autoload.cc

cygwin, 著名的在win32下模拟unix操作系统的东东

/* autoload.cc: all dynamic load stuff.

   Copyright 2000, 2001, 2002 Red Hat, Inc.

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#include "winsup.h"
#define USE_SYS_TYPES_FD_SET
#include <winsock2.h>

/* Macro for defining "auto-load" functions.
 * Note that this is self-modifying code *gasp*.
 * The first invocation of a routine will trigger the loading of
 * the DLL.  This will then be followed by the discovery of
 * the procedure's entry point, which is placed into the location
 * pointed to by the stack pointer.  This code then changes
 * the "call" operand which invoked it to a "jmp" which will
 * transfer directly to the DLL function on the next invocation.
 *
 * Subsequent calls to routines whose transfer address has not been
 * determined will skip the "load the dll" step, starting at the
 * "discovery of the entry point" step.
 *
 * So, immediately following the the call to one of the above routines
 * we have:
 *  DLL info (4 bytes)	 Pointer to a block of information concerning
 *			 the DLL (see below).
 *  DLL args (4 bytes)	 The number of arguments pushed on the stack by
 *			 the call.  If this is an odd value then this
 *			 is a flag that non-existence of this function
 *			 is not a fatal error
 *  func name (n bytes)	 asciz string containing the name of the function
 *			 to be loaded.
 *
 * The DLL info block consists of the following
 *  load_state (4 bytes) Pointer to a word containing the routine used
 *			 to eventually invoke the function.  Initially
 *			 points to an init function which loads the
 *			 DLL, gets the process's load address,
 *			 changes the contents here to point to the
 *			 function address, and changes the call *(%eax)
 *			 to a jmp func.  If the initialization has been
 *			 done, only the load part is done.
 *  DLL handle (4 bytes) The handle to use when loading the DLL.
 *  DLL locker (4 bytes) Word to use to avoid multi-thread access during
 *			 initialization.
 *  extra init (4 bytes) Extra initialization function.
 *  DLL name (n bytes)	 asciz string containing the name of the DLL.
 */

/* LoadDLLprime is used to prime the DLL info information, providing an
   additional initialization routine to call prior to calling the first
   function.  */
#define LoadDLLprime(dllname, init_also) __asm__ ("	\n\
  .section	." #dllname "_info,\"w\"		\n\
  .linkonce						\n\
  .long		std_dll_init				\n\
  .long		0					\n\
  .long		-1					\n\
  .long		" #init_also "				\n\
  .asciz	\"" #dllname "\"			\n\
  .text							\n\
");

/* Create a "decorated" name */
#define mangle(name, n) #name "@" #n

/* Standard DLL load macro.  Invokes a fatal warning if the function isn't
   found. */
#define LoadDLLfunc(name, n, dllname) LoadDLLfuncEx (name, n, dllname, 0)
#define LoadDLLfuncEx(name, n, dllname, notimp) LoadDLLfuncEx2(name, n, dllname, notimp, 0)

/* Main DLL setup stuff. */
#define LoadDLLfuncEx2(name, n, dllname, notimp, err) \
  LoadDLLprime (dllname, dll_func_load)			\
  __asm__ ("						\n\
  .section	." #dllname "_text,\"wx\"		\n\
  .global	_" mangle (name, n) "			\n\
  .global	_win32_" mangle (name, n) "		\n\
  .align	8					\n\
_" mangle (name, n) ":					\n\
_win32_" mangle (name, n) ":				\n\
  .byte		0xe9					\n\
  .long		-4 + 1f - .				\n\
1:movl		(2f),%eax				\n\
  call		*(%eax)					\n\
2:.long		." #dllname "_info			\n\
  .long		(" #n "+" #notimp ") | " #err "<<16	\n\
  .asciz	\"" #name "\"				\n\
  .text							\n\
");

/* DLL loader helper functions used during initialization. */

/* The function which finds the address, given the name and overwrites
   the call so that future invocations go straight to the function in
   the DLL. */
extern "C" void dll_func_load () __asm__ ("dll_func_load");

/* Called by the primary initialization function "init_std_dll" to
   setup the stack and eliminate future calls to init_std_dll for other
   functions from this DLL.  */
extern "C" void dll_chain () __asm__ ("dll_chain");

