Implement POSIX signal handling infrastructure #56
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This adds complete signal handling support to Breenix including: Kernel signal infrastructure: - SignalState per-process with pending/blocked masks and 64 handlers - Signal constants (SIGHUP through SIGSYS, NSIG=64) - Default actions (terminate, core dump, stop, continue, ignore) - Signal delivery from context switch before return to userspace - Signal trampoline that calls rt_sigreturn on handler return Syscalls implemented: - kill(pid, sig) - Send signal to process - rt_sigaction(sig, act, oldact, sigsetsize) - Set signal handler - rt_sigprocmask(how, set, oldset, sigsetsize) - Block/unblock signals - rt_sigreturn() - Return from signal handler, restore context Security measures: - Userspace pointer validation (copy_from_user/copy_to_user) - Signal frame magic number to detect forgery - RIP/RSP validation to prevent kernel address injection - RFLAGS sanitization to prevent disabling interrupts - SIGKILL/SIGSTOP cannot be caught or blocked Userspace support (libbreenix): - kill(), sigaction(), sigprocmask() wrappers - Sigaction struct with SA_* flags End-to-end tests: - signal_handler_test: Proves handlers execute - signal_return_test: Proves trampoline/sigreturn works - signal_regs_test: Proves registers preserved across signals All 63 boot stages pass including new signal-specific stages. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
The libs/libbreenix/src/signal.rs file was created but not committed because libs/ is in .gitignore. Force-add it to match other libs files. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Two bugs fixed: 1. delivery.rs: Convert recursive signal delivery to iterative loop - The SIG_IGN case was recursively calling deliver_pending_signals - This caused unbounded stack growth with many ignored signals - Now uses a loop to process all deliverable signals with O(1) stack 2. signal.rs: Fix off-by-8 error in sigreturn frame pointer - When signal handler executes 'ret', it pops trampoline_addr from stack - This increments RSP by 8, so frame pointer was pointing past the frame - Now subtracts 8 from RSP to find the actual SignalFrame start All signal tests now pass: - Signal handler execution verified - Signal handler return verified - Signal register preservation verified 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
This PR adds complete POSIX signal handling support to Breenix, enabling userspace programs to register signal handlers, send signals between processes, and properly handle asynchronous events.
Key Features
Files Changed
kernel/src/signal/kernel/src/syscall/signal.rs,userptr.rscontext_switch.rs,handler.rslibs/libbreenix/src/signal.rsuserspace/tests/signal_*.rsTesting
Three end-to-end tests verify the implementation:
SIGNAL_HANDLER_EXECUTEDSIGNAL_RETURN_WORKSSIGNAL_REGS_PRESERVEDAll 63 boot stages pass.
Security
Test plan
🤖 Generated with Claude Code