Add some basic signal support.

It only works for sending a signal to a process that's in userspace code.

We implement reception by synthesizing a PUSHA+PUSHF in the receiving process
(operating on values in the TSS.)
The TSS CS:EIP is then rerouted to the signal handler and a tiny return
trampoline is constructed in a dedicated region in the receiving process.

Also hacked up /bin/kill to be able to send arbitrary signals (kill -N PID)

1 files changed, 28 insertions, 11 deletions

diff --git a/Userland/kill.cpp b/Userland/kill.cpp
index 573b58fe4c..10cc9c1b62 100644
--- a/Userland/kill.cpp
+++ b/Userland/kill.cpp
@@ -1,6 +1,7 @@
-#include <LibC/unistd.h>
-#include <LibC/stdio.h>
-#include <LibC/signal.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <signal.h>
+#include <stdlib.h>
 #include <AK/String.h>
 
 static unsigned parseUInt(const String& str, bool& ok)
@@ -18,20 +19,36 @@ static unsigned parseUInt(const String& str, bool& ok)
     return value;
 }
 
+static void print_usage_and_exit()
+{
+    printf("usage: kill [-signal] <PID>\n");
+    exit(1);
+}
+
 int main(int argc, char** argv)
 {
-    if (argc < 2) {
-        printf("usage: kill <PID>\n");
-        return 1;
-    }
+    if (argc != 2 && argc != 3)
+        print_usage_and_exit();
     bool ok;
-    unsigned value = parseUInt(argv[1], ok);
+    unsigned signum = SIGTERM;
+    int pid_argi = 1;
+    if (argc == 3) {
+        pid_argi = 2;
+        if (argv[1][0] != '-')
+            print_usage_and_exit();
+        signum = parseUInt(&argv[1][1], ok);
+        if (!ok) {
+            printf("%s is not a valid signal number\n", &argv[1][1]);
+            return 2;
+        }
+    }
+    unsigned pid = parseUInt(argv[pid_argi], ok);
     if (!ok) {
-        printf("%s is not a valid PID\n", argv[1]);
-        return 2;
+        printf("%s is not a valid PID\n", argv[pid_argi]);
+        return 3;
     }
 
-    kill((pid_t)value, SIGKILL);
+    kill((pid_t)pid, signum);
     return 0;
 }