create a separate library for kernel code that should run in PL0 mode

5 files changed, 113 insertions, 18 deletions

diff --git a/Makefile b/Makefile
index ce29a19..f07bced 100644
--- a/Makefile
+++ b/Makefile
@@ -3,6 +3,10 @@ ELFFLAGS=-ffreestanding -O2 -nostdlib -lgcc -I.
 
 ARM_OBJECTS=kernel.o paging.o demo_functionality.o PL0_test.o uart.o loader_stage1.o loader_stage2.o
 
+EMBEDDABLE_OBJECTS=PL_0_test_embeddable.o loader_stage2_embeddable.o
+
+RENAME_FLAGS=--rename-section .data=.renamed_data --rename-section .rodata=.renamed_rodata --rename-section .text=.renamed_text --rename-section .bss=.renamed_bss
+
 all : kernel7.img
 
 %.o : %.c
@@ -17,10 +21,16 @@ all : kernel7.img
 %_embeddable.o : %.img
 	arm-none-eabi-objcopy -I binary -O elf32-littlearm -B arm --rename-section .data=.rodata $^ $@
 
+libkernel.o : libkernel.c
+	arm-none-eabi-gcc $(CFLAGS) -fPIC -c $^ -o $@
+
+libkernel_renamed.o : libkernel.o
+	arm-none-eabi-objcopy $(RENAME_FLAGS) $^ $@
+
 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 PL_0_test_embeddable.o demo_functionality.o paging.o
+kernel.elf : boot.o kernel.o uart.o PL_0_test_embeddable.o demo_functionality.o paging.o libkernel_renamed.o
 	arm-none-eabi-gcc -T linker.ld -o $@ $(ELFFLAGS) $^
 
 loader_stage2.elf : loader_stage2.o uart.o
diff --git a/PL0_test.c b/PL0_test.c
index 2216436..1b93024 100644
--- a/PL0_test.c
+++ b/PL0_test.c
@@ -5,9 +5,6 @@ void PL0_main(void)
 {
   uart_puts("hello PL0! Switching to user mode!\n\r");
 
-  asm("cps #0b10000\n\r"
-      "isb" ::: "memory");
-
   // if all went correct, Success! gets printed
   uart_puts("Success!\n\r");
 
diff --git a/demo_functionality.c b/demo_functionality.c
index eddb1d2..753a7d3 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -2,6 +2,7 @@
 #include "psr.h"
 #include "memory.h"
 #include "translation_table_descriptors.h"
+#include "libkernel.h"
 
 void demo_paging_support(void)
 {
@@ -56,6 +57,11 @@ void demo_mode_to_system(void)
 }
 
 extern char
+  __renamed_start,
+  __renamed_end,
+  __renamed_size;
+
+extern char
   _binary_PL_0_test_img_start,
   _binary_PL_0_test_img_end,
   _binary_PL_0_test_img_size;
@@ -65,15 +71,26 @@ void demo_go_unprivileged(void)
   short_section_descriptor_t *translation_table =
     (short_section_descriptor_t*) TRANSLATION_TABLE_BASE;
 
+  short_section_descriptor_t volatile *libkernel_section_entry =
+    &translation_table[LIBKERNEL_SECTION_NUMBER];
   short_section_descriptor_t volatile *PL0_section_entry =
     &translation_table[PL0_SECTION_NUMBER];
   short_section_descriptor_t volatile *UART_memory_section_entry =
     &translation_table[((uint32_t) GPIO_BASE) >> 20];
 
   short_section_descriptor_t
+    libkernel_section = *libkernel_section_entry,
     PL0_section = *PL0_section_entry,
     UART_memory_section = *UART_memory_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;
+  
+  // set up address of PL0 section
   PL0_section.SECTION_BASE_ADDRESS_31_20 =
     UNPRIVILEGED_MEMORY_START >> 20;
 
@@ -88,6 +105,7 @@ void demo_go_unprivileged(void)
   UART_memory_section.ACCESS_PERMISSIONS_1_0 =
     AP_2_0_MODEL_RW_ALL & 0b011;
 
+  *libkernel_section_entry = libkernel_section;
   *PL0_section_entry = PL0_section;
   *UART_memory_section_entry = UART_memory_section;
 
@@ -105,17 +123,32 @@ void demo_go_unprivileged(void)
   
   uart_puts((char*) VIRTUAL_PL0_MEMORY_START);
 
