branches/zip: implement the delayloading of externals for the plugin

on Windows, which includes:

 * Load mysqld.map and insert all symbol/address pairs into hash for
   quick access
 * Resolves all external data variables. The delayloading mechanism
   in MSVC does not support automatic imports of data variables.
   A workaround is to explicitly handle the data import using the delay
   loader during the initialization of the plugin.
 * Resolves all external functions during run-time, by implementing
   the delayed loading helper function delayLoadHelper2, which is
   called by run-time as well as HrLoadAllImportsForDll. 

The delay loader reuses the hash implementation in InnoDB. The normal
hash_create (in hash0hash.c) creates hash tables in buffer pool. But
the delay loader is invoked before the engine is initialized, and 
buffer pools are not ready yet. Instead, the delay loader has its own
implementation of hash_create() and hash_table_free(), called
wdl_hash_create() and wdl_hash_table_free().

This patch should be used with other two patches in order to build
a dynamically linked plugin on Windows:
 * patch for tmpfile functions (r2886)
 * patch for "build" files (to be committed)
 
The list of file changed:

handler/handler0vars.h: new file, defines a list of external data
variables (no external functions).

handler/win_delay_loader.cc: new file, the implementation of the delay
loader for Windows plugin.

handler/ha_innodb.cc: add a header file, and changes for copying the
system variables.

handler/handler0alter.cc: add a header file

handler/i_s.cc: add a header file

rb://27

Reviewed by:	Sunny, Marko
Approved by:	Sunny

handler/ha_innodb.cc

@@ -69,6 +69,7 @@ extern "C" {
 
 #include "ha_innodb.h"
 #include "i_s.h"
+#include "handler0vars.h"
 
 #ifndef MYSQL_SERVER
 /* This is needed because of Bug #3596.  Let us hope that pthread_mutex_t
@@ -107,7 +108,11 @@ undefined.  Map it to NULL. */
 #ifdef MYSQL_DYNAMIC_PLUGIN
 /* These must be weak global variables in the dynamic plugin. */
 struct handlerton* innodb_hton_ptr;
+#ifdef __WIN__
+struct st_mysql_plugin*	builtin_innobase_plugin_ptr;
+#else
 int builtin_innobase_plugin;
+#endif /* __WIN__ */
 /********************************************************************
 Copy InnoDB system variables from the static InnoDB to the dynamic
 plugin. */
@@ -9662,6 +9667,20 @@ innodb_plugin_init(void)
 #error "MYSQL_STORAGE_ENGINE_PLUGIN must be nonzero."
 #endif
 
+	/* Copy the system variables. */
+
+	struct st_mysql_plugin*		builtin;
+	struct st_mysql_sys_var**	sta; /* static parameters */
+	struct st_mysql_sys_var**	dyn; /* dynamic parameters */
+
+#ifdef __WIN__
+	if (!builtin_innobase_plugin_ptr) {
+
+		return(true);
+	}
+
+	builtin = builtin_innobase_plugin_ptr;
+#else
 	switch (builtin_innobase_plugin) {
 	case 0:
 		return(true);
@@ -9671,13 +9690,8 @@ innodb_plugin_init(void)
 		return(false);
 	}
 
-	/* Copy the system variables. */
-
-	struct st_mysql_plugin*		builtin;
-	struct st_mysql_sys_var**	sta; /* static parameters */
-	struct st_mysql_sys_var**	dyn; /* dynamic parameters */
-
 	builtin = (struct st_mysql_plugin*) &builtin_innobase_plugin;
+#endif
 
 	for (sta = builtin->system_vars; *sta != NULL; sta++) {
 

handler/handler0alter.cc

@@ -18,6 +18,7 @@ extern "C" {
 }
 
 #include "ha_innodb.h"
+#include "handler0vars.h"
 
