kernel: x86: MMU: Macros & Linker scripts for Boot time table creation

Macro is used to create a structure to specify the boot time
page table configuration. Needed by the gen_mmu.py script to generate
the actual page tables.

Linker script is needed for the following:
     1. To place the MMU page tables at 4KByte boundary.
     2. To keep the configuration structure created by
        the Macro(mentioned above).

Signed-off-by: Adithya Baglody <adithya.nagaraj.baglody@intel.com>

arch/x86/core/offsets/offsets.c

@@ -28,7 +28,7 @@
 
 #include <kernel_structs.h>
 #include <swapstk.h>
-
+#include <mmustructs.h>
 
 #include <kernel_offsets.h>
 
@@ -88,6 +88,7 @@ GEN_OFFSET_SYM(NANO_ESF, eflags);
 /* size of the ISR_LIST structure. Used by linker scripts */
 
 GEN_ABSOLUTE_SYM(__ISR_LIST_SIZEOF, sizeof(ISR_LIST));
+GEN_ABSOLUTE_SYM(__MMU_REGION_SIZEOF, sizeof(struct mmu_region));
 
 
 GEN_ABS_SYM_END

arch/x86/include/mmustructs.h

@@ -116,6 +116,30 @@
 #ifndef _ASMLANGUAGE
 #include <zephyr/types.h>
 
+/* Structure used by gen_mmu.py to create page directories and page tables.
+ * In order to populate this structure use macro MMU_BOOT_REGION.
+ */
+struct mmu_region {
+	u32_t address; /*Start address of the memory region */
+	u32_t size; /* Size of the memory region*/
+	u32_t flags; /* Permissions needed for this region*/
+};
+
+/* permission_flags are calculated using the macros
+ * region_size has to be provided in bytes
+ * for read write access = MMU_ENTRY_READ/MMU_ENTRY_WRITE
+ * for supervisor/user mode access = MMU_ENTRY_SUPERVISOR/MMU_ENTRY_USER
+ */
+
+#define MMU_BOOT_REGION(addr, region_size, permission_flags)		\
+	static struct mmu_region region_##addr				\
+	__attribute__((__section__(".mmulist"), used))  =		\
+	{								\
+		.address = addr,					\
+		.size = region_size,					\
+		.flags = permission_flags,				\
+	}
+
 /*
  * The following defines the format of a 32-bit page directory entry
  * that references a page table (as opposed to a 4 Mb page).

arch/x86/soc/ia32/linker.ld

@@ -39,6 +39,7 @@ MEMORY
      */
 
     IDT_LIST        : ORIGIN = 2K, LENGTH = 2K
+    MMU_LIST	    : ORIGIN = 4k, LENGTH = 1K
     }
 
 #include <arch/x86/linker.ld>

include/arch/x86/linker.ld

@@ -140,6 +140,13 @@ SECTIONS
 #include <custom-rwdata.ld>
 #endif
 
+#ifdef CONFIG_X86_MMU
+       /* Page Tables are located here if MMU is enabled.*/
+	. = ALIGN(4096);
+	__mmu_tables_start = .;
+	KEEP(*(.mmu_data));
+	__mmu_tables_end = .;
+#endif
 	. = ALIGN(4);
 	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
 
@@ -214,6 +221,23 @@ SECTIONS
 	KEEP(*(.gnu.linkonce.intList.*))
 	__INT_LIST_END__ = .;
 	} > IDT_LIST
+
+#ifdef CONFIG_X86_MMU
+	/* Memory management unit*/
+	SECTION_PROLOGUE(mmulist, (OPTIONAL),)
+	{
+	/* get size of the mmu lists needed for gen_mmu.py*/
+	LONG((__MMU_LIST_END__ - __MMU_LIST_START__) / __MMU_REGION_SIZEOF)
+	/* Get the start of mmu tables in data section so that the address
+	 * of the page tables can be calculated.
+	 */
+	LONG(__mmu_tables_start)
+	__MMU_LIST_START__ = .;
+	KEEP(*(.mmulist))
+	__MMU_LIST_END__ = .;
+	} > MMU_LIST
+#endif /* CONFIG_X86_MMU */
+
 #else
 	/DISCARD/ :
 	{
@@ -221,9 +245,12 @@ SECTIONS
 	KEEP(*(.spurNoErrIsr))
 	KEEP(*(.intList))
 	KEEP(*(.gnu.linkonce.intList.*))
+	KEEP(*(.mmulist))
 	}
 #endif
 
+
+
 #ifdef CONFIG_CUSTOM_SECTIONS_LD
 /* Located in project source directory */
 #include <custom-sections.ld>