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/* tag: x86 context switching
*
* 2003-10 by SONE Takeshi
*
* See the file "COPYING" for further information about
* the copyright and warranty status of this work.
*/
#include "openbios/config.h"
#include "openbios/kernel.h"
#include "segment.h"
#include "context.h"
#include "sys_info.h"
#include "boot.h"
#define MAIN_STACK_SIZE 16384
#define IMAGE_STACK_SIZE 4096
#define debug printk
static void start_main(void); /* forward decl. */
void __exit_context(void); /* assembly routine */
/*
* Main context structure
* It is placed at the bottom of our stack, and loaded by assembly routine
* to start us up.
*/
static struct context main_ctx __attribute__((section (".initctx"))) = {
.gdt_base = (uint32_t) gdt,
.gdt_limit = GDT_LIMIT,
.cs = FLAT_CS,
.ds = FLAT_DS,
.es = FLAT_DS,
.fs = FLAT_DS,
.gs = FLAT_DS,
.ss = FLAT_DS,
.esp = (uint32_t) ESP_LOC(&main_ctx),
.eip = (uint32_t) start_main,
.return_addr = (uint32_t) __exit_context,
};
/* This is used by assembly routine to load/store the context which
* it is to switch/switched. */
struct context *__context = &main_ctx;
/* Stack for loaded ELF image */
static uint8_t image_stack[IMAGE_STACK_SIZE];
/* Pointer to startup context (physical address) */
unsigned long __boot_ctx;
/*
* Main starter
* This is the C function that runs first.
*/
static void start_main(void)
{
int retval;
extern int openbios(void);
extern void init_exceptions(void);
/* Save startup context, so we can refer to it later.
* We have to keep it in physical address since we will relocate. */
__boot_ctx = virt_to_phys(__context);
init_exceptions();
/* Start the real fun */
retval = openbios();
/* Pass return value to startup context. Bootloader may see it. */
boot_ctx->eax = retval;
/* Returning from here should jump to __exit_context */
__context = boot_ctx;
}
/* Setup a new context using the given stack.
*/
struct context *
init_context(uint8_t *stack, uint32_t stack_size, int num_params)
{
struct context *ctx;
ctx = (struct context *)
(stack + stack_size - (sizeof(*ctx) + num_params*sizeof(uint32_t)));
memset(ctx, 0, sizeof(*ctx));
/* Fill in reasonable default for flat memory model */
ctx->gdt_base = virt_to_phys(gdt);
ctx->gdt_limit = GDT_LIMIT;
ctx->cs = FLAT_CS;
ctx->ds = FLAT_DS;
ctx->es = FLAT_DS;
ctx->fs = FLAT_DS;
ctx->gs = FLAT_DS;
ctx->ss = FLAT_DS;
ctx->esp = virt_to_phys(ESP_LOC(ctx));
ctx->return_addr = virt_to_phys(__exit_context);
return ctx;
}
/* Switch to another context. */
struct context *switch_to(struct context *ctx)
{
struct context *save, *ret;
debug("switching to new context:\n");
save = __context;
__context = ctx;
asm ("pushl %cs; call __switch_context");
ret = __context;
__context = save;
return ret;
}
/* Start ELF Boot image */
unsigned int start_elf(unsigned long entry_point, unsigned long param)
{
struct context *ctx;
ctx = init_context(image_stack, sizeof image_stack, 1);
ctx->eip = entry_point;
ctx->param[0] = param;
ctx->eax = 0xe1fb007;
ctx->ebx = param;
ctx = switch_to(ctx);
return ctx->eax;
}
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