FreeBSD/Linux Kernel Cross Reference
sys/compat/ndis/winx32_wrap.S

     /*-
      * Copyright (c) 2005
      *      Bill Paul <wpaul@windriver.com>.  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Bill Paul.
     * 4. Neither the name of the author nor the names of any co-contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY Bill Paul AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL Bill Paul OR THE VOICES IN HIS HEAD
     * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
     * THE POSSIBILITY OF SUCH DAMAGE.
     *
     * $FreeBSD: releng/6.0/sys/compat/ndis/winx32_wrap.S 151742 2005-10-27 17:08:57Z wpaul $
     */
    
    #include <machine/asmacros.h>
    
    /*
     * This file contains assembly language wrappers for the different
     * calling conventions supported by Windows on the i386 architecture.
     * In FreeBSD, the whole OS typically use same C calling convention
     * everywhere, namely _cdecl. Windows, on the other hand, uses several
     * different C calling conventions depending on the circumstances:
     *
     * _stdcall: Used for most ordinary Windows APIs. With _stdcall,
     * arguments are passed on the stack, and the callee unwinds the stack
     * before returning control to the caller. Not suitable for variadic
     * functions.
     *
     * _fastcall: Used for some APIs that may be invoked frequently and
     * where speed is a critical factor (e.g. KeAcquireSpinLock() and
     * KeReleaseSpinLock()) Similar to _stdcall, except the first 2 32-bit
     * or smaller arguments are passed in the %ecx and %edx registers
     * instead of on the stack. Not suitable for variadic functions.
     *
     * _cdecl: Used for standard C library routines and for variadic
     * functions.
     *
     * _regparm(3): Used for certain assembly routines. All arguments
     * passed in %eax, %ecx and %edx.
     *
     * Furthermore, there is an additional wrinkle that's not obvious
     * with all code: Microsoft supports the use of exceptions in C
     * (__try/__except) both in user _and_ kernel mode. Sadly, Windows
     * structured exception handling uses machine-specific features
     * that conflict rather badly with FreeBSD. (See utility routines
     * at the end of this module for more details.)
     *
     * We want to support these calling conventions in as portable a manner
     * as possible. The trick is doing it not only with different versions
     * of GNU C, but with compilers other than GNU C (e.g. the Solaris
     * SunOne C compiler). The only sure fire method is with assembly
     * language trampoline code which both fixes up the argument passing,
     * stack unwinding and exception/thread context all at once.
     *
     * You'll notice that we call the thunk/unthunk routines in the
     * *_wrap() functions in an awkward way. Rather than branching
     * directly to the address, we load the address into a register
     * first as a literal value, then we branch to it. This is done
     * to insure that the assembler doesn't translate the branch into
     * a relative branch. We use the *_wrap() routines here as templates
     * and create the actual trampolines at run time, at which point
     * we only know the absolute addresses of the thunk and unthunk
     * routines. So we need to make sure the templates have enough
     * room in them for the full address.
     *
     * Also note that when we call the a thunk/unthunk routine after
     * invoking a wrapped function, we have to make sure to preserve
     * the value returned from that function. Most functions return
     * a 32-bit value in %eax, however some routines return 64-bit
     * values, which span both %eax and %edx. Consequently, we have
     * to preserve both registers.
     */
    
    /*
     * Handle _stdcall going from Windows to UNIX.
     * This is frustrating, because to do it right you have to
     * know how many arguments the called function takes, and there's
     * no way to figure this out on the fly: you just have to be told
     * ahead of time. We assume there will be 16 arguments. I don't
    * think there are any Windows APIs that require this many.
    */
    
           .globl x86_stdcall_wrap_call
           .globl x86_stdcall_wrap_arg
           .globl x86_stdcall_wrap_end
   
