Implement basic sys$kill() and add a /bin/kill

All it can do right now is send SIGKILL which just murders the target task.

Kernel/Syscall.cpp

@@ -80,7 +80,6 @@ DWORD handle(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
         kprintf("syscall: seek(%d, %d)\n", arg1, arg2);
         return current->sys$seek((int)arg1, (int)arg2);
     case Syscall::PosixKill:
-        kprintf("syscall: kill(%d, %d)\n", arg1, arg2);
         return current->sys$kill((pid_t)arg1, (int)arg2);
     case Syscall::PosixGetuid:
         return current->sys$getuid();

Kernel/Task.cpp

@@ -513,6 +513,24 @@ void Task::sys$exit(int status)
     switchNow();
 }
 
+void Task::murder()
+{
+    ASSERT_INTERRUPTS_DISABLED();
+    bool wasCurrent = current == this;
+    setState(Exiting);
+    s_tasks->remove(this);
+    if (wasCurrent) {
+        MM.unmapRegionsForTask(*this);
+        if (!scheduleNewTask()) {
+            kprintf("Task::murder: Failed to schedule a new task :(\n");
+            HANG;
+        }
+    }
+    s_deadTasks->append(this);
+    if (wasCurrent)
+        switchNow();
+}
+
 void Task::taskDidCrash(Task* crashedTask)
 {
     ASSERT_INTERRUPTS_DISABLED();
@@ -749,7 +767,7 @@ int Task::sys$seek(int fd, int offset)
 {
     auto* handle = fileHandleIfExists(fd);
     if (!handle)
-        return -EBADF;
+        return -1;
     return handle->seek(offset, SEEK_SET);
 }
 
@@ -924,11 +942,15 @@ int Task::sys$kill(pid_t pid, int sig)
         // FIXME: Send to all processes.
         ASSERT(pid != -1);
     }
-    ASSERT_NOT_REACHED();
-    Task* peer = Task::fromPID(pid);
-    if (!peer) {
-        // errno = ESRCH;
-        return -1;
+    ASSERT(pid != current->pid()); // FIXME: Support this scenario.
+    InterruptDisabler disabler;
+    auto* peer = Task::fromPID(pid);
+    if (!peer)
+        return -ESRCH;
+    if (sig == 9) {
+        peer->murder();
+    } else {
+        ASSERT_NOT_REACHED();
     }
     return -1;
 }

Kernel/Task.h

@@ -216,6 +216,8 @@ private:
 
     pid_t m_parentPID { 0 };
 
+    void murder();
+
     Vector<String> m_arguments;
 };
 

Kernel/sync-sh

@@ -16,6 +16,7 @@ cp ../Userland/uname mnt/bin/uname
 cp ../Userland/clear mnt/bin/clear
 cp ../Userland/tst mnt/bin/tst
 cp ../Userland/mm mnt/bin/mm
+cp ../Userland/kill mnt/bin/kill
 cp kernel.map mnt/
 umount mnt
 sync

LibC/Makefile

@@ -16,6 +16,7 @@ LIBC_OBJS = \
        time.o \
        utsname.o \
        assert.o \
+       signal.o \
        entry.o
 
 OBJS = $(AK_OBJS) $(LIBC_OBJS)

LibC/signal.cpp

@@ -0,0 +1,14 @@
+#include "unistd.h"
+#include "errno.h"
+#include <Kernel/Syscall.h>
+
+extern "C" {
+
+int kill(pid_t pid, int sig)
+{
+    int rc = Syscall::invoke(Syscall::PosixKill, (dword)pid, (dword)sig);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
+}
+

LibC/signal.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "types.h"
+
+extern "C" {
+
+int kill(pid_t, int sig);
+
+#define SIGHUP    1
+#define SIGINT    2
+#define SIGQUIT   3 
+#define SIGILL    4 
+#define SIGTRAP   5
+#define SIGABRT   6 
+#define SIGBUS    7
+#define SIGFPE    8
+#define SIGKILL   9
+#define SIGUSR1  10
+#define SIGSEGV  11
+#define SIGUSR2  12
+#define SIGPIPE  13
+#define SIGALRM  14
+#define SIGTERM  15
+
+}
+

Userland/.gitignore

@@ -14,3 +14,4 @@ uname
 clear
 tst
 mm
+kill

Userland/Makefile

@@ -13,7 +13,8 @@ OBJS = \
        uname.o \
        clear.o \
        tst.o \
-       mm.o
+       mm.o \
+       kill.o
 
 APPS = \
        id \
@@ -30,7 +31,8 @@ APPS = \
        uname \
        clear \
        tst \
-       mm
+       mm \
+       kill
 
 ARCH_FLAGS =
 STANDARD_FLAGS = -std=c++17 -nostdinc++ -nostdlib
@@ -95,6 +97,9 @@ tst: tst.o
 mm: mm.o
 	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
 
+kill: kill.o
+	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
+
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
 

Userland/kill.cpp

@@ -0,0 +1,37 @@
+#include <LibC/unistd.h>
+#include <LibC/stdio.h>
+#include <LibC/signal.h>
+#include <AK/String.h>
+
+static unsigned parseUInt(const String& str, bool& ok)
+{
+    unsigned value = 0;
+    for (size_t i = 0; i < str.length(); ++i) {
+        if (str[i] < '0' || str[i] > '9') {
+            ok = false;
+            return 0;
+        }
+        value = value * 10;
+        value += str[i] - '0';
+    }
+    ok = true;
+    return value;
+}
+
+int main(int argc, char** argv)
+{
+    if (argc < 2) {
+        printf("usage: kill <PID>\n");
+        return 1;
+    }
+    bool ok;
+    unsigned value = parseUInt(argv[1], ok);
+    if (!ok) {
+        printf("%s is not a valid PID\n", argv[1]);
+        return 2;
+    }
+
+    kill((pid_t)value, SIGKILL);
+    return 0;
+}
+