[palacios.git] / palacios / src / geekos / lowlevel.asm

; -*- fundamental -*-
; Low level interrupt/thread handling code for GeekOS.
; Copyright (c) 2001,2003,2004 David H. Hovemeyer <daveho@cs.umd.edu>
; Copyright (c) 2003, Jeffrey K. Hollingsworth <hollings@cs.umd.edu>
; $Revision: 1.5 $

; This is free software.  You are permitted to use,
; redistribute, and modify it as specified in the file "COPYING".

; This is 32 bit code to be linked into the kernel.
; It defines low level interrupt handler entry points that we'll use
; to populate the IDT.  It also contains the interrupt handling
; and thread context switch code.

%include "defs.asm"
%include "symbol.asm"
%include "util.asm"


[BITS 32]

; ----------------------------------------------------------------------
; Definitions
; ----------------------------------------------------------------------

; This is the size of the Interrupt_State struct in int.h
INTERRUPT_STATE_SIZE equ 64

; Save registers prior to calling a handler function.
; This must be kept up to date with:
;   - Interrupt_State struct in int.h
;   - Setup_Initial_Thread_Context() in kthread.c
%macro Save_Registers 0
        push    eax
        push    ebx
        push    ecx
        push    edx
        push    esi
        push    edi
        push    ebp
        push    ds
        push    es
        push    fs
        push    gs
%endmacro

; Restore registers and clean up the stack after calling a handler function
; (i.e., just before we return from the interrupt via an iret instruction).
%macro Restore_Registers 0
        pop     gs
        pop     fs
        pop     es
        pop     ds
        pop     ebp
        pop     edi
        pop     esi
        pop     edx
        pop     ecx
        pop     ebx
        pop     eax
        add     esp, 8  ; skip int num and error code
%endmacro

; Code to activate a new user context (if necessary), before returning
; to executing a thread.  Should be called just before restoring
; registers (because the interrupt context is used).
%macro Activate_User_Context 0  
        ; If the new thread has a user context which is not the current
        ; one, activate it.
        push    esp                     ; Interrupt_State pointer
        push    dword [g_currentThread] ; Kernel_Thread pointer
;       call    Switch_To_User_Context 
        add     esp, 8                  ; clear 2 arguments
%endmacro

; Number of bytes between the top of the stack and
; the interrupt number after the general-purpose and segment
; registers have been saved.
REG_SKIP equ (11*4)

; Template for entry point code for interrupts that have
; an explicit processor-generated error code.
; The argument is the interrupt number.
%macro Int_With_Err 1
align 8
        push    dword %1        ; push interrupt number
        jmp     Handle_Interrupt ; jump to common handler
%endmacro

; Template for entry point code for interrupts that do not
; generate an explicit error code.  We push a dummy error
; code on the stack, so the stack layout is the same
; for all interrupts.
%macro Int_No_Err 1
align 8
        push    dword 0         ; fake error code
        push    dword %1        ; push interrupt number
        jmp     Handle_Interrupt ; jump to common handler
%endmacro


; ----------------------------------------------------------------------
; Symbol imports and exports
; ----------------------------------------------------------------------

; This symbol is defined in idt.c, and is a table of addresses
; of C handler functions for interrupts.
IMPORT g_interruptTable

; Global variable pointing to context struct for current thread.
IMPORT g_currentThread

; Set to non-zero when we need to choose a new thread
; in the interrupt return code.
IMPORT g_needReschedule

; Set to non-zero when preemption is disabled.
IMPORT g_preemptionDisabled

; This is the function that returns the next runnable thread.
IMPORT Get_Next_Runnable

; Function to put a thread on the run queue.
IMPORT Make_Runnable

; Function to activate a new user context (if needed).
IMPORT Switch_To_User_Context

; Sizes of interrupt handler entry points for interrupts with
; and without error codes.  The code in idt.c uses this
; information to infer the layout of the table of interrupt
; handler entry points, without needing a separate linker
; symbol for each one (which is quite tedious to type :-)
EXPORT g_handlerSizeNoErr
EXPORT g_handlerSizeErr

; Simple functions to load the IDTR, GDTR, and LDTR.
EXPORT Load_IDTR
EXPORT Load_GDTR
EXPORT Load_LDTR

; Beginning and end of the table of interrupt entry points.
EXPORT g_entryPointTableStart
EXPORT g_entryPointTableEnd

; Thread context switch function.
EXPORT Switch_To_Thread

; Return current value of eflags register.
EXPORT Get_Current_EFLAGS

; Return the return address
EXPORT Get_EIP
; ESP
EXPORT Get_ESP
; EBP
EXPORT Get_EBP

; Virtual memory support.
EXPORT Enable_Paging
EXPORT Set_PDBR
EXPORT Get_PDBR
EXPORT Flush_TLB

; CPUID functions
EXPORT cpuid_ecx
EXPORT cpuid_eax
EXPORT cpuid_edx

; Utility Functions
EXPORT Set_MSR
EXPORT Get_MSR


EXPORT Get_CR2
EXPORT Get_CR3


EXPORT Proc_test

; ----------------------------------------------------------------------
; Code
; ----------------------------------------------------------------------