   ENTRY(x86_stdcall_wrap)
           push    %esi
           push    %edi
           sub     $64,%esp
           mov     %esp,%esi
           add     $64+8+4,%esi
           mov     %esp,%edi
           mov     $16,%ecx        # handle up to 16 args
           rep
           movsl
   
           movl    $ctxsw_wtou, %eax
           call    *%eax           # unthunk
   
   x86_stdcall_wrap_call:
           movl    $0,%eax
           call    *%eax           # jump to routine
           push    %eax            # preserve return val
           push    %edx
   
           movl    $ctxsw_utow, %eax
           call    *%eax           # thunk
   
           pop     %edx
           pop     %eax            # restore return val
   
           add     $64,%esp        # clean the stack
           pop     %edi
           pop     %esi
   x86_stdcall_wrap_arg:
           ret     $0xFF
   x86_stdcall_wrap_end:
   
   
   /*
    * Handle _stdcall going from UNIX to Windows. This routine
    * expects to be passed the function to be called, number of
    * args and the arguments for the Windows function on the stack.
    */
   
   ENTRY(x86_stdcall_call)
           push    %esi            # must preserve %esi
           push    %edi            # and %edi
   
           mov     16(%esp),%eax   # get arg cnt
           mov     %eax,%ecx       # save as copy count
           mov     %esp,%esi       # Set source address register to point to
           add     $20,%esi        # first agument to be forwarded.
           shl     $2,%eax         # turn arg cnt into offset
           sub     %eax,%esp       # shift stack to new location 
           mov     %esp,%edi       # store dest copy addr
           rep                     # do the copy
           movsl
   
           call    ctxsw_utow      # thunk
   
           call    *12(%edi)       # branch to stdcall routine
           push    %eax            # preserve return val
           push    %edx
   
           call    ctxsw_wtou      # unthunk
   
           pop     %edx
           pop     %eax            # restore return val
           mov     %edi,%esp       # restore stack
           pop     %edi            # restore %edi
           pop     %esi            # and %esi
           ret
   
   /*
    * Fastcall support. Similar to _stdcall, except the first
    * two arguments are passed in %ecx and %edx. It happens we
    * only support a small number of _fastcall APIs, none of them
    * take more than three arguments. So to keep the code size
    * and complexity down, we only handle 3 arguments here.
    */
   
   /* Call _fastcall function going from Windows to UNIX. */
   
           .globl x86_fastcall_wrap_call
           .globl x86_fastcall_wrap_arg
           .globl x86_fastcall_wrap_end
   
   ENTRY(x86_fastcall_wrap)
           mov     4(%esp),%eax
           push    %eax
           push    %edx
           push    %ecx
   
           movl    $ctxsw_wtou, %eax
           call    *%eax           # unthunk
   
   x86_fastcall_wrap_call:
           mov     $0,%eax
           call    *%eax           # branch to fastcall routine
           push    %eax            # preserve return val
           push    %edx
   
           movl    $ctxsw_utow, %eax
           call    *%eax           # thunk
   
           pop     %edx
           pop     %eax            # restore return val
           add     $12,%esp        # clean the stack
   x86_fastcall_wrap_arg:
           ret     $0xFF
   x86_fastcall_wrap_end:
   
   /*
    * Call _fastcall function going from UNIX to Windows.
    * This routine isn't normally used since NDIS miniport drivers
    * only have _stdcall entry points, but it's provided anyway
    * to round out the API, and for testing purposes.
    */
   
   ENTRY(x86_fastcall_call)
           mov     4(%esp),%eax
           push    16(%esp)
   
           call    ctxsw_utow      # thunk
   
           mov     12(%esp),%ecx
           mov     16(%esp),%edx
           call    *8(%esp)        # branch to fastcall routine
           push    %eax            # preserve return val
           push    %edx
   
           call    ctxsw_wtou      # unthunk
   
           pop     %edx
           pop     %eax            # restore return val
           add     $4,%esp         # clean the stack
           ret
   
   /*
    * Call regparm(3) function going from Windows to UNIX. Arguments
    * are passed in %eax, %edx and %ecx. Note that while additional
    * arguments are passed on the stack, we never bother when them,
    * since the only regparm(3) routines we need to wrap never take
    * more than 3 arguments.
    */
   
