4 files changed, 78 insertions, 0 deletions
diff --git a/src/PL0/PL0_test.c b/src/PL0/PL0_test.c
new file mode 100644
index 0000000..0bfebc7
--- /dev/null
+++ b/src/PL0/PL0_test.c
@@ -0,0 +1,34 @@
+#include "PL0_utils.h"
+
+// entry point - must remain the only function in the file!
+void PL0_main(void)
+{
+  // If loading program to userspace and handling of svc are
+  // implemented correctly, this shall get printed
+  puts("Hello userspace! Type 'f' if you want me to try accessing "
+       "kernel memory!");
+
+  while (1)
+    {
+      char c = getchar();
+      
+      if (c == '\r')
+	putchar('\n');
+      
+      putchar(c);
+      
+      if (c == 'f')
+	{
+	  // if we're indeed in PL0, we should trigger the abort
+	  // handler now, when trying to access memory we're not
+	  // allowed to
+	  puts("Attempting to read kernel memory from userspace :d");
+	  char first_kernel_byte[2];
+
+	  first_kernel_byte[0] = *(char*) 0x0;
+	  first_kernel_byte[1] = '\0';
+
+	  puts(first_kernel_byte);
+	}
+    }
+}
diff --git a/src/PL0/PL0_test.ld b/src/PL0/PL0_test.ld
new file mode 100644
index 0000000..b1d06f4
--- /dev/null
+++ b/src/PL0/PL0_test.ld
@@ -0,0 +1,19 @@
+/* linker script for creating the example userspace program PL0_test
+ */
+
+/* no ENTRY() statement - this executable is run by jumping to it */
+
+SECTIONS
+{
+    /* my thought up address userspace programs should run from */
+    . = 0xaaa00000;
+    
+    __start = .;
+    .another_weird_section_name_that_doesnt_matter :
+    {
+        /* have entry point at the beginning */
+        KEEP(PL0_test.o)
+        *(*)
+    }
+    __end = .;
+}
diff --git a/src/PL0/PL0_utils.c b/src/PL0/PL0_utils.c
new file mode 100644
index 0000000..d83edb9
--- /dev/null
+++ b/src/PL0/PL0_utils.c
@@ -0,0 +1,19 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#include "svc_interface.h"
+#include "PL0_utils.h"
+
+// most generic definition possible
+// the actual function defined in svc.S
+uint32_t svc(enum svc_type, ...);
+
+void putchar(char character)
+{
+  svc(UART_PUTCHAR, character);
+}
+
+char getchar(void)
+{
+  return svc(UART_GETCHAR);
+}
diff --git a/src/PL0/PL0_utils.h b/src/PL0/PL0_utils.h
new file mode 100644
index 0000000..c26a100
--- /dev/null
+++ b/src/PL0/PL0_utils.h
@@ -0,0 +1,6 @@
+#ifndef PL0_UTILS_H
+#define PL0_UTILS_H
+
+#include "io.h"
+
+#endif // PL0_UTILS_H