[SECTION .text]

; Load IDTR with 6-byte pointer whose address is passed as
; the parameter.
align 8
Load_IDTR:
        mov     eax, [esp+4]
        lidt    [eax]
        ret

;  Load the GDTR with 6-byte pointer whose address is
; passed as the parameter.  Assumes that interrupts
; are disabled.
align 8
Load_GDTR:
        mov     eax, [esp+4]
        lgdt    [eax]
        ; Reload segment registers
        mov     ax, KERNEL_DS
        mov     ds, ax
        mov     es, ax
        mov     fs, ax
        mov     gs, ax
        mov     ss, ax
        jmp     KERNEL_CS:.here
.here:
        ret

; Load the LDT whose selector is passed as a parameter.
align 8
Load_LDTR:
        mov     eax, [esp+4]
        lldt    ax
        ret

;
; Start paging
;       load crt3 with the passed page directory pointer
;       enable paging bit in cr2
align 8
Enable_Paging:
        push    ebp
        mov     ebp, esp
        push    eax
        push    ebx
        mov     eax, [ebp+8]
        mov     cr3, eax
        mov     eax, cr3
        mov     cr3, eax
        mov     ebx, cr0
        or      ebx, 0x80000000
        mov     cr0, ebx
        pop     ebx
        pop     eax
        pop     ebp
        ret




        
;
; Change PDBR 
;       load cr3 with the passed page directory pointer
align 8
Set_PDBR:
        mov     eax, [esp+4]
        mov     cr3, eax
        ret

;
; Get the current PDBR.
; This is useful for lazily switching address spaces;
; only switch if the new thread has a different address space.
;
align 8
Get_PDBR:
        mov     eax, cr3
        ret

;
; Flush TLB - just need to re-load cr3 to force this to happen
;
align 8
Flush_TLB:
        mov     eax, cr3
        mov     cr3, eax
        ret



;
; cpuid_edx - return the edx register from cpuid
;
align 8
cpuid_edx:
        push    ebp
        mov     ebp, esp
        push    edx
        push    ecx
        push    ebx

        mov     eax, [ebp + 8]
        cpuid
        mov     eax, edx

        pop     ebx
        pop     ecx
        pop     edx
        pop     ebp
        ret


;
; cpuid_ecx - return the ecx register from cpuid
;
align 8
cpuid_ecx:
        push    ebp
        mov     ebp, esp
        push    edx
        push    ecx
        push    ebx

        mov     eax, [ebp + 8]
        cpuid
        mov     eax, ecx

        pop     ebx
        pop     ecx
        pop     edx
        pop     ebp
        ret

;
; cpuid_eax - return the eax register from cpuid
;
align 8
cpuid_eax:
        push    ebp
        mov     ebp, esp
        push    edx
        push    ecx
        push    ebx

        mov     eax, [esp+4]
        cpuid

        pop     ebx
        pop     ecx
        pop     edx
        pop     ebp
        ret

;
; Set_MSR  - Set the value of a given MSR
;
align 8
Set_MSR:
        push    ebp
        mov     ebp, esp
        pusha
        mov     eax, [ebp+16]
        mov     edx, [ebp+12]
        mov     ecx, [ebp+8]
        wrmsr
        popa
        pop     ebp
        ret



;
; Get_MSR  -  Get the value of a given MSR
; void Get_MSR(int MSR, void * high_byte, void * low_byte);
;
align 8
Get_MSR:
        push    ebp
        mov     ebp, esp
        pusha
        mov     ecx, [ebp+8]
        rdmsr
        mov     ebx, [ebp+12]
        mov     [ebx], edx
        mov     ebx, [ebp+16]
        mov     [ebx], eax
        popa
        pop     ebp
        ret




align 8
Get_CR2:
        mov     eax, cr2
        ret


align 8
Get_CR3:
        mov     eax, cr3
        ret

align 8
Proc_test:
        push    ebp
        mov     ebp, esp
        push    ebx
        mov     ebx, [ebp + 8]
        mov     eax, [ebp + 12]

        add     eax, ebx
        pop     ebx
        pop     ebp
        ret


; Common interrupt handling code.
; Save registers, call C handler function,
; possibly choose a new thread to run, restore
; registers, return from the interrupt.
align 8
Handle_Interrupt:
        ; Save registers (general purpose and segment)
        Save_Registers

        ; Ensure that we're using the kernel data segment
        mov     ax, KERNEL_DS
        mov     ds, ax
        mov     es, ax

        ; Get the address of the C handler function from the
        ; table of handler functions.
        mov     eax, g_interruptTable   ; get address of handler table
        mov     esi, [esp+REG_SKIP]     ; get interrupt number
        mov     ebx, [eax+esi*4]        ; get address of handler function

        ; Call the handler.
        ; The argument passed is a pointer to an Interrupt_State struct,
        ; which describes the stack layout for all interrupts.
        push    esp
        call    ebx
        add     esp, 4                  ; clear 1 argument

        ; If preemption is disabled, then the current thread
        ; keeps running.
        cmp     [g_preemptionDisabled], dword 0
        jne     .restore