/* called by the secondary initialization function to call dll_func_load. */
extern "C" void dll_chain1 () __asm__ ("dll_chain1");

extern "C" {

/* FIXME: This is not thread-safe? */
__asm__ ("								\n\
msg1:									\n\
	.ascii	\"couldn't dynamically determine load address for '%s' (handle %p), %E\\0\"\n\
									\n\
	.align	32							\n\
noload:									\n\
	popl	%edx		# Get the address of the information block\n\
	movl	4(%edx),%eax	# Should we 'ignore' the lack		\n\
	test	$1,%eax		#  of this function?			\n\
	jz	1f		# Nope.					\n\
	decl	%eax		# Yes.  This is the # of bytes + 1	\n\
	popl	%edx		# Caller's caller			\n\
	addl	%eax,%esp	# Pop off bytes				\n\
	andl	$0xffff0000,%eax# upper word				\n\
	subl	%eax,%esp	# adjust for possible return value	\n\
	pushl	%eax		# Save for later			\n\
	movl	$127,%eax	# ERROR_PROC_NOT_FOUND			\n\
	pushl	%eax		# First argument			\n\
	call	_SetLastError@4	# Set it				\n\
	popl	%eax		# Get back argument			\n\
	shrl	$16,%eax	# return value in high order word	\n\
	jmp	*%edx		# Return				\n\
1:									\n\
	movl	(%edx),%eax	# Handle value				\n\
	pushl	4(%eax)							\n\
	leal	8(%edx),%eax	# Location of name of function		\n\
	push	%eax							\n\
	push	$msg1		# The message				\n\
	call	___api_fatal	# Print message. Never returns		\n\
									\n\
	.globl	dll_func_load						\n\
dll_func_load:								\n\
	movl	(%esp),%eax	# 'Return address' contains load info	\n\
	addl	$8,%eax		# Address of name of function to load	\n\
	pushl	%eax		# Second argument			\n\
	movl	-8(%eax),%eax	# Where handle lives			\n\
	movl	4(%eax),%eax	# Address of Handle to DLL		\n\
	pushl	%eax		# Handle to DLL				\n\
	call	_GetProcAddress@8# Load it				\n\
	test	%eax,%eax	# Success?				\n\
	jne	gotit		# Yes					\n\
	jmp	noload		# Issue an error or return		\n\
gotit:									\n\
	popl	%edx		# Pointer to 'return address'		\n\
	subl	%edx,%eax	# Make it relative			\n\
	addl	$7,%eax		# Tweak					\n\
	subl	$12,%edx	# Point to jmp				\n\
	movl	%eax,1(%edx)	# Move relative address after jump	\n\
	jmp	*%edx		# Jump to actual function		\n\
									\n\
	.global	dll_chain						\n\
dll_chain:								\n\
	pushl	%eax		# Restore 'return address'		\n\
	movl	(%eax),%eax	# Get address of DLL info block		\n\
	movl	$dll_func_load,(%eax) # Just load func now		\n\
	jmp	*%edx		# Jump to next init function		\n\
									\n\
dll_chain1:								\n\
	pushl	%eax		# Restore 'return address'		\n\
	jmp	*%edx		# Jump to next init function		\n\
");

/* C representations of the two info blocks described above.
   FIXME: These structures confuse gdb for some reason.  GDB can print
   the whole structure but has problems with the name field? */
struct dll_info
{
  DWORD load_state;
  HANDLE handle;
  LONG here;
  void (*init) ();
  char name[];
};

struct func_info
{
  struct dll_info *dll;
  LONG decoration;
  char name[];
};

/* Mechanism for setting up info for passing to dll_chain routines. */
union retchain
{
  struct {long high; long low;};
  long long ll;
};

/* The standard DLL initialization routine. */
static long long std_dll_init () __asm__ ("std_dll_init") __attribute__ ((unused));
static long long
std_dll_init ()
{
  HANDLE h;
  struct func_info *func = (struct func_info *) __builtin_return_address (0);
  struct dll_info *dll = func->dll;
  retchain ret;

  if (InterlockedIncrement (&dll->here))
    do
      {
	InterlockedDecrement (&dll->here);
	low_priority_sleep (0);
      }
    while (InterlockedIncrement (&dll->here));
  else if (!dll->handle)
    {
      if ((h = LoadLibrary (dll->name)) != NULL)
	dll->handle = h;
      else if (!(func->decoration & 1))
	api_fatal ("could not load %s, %E", dll->name);
      else
	dll->handle = INVALID_HANDLE_VALUE;
    }

  InterlockedDecrement (&dll->here);

  /* Kludge alert.  Redirects the return address to dll_chain. */
  __asm__ __volatile__ ("		\n\
	movl	$dll_chain,4(%ebp)	\n\
  ");

  /* Set "arguments for dll_chain. */
  ret.low = (long) dll->init;
  ret.high = (long) func;
  return ret.ll;
}

/* Initialization function for winsock stuff. */
static long long wsock_init () __asm__ ("wsock_init") __attribute__ ((unused, regparm(1)));
bool NO_COPY wsock_started = 0;
static long long
wsock_init ()
{
  static LONG NO_COPY here = -1L;
  struct func_info *func = (struct func_info *) __builtin_return_address (0);
  struct dll_info *dll = func->dll;

  __asm__ ("						\n\
	.section .ws2_32_info				\n\
	.equ	_ws2_32_handle,.ws2_32_info + 4		\n\
	.global _ws2_32_handle				\n\
	.section .wsock32_info				\n\
	.equ	_wsock32_handle,.wsock32_info + 4	\n\
	.global	_wsock32_handle				\n\
	.text						\n\