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matos/core/cpu_context.c
Mathieu Maret 3bca737990 Add context switch 
This is taken from SOS
2019-05-15 23:22:28 +02:00

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8.1 KiB
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/* Copyright (C) 2005 David Decotigny
Copyright (C) 2000-2004, The KOS team
Initially taken from SOS
*/
#include "assert.h"
#include "klibc.h"
#include "segment.h"
#include "cpu_context.h"
/**
* Here is the definition of a CPU context for IA32 processors. This
* is a Matos/SOS convention, not a specification given by the IA32
* spec. However there is a strong constraint related to the x86
* interrupt handling specification: the top of the stack MUST be
* compatible with the 'iret' instruction, ie there must be the
* err_code (might be 0), eip, cs and eflags of the destination
* context in that order (see Intel x86 specs vol 3, figure 5-4).
*
* @note IMPORTANT: This definition MUST be consistent with the way
* the registers are stored on the stack in
* irq_wrappers.S/exception_wrappers.S !!! Hence the constraint above.
*/
struct cpu_state {
/* (Lower addresses) */
/* These are Matos/SOS convention */
uint16_t gs;
uint16_t fs;
uint16_t es;
uint16_t ds;
uint16_t cpl0_ss; /* This is ALWAYS the Stack Segment of the
Kernel context (CPL0) of the interrupted
thread, even for a user thread */
uint16_t alignment_padding; /* unused */
uint32_t eax;
uint32_t ebx;
uint32_t ecx;
uint32_t edx;
uint32_t esi;
uint32_t edi;
uint32_t ebp;
/* MUST NEVER CHANGE (dependent on the IA32 iret instruction) */
uint32_t error_code;
vaddr_t eip;
uint32_t cs; /* 32bits according to the specs ! However, the CS
register is really 16bits long */
uint32_t eflags;
/* (Higher addresses) */
} __attribute__((packed));
/**
* The CS value pushed on the stack by the CPU upon interrupt, and
* needed by the iret instruction, is 32bits long while the real CPU
* CS register is 16bits only: this macro simply retrieves the CPU
* "CS" register value from the CS value pushed on the stack by the
* CPU upon interrupt.
*
* The remaining 16bits pushed by the CPU should be considered
* "reserved" and architecture dependent. IMHO, the specs don't say
* anything about them. Considering that some architectures generate
* non-zero values for these 16bits (at least Cyrix), we'd better
* ignore them.
*/
#define GET_CPU_CS_REGISTER_VALUE(pushed_ui32_cs_value) ((pushed_ui32_cs_value)&0xffff)
/**
* Structure of an interrupted Kernel thread's context
*/
struct cpu_kstate {
struct cpu_state regs;
} __attribute__((packed));
/**
* THE main operation of a kernel thread. This routine calls the
* kernel thread function start_func and calls exit_func when
* start_func returns.
*/
static void core_routine(cpu_kstate_function_arg1_t *start_func, void *start_arg,
cpu_kstate_function_arg1_t *exit_func, void *exit_arg)
__attribute__((noreturn));
static void core_routine(cpu_kstate_function_arg1_t *start_func, void *start_arg,
cpu_kstate_function_arg1_t *exit_func, void *exit_arg)
{
start_func(start_arg);
exit_func(exit_arg);
assert(!"The exit function of the thread should NOT return !");
for (;;)
;
}
int cpu_kstate_init(struct cpu_state **ctxt, cpu_kstate_function_arg1_t *start_func,
uint32_t start_arg, vaddr_t stack_bottom, size_t stack_size,
cpu_kstate_function_arg1_t *exit_func, uint32_t exit_arg)
{
/* We are initializing a Kernel thread's context */
struct cpu_kstate *kctxt;
/* This is a critical internal function, so that it is assumed that
the caller knows what he does: we legitimally assume that values
for ctxt, start_func, stack_* and exit_func are allways VALID ! */
/* Setup the stack.
*
* On x86, the stack goes downward. Each frame is configured this
* way (higher addresses first):
*
* - (optional unused space. As of gcc 3.3, this space is 24 bytes)
* - arg n
* - arg n-1
* - ...
* - arg 1
* - return instruction address: The address the function returns to
* once finished
* - local variables
*
* The remaining of the code should be read from the end upward to
* understand how the processor will handle it.