-  // now paste a userspace program to that section, jump to it and
-  // switch to PL0
+  // copy libkernel code to libkernel section
+  for (size_t i = 0; i < (size_t) &__renamed_size; i++)
+    ((volatile char*) LIBKERNEL_SECTION_START)[i] =
+      (&__renamed_start)[i];  
+  
+  // now paste a userspace program to that section
   for (size_t i = 0; i < (size_t) &_binary_PL_0_test_img_size; i++)
     ((volatile char*) VIRTUAL_PL0_MEMORY_START)[i] =
       (&_binary_PL_0_test_img_start)[i];
 
-  // jump to that copied code (switch to PL0 is done by that code)
-  asm volatile("mov  r5, #0\n\r"
-  	       "movt r5, #"PL0_SECTION_NUMBER_STR"1111\n\r"
-  	       "mov  sp, r5\n\r" // setting stack is important :D
-  	       "mov  r5, #0\n\r"
-  	       "movt r5, #"PL0_SECTION_NUMBER_STR"0000\n\r"
-  	       "blx  r5\n\r");
+  uart_puts("copied PL0 and libkernel code to their sections");
+  
+  size_t call_unprivileged_offset =
+    (size_t) &call_unprivileged - (size_t) &__renamed_start;
+
+  void *call_unprivileged_new_location =
+    (void*) (LIBKERNEL_SECTION_START + call_unprivileged_offset);
+  
+  // 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");
 }
diff --git a/linker.ld b/linker.ld
index e7bfdb8..199cc0f 100644
--- a/linker.ld
+++ b/linker.ld
@@ -49,5 +49,46 @@ SECTIONS
     . = ALIGN(4096); /* align to page size */
     __bss_end = .;
     __bss_size = __bss_end - __bss_start;
+
+
+
+    /* Here come the definitions for renamed sections */
+    __renamed_start = .;
+    __renamed_text_start = .;
+    .renamed_text :
+    {
+        *(.renamed_text)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __renamed_text_end = .;
+ 
+    __renamed_rodata_start = .;
+    .renamed_rodata :
+    {
+        *(.renamed_rodata)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __renamed_rodata_end = .;
+ 
+    __renamed_data_start = .;
+    .renamed_data :
+    {
+        *(.renamed_data)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __renamed_data_end = .;
+ 
+    __renamed_bss_start = .;
+    .renamed_bss :
+    {
+        renamed_bss = .;
+        *(.renamed_bss)
+    }
+    . = ALIGN(4096); /* align to page size */
+    __renamed_bss_end = .;
+    __renamed_bss_size = __renamed_bss_end - __renamed_bss_start;
+    __renamed_end = .;
+    __renamed_size = __renamed_end - __renamed_start;
+    
     __end = .;
 }
diff --git a/memory.h b/memory.h
index 1472a8b..2211c9d 100644
--- a/memory.h
+++ b/memory.h
@@ -1,6 +1,10 @@
 #ifndef MEMORY_H
 #define MEMORY_H
 
+#include "paging.h"
+
+#define SECTION_SIZE (((uint32_t) 1) << 20)
+
 #define INTERRUPT_VECTOR_TABLE_START ((uint32_t) 0x0)
 
 #define STACK_START ((uint32_t) 0x4000)
@@ -20,11 +24,21 @@ extern char __start;
 #define TRANSLATION_TABLE_END				\
   (TRANSLATION_TABLE_BASE + (uint32_t) (4096 * 4))
 
-#define PRIVILEGED_MEMORY_END TRANSLATION_TABLE_END
+#define LIBKERNEL_SECTION_START					\
+  (((TRANSLATION_TABLE_END - (uint32_t) 1) & ~((uint32_t) 0xfffff))	\
+   + SECTION_SIZE)
+
+#define LIBKERNEL_SECTION_END			\
+  (LIBKERNEL_SECTION_START + SECTION_SIZE)
 
-#define UNPRIVILEGED_MEMORY_START					\
-  (((PRIVILEGED_MEMORY_END - (uint32_t) 1) & ~((uint32_t) 0xfffff))	\
-   + (uint32_t) 0x100000)
+// 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"
@@ -32,4 +46,4 @@ extern char __start;
 #define VIRTUAL_PL0_MEMORY_START (PL0_SECTION_NUMBER << 20)
 
 #endif // MEMORY_H
- 
+