        ; See if we need to choose a new thread to run.
        cmp     [g_needReschedule], dword 0
        je      .restore

        ; Put current thread back on the run queue
        push    dword [g_currentThread]
        call    Make_Runnable
        add     esp, 4                  ; clear 1 argument

        ; Save stack pointer in current thread context, and
        ; clear numTicks field.
        mov     eax, [g_currentThread]
        mov     [eax+0], esp            ; esp field
        mov     [eax+4], dword 0        ; numTicks field

        ; Pick a new thread to run, and switch to its stack
        call    Get_Next_Runnable
        mov     [g_currentThread], eax
        mov     esp, [eax+0]            ; esp field

        ; Clear "need reschedule" flag
        mov     [g_needReschedule], dword 0

.restore:
        ; Activate the user context, if necessary.
        Activate_User_Context

        ; Restore registers
        Restore_Registers

        ; Return from the interrupt.
        iret

; ----------------------------------------------------------------------
; Switch_To_Thread()
;   Save context of currently executing thread, and activate
;   the thread whose context object is passed as a parameter.
; 
; Parameter: 
;   - ptr to Kernel_Thread whose state should be restored and made active
;
; Notes:
; Called with interrupts disabled.
; This must be kept up to date with definition of Kernel_Thread
; struct, in kthread.h.
; ----------------------------------------------------------------------
align 16
Switch_To_Thread:
        ; Modify the stack to allow a later return via an iret instruction.
        ; We start with a stack that looks like this:
        ;
        ;            thread_ptr
        ;    esp --> return addr
        ;
        ; We change it to look like this:
        ;
        ;            thread_ptr
        ;            eflags
        ;            cs
        ;    esp --> return addr

        push    eax             ; save eax
        mov     eax, [esp+4]    ; get return address
        mov     [esp-4], eax    ; move return addr down 8 bytes from orig loc
        add     esp, 8          ; move stack ptr up
        pushfd                  ; put eflags where return address was
        mov     eax, [esp-4]    ; restore saved value of eax
        push    dword KERNEL_CS ; push cs selector
        sub     esp, 4          ; point stack ptr at return address

        ; Push fake error code and interrupt number
        push    dword 0
        push    dword 0

        ; Save general purpose registers.
        Save_Registers

        ; Save stack pointer in the thread context struct (at offset 0).
        mov     eax, [g_currentThread]
        mov     [eax+0], esp

        ; Clear numTicks field in thread context, since this
        ; thread is being suspended.
        mov     [eax+4], dword 0

        ; Load the pointer to the new thread context into eax.
        ; We skip over the Interrupt_State struct on the stack to
        ; get the parameter.
        mov     eax, [esp+INTERRUPT_STATE_SIZE]

        ; Make the new thread current, and switch to its stack.
        mov     [g_currentThread], eax
        mov     esp, [eax+0]

        ; Activate the user context, if necessary.
        Activate_User_Context

        ; Restore general purpose and segment registers, and clear interrupt
        ; number and error code.
        Restore_Registers

        ; We'll return to the place where the thread was
        ; executing last.
        iret

; Return current contents of eflags register.
align 16
Get_Current_EFLAGS:
        pushfd                  ; push eflags
        pop     eax             ; pop contents into eax
        ret



; Return the eip of the next instruction after the caller
align 16
Get_EIP:
        mov     eax, [esp]
        ret

; Return the current esp in the procedure
align 16
Get_ESP:
        mov     eax, esp
        ret

; Return the current ebp in the procedure
align 16
Get_EBP:
        mov     eax, ebp
        ret



; ----------------------------------------------------------------------
; Generate interrupt-specific entry points for all interrupts.
; We also define symbols to indicate the extend of the table
; of entry points, and the size of individual entry points.
; ----------------------------------------------------------------------
align 8
g_entryPointTableStart:

; Handlers for processor-generated exceptions, as defined by
; Intel 486 manual.
Int_No_Err 0
align 8
Before_No_Err:
Int_No_Err 1
align 8
After_No_Err:
Int_No_Err 2    ; FIXME: not described in 486 manual
Int_No_Err 3
Int_No_Err 4
Int_No_Err 5
Int_No_Err 6
Int_No_Err 7
align 8
Before_Err:
Int_With_Err 8
align 8
After_Err:
Int_No_Err 9    ; FIXME: not described in 486 manual
Int_With_Err 10
Int_With_Err 11
Int_With_Err 12
Int_With_Err 13
Int_With_Err 14
Int_No_Err 15   ; FIXME: not described in 486 manual
Int_No_Err 16
Int_With_Err 17

; The remaining interrupts (18 - 255) do not have error codes.
; We can generate them all in one go with nasm's %rep construct.
%assign intNum 18
%rep (256 - 18)
Int_No_Err intNum
%assign intNum intNum+1
%endrep

align 8
g_entryPointTableEnd:

[SECTION .data]

; Exported symbols defining the size of handler entry points
; (both with and without error codes).
align 4
g_handlerSizeNoErr: dd (After_No_Err - Before_No_Err)
align 4
g_handlerSizeErr: dd (After_Err - Before_Err)