diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index daf0438..1c14b54 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -396,7 +396,7 @@ static HeapTuple make_tuple_from_result_row(PGresult *res,
 						   List *retrieved_attrs,
 						   ForeignScanState *fsstate,
 						   MemoryContext temp_context);
-static void conversion_error_callback(void *arg);
+static void conversion_error_callback(const void *arg);
 static bool foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel,
 				JoinType jointype, RelOptInfo *outerrel, RelOptInfo *innerrel,
 				JoinPathExtraData *extra);
@@ -4521,12 +4521,12 @@ make_tuple_from_result_row(PGresult *res,
  * conversion.  Print names of column and relation.
  */
 static void
-conversion_error_callback(void *arg)
+conversion_error_callback(const void *arg)
 {
 	const char *attname = NULL;
 	const char *relname = NULL;
 	bool		is_wholerow = false;
-	ConversionLocation *errpos = (ConversionLocation *) arg;
+	const ConversionLocation *errpos = (const ConversionLocation *) arg;
 
 	if (errpos->rel)
 	{
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index c1b9a97..6039972 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -849,7 +849,7 @@ static bool read_backup_label(XLogRecPtr *checkPointLoc,
 				  bool *backupEndRequired, bool *backupFromStandby);
 static bool read_tablespace_map(List **tablespaces);
 
-static void rm_redo_error_callback(void *arg);
+static void rm_redo_error_callback(const void *arg);
 static int	get_sync_bit(int method);
 
 static void CopyXLogRecordToWAL(int write_len, bool isLogSwitch,
@@ -10937,8 +10937,13 @@ read_tablespace_map(List **tablespaces)
  * Error context callback for errors occurring during rm_redo().
  */
 static void
-rm_redo_error_callback(void *arg)
+rm_redo_error_callback(const void *arg)
 {
+	/*
+	 * We have to cast away the const because xlog_outdesc passes
+	 * 'record' through the rm_desc functor which modifies the
+	 * data.  This is ugly, but there is no obvious workaround.
+	 */
 	XLogReaderState *record = (XLogReaderState *) arg;
 	StringInfoData buf;
 
diff --git a/src/backend/catalog/pg_proc.c b/src/backend/catalog/pg_proc.c
index c1d1505..f3a20dd 100644
--- a/src/backend/catalog/pg_proc.c
+++ b/src/backend/catalog/pg_proc.c
@@ -51,7 +51,7 @@ typedef struct
 	char	   *prosrc;
 } parse_error_callback_arg;
 
-static void sql_function_parse_error_callback(void *arg);
+static void sql_function_parse_error_callback(const void *arg);
 static int match_prosrc_to_query(const char *prosrc, const char *queryText,
 					  int cursorpos);
 static bool match_prosrc_to_literal(const char *prosrc, const char *literal,
@@ -962,9 +962,9 @@ fmgr_sql_validator(PG_FUNCTION_ARGS)
  * Error context callback for handling errors in SQL function definitions
  */
 static void
-sql_function_parse_error_callback(void *arg)
+sql_function_parse_error_callback(const void *arg)
 {
-	parse_error_callback_arg *callback_arg = (parse_error_callback_arg *) arg;
+	const parse_error_callback_arg *callback_arg = (const parse_error_callback_arg *) arg;
 
 	/* See if it's a syntax error; if so, transpose to CREATE FUNCTION */
 	if (!function_parse_error_transpose(callback_arg->prosrc))
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 432b0ca..c79ad26 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -2122,9 +2122,9 @@ CopyOneRowTo(CopyState cstate, Oid tupleOid, Datum *values, bool *nulls)
  * The argument for the error context must be CopyState.
  */
 void
-CopyFromErrorCallback(void *arg)
+CopyFromErrorCallback(const void *arg)
 {
-	CopyState	cstate = (CopyState) arg;
+	const CopyStateData *cstate = (const CopyStateData *) arg;
 
 	if (cstate->binary)
 	{
diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index eb531af..f0e4476 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -46,7 +46,7 @@ typedef struct
 } import_error_callback_arg;
 
 /* Internal functions */
-static void import_error_callback(void *arg);
+static void import_error_callback(const void *arg);
 
 
 /*
@@ -1613,9 +1613,9 @@ ImportForeignSchema(ImportForeignSchemaStmt *stmt)
  * error context callback to let us supply the failing SQL statement's text
  */
 static void
-import_error_callback(void *arg)
+import_error_callback(const void *arg)
 {
-	import_error_callback_arg *callback_arg = (import_error_callback_arg *) arg;
+	const import_error_callback_arg *callback_arg = (const import_error_callback_arg *) arg;
 	int			syntaxerrposition;
 
 	/* If it's a syntax error, convert to internal syntax error report */
diff --git a/src/backend/executor/functions.c b/src/backend/executor/functions.c
index 470db5b..db58839 100644
--- a/src/backend/executor/functions.c
+++ b/src/backend/executor/functions.c
@@ -164,7 +164,7 @@ static Datum postquel_get_single_result(TupleTableSlot *slot,
 						   FunctionCallInfo fcinfo,
 						   SQLFunctionCachePtr fcache,
 						   MemoryContext resultcontext);
-static void sql_exec_error_callback(void *arg);
+static void sql_exec_error_callback(const void *arg);
 static void ShutdownSQLFunction(Datum arg);
 static void sqlfunction_startup(DestReceiver *self, int operation, TupleDesc typeinfo);
 static bool sqlfunction_receive(TupleTableSlot *slot, DestReceiver *self);
@@ -1357,9 +1357,9 @@ fmgr_sql(PG_FUNCTION_ARGS)
  * error context callback to let us supply a call-stack traceback
  */
 static void
-sql_exec_error_callback(void *arg)
+sql_exec_error_callback(const void *arg)
 {
-	FmgrