use ldm instruction instead of libkernel for entering user mode; get rid of libkernel (no longer needed)

8 files changed, 40 insertions, 90 deletions

diff --git a/Makefile b/Makefile
index b8800cc..55d0d1b 100644
--- a/Makefile
+++ b/Makefile
@@ -24,7 +24,7 @@ all : kernel7.img
 PL_0_test.elf : PL0_test.o uart.o
 	arm-none-eabi-gcc -T PL0_test.ld -o $@ $(ELFFLAGS) $^
 
-kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o libkernel.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
+kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
 	arm-none-eabi-gcc -T linker.ld -o $@ $(ELFFLAGS) $^
 
 loader.elf : boot.o loader_stage1.o loader_stage2.o uart.o
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)
@@ -58,37 +57,6 @@ void demo_current_mode(void)
   ((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,
   _binary_ramfs_img_size;
@@ -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
diff --git a/kernel.c b/kernel.c
index fc629e1..9cdb82a 100644
--- a/kernel.c
+++ b/kernel.c
@@ -27,8 +27,6 @@ void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
   // prints some info and sets upp translation table, turns on MMU
   setup_flat_map();
 
-  demo_setup_libkernel();
-
   demo_setup_PL0();
 
   demo_setup_interrupts();
diff --git a/libkernel.c b/libkernel.c
deleted file mode 100644
index 0955e0e..0000000
--- a/libkernel.c
+++ /dev/null
@@ -1,12 +0,0 @@
-// This is the privileged code, that gets placed somewhere in
-// unprivileged process' address space. It's compiled as relocatable,
-// so it can be loaded at different address for different processes.
-
-void call_unprivileged(void (*address) (void)) {
-  // switch to PL0
-  asm("cps #0b10000\n\r"
-      "isb" ::: "memory");
-
-  // jump to that unprivileged code
-  address();
-}
diff --git a/libkernel.h b/libkernel.h
deleted file mode 100644
index a8af348..0000000
--- a/libkernel.h
+++ /dev/null
@@ -1,6 +0,0 @@
-#ifndef LIBKERNEL_H
-#define LIBKERNEL_H
-
-void call_unprivileged(void (*address) (void));
-
-#endif // LIBKERNEL_H
diff --git a/linker.ld b/linker.ld
index 7b585dc..673d7e2 100644
--- a/linker.ld
+++ b/linker.ld
@@ -30,17 +30,6 @@ SECTIONS
     }
     __kernel_size = __kernel_end - __kernel_start;
 
-
-    /* libkernel */
-    .libkernel :
-    {
-	__libkernel_start = .;
-	libkernel.o
-	__libkernel_end = .;
-    }
-    __libkernel_size = __libkernel_end - __libkernel_start;
-
-
     .interrupts :
     {
 	__interrupts_start = .;
diff --git a/memory.h b/memory.h
index 1c9ae35..d369694 100644
--- a/memory.h
+++ b/memory.h
@@ -24,24 +24,15 @@ extern const char __start;
 #define TRANSLATION_TABLE_END				\
   (TRANSLATION_TABLE_BASE + (uint32_t) (4096 * 4))
 
-#define LIBKERNEL_SECTION_START					\
-  (((TRANSLATION_TABLE_END - (uint32_t) 1) & ~((uint32_t) 0xfffff))	\
+#define PRIVILEGED_MEMORY_END					     \
+  (((TRANSLATION_TABLE_END - (uint32_t) 1) & ~((uint32_t) 0xfffff))  \
    + SECTION_SIZE)
 
-#define LIBKERNEL_SECTION_END			\
-  (LIBKERNEL_SECTION_START + SECTION_SIZE)
-
-// section for libkernel is flat-mapped
-#define LIBKERNEL_SECTION_NUMBER (LIBKERNEL_SECTION_START >> 20)
-
-#define PRIVILEGED_MEMORY_END LIBKERNEL_SECTION_END
-
 #define UNPRIVILEGED_MEMORY_START PRIVILEGED_MEMORY_END
 #define UNPRIVILEGED_MEMORY_END			\
   (UNPRIVILEGED_MEMORY_START + SECTION_SIZE)
 
 #define PL0_SECTION_NUMBER     ((uint32_t) 0b101010101010)
-#define PL0_SECTION_NUMBER_STR "0b101010101010"
 
 #define VIRTUAL_PL0_MEMORY_START (PL0_SECTION_NUMBER << 20)
 
diff --git a/psr.h b/psr.h
index 9809fc4..b2adafb 100644
--- a/psr.h
+++ b/psr.h
@@ -64,4 +64,19 @@ inline static PSR_t read_CPSR(void)
   return CPSR;
 }
 
+inline static PSR_t read_SPSR(void)
+{
+  PSR_t SPSR;
+  // get content of saved program status register
+  asm("mrs %0, spsr" : "=r" (SPSR.raw) :: "memory");
+  
+  return SPSR;
+}
+
+inline static void write_SPSR(PSR_t SPSR)
+{
+  // set content of saved program status register
+  asm("msr spsr, %0" :: "r" (SPSR.raw));
+}
+
 #endif // PSR_H