 /*****************************************************************
 Copies an InnoDB column to a MySQL field.  This function is

handler/handler0vars.h

+/***********************************************************************
+This file contains accessor functions for dynamic plugin on Windows.
+
+(c) 2008 Innobase Oy
+***********************************************************************/
+#if defined __WIN__ && defined MYSQL_DYNAMIC_PLUGIN
+/***********************************************************************
+This is a list of externals that can not be resolved by delay loading.
+They have to be resolved indirectly via their addresses in the .map file.
+All of them are external variables. */
+extern	CHARSET_INFO*		wdl_my_charset_bin;
+extern	CHARSET_INFO*		wdl_my_charset_latin1;
+extern	CHARSET_INFO*		wdl_my_charset_filename;
+extern	CHARSET_INFO**		wdl_system_charset_info;
+extern	CHARSET_INFO**		wdl_default_charset_info;
+extern	CHARSET_INFO**		wdl_all_charsets;
+extern	system_variables*	wdl_global_system_variables;
+extern	char*			wdl_mysql_real_data_home;
+extern	char**			wdl_mysql_data_home;
+extern	char**			wdl_tx_isolation_names;
+extern	char**			wdl_binlog_format_names;
+extern	char*			wdl_reg_ext;
+extern	pthread_mutex_t*	wdl_LOCK_thread_count;
+extern	key_map*		wdl_key_map_full;
+extern	MY_TMPDIR*		wdl_mysql_tmpdir_list;
+extern	bool*			wdl_mysqld_embedded;
+extern	uint*			wdl_lower_case_table_names;
+extern	ulong*			wdl_specialflag;
+extern	int*			wdl_my_umask;
+
+#define my_charset_bin		(*wdl_my_charset_bin)
+#define my_charset_latin1	(*wdl_my_charset_latin1)
+#define my_charset_filename	(*wdl_my_charset_filename)
+#define system_charset_info	(*wdl_system_charset_info)
+#define default_charset_info	(*wdl_default_charset_info)
+#define all_charsets		(wdl_all_charsets)
+#define global_system_variables	(*wdl_global_system_variables)
+#define mysql_real_data_home	(wdl_mysql_real_data_home)
+#define mysql_data_home		(*wdl_mysql_data_home)
+#define tx_isolation_names	(*wdl_tx_isolation_names)
+#define binlog_format_names	(*wdl_binlog_format_names)
+#define reg_ext			(wdl_reg_ext)
+#define LOCK_thread_count	(*wdl_LOCK_thread_count)
+#define key_map_full		(*wdl_key_map_full)
+#define mysql_tmpdir_list	(*wdl_mysql_tmpdir_list)
+#define mysqld_embedded		(*wdl_mysqld_embedded)
+#define lower_case_table_names	(*wdl_lower_case_table_names)
+#define specialflag		(*wdl_specialflag)
+#define my_umask		(*wdl_my_umask)
+
+#endif

handler/i_s.cc

@@ -25,6 +25,7 @@ extern "C" {
 #include "ha_prototypes.h" /* for innobase_convert_name() */
 #include "srv0start.h" /* for srv_was_started */
 }
+#include "handler0vars.h"
 
 static const char plugin_author[] = "Innobase Oy";
 

