From c374eaacbc0d16983bbd1112fefa74dbe88e1e53 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Sat, 28 Dec 2019 15:55:29 +0100
Subject: use ldm instruction instead of libkernel for entering user mode; get
 rid of libkernel (no longer needed)

---
 demo_functionality.c | 69 +++++++++++++++++-----------------------------------
 1 file changed, 22 insertions(+), 47 deletions(-)

(limited to 'demo_functionality.c')

diff --git a/demo_functionality.c b/demo_functionality.c
index 206dd2b..4b002d6 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -2,7 +2,6 @@
 #include "psr.h"
 #include "memory.h"
 #include "translation_table_descriptors.h"
-#include "libkernel.h"
 #include "ramfs.h"
 
 void demo_paging_support(void)
@@ -57,37 +56,6 @@ void demo_current_mode(void)
 #define TRANSLATION_TABLE						\
   ((short_section_descriptor_t volatile*) TRANSLATION_TABLE_BASE)
 
-extern char
-  __libkernel_start,
-  __libkernel_end,
-  __libkernel_size;
-
-void demo_setup_libkernel(void) {
-  short_section_descriptor_t volatile *libkernel_section_entry =
-    &TRANSLATION_TABLE[LIBKERNEL_SECTION_NUMBER];
-
-  short_section_descriptor_t
-    libkernel_section = *libkernel_section_entry;
-
-  // make libkernel section executable and read-only for
-  // unprivileged code
-  libkernel_section.ACCESS_PERMISSIONS_2 =
-    AP_2_0_MODEL_RW_PL1_RO_PL0 >> 2;
-  libkernel_section.ACCESS_PERMISSIONS_1_0 =
-    AP_2_0_MODEL_RW_PL1_RO_PL0 & 0b011;
-
-  *libkernel_section_entry = libkernel_section;  
-
-  // invalidate main Translation Lookup Buffer (just in case)
-  asm("mcr p15, 0, %0, c8, c7, 0\n\r"
-      "isb" :: "r" (0) : "memory");
-  
-  // copy libkernel code to libkernel section
-  for (size_t i = 0; i < (size_t) &__libkernel_size; i++)
-    ((volatile char*) LIBKERNEL_SECTION_START)[i] =
-      (&__libkernel_start)[i];
-}
-
 extern char
   _binary_ramfs_img_start,
   _binary_ramfs_img_end,
@@ -151,27 +119,34 @@ void demo_setup_PL0(void)
     ((volatile char*) VIRTUAL_PL0_MEMORY_START)[i] =
       PL_0_test_img.file_contents[i];
 
-  uart_puts("copied PL0 and libkernel code to their sections\n\r");
+  uart_puts("copied PL0 code to it's section\n\r");
+}
+
+// needed for array initialization in demo_go_unprivileged()
+void *memset(void *s, int c, size_t n)
+{
+  char *mem = s;
+  
+  for (size_t i = 0; i < n; i++)
+    mem[i] = c;
+  
+  return s;
 }
 
 void demo_go_unprivileged(void)
 {
-  size_t call_unprivileged_offset =
-    (size_t) &call_unprivileged - (size_t) &__libkernel_start;
+  uint32_t PL0_regs[16] = {0};
+  PL0_regs[15] = VIRTUAL_PL0_MEMORY_START;       // the new pc
+  PL0_regs[13] = (PL0_SECTION_NUMBER + 1) << 20; // the new sp
+
+  PSR_t new_SPSR = read_CPSR();
+  new_SPSR.fields.PSR_MODE_4_0 = MODE_USER;
+  write_SPSR(new_SPSR);
 
-  void *call_unprivileged_new_location =
-    (void*) (LIBKERNEL_SECTION_START + call_unprivileged_offset);
+  uart_puts("All ready, jumping to PL0 code\n\r");
   
-  // call call_unprivileged from libkernel
-  asm volatile("mov  r5, %0\n\r"
-	       "mov  r0, %1\n\r"
-	       "mov  r4, #0\n\r"
-  	       "movt r4, #"PL0_SECTION_NUMBER_STR"1111\n\r"
-  	       "mov  sp, r4\n\r" // setting stack is important :D
-  	       "blx  r5\n\r" ::
-	       "r" (call_unprivileged_new_location),
-	       "r" (VIRTUAL_PL0_MEMORY_START)
-	       : "memory", "r4", "r5", "r0");
+  asm volatile("ldm %0, {r0 - r15} ^" ::
+	       "r" (PL0_regs));
 }
 
 extern char
-- 
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