaphore, optionally signaling another and applying a timeout.

Implementation: __semwait_signal. The common body converts timeout form and selects semaphore wait/timed-wait or wait-signal trap helpers; the ordinary wrapper performs its cancellation-point test.

410: sigsuspend_nocancel

int sigsuspend_nocancel(sigset_t mask) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_NULL.

Temporarily replace the signal mask and sleep for signal handling.

Implementation: sigsuspend_nocancel. The nocancel body records restoration state and enters interruptible tsleep0; signal delivery/return restores the appropriate mask. The ordinary entry first tests cancellation.

422: __sigwait_nocancel

int __sigwait_nocancel(user_addr_t set, user_addr_t sig) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_SIGWAIT.

Synchronously wait for and consume a signal from a supplied set.

Implementation: __sigwait_nocancel. The common body coordinates process signal state, waits when no matching pending bit exists and copies the selected signal number out. The ordinary entry first tests cancellation.

423: __semwait_signal_nocancel

int __semwait_signal_nocancel(int cond_sem, int mutex_sem, int timeout, int relative, int64_t tv_sec, int32_t tv_nsec);

Declaration: syscalls.master · Condition: always · Audit event: AUE_SEMWAITSIGNAL.

Wait on a Mach semaphore, optionally signaling another and applying a timeout.

Implementation: __semwait_signal_nocancel. The common body converts timeout form and selects semaphore wait/timed-wait or wait-signal trap helpers; the ordinary wrapper performs its cancellation-point test.

520: terminate_with_payload

int terminate_with_payload(int pid, uint32_t reason_namespace, uint64_t reason_code, void *payload, uint32_t payload_size, const char *reason_string, uint64_t reason_flags) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_KILL.

Terminate an authorized target process with a structured reason/payload.

Implementation: terminate_with_payload. terminate_with_payload_internal validates and constructs reason state, checks the target and posts the fatal termination action; userspace strings/data are copied rather than retained as raw user pointers.

521: abort_with_payload

void abort_with_payload(uint32_t reason_namespace, uint64_t reason_code, void *payload, uint32_t payload_size, const char *reason_string, uint64_t reason_flags) NO_SYSCALL_STUB;

Declaration: syscalls.master · Condition: always · Audit event: AUE_EXIT.

Abort the caller with a structured termination reason.

Implementation: abort_with_payload. abort_with_payload_internal constructs the reason object and follows fatal exit/notification behavior for the current process.

529: os_fault_with_payload

int os_fault_with_payload(uint32_t reason_namespace, uint64_t reason_code, void *payload, uint32_t payload_size, const char *reason_string, uint64_t reason_flags);

Declaration: syscalls.master · Condition: always · Audit event: AUE_NULL.

Report a structured process fault through the reason/payload interface.

Implementation: os_fault_with_payload. Calls abort_with_payload_internal with OS_REASON_IFLAG_USER_FAULT, enabling throttling and a user-fault branch. Security soft traps send an analytics event; other namespaces construct a user guard exception and invoke task_violated_guard, then free the reason and translate its result. This differs from the abort entry's SIGABRT delivery.