handler/win_delay_loader.cc

+/***********************************************************************
+This file contains functions that implement the delay loader on Windows.
+
+This is a customized version of delay loader with limited functionalities.
+It does not support:
+
+* (manual) unloading
+* multiple delay loaded DLLs
+* multiple loading of the same DLL
+
+This delay loader is used only by the InnoDB plugin. Other components (DLLs)
+can still use the default delay loader, provided by MSVC.
+
+Several acronyms used by Microsoft:
+ * IAT: import address table
+ * INT: import name table
+ * RVA: Relative Virtual Address
+
+See http://msdn.microsoft.com/en-us/magazine/bb985992.aspx for details of
+PE format.
+
+(c) 2008 Innobase Oy
+***********************************************************************/
+#if defined (__WIN__) && defined (MYSQL_DYNAMIC_PLUGIN)
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+# include <delayimp.h>
+# include <mysql_priv.h>
+
+extern "C" {
+# include "univ.i"
+# include "hash0hash.h"
+}
+
+/***********************************************************************
+This following contains a list of externals that can not be resolved by
+delay loading. They have to be resolved indirectly via their addresses
+in the .map file. All of them are external variables. */
+CHARSET_INFO*		wdl_my_charset_bin;
+CHARSET_INFO*		wdl_my_charset_latin1;
+CHARSET_INFO*		wdl_my_charset_filename;
+CHARSET_INFO**		wdl_system_charset_info;
+CHARSET_INFO**		wdl_default_charset_info;
+CHARSET_INFO**		wdl_all_charsets;
+system_variables*	wdl_global_system_variables;
+char*			wdl_mysql_real_data_home;
+char**			wdl_mysql_data_home;
+char**			wdl_tx_isolation_names;
+char**			wdl_binlog_format_names;
+char*			wdl_reg_ext;
+pthread_mutex_t*	wdl_LOCK_thread_count;
+key_map*		wdl_key_map_full;
+MY_TMPDIR*		wdl_mysql_tmpdir_list;
+bool*			wdl_mysqld_embedded;
+uint*			wdl_lower_case_table_names;
+ulong*			wdl_specialflag;
+int*			wdl_my_umask;
+
+/***********************************************************************
+The following is defined in ha_innodb.cc. It is used for copying the
+system variables from the builtin innodb plugin to the dynamic plugin.
+*/
+extern struct st_mysql_plugin*	builtin_innobase_plugin_ptr;
+
+/***********************************************************************
+The preffered load-address defined in PE (portable executable format).*/
+#if defined(_M_IA64)
+#pragma section(".base", long, read)
+extern "C"
+__declspec(allocate(".base"))
+const IMAGE_DOS_HEADER __ImageBase;
+#else
+extern "C"
+const IMAGE_DOS_HEADER __ImageBase;
+#endif
+
+/***********************************************************************
+A template function for converting a relative address (RVA) to an
+absolute address (VA). This is due to the pointers in the delay
+descriptor (ImgDelayDescr in delayimp.h) have been changed from
+VAs to RVAs to work on both 32- and 64-bit platforms. */
+template <class X>
+X PFromRva(RVA rva) {
+	return X(PBYTE(&__ImageBase) + rva);
+}
+
+/***********************************************************************
+Convert to the old format for convenience. The structure as well as its
+element names follow the definition of ImgDelayDescr in delayimp.h. */
+struct InternalImgDelayDescr {
+	DWORD		grAttrs;	/* attributes */
+	LPCSTR		szName;		/* pointer to dll name */
+	HMODULE*	phmod;		/* address of module handle */
+	PImgThunkData	pIAT;		/* address of the IAT */
+	PCImgThunkData	pINT;		/* address of the INT */
+	PCImgThunkData	pBoundIAT;	/* address of the optional bound IAT */
