M6.5 Phase 4: Signal Contracts

Phase 4 validates Linux signal delivery contracts: handler registration, signal masking, delivery order, and coalescing.

Tests implemented

delivery_order — Sends SIGUSR1 to self 5 times while masked. After unmasking, verifies the handler ran exactly once (standard signal coalescing). This confirms that Kevlar's signal pending bitmask correctly coalesces multiple sends of the same standard signal.

handler_context — Registers a SIGUSR2 handler via sigaction(), sends the signal, verifies the handler ran with the correct signal number. Also tests that replacing a handler returns the old one, and that SIG_IGN suppresses delivery.

mask_semantics — Already passing from Phase 1. Tests sigprocmask block/unblock with pending signal delivery after unmasking.

sa_restart — Existing test, requires setitimer/SIGALRM to deliver a signal during a blocking read(). Kevlar's alarm() is stubbed, so this test timeouts. Tracked for M7.

Known gaps

• SA_RESTART: Requires alarm() or setitimer() to deliver SIGALRM during a blocking syscall. Currently stubbed.
• Coredumps: Not implemented (M9 scope).
• Real-time signals: sigqueue() not tested. Standard signal coalescing works; real-time queueing is untested.
• Signal during syscall: The interaction between signal delivery and in-progress syscalls (EINTR vs SA_RESTART) is not validated yet.

Results

Full suite: 15/16 PASS.