execute user code

can't halt yet, but that's fine.

kernel/Syscalls/execute.c

 #include <types.h>
 #include <lib.h>
+#include <x86_desc.h>
 #include <Devices/Storage/ext2.h>
 #include <paging.h>
 
 #include "execute.h"
 
+#define PCB_MASK	0xffffe000
+
 // TEMPORARY!!!
 static uint32_t pid = 0;
 
+void get_ret_addr()
+{
+	uint32_t ret_eip;
+
+	// get the return address from the stack. 
+	asm volatile ("         \n\
+	mov 20(%%esp), %0"
+	: "=r"(ret_eip));
+
+	// add 1 so it skips over the iret;
+	ret_eip++;
+
+	// don't pass in pcb pointers cause this should be easy to call from asm
+	pcb_t* pcb = (pcb_t*)(_8MB - _8KB - _8KB*pid);
+	pcb->execute_return = ret_eip;
+}
+
+pcb_t* get_pcb_ptr()
+{
+	pcb_t* pcb;
+
+	/* get the PCB pointer passed from assembly */
+	asm volatile("              \n\
+		andl %%esp, %%eax       \n\
+		movl %%eax, %0"
+		: "=r"(pcb)
+		: "a"(PCB_MASK)
+		);
+
+	return pcb;
+}
+
+
 int32_t _sys_exec(uint8_t* name)
 {
 	printf("In _sys_exec\n");
@@ -36,14 +72,54 @@ int32_t _sys_exec(uint8_t* name)
 	map_large(EXEC_BASE_ADDR, _8MB + pid * _4MB);
 	ext2_read_data(parsed_inode, 0, (uint16_t*)EXEC_LOAD_ADDR);
 
-	printf("Some code for you: ");
+	/* populate tss */
+	tss.ss0 = KERNEL_DS;
+	tss.esp0 = _8MB - _8KB*pid - 4;
+
+	pcb_t* pcb = (pcb_t*)(_8MB - _8KB - _8KB*pid);
+	pcb->pid = pid;
+	pcb->parent_pid = get_pcb_ptr()->pid;
+
+
+	/* increment pid and run process; decrement it after termination */
+	pid++;
+
+	uint32_t status;
+
+	printf("Some code for you: %x\n", header->e_entry);
 	int i;
 	for (i = 0; i < 16; i++) {
 		printf("%x ", *((uint8_t*)(header->e_entry) + i));
 	}
 	printf("\n");
 
-	return 1;
+	printf("gonna execute now, wish me luck! %x\n", header->e_entry);
+
+	/* push use data segment, user stack pointer,
+	* flags, user code segment, entry point, then iret */
+	asm volatile("           \n\
+	movl %%ebp, %0       \n\
+	movl %%esp, %1       \n\
+	pushl $0x2B          \n\
+	pushl $0x83ffffc     \n\
+	pushfl               \n\
+	pop %%eax            \n\
+	orl $0x200, %%eax    \n\
+	push %%eax           \n\
+	pushl $0x23          \n\
+	pushl %3             \n\
+	call get_ret_addr    \n\
+	iret                 \n\
+	pop %2"
+	: "=m"(pcb->parent_ebp), "=m"(pcb->parent_esp), "=m"(status)
+	: "r"(header->e_entry)
+	: "%eax"
+	);
+
+	pid--;
+
+
+	return status;
 }
 
 int32_t _sys_exit()

kernel/Syscalls/execute.h

@@ -49,7 +49,7 @@
 
 #define EI_NIDENT 16
 
-typedef struct {
+typedef struct elf_header{
         uint8_t  e_ident[EI_NIDENT];
         uint16_t e_type;
         uint16_t e_machine;
@@ -66,6 +66,14 @@ typedef struct {
         uint16_t e_shstrndx;
 } elf_header_t;
 
+typedef struct pcb {
+	uint32_t pid;
+	uint32_t parent_pid;
+	uint32_t parent_ebp;
+	uint32_t parent_esp;
+	uint32_t execute_return;
+} pcb_t;
+
 int32_t _sys_exec(uint8_t* name);
 int32_t _sys_exit();
 

kernel/Syscalls/syscalls.c

@@ -13,6 +13,10 @@ int32_t sys_read(int32_t fd, const void* buf, int32_t len)
 int32_t sys_write(int32_t fd, const void* buf, int32_t len)
 {
 	printf("syswrite\n");
+	int i;
+	for (i = 0; i < len; i++) {
+		putc(*((uint8_t*)buf + i));
+	}
 	return -1;
 }
 

kernel/kernel.c

@@ -103,8 +103,6 @@ void entry(unsigned long magic, unsigned long addr) {
 	init_paging();
 	kmap_large(fb_addr, fb_addr);
 
-	printf("Does this work?\n");
-
 	i8259_init();
 	interrupts_init();
 	i8259_enable_irq(1);
@@ -119,7 +117,6 @@ void entry(unsigned long magic, unsigned long addr) {
 	ata_read_sectors(ATA_MASTER, 0, 1, mbr.data);
 	ext2_init(mbr.partitions[0].lba_start);
 
-
 	int32_t error = sys_exec((uint8_t*)"/Programs/bin/hello");
 	if (error) {
 		printf("Error executing file: %d\n", error);

kernel/lib.h

@@ -8,6 +8,7 @@
 
 #define _4MB 0x400000
 #define _8MB 0x800000
+#define _8KB 0x2000
 
 
 typedef struct bmp {