+	PCImgThunkData	pUnloadIAT;	/* address of optional copy of
+					   original IAT */
+	DWORD		dwTimeStamp;	/* 0 if not bound,
+					   otherwise date/time stamp of DLL
+					   bound to (Old BIND) */
+};
+
+typedef struct map_hash_chain_struct	map_hash_chain_t;
+
+struct map_hash_chain_struct {
+	char*			symbol;	/* pointer to a symbol */
+	ulint			value;	/* address of the symbol */
+	map_hash_chain_t*	next;	/* pointer to the next cell
+					in the same folder. */
+	map_hash_chain_t*	chain;	/* a linear chain used for
+					cleanup. */
+};
+
+static HMODULE				my_hmod = 0;
+static struct hash_table_struct*	m_htbl = NULL ;
+static map_hash_chain_t*		chain_header = NULL;
+static ibool				wdl_init = FALSE;
+const ulint				MAP_HASH_CELLS_NUM = 10000;
+
+/*****************************************************************
+Creates a hash table with >= n array cells. The actual number of cells is
+chosen to be a prime number slightly bigger than n.
+
+This is the same function as hash_create in hash0hash.c, except the
+memory allocation. This function is invoked before the engine is
+initialized, and buffer pools are not ready yet. */
+static
+hash_table_t*
+wdl_hash_create(
+/*============*/
+			/* out, own: created hash table */
+	ulint	n)	/* in: number of array cells */
+{
+	hash_cell_t*	array;
+	ulint		prime;
+	hash_table_t*	table;
+
+	prime = ut_find_prime(n);
+
+	table = (hash_table_t*) malloc(sizeof(hash_table_t));
+	if (table == NULL) {
+		return(NULL);
+	}
+
+	array = (hash_cell_t*) malloc(sizeof(hash_cell_t) * prime);
+	if (array == NULL) {
+		free(table);
+		return(NULL);
+	}
+
+	table->array = array;
+	table->n_cells = prime;
+	table->n_mutexes = 0;
+	table->mutexes = NULL;
+	table->heaps = NULL;
+	table->heap = NULL;
+	table->magic_n = HASH_TABLE_MAGIC_N;
+
+	/* Initialize the cell array */
+	hash_table_clear(table);
+
+	return(table);
+}
+
+/*****************************************************************
+Frees a hash table. */
+static
+void
+wdl_hash_table_free(
+/*================*/
+	hash_table_t*	table)	/* in, own: hash table */
+{
+	ut_a(table != NULL);
+	ut_a(table->mutexes == NULL);
+
+	free(table->array);
+	free(table);
+}
+
+/***********************************************************************
+Function for calculating the count of imports given the base of the IAT. */
+static
+ulint
+wdl_import_count(
+/*=============*/
+					/* out: number of imports */
+	PCImgThunkData	pitd_base)	/* in: base of the IAT */
+{
+	ulint		ret = 0;
+	PCImgThunkData	pitd = pitd_base;
+
+	while (pitd->u1.Function) {
+		pitd++;
+		ret++;
+	}
+
+	return(ret);
+}
+
+/***********************************************************************
+Read Mapfile to a hashtable for faster access */
+static
+ibool
+wdl_load_mapfile(
+/*=============*/
+					/* out: TRUE if the mapfile is
+					loaded successfully. */
+	const char*	filename)	/* in: name of the mapfile. */
+{
+	FILE*		fp;
+	const size_t	nSize = 256;
+	char		tmp_buf[nSize];
+	char*		func_name;
+	char*		func_addr;
+	ulint		load_addr = 0;
+	ibool		valid_load_addr = FALSE;
+
+	fp = fopen(filename, "r");
+	if (fp == NULL) {
+
+		return(FALSE);
+	}
+
+	/* Check whether to create the hashtable */
+	if (m_htbl == NULL) {
+
+		m_htbl = wdl_hash_create(MAP_HASH_CELLS_NUM);
+
+		if (m_htbl == NULL) {
+
+			fclose(fp);
+			return(FALSE);
+		}
+	}
+
+	/* Search start of symbol list and get the preferred load address */
+	while (fgets(tmp_buf, sizeof(tmp_buf), fp)) {
+
+		if (sscanf(tmp_buf, " Preferred load address is %16X",
+			   &load_addr) == 1) {
+
+			valid_load_addr = TRUE;
