implement getchar() and putchar() in terms of supervisor call

7 files changed, 88 insertions, 20 deletions

diff --git a/Makefile b/Makefile
index d44fc2b..48bbd14 100644
--- a/Makefile
+++ b/Makefile
@@ -5,6 +5,8 @@ ARM_OBJECTS=kernel.o paging.o demo_functionality.o PL0_test.o uart.o loader_stag
 
 KERNEL_STAGE2_OBJECTS=setup.o interrupt_vector.o interrupts.o uart.o demo_functionality.o paging.o ramfs_embeddable.o ramfs.o
 
+PL_0_TEST_OBJECTS=PL0_utils.o svc.o PL0_test.o uart.o
+
 RAMFS_FILES=PL_0_test.img
 
 all : kernel.img
@@ -21,8 +23,8 @@ all : kernel.img
 %_embeddable.o : %.img
 	arm-none-eabi-objcopy -I binary -O elf32-littlearm -B arm  $^ $@
 
-PL_0_test.elf : PL0_test.ld PL0_test.o uart.o
-	arm-none-eabi-gcc -T $< -o $@ $(ELFFLAGS) PL0_test.o uart.o
+PL_0_test.elf : PL0_test.ld $(PL_0_TEST_OBJECTS)
+	arm-none-eabi-gcc -T $< -o $@ $(ELFFLAGS) $(PL_0_TEST_OBJECTS)
 
 kernel_stage1.o : kernel_stage1.S kernel_stage2.img
 	arm-none-eabi-as -mcpu=cortex-a7 $< -o $@
diff --git a/PL0_test.c b/PL0_test.c
index 2e008a2..f476eb7 100644
--- a/PL0_test.c
+++ b/PL0_test.c
@@ -1,34 +1,29 @@
-#include "uart.h"
-#include "psr.h"
+#include "PL0_utils.h"
 
 // entry point - must remain the only function in the file!
 void PL0_main(void)
 {
-  // If all went correct, Success! gets printed
-  uart_puts("Success!\n\r");
-
-  uart_puts("calling supervisor\n\r");
-  
-  asm volatile("svc #0");
-
-  uart_puts("back from supervisor call\n\r");
+  // If loading program to userspace and handling of svc are
+  // implemented correctly, this shall get printed
+  puts("Hello userspace!");
   
-  // if we're indeed in PL0, we should crash now, when trying to access
-  // memory we're not allowed to
+  // 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 meddle with kernel memory from userspace :d");
   char first_kernel_byte[2];
 
-  first_kernel_byte[0] = *(char*) ((uint32_t) 0x0);
+  first_kernel_byte[0] = *(char*) 0x0;
   first_kernel_byte[1] = '\0';
 
   uart_puts(first_kernel_byte);
     
   while (1)
     {
-      char c = uart_getc();
+      char c = getchar();
 
-      uart_putc(c);
+      putchar(c);
       
       if (c == '\r')
-	uart_putc('\n');
+	putchar('\n');
     }
 }
diff --git a/PL0_utils.c b/PL0_utils.c
new file mode 100644
index 0000000..2cede90
--- /dev/null
+++ b/PL0_utils.c
@@ -0,0 +1,27 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#include "svc_interface.h"
+
+// most generic definition possible
+// the actual function defined in svc.S
+uint32_t svc(enum svc_type, ...);
+
+void putchar(int character)
+{
+  svc(UART_PUTCHAR, character);
+}
+
+int getchar(void)
+{
+  return svc(UART_GETCHAR);
+}
+
+void puts(char *string)
+{
+  for (size_t i = 0; string[i]; i++)
+    putchar(string[i]);
+
+  putchar('\n');
+  putchar('\r');
+}
diff --git a/PL0_utils.h b/PL0_utils.h
new file mode 100644
index 0000000..ba72fd3
--- /dev/null
+++ b/PL0_utils.h
@@ -0,0 +1,10 @@
+#ifndef PL0_UTILS_H
+#define PL0_UTILS_H
+
+void putchar(int character);
+
+int getchar(void);
+
+void puts(char *string);
+
+#endif // PL0_UTILS_H
diff --git a/interrupts.c b/interrupts.c
index 7932d23..f47bc1d 100644
--- a/interrupts.c
+++ b/interrupts.c
@@ -1,4 +1,5 @@
 #include "uart.h"
+#include "svc_interface.h"
 
 void setup(void);
 
@@ -24,9 +25,26 @@ void undefined_instruction_vector(void)
     }
 }
 
-void supervisor_call_handler(void)
+uint32_t supervisor_call_handler(enum svc_type request, uint32_t arg1,
+				 uint32_t arg2, uint32_t arg3)
 {
-  uart_puts("something svc happened\n\r");
+  (void) arg2; (void) arg3; // unused for now
+  
+  switch(request) {
+  case UART_PUTCHAR:
+    uart_putc(arg1);
+    break;
+  case UART_GETCHAR:
+    return uart_getc();
+  case UART_WRITE:
+    uart_puts("UART_WRITE not implemented!!!!!\n\r");
+    break;
+  default:
+    // perhaps we should kill the process now?
+    uart_puts("unknown supervisor call type!!!!!\n\r");
+  }
+
+  return 0; // a dummy value
 }
 
 void abort_handler(void)
diff --git a/svc.S b/svc.S
new file mode 100644
index 0000000..65200d8
--- /dev/null
+++ b/svc.S
@@ -0,0 +1,5 @@
+.global svc
+
+svc:
+	svc #0
+	mov pc, lr
diff --git a/svc_interface.h b/svc_interface.h
new file mode 100644
index 0000000..aa478ce
--- /dev/null
+++ b/svc_interface.h
@@ -0,0 +1,11 @@
+#ifndef SVC_INTERFACE_H
+#define SVC_INTERFACE_H
+
+enum svc_type
+  {
+    UART_PUTCHAR,
+    UART_GETCHAR,
+    UART_WRITE
+  };
+
+#endif // SVC_INTERFACE_H