kernel+libc: Implement sigprocmask() and friends

Userspace can now catch segfaults!

apps/signal-test.cpp

@@ -1,20 +1,25 @@
 #include <signal.h>
 #include <stdio.h>
+#include <string.h>
 
 void handler(int)
 {
-    puts("I'm a signal handler");
+    puts("I caught a segfault!");
+
+    struct sigaction sa;
+    sa.sa_handler = SIG_DFL;
+    sigaction(SIGSEGV, &sa, NULL);
 }
 
 int main()
 {
     struct sigaction sa;
     sa.sa_handler = handler;
-    sigaction(SIGABRT, &sa, NULL);
+    sigaction(SIGSEGV, &sa, NULL);
 
-    raise(SIGABRT);
-
-    puts("I'm outside the signal handler!");
+#pragma GCC diagnostic ignored "-Wnonnull"
+    char* str = nullptr;
+    memset(str, 0, 2);
 
     return 0;
 }

kernel/src/arch/x86_64/CPU.cpp

@@ -9,6 +9,7 @@
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
 #include "video/TextConsole.h"
+#include <bits/signal.h>
 #include <cpuid.h>
 #include <luna/CString.h>
 #include <luna/CircularQueue.h>
@@ -70,64 +71,65 @@ void decode_page_fault_error_code(u64 code)
             (code & PF_RESERVED) ? " | Reserved bits set" : "", (code & PF_NX_VIOLATION) ? " | NX violation" : "");
 }
 
-[[noreturn]] void handle_page_fault(Registers* regs)
+void handle_cpu_exception(int signo, const char* err, Registers* regs)
 {
-    CPU::disable_interrupts();
+    if (err) kerrorln("Caught CPU exception: %s", err);
 
-    u64 cr2;
-    asm volatile("mov %%cr2, %0" : "=r"(cr2));
-    kerrorln("Page fault at RIP %lx while accessing %lx!", regs->rip, cr2);
-
-    decode_page_fault_error_code(regs->error);
+    kerrorln("RAX: %.16lx RBX: %.16lx RCX: %.16lx RDX:   %.16lx", regs->rax, regs->rbx, regs->rcx, regs->rdx);
+    kerrorln("RBP: %.16lx RSP: %.16lx RDI: %.16lx RSI:   %.16lx", regs->rbp, regs->rsp, regs->rdi, regs->rsi);
+    kerrorln("R8:  %.16lx R9:  %.16lx R10: %.16lx R11:   %.16lx", regs->r8, regs->r9, regs->r10, regs->r11);
+    kerrorln("R12: %.16lx R13: %.16lx R14: %.16lx R15:   %.16lx", regs->r12, regs->r13, regs->r14, regs->r15);
+    kerrorln("RIP: %.16lx CS:  %.16lx SS:  %.16lx FLAGS: %.16lx", regs->rip, regs->cs, regs->ss, regs->rflags);
 
     CPU::print_stack_trace_at(regs);
 
     if (!is_in_kernel(regs))
     {
-        // FIXME: Kill this process with SIGSEGV once we have signals and all that.
-        kerrorln("Current task %zu was terminated because of a page fault", Scheduler::current()->id);
-        Scheduler::current()->exit_and_signal_parent(127);
+        Scheduler::current()->send_signal(signo);
+        Scheduler::current()->process_pending_signals(regs);
+        return;
     }
 
     CPU::efficient_halt();
 }
 
-[[noreturn]] void handle_general_protection_fault(Registers* regs)
+void handle_page_fault(Registers* regs)
 {
-    CPU::disable_interrupts();
+    u64 cr2;
+    asm volatile("mov %%cr2, %0" : "=r"(cr2));
+    kerrorln("Page fault while accessing %lx!", cr2);
 
+    decode_page_fault_error_code(regs->error);
+
+    handle_cpu_exception(SIGSEGV, nullptr, regs);
+}
+
+void handle_general_protection_fault(Registers* regs)
+{
     kerrorln("General protection fault at RIP %lx, error code %lx!", regs->rip, regs->error);
 
-    CPU::print_stack_trace_at(regs);
-
-    if (!is_in_kernel(regs))
-    {
-        // FIXME: Kill this process with SIGSEGV once we have signals and all that.
-        kerrorln("Current task %zu was terminated because of a general protection fault", Scheduler::current()->id);
-        Scheduler::current()->exit_and_signal_parent(127);
-    }
-
-    CPU::efficient_halt();
+    handle_cpu_exception(SIGSEGV, nullptr, regs);
 }
 