+		}
+
+		if (strstr(tmp_buf, "Rva+Base") != NULL) {
+
+			break;
+		}
+	}
+
+	if (valid_load_addr == FALSE) {
+
+		/* No "Preferred load address", the map file is wrong. */
+		fclose(fp);
+		return(FALSE);
+	}
+
+	/* Read symbol list */
+	while (fgets(tmp_buf, sizeof(tmp_buf), fp))
+	{
+		map_hash_chain_t*	map_cell;
+		ulint			map_fold;
+
+		if (*tmp_buf == 0) {
+
+			continue;
+		}
+
+		func_name = strtok(tmp_buf, " ");
+		func_name = strtok(NULL, " ");
+		func_addr = strtok(NULL, " ");
+
+		if (func_name && func_addr) {
+
+			ut_snprintf(tmp_buf, nSize, "0x%s", func_addr);
+			if (*func_name == '_') {
+
+				func_name++;
+			}
+
+			map_cell = (map_hash_chain_t*)
+				   malloc(sizeof(map_hash_chain_t));
+			if (map_cell == NULL) {
+				return(FALSE);
+			}
+
+			/* Chain all cells together */
+			map_cell->chain = chain_header;
+			chain_header = map_cell;
+
+			map_cell->symbol = strdup(func_name);
+			map_cell->value = strtoul(tmp_buf, NULL, 0)
+					  - load_addr;
+			map_fold = ut_fold_string(map_cell->symbol);
+
+			HASH_INSERT(map_hash_chain_t,
+				    next,
+				    m_htbl,
+				    map_fold,
+				    map_cell);
+		}
+	}
+
+	fclose(fp);
+
+	return(TRUE);
+}
+
+/*****************************************************************
+Cleanup.during DLL unload */
+static
+void
+wdl_cleanup(void)
+/*=============*/
+{
+	while (chain_header != NULL) {
+		map_hash_chain_t*	tmp;
+
+		tmp = chain_header->chain;
+		free(chain_header->symbol);
+		free(chain_header);
+		chain_header = tmp;
+	}
+
+	if (m_htbl != NULL) {
+
+		wdl_hash_table_free(m_htbl);
+	}
+}
+
+/***********************************************************************
+Load the mapfile mysqld.map. */
+static
+HMODULE
+wdl_get_mysqld_mapfile(void)
+/*========================*/
+			/* out: the module handle */
+{
+	char	file_name[MAX_PATH];
+	char*	ext;
+	ulint	err;
+
+	if (my_hmod == 0) {
+
+		size_t	nSize = MAX_PATH - strlen(".map") -1;
+
+		/* First find out the name of current executable */
+		my_hmod = GetModuleHandle(NULL);
+		if (my_hmod == 0) {
+
+			return(my_hmod);
+		}
+
+		err = GetModuleFileName(my_hmod, file_name, nSize);
+		if (err == 0) {
+
+			my_hmod = 0;
+			return(my_hmod);
+		}
+
+		ext = strrchr(file_name, '.');
+		if (ext != NULL) {
+
+			*ext = 0;
+			strcat(file_name, ".map");
+
+			err = wdl_load_mapfile(file_name);
+			if (err == 0) {
+
+				my_hmod = 0;
+			}
+		} else {
+
+			my_hmod = 0;
+		}
+	}
+
+	return(my_hmod);
+}
+
+/***********************************************************************
+Retrieves the address of an exported function. It follows the convention
+of GetProcAddress(). */
+static
+FARPROC
+wdl_get_procaddr_from_map(
+/*======================*/
+					/* out: address of exported
+					function. */
+	HANDLE		m_handle,	/* in: module handle */
+	const char*	import_proc)	/* in: procedure name */
+{
+	map_hash_chain_t*	hash_chain;
+	ulint			map_fold;
+
+	map_fold = ut_fold_string(import_proc);
+	HASH_SEARCH(
+		next,
+		m_htbl,
+		map_fold,
+		map_hash_chain_t*,
+		hash_chain,
+		(ut_strcmp(hash_chain->symbol, import_proc) == 0));
+
+	if (hash_chain == NULL) {
+
+#ifdef _WIN64
+		/* On Win64, the leading '_' may not be taken out. In this
+		case, search again without the leading '_'. */
+		if (*import_proc == '_') {
+
+			import_proc++;
+		}
+
+		map_fold = ut_fold_string(import_proc);
+		HASH_SEARCH(
+			next,
+			m_htbl,
+			map_fold,
+			map_hash_chain_t*,
+			hash_chain,
+			(ut_strcmp(hash_chain->symbol, import_proc) == 0));
+
+		if (hash_chain == NULL) {
+#endif
+			if (wdl_init == TRUE) {
+
+				sql_print_error(
