1 files changed, 40 insertions, 4 deletions
diff --git a/Userland/strace.cpp b/Userland/strace.cpp
index 374ac1cf80..bd8b9cf61b 100644
--- a/Userland/strace.cpp
+++ b/Userland/strace.cpp
@@ -1,22 +1,58 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include <string.h>
+#include <signal.h>
 #include <AK/Assertions.h>
 #include <AK/Types.h>
 #include <Kernel/Syscall.h>
 
+static int usage()
+{
+    printf("usage: strace [-p PID] [command...]\n");
+    return 0;
+}
+
 int main(int argc, char** argv)
 {
-    if (argc < 2)
-        return 1;
+    if (argc == 1)
+        return usage();
+
+    pid_t pid = -1;
+    bool pid_is_child = false;
+
+    if (!strcmp(argv[1], "-p")) {
+        if (argc != 3)
+            return usage();
+        pid = atoi(argv[2]);
+    } else {
+        pid_is_child = true;
+        pid = fork();
+        if (!pid) {
+            kill(getpid(), SIGSTOP);
+            int rc = execvp(argv[1], &argv[1]);
+            if (rc < 0) {
+                perror("execvp");
+                exit(1);
+            }
+            ASSERT_NOT_REACHED();
+        }
+    }
 
-    int pid = atoi(argv[1]);
     int fd = systrace(pid);
     if (fd < 0) {
         perror("systrace");
         return 1;
     }
 
+    if (pid_is_child) {
+        int rc = kill(pid, SIGCONT);
+        if (rc < 0) {
+            perror("kill(pid, SIGCONT)");
+            return 1;
+        }
+    }
+
     for (;;) {
         dword call[5];
         int nread = read(fd, &call, sizeof(call));
@@ -27,7 +63,7 @@ int main(int argc, char** argv)
             return 1;
         }
         ASSERT(nread == sizeof(call));
-        printf("%s(%#x, %#x, %#x) = %#x\n", Syscall::to_string((Syscall::Function)call[0]), call[1], call[2], call[3], call[4]);
+        fprintf(stderr, "%s(%#x, %#x, %#x) = %#x\n", Syscall::to_string((Syscall::Function)call[0]), call[1], call[2], call[3], call[4]);
     }
 
     int rc = close(fd);