 extern "C" void handle_x86_exception(Registers* regs)
 {
+    CPU::disable_interrupts();
     switch (regs->isr)
     {
-    case 0: FIXME_UNHANDLED_INTERRUPT("Division by zero");
+    case 0: handle_cpu_exception(SIGFPE, "Division by zero", regs); return;
     case 1: FIXME_UNHANDLED_INTERRUPT("Debug interrupt");
     case 2: FIXME_UNHANDLED_INTERRUPT("NMI (Non-maskable interrupt)");
     case 3: FIXME_UNHANDLED_INTERRUPT("Breakpoint");
     case 4: FIXME_UNHANDLED_INTERRUPT("Overflow");
     case 5: FIXME_UNHANDLED_INTERRUPT("Bound range exceeded");
-    case 6: FIXME_UNHANDLED_INTERRUPT("Invalid opcode");
+    case 6: handle_cpu_exception(SIGILL, "Invalid opcode", regs); return;
     case 7: FIXME_UNHANDLED_INTERRUPT("Device not available");
     case 10: FIXME_UNHANDLED_INTERRUPT("Invalid TSS");
     case 11: FIXME_UNHANDLED_INTERRUPT("Segment not present");
     case 12: FIXME_UNHANDLED_INTERRUPT("Stack-segment fault");
-    case 13: handle_general_protection_fault(regs);
-    case 14: handle_page_fault(regs);
-    case 16: FIXME_UNHANDLED_INTERRUPT("x87 floating-point exception");
+    case 13: handle_general_protection_fault(regs); return;
+    case 14: handle_page_fault(regs); return;
+    case 16: handle_cpu_exception(SIGFPE, "x87 floating-point exception", regs); return;
     case 17: FIXME_UNHANDLED_INTERRUPT("Alignment check");
     case 19: FIXME_UNHANDLED_INTERRUPT("SIMD floating-point exception");
     case 20: FIXME_UNHANDLED_INTERRUPT("Virtualization exception");

kernel/src/sys/signal.cpp

@@ -2,6 +2,7 @@
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
+#include <bits/signal.h>
 
 Result<u64> sys_sigreturn(Registers* regs, SyscallArgs)
 {
@@ -66,3 +67,33 @@ Result<u64> sys_kill(Registers*, SyscallArgs args)
 
     return 0;
 }
+
+Result<u64> sys_sigprocmask(Registers*, SyscallArgs args)
+{
+    auto* current = Scheduler::current();
+
+    int how = (int)args[0];
+    const sigset_t* set = (const sigset_t*)args[1];
+    sigset_t* oldset = (sigset_t*)args[2];
+
+    if (oldset)
+    {
+        if (!MemoryManager::copy_to_user_typed(oldset, &current->signal_mask)) return err(EFAULT);
+    }
+
+    if (set)
+    {
+        sigset_t kset;
+        if (!MemoryManager::copy_from_user_typed(set, &kset)) return err(EFAULT);
+
+        switch (how)
+        {
+        case SIG_BLOCK: current->signal_mask |= kset;
+        case SIG_UNBLOCK: current->signal_mask &= ~kset;
+        case SIG_SETMASK: current->signal_mask = kset;
+        default: return err(EINVAL);
+        }
+    }
+
+    return 0;
+}

kernel/src/thread/Thread.cpp

@@ -4,6 +4,7 @@
 #include "thread/Scheduler.h"
 #include <bits/atfile.h>
 #include <bits/open-flags.h>
+#include <bits/signal.h>
 #include <bits/waitpid.h>
 #include <luna/Alloc.h>
 #include <luna/Atomic.h>
@@ -82,7 +83,9 @@ Result<SharedPtr<VFS::Inode>> Thread::resolve_atfile(int dirfd, const String& pa
             return true;
         });
 
-        if (parent && parent->state == ThreadState::Waiting)
+        if (parent)
+        {
+            if (parent->state == ThreadState::Waiting)
             {
                 auto child = *parent->child_being_waited_for;
                 if (child == -1 || child == (pid_t)id)
@@ -91,6 +94,8 @@ Result<SharedPtr<VFS::Inode>> Thread::resolve_atfile(int dirfd, const String& pa
                     parent->wake_up();
                 }
             }
+            else { parent->send_signal(SIGCHLD); }
+        }
 
         state = ThreadState::Exited;
     }
@@ -106,26 +111,40 @@ enum class DefaultSignalAction
 };
 
 static constexpr DefaultSignalAction default_actions[] = {
-    DefaultSignalAction::Terminate // SIGABRT
+    DefaultSignalAction::Terminate, // SIGHUP
+    DefaultSignalAction::Terminate, // SIGINT
+    DefaultSignalAction::Terminate, // SIGQUIT (dump core)
+    DefaultSignalAction::Terminate, // SIGILL  (dump core)
+    DefaultSignalAction::Terminate, // SIGTRAP (dump core)
+    DefaultSignalAction::Terminate, // SIGABRT (dump core)
+    DefaultSignalAction::Ignore,    // SIGCHLD
+    DefaultSignalAction::Terminate, // SIGFPE  (dump core)
+    DefaultSignalAction::Terminate, // SIGKILL
+    DefaultSignalAction::Terminate, // SIGSTOP (FIXME: Support stopping and continuing)
+    DefaultSignalAction::Terminate, // SIGSEGV (dump core)
+    DefaultSignalAction::Ignore,    // SIGCONT (FIXME: Support stopping and continuing)
+    DefaultSignalAction::Terminate, // SIGPIPE
+    DefaultSignalAction::Terminate, // SIGALRM
+    DefaultSignalAction::Terminate, // SIGTERM
 };
 