+					"InnoDB: the procedure pointer of %s"
+					" is not found.",
+					import_proc);
+			}
+
+			return(0);
+#ifdef _WIN64
+		}
+#endif
+	}
+
+	return((FARPROC) ((ulint) m_handle + hash_chain->value));
+}
+
+/***********************************************************************
+Retrieves the address of an exported variable.
+Note: It does not follow the Windows call convention FARPROC. */
+static
+void*
+wdl_get_varaddr_from_map(
+/*=====================*/
+						/* out: address of exported
+						variable. */
+	HANDLE		m_handle,		/* in: module handle */
+	const char*	import_variable)	/* in: variable name */
+{
+	map_hash_chain_t*	hash_chain;
+	ulint			map_fold;
+
+	map_fold = ut_fold_string(import_variable);
+	HASH_SEARCH(
+		next,
+		m_htbl,
+		map_fold,
+		map_hash_chain_t*,
+		hash_chain,
+		(ut_strcmp(hash_chain->symbol, import_variable) == 0));
+
+	if (hash_chain == NULL) {
+
+#ifdef _WIN64
+		/* On Win64, the leading '_' may not be taken out. In this
+		case, search again without the leading '_'. */
+		if (*import_variable == '_') {
+
+			import_variable++;
+		}
+
+		map_fold = ut_fold_string(import_variable);
+		HASH_SEARCH(
+			next,
+			m_htbl,
+			map_fold,
+			map_hash_chain_t*,
+			hash_chain,
+			(ut_strcmp(hash_chain->symbol, import_variable) == 0));
+
+		if (hash_chain == NULL) {
+#endif
+			if (wdl_init == TRUE) {
+
+				sql_print_error(
+					"InnoDB: the variable address of %s"
+					" is not found.",
+					import_variable);
+			}
+
+			return(0);
+#ifdef _WIN64
+		}
+#endif
+	}
+
+	return((void*) ((ulint) m_handle + hash_chain->value));
+}
+
+/***********************************************************************
+Bind all unresolved external variables from the MySQL executable. */
+static
+bool
+wdl_get_external_variables(void)
+/*============================*/
+			/* out: TRUE if successful */
+{
+	HMODULE	hmod = wdl_get_mysqld_mapfile();
+
+	if (hmod == 0) {
+
+		return(FALSE);
+	}
+
+#define GET_SYM(sym, var, type)					\
+	var = (type*) wdl_get_varaddr_from_map(hmod, sym);	\
+	if (var == NULL) return(FALSE)
+#ifdef _WIN64
+#define GET_SYM2(sym1, sym2, var, type)				\
+	var = (type*) wdl_get_varaddr_from_map(hmod, sym1);	\
+	if (var == NULL) return(FALSE)
+#else
+#define GET_SYM2(sym1, sym2, var, type)				\
+	var = (type*) wdl_get_varaddr_from_map(hmod, sym2);	\
+	if (var == NULL) return(FALSE)
+#endif // (_WIN64)
+#define GET_C_SYM(sym, type) GET_SYM(#sym, wdl_##sym, type)
+
+	GET_C_SYM(my_charset_bin, CHARSET_INFO);
+	GET_C_SYM(my_charset_latin1, CHARSET_INFO);
+	GET_C_SYM(my_charset_filename, CHARSET_INFO);
+	GET_C_SYM(default_charset_info, CHARSET_INFO*);
+	GET_C_SYM(all_charsets, CHARSET_INFO*);
+	GET_C_SYM(my_umask, int);
+
+	GET_SYM("?global_system_variables@@3Usystem_variables@@A",
+		wdl_global_system_variables, struct system_variables);
+	GET_SYM("?mysql_real_data_home@@3PADA",
+		wdl_mysql_real_data_home, char);
+	GET_SYM("?reg_ext@@3PADA", wdl_reg_ext, char);
+	GET_SYM("?LOCK_thread_count@@3U_RTL_CRITICAL_SECTION@@A",
+		wdl_LOCK_thread_count, pthread_mutex_t);
+	GET_SYM("?key_map_full@@3V?$Bitmap@$0EA@@@A",
+		wdl_key_map_full, key_map);
+	GET_SYM("?mysql_tmpdir_list@@3Ust_my_tmpdir@@A",
+		wdl_mysql_tmpdir_list, MY_TMPDIR);
+	GET_SYM("?mysqld_embedded@@3_NA",
+		wdl_mysqld_embedded, bool);
+	GET_SYM("?lower_case_table_names@@3IA",
+		wdl_lower_case_table_names, uint);
+	GET_SYM("?specialflag@@3KA", wdl_specialflag, ulong);
+	GET_SYM("?builtin_innobase_plugin@@3PAUst_mysql_plugin@@A",
+		builtin_innobase_plugin_ptr, struct st_mysql_plugin);
+