*/
vaddr_t tmp_vaddr = stack_bottom + stack_size;
uint32_t *stack = (uint32_t *)tmp_vaddr;
/* If needed, poison the stack */
#ifdef CPU_STATE_DETECT_UNINIT_KERNEL_VARS
memset((void *)stack_bottom, CPU_STATE_STACK_POISON, stack_size);
#elif defined(CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW)
cpu_state_prepare_detect_kernel_stack_overflow(stack_bottom, stack_size);
#endif
/* Simulate a call to the core_routine() function: prepare its
arguments */
*(--stack) = exit_arg;
*(--stack) = (uint32_t)exit_func;
*(--stack) = start_arg;
*(--stack) = (uint32_t)start_func;
*(--stack) = 0; /* Return address of core_routine => force page fault */
/*
* Setup the initial context structure, so that the CPU will execute
* the function core_routine() once this new context has been
* restored on CPU
*/
/* Compute the base address of the structure, which must be located
below the previous elements */
tmp_vaddr = ((vaddr_t)stack) - sizeof(struct cpu_kstate);
kctxt = (struct cpu_kstate *)tmp_vaddr;
/* Initialize the CPU context structure */
memset(kctxt, 0x0, sizeof(struct cpu_kstate));
/* Tell the CPU context structure that the first instruction to
execute will be that of the core_routine() function */
kctxt->regs.eip = (uint32_t)core_routine;
/* Setup the segment registers */
kctxt->regs.cs = BUILD_SEGMENT_REG_VALUE(0, FALSE, SEG_KCODE); /* Code */
kctxt->regs.ds = BUILD_SEGMENT_REG_VALUE(0, FALSE, SEG_KDATA); /* Data */
kctxt->regs.es = BUILD_SEGMENT_REG_VALUE(0, FALSE, SEG_KDATA); /* Data */
kctxt->regs.cpl0_ss = BUILD_SEGMENT_REG_VALUE(0, FALSE, SEG_KDATA); /* Stack */
/* fs and gs unused for the moment. */
/* The newly created context is initially interruptible */
kctxt->regs.eflags = (1 << 9); /* set IF bit */
/* Finally, update the generic kernel/user thread context */
*ctxt = (struct cpu_state *)kctxt;
return 0;
}
#if defined(CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW)
void cpu_state_prepare_detect_kernel_stack_overflow(const struct cpu_state *ctxt,
vaddr_t stack_bottom, size_t stack_size)
{
(void)ctxt;
size_t poison_size = CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW;
if (poison_size > stack_size)
poison_size = stack_size;
memset((void *)stack_bottom, CPU_STATE_STACK_POISON, poison_size);
}
void cpu_state_detect_kernel_stack_overflow(const struct cpu_state *ctxt, vaddr_t stack_bottom,
size_t stack_size)
{
unsigned char *c;
size_t i;
/* On Matos/SOS, "ctxt" corresponds to the address of the esp register of
the saved context in Kernel mode (always, even for the interrupted
context of a user thread). Here we make sure that this stack
pointer is within the allowed stack area */
assert(((vaddr_t)ctxt) >= stack_bottom);
assert(((vaddr_t)ctxt) + sizeof(struct cpu_kstate) <= stack_bottom + stack_size);
/* Check that the bottom of the stack has not been altered */
for (c = (unsigned char *)stack_bottom, i = 0;
(i < CPU_STATE_DETECT_KERNEL_STACK_OVERFLOW) && (i < stack_size); c++, i++) {
assert(CPU_STATE_STACK_POISON == *c);
}
}
#endif
/* =======================================================================
* Public Accessor functions
*/
vaddr_t cpu_context_get_PC(const struct cpu_state *ctxt)
{
assert(NULL != ctxt);
/* This is the PC of the interrupted context (ie kernel or user
context). */
return ctxt->eip;
}
vaddr_t cpu_context_get_SP(const struct cpu_state *ctxt)
{
assert(NULL != ctxt);
/* On Matos/SOS, "ctxt" corresponds to the address of the esp register of
the saved context in Kernel mode (always, even for the interrupted
context of a user thread). */
return (vaddr_t)ctxt;
}
void cpu_context_dump(const struct cpu_state *ctxt)
{
printf("CPU: eip=%x esp=%x eflags=%x cs=%x ds=%x ss=%x err=%x", (unsigned)ctxt->eip,
(unsigned)ctxt, (unsigned)ctxt->eflags, (unsigned)GET_CPU_CS_REGISTER_VALUE(ctxt->cs),
(unsigned)ctxt->ds, (unsigned)ctxt->cpl0_ss, (unsigned)ctxt->error_code);
}
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