 void Thread::process_pending_signals(Registers* current_regs)
 {
     for (int i = 0; i < NSIG; i++)
     {
-        if (signal_mask & (1 << i)) continue;
+        int signo = i + 1;
+        if (signo != SIGKILL && signo != SIGSTOP && signal_mask & (1 << i)) continue;
         if (pending_signals & (1 << i))
         {
-            int signo = i + 1;
             pending_signals &= ~(1 << i);
             kinfoln("signal: executing signal %d for thread %ld", signo, id);
             auto handler = signal_handlers[i];
-            if (handler.sa_handler == SIG_IGN)
+            if (signo != SIGKILL && signo != SIGSTOP && handler.sa_handler == SIG_IGN)
             {
                 kinfoln("signal: ignoring signal (handler=SIG_IGN)");
                 return;
             }
-            if (handler.sa_handler == SIG_DFL)
+            if (handler.sa_handler == SIG_DFL || signo == SIGKILL || signo == SIGSTOP)
             {
             default_signal:
                 if (id == 1)

libc/include/bits/signal.h

@@ -18,9 +18,30 @@ struct sigaction
     void* __sa_sigreturn = nullptr;
 };
 
+// Constants for the 'how' parameter in sigprocmask().
+#define SIG_BLOCK 0
+#define SIG_UNBLOCK 1
+#define SIG_SETMASK 2
+
+// The signals with explicit numbers have portable signal numbers.
 enum __signals
 {
-    SIGABRT = 1,
+    SIGHUP = 1,
+    SIGINT = 2,
+    SIGQUIT = 3,
+    SIGILL = 4,
+    SIGTRAP = 5,
+    SIGABRT = 6,
+    SIGCHLD,
+    SIGFPE = 8,
+    SIGKILL = 9,
+    SIGSTOP,
+    SIGSEGV = 11,
+    SIGCONT,
+    SIGPIPE = 13,
+    SIGALRM = 14,
+    SIGTERM = 15,
+    // FIXME: Add the remaining signals.
     __NSIG,
 };
 

libc/include/signal.h

@@ -25,6 +25,24 @@ extern "C"
     /* Send a signal to the current thread. */
     int raise(int signo);
 
+    /* Modify the current thread's signal mask. */
+    int sigprocmask(int how, const sigset_t* set, sigset_t* oldset);
+
+    /* Clear all signals from set. */
+    int sigemptyset(sigset_t* set);
+
+    /* Add all signals to set. */
+    int sigfillset(sigset_t* set);
+
+    /* Add a specific signal to set. */
+    int sigaddset(sigset_t* set, int signo);
+
+    /* Remove a specific signal from set. */
+    int sigdelset(sigset_t* set, int signo);
+
+    /* Check if a signal is in set.*/
+    int sigismember(const sigset_t* set, int signo);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/signal.cpp

@@ -23,4 +23,57 @@ extern "C"
     {
         return kill(getpid(), signo);
     }
+
+    int sigprocmask(int how, const sigset_t* set, sigset_t* oldset)
+    {
+        long rc = syscall(SYS_sigprocmask, how, set, oldset);
+        __errno_return(rc, int);
+    }
+
+    int sigemptyset(sigset_t* set)
+    {
+        *set = 0;
+        return 0;
+    }
+
+    int sigfillset(sigset_t* set)
+    {
+        *set = 0xffffffff;
+        return 0;
+    }
+
+    int sigaddset(sigset_t* set, int signo)
+    {
+        if (signo <= 0 || signo > NSIG)
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        *set |= (1 << (signo - 1));
+        return 0;
+    }
+
+    int sigdelset(sigset_t* set, int signo)
+    {
+        if (signo <= 0 || signo > NSIG)
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        *set &= ~(1 << (signo - 1));
+        return 0;
+    }
+
+    int sigismember(const sigset_t* set, int signo)
+    {
+        if (signo <= 0 || signo > NSIG)
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        return (*set & (1 << (signo - 1))) > 0;
+    }
 }

libluna/include/luna/Syscall.h

@@ -6,7 +6,7 @@
             _e(getgid) _e(getegid) _e(setuid) _e(setgid) _e(seteuid) _e(setegid) _e(fchmodat) _e(fchownat) _e(ioctl)   \
                 _e(fstatat) _e(chdir) _e(getcwd) _e(unlinkat) _e(uname) _e(sethostname) _e(dup2) _e(pipe) _e(mount)    \
                     _e(umount) _e(pstat) _e(getrusage) _e(symlinkat) _e(readlinkat) _e(umask) _e(linkat) _e(faccessat) \
-                        _e(pivot_root) _e(sigreturn) _e(sigaction) _e(kill)
+                        _e(pivot_root) _e(sigreturn) _e(sigaction) _e(kill) _e(sigprocmask)
 
 enum Syscalls
 {