+	GET_SYM2("?system_charset_info@@3PEAUcharset_info_st@@EA",
+		 "?system_charset_info@@3PAUcharset_info_st@@A",
+		 wdl_system_charset_info, CHARSET_INFO*);
+	GET_SYM2("?mysql_data_home@@3PEADEA",
+		 "?mysql_data_home@@3PADA",
+		 wdl_mysql_data_home, char*);
+	GET_SYM2("?tx_isolation_names@@3PAPEBDA",
+		 "?tx_isolation_names@@3PAPBDA",
+		 wdl_tx_isolation_names, char*);
+	GET_SYM2("?binlog_format_names@@3PAPEBDA",
+		 "?binlog_format_names@@3PAPBDA",
+		 wdl_binlog_format_names, char*);
+
+	wdl_init = TRUE;
+	return(TRUE);
+
+#undef GET_SYM
+#undef GET_SYM2
+#undef GET_C_SYM
+}
+
+/***********************************************************************
+The DLL Delayed Loading Helper Function for resolving externals.
+
+The function may fail due to one of the three reasons:
+
+* Invalid parameter, which happens if the attributes in pidd aren't
+  specified correctly.
+* Failed to load the map file mysqld.map.
+* Failed to find an external name in the map file mysqld.map.
+
+Note: this function is called by run-time as well as __HrLoadAllImportsForDll.
+So, it has to follow Windows call convention. */
+extern "C"
+FARPROC WINAPI
+__delayLoadHelper2(
+/*===============*/
+					/* out: the address of the imported
+					function*/
+	PCImgDelayDescr	pidd,		/* in: a const pointer to a
+					ImgDelayDescr, see delayimp.h. */
+	FARPROC*	iat_entry)	/* in/out: A pointer to the slot in
+					the delay load import address table
+					to be updated with the address of the
+					imported function. */
+{
+	ulint		iIAT, iINT;
+	HMODULE		hmod;
+	PCImgThunkData	pitd;
+	FARPROC		fun = NULL;
+
+	/* Set up data used for the hook procs  */
+	InternalImgDelayDescr	idd = {
+				pidd->grAttrs,
+				PFromRva<LPCSTR>(pidd->rvaDLLName),
+				PFromRva<HMODULE*>(pidd->rvaHmod),
+				PFromRva<PImgThunkData>(pidd->rvaIAT),
+				PFromRva<PCImgThunkData>(pidd->rvaINT),
+				PFromRva<PCImgThunkData>(pidd->rvaBoundIAT),
+				PFromRva<PCImgThunkData>(pidd->rvaUnloadIAT),
+				pidd->dwTimeStamp
+	};
+
+	DelayLoadInfo		dli = {
+				sizeof(DelayLoadInfo),
+				pidd,
+				iat_entry,
+				idd.szName,
+				{0},
+				0,
+				0,
+				0
+	};
+
+	/* Check the Delay Load Attributes, log an error of invalid
+	parameter, which happens if the attributes in pidd are not
+	specified correctly. */
+	if ((idd.grAttrs & dlattrRva) == 0) {
+
+		sql_print_error("InnoDB: invalid parameter for delay loader.");
+		return(0);
+	}
+
+	hmod = *idd.phmod;
+
+	/* Calculate the index for the IAT entry in the import address table.
+	The INT entries are ordered the same as the IAT entries so the
+	calculation can be done on the IAT side. */
+	iIAT = (PCImgThunkData) iat_entry - idd.pIAT;
+	iINT = iIAT;
+
+	pitd = &(idd.pINT[iINT]);
+
+	dli.dlp.fImportByName = !IMAGE_SNAP_BY_ORDINAL(pitd->u1.Ordinal);
+
+	if (dli.dlp.fImportByName) {
+
+		dli.dlp.szProcName = (LPCSTR) (PFromRva<PIMAGE_IMPORT_BY_NAME>
+			((RVA) ((UINT_PTR) pitd->u1.AddressOfData))->Name);
+	} else {
+
+		dli.dlp.dwOrdinal = (ulint) IMAGE_ORDINAL(pitd->u1.Ordinal);
+	}
+
+	/* Now, load the mapfile, if it has not been done yet */
+	if (hmod == 0) {
+
+		hmod = wdl_get_mysqld_mapfile();
+	}
+
+	if (hmod == 0) {
+		/* LoadLibrary failed. */
+		PDelayLoadInfo	rgpdli[1] = {&dli};
+
+		dli.dwLastError = ::GetLastError();
+
+		sql_print_error(
+			"InnoDB: failed to load mysqld.map with error %d.",
+			dli.dwLastError);
+
+		return(0);
+	}
+
+	/* Store the library handle. */
+	idd.phmod = &hmod;
+
+	/* Go for the procedure now. */
+	dli.hmodCur = hmod;
+
+	if (pidd->rvaBoundIAT && pidd->dwTimeStamp) {
+
+		/* Bound imports exist, check the timestamp from the target
+		image */
+		PIMAGE_NT_HEADERS	pinh;
+
+		pinh = (PIMAGE_NT_HEADERS) ((byte*) hmod
+				+ ((PIMAGE_DOS_HEADER) hmod)->e_lfanew);
+
+		if (pinh->Signature == IMAGE_NT_SIGNATURE
+		    && pinh->FileHeader.TimeDateStamp == idd.dwTimeStamp
+		    && (DWORD) hmod == pinh->OptionalHeader.ImageBase) {
+
+			/* We have a decent address in the bound IAT. */
+			fun = (FARPROC) (UINT_PTR)
+					idd.pBoundIAT[iIAT].u1.Function;
+
+			if (fun) {
+
+				*iat_entry = fun;
+				return(fun);
+			}
+		}
+	}
+
+	fun = wdl_get_procaddr_from_map(hmod, dli.dlp.szProcName);
+
+	if (fun == 0) {
+
+		return(0);
+	}
+
+	*iat_entry = fun;
+	return(fun);
+}
+
+/***********************************************************************
+Unload a DLL that was delay loaded. This function is called by run-time. */
+extern "C"
+BOOL WINAPI
+__FUnloadDelayLoadedDLL2(
+/*=====================*/
+				/* out: TRUE is returned if the DLL is found
+				and the IAT matches the original one. */
+	LPCSTR	module_name)	/* in: DLL name */
+{
+	return(TRUE);
+}
+
+/******************************************************************
+Load all imports from a DLL that was specified with the /delayload linker
+option.
+Note: this function is called by run-time. So, it has to follow Windows call
+convention. */
+extern "C"
+HRESULT WINAPI
+__HrLoadAllImportsForDll(
+/*=====================*/
+				/* out: S_OK if the DLL matches, otherwise
+				ERROR_MOD_NOT_FOUND is returned. */
+	LPCSTR	module_name)	/* in: DLL name */
+{
+	PIMAGE_NT_HEADERS	img;
+	PCImgDelayDescr		pidd;
+	IMAGE_DATA_DIRECTORY*	image_data;
+	LPCSTR			current_module;
+	HRESULT			ret = ERROR_MOD_NOT_FOUND;
+	HMODULE			hmod = (HMODULE) &__ImageBase;
+
+	img = (PIMAGE_NT_HEADERS) ((byte*) hmod
+				   + ((PIMAGE_DOS_HEADER) hmod)->e_lfanew);
+	image_data =
+	 &img->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT];
+
+	/* Scan the delay load IAT/INT for the DLL */
+	if (image_data->Size) {
+
+		pidd = PFromRva<PCImgDelayDescr>(image_data->VirtualAddress);
+
+		/* Check all of the listed DLLs we want to load. */
+		while (pidd->rvaDLLName) {
+
+			current_module = PFromRva<LPCSTR>(pidd->rvaDLLName);
+
+			if (stricmp(module_name, current_module) == 0) {
+
+				/* Found it, break out with pidd and
+				current_module set appropriately */
+				break;
+			}
+
+			/* To the next delay import descriptor */
+			pidd++;
+		}
+
+		if (pidd->rvaDLLName) {
+
+			/* Found a matching DLL, now process it. */
+			FARPROC*	iat_entry;
+			size_t		count;
+
+			iat_entry = PFromRva<FARPROC*>(pidd->rvaIAT);
+			count = wdl_import_count((PCImgThunkData) iat_entry);
+
+			/* now load all the imports from the DLL */
+			while (count > 0) {
+
+				/* No need to check the return value */
+				__delayLoadHelper2(pidd, iat_entry);
+				iat_entry++;
+				count--;
+			}
+
+			ret = S_OK;
+		}
+	}
+
+	return ret;
+}
+
+/******************************************************************
+The main function of a DLL */
+BOOL
+WINAPI
+DllMain(
+/*====*/
+					/* out: TRUE if the call succeeds */
+	HINSTANCE	hinstDLL,	/* in: handle to the DLL module */
+	DWORD		fdwReason,	/* Reason code that indicates why the
+					DLL entry-point function is being
+					called.*/
+	LPVOID		lpvReserved)	/* in: additional parameter based on
+					fdwReason */
+{
+	BOOL	success = TRUE;
+
+	switch (fdwReason) {
+
+	case DLL_PROCESS_ATTACH:
+		success = wdl_get_external_variables();
+		break;
+
+	case DLL_PROCESS_DETACH:
+		wdl_cleanup();
+		break;
+	}
+
+	return(success);
+}
+
+#endif /* defined (__WIN__) && defined (MYSQL_DYNAMIC_PLUGIN) */