           .globl x86_regparm_wrap_call
           .globl x86_regparm_wrap_end
   
   ENTRY(x86_regparm_wrap)
           push    %ecx
           push    %edx
           push    %eax
   
           movl    $ctxsw_wtou, %eax
           call    *%eax           # unthunk
   
   x86_regparm_wrap_call:
           movl    $0,%eax
           call    *%eax           # jump to routine
           push    %eax            # preserve return val
           push    %edx            # preserve return val
   
           movl    $ctxsw_utow, %eax
           call    *%eax           # thunk
   
           pop     %edx            # restore return val
           pop     %eax            # restore return val
           add     $12,%esp        # restore stack
           ret
   x86_regparm_wrap_end:
   
   /*
    * Call regparm(3) function going from UNIX to Windows.
    * This routine isn't normally used since NDIS miniport drivers
    * only have _stdcall entry points, but it's provided anyway
    * to round out the API, and for testing purposes.
    */
   
   ENTRY(x86_regparm_call)
           call    ctxsw_utow      # thunk
   
           mov     8(%esp),%eax
           mov     12(%esp),%edx
           mov     16(%esp),%ecx
           call    *4(%esp)        # branch to fastcall routine
           push    %eax            # preserve return val
           push    %edx            # preserve return val
   
           call    ctxsw_wtou      # unthunk
   
           pop     %edx            # restore return val
           pop     %eax            # restore return val
           ret
   
   /*
    * Ugly hack alert:
    *
    * On Win32/i386, using __try/__except results in code that tries to
    * manipulate what's supposed to be the Windows Threada Environment 
    * Block (TEB), which one accesses via the %fs register. In particular,
    * %fs:0 (the first DWORD in the TEB) points to the exception
    * registration list. Unfortunately, FreeBSD uses %fs for the
    * per-cpu data structure (pcpu), and we can't allow Windows code
    * to muck with that. I don't even know what Solaris uses %fs for
    * (or if it even uses it at all).
    *
    * Even worse, in 32-bit protected mode, %fs is a selector that
    * refers to an entry in either the GDT or the LDT. Ideally, we would
    * like to be able to temporarily point it at another descriptor
    * while Windows code executes, but to do that we need a separate
    * descriptor entry of our own to play with.
    *
    * Therefore, we go to some trouble to learn the existing layout of
    * the GDT and update it to include an extra entry that we can use.
    * We need the following utility routines to help us do that. On
    * FreeBSD, index #7 in the GDT happens to be unused, so we turn
    * this into our own data segment descriptor. It would be better
    * if we could use a private LDT entry, but there's no easy way to
    * do that in SMP mode because of the way FreeBSD handles user LDTs.
    *
    * Once we have a custom descriptor, we have to thunk/unthunk whenever
    * we cross between FreeBSD code and Windows code. The thunking is
    * based on the premise that when executing instructions in the
    * Windows binary itself, we won't go to sleep. This is because in
    * order to yield the CPU, the code has to call back out to a FreeBSD
    * routine first, and when that happens we can unthunk in order to
    * restore FreeBSD context. What we're desperately trying to avoid is
    * being involuntarily pre-empted with the %fs register still pointing
    * to our fake TIB: if FreeBSD code runs with %fs pointing at our
    * Windows TIB instead of pcpu, we'll panic the kernel. Fortunately,
    * the only way involuntary preemption can occur is if an interrupt
    * fires, and the trap handler saves/restores %fs for us.
    *
    * The thunking routines themselves, ctxsw_utow() (Context SWitch UNIX
    * to Windows) and ctxsw_wtou() (Context SWitch Windows to UNIX), are
    * external to this module. This is done simply because it's easier 
    * to manipulate data structures in C rather than assembly.
    */
   
   ENTRY(x86_getldt)
           movl    4(%esp),%eax
           sgdtl   (%eax)
           movl    8(%esp),%eax
           sldt    (%eax)
           xor     %eax,%eax
           ret
   
   ENTRY(x86_setldt)
           movl    4(%esp),%eax
           lgdt    (%eax)
           jmp     1f
           nop
   1:
           movl    8(%esp),%eax
           lldt    %ax
           xor     %eax,%eax
           ret
   
   ENTRY(x86_getfs)
           mov     %fs,%ax
           ret
   
   ENTRY(x86_setfs)
           movl    4(%esp),%fs
           ret
   
   ENTRY(x86_gettid)
           mov     %fs:12,%eax
           ret

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