arch/x86/context.c

   1 /* tag: x86  context switching
   2  *
   3  * 2003-10 by SONE Takeshi
   4  *
   5  * See the file "COPYING" for further information about
   6  * the copyright and warranty status of this work.
   7  */
   8
   9 #include "config.h"
  10 #include "kernel/kernel.h"
  11 #include "segment.h"
  12 #include "context.h"
  13 #include "libopenbios/sys_info.h"
  14 #include "boot.h"
  15 #include "openbios.h"
  16
  17 #define MAIN_STACK_SIZE 16384
  18 #define IMAGE_STACK_SIZE 4096
  19
  20 #define debug printk
  21
  22 static void start_main(void); /* forward decl. */
  23 void __exit_context(void); /* assembly routine */
  24
  25 /*
  26  * Main context structure
  27  * It is placed at the bottom of our stack, and loaded by assembly routine
  28  * to start us up.
  29  */
  30 static struct context main_ctx __attribute__((section (".initctx"))) = {
  31     .gdt_base = (uint32_t) gdt,
  32     .gdt_limit = GDT_LIMIT,
  33     .cs = FLAT_CS,
  34     .ds = FLAT_DS,
  35     .es = FLAT_DS,
  36     .fs = FLAT_DS,
  37     .gs = FLAT_DS,
  38     .ss = FLAT_DS,
  39     .esp = (uint32_t) ESP_LOC(&main_ctx),
  40     .eip = (uint32_t) start_main,
  41     .return_addr = (uint32_t) __exit_context,
  42 };
  43
  44 /* This is used by assembly routine to load/store the context which
  45  * it is to switch/switched.  */
  46 struct context *__context = &main_ctx;
  47
  48 /* Stack for loaded ELF image */
  49 static uint8_t image_stack[IMAGE_STACK_SIZE];
  50
  51 /* Pointer to startup context (physical address) */
  52 unsigned long __boot_ctx;
  53
  54 /*
  55  * Main starter
  56  * This is the C function that runs first.
  57  */
  58 static void start_main(void)
  59 {
  60     int retval;
  61
  62     /* Save startup context, so we can refer to it later.
  63      * We have to keep it in physical address since we will relocate. */
  64     __boot_ctx = virt_to_phys(__context);
  65
  66     init_exceptions();
  67     /* Start the real fun */
  68     retval = openbios();
  69
  70     /* Pass return value to startup context. Bootloader may see it. */
  71     boot_ctx->eax = retval;
  72
  73     /* Returning from here should jump to __exit_context */
  74     __context = boot_ctx;
  75 }
  76
  77 /* Setup a new context using the given stack.
  78  */
  79 struct context *
  80 init_context(uint8_t *stack, uint32_t stack_size, int num_params)
  81 {
  82     struct context *ctx;
  83
  84     ctx = (struct context *)
  85         (stack + stack_size - (sizeof(*ctx) + num_params*sizeof(uint32_t)));
  86     memset(ctx, 0, sizeof(*ctx));
  87
  88     /* Fill in reasonable default for flat memory model */
  89     ctx->gdt_base = virt_to_phys(gdt);
  90     ctx->gdt_limit = GDT_LIMIT;
  91     ctx->cs = FLAT_CS;
  92     ctx->ds = FLAT_DS;
  93     ctx->es = FLAT_DS;
  94     ctx->fs = FLAT_DS;
  95     ctx->gs = FLAT_DS;
  96     ctx->ss = FLAT_DS;
  97     ctx->esp = virt_to_phys(ESP_LOC(ctx));
  98     ctx->return_addr = virt_to_phys(__exit_context);
  99
 100     return ctx;
 101 }
 102
 103 /* Switch to another context. */
 104 struct context *switch_to(struct context *ctx)
 105 {
 106     struct context *save, *ret;
 107
 108     debug("switching to new context:\n");
 109     save = __context;
 110     __context = ctx;
 111     asm ("pushl %cs; call __switch_context");
 112     ret = __context;
 113     __context = save;
 114     return ret;
 115 }
 116
 117 /* Start ELF Boot image */
 118 unsigned int start_elf(unsigned long entry_point, unsigned long param)
 119 {
 120     struct context *ctx;
 121
 122     ctx = init_context(image_stack, sizeof image_stack, 1);
 123     ctx->eip = entry_point;
 124     ctx->param[0] = param;
 125     ctx->eax = 0xe1fb007;
 126     ctx->ebx = param;
 127
 128     ctx = switch_to(ctx);
 129     return ctx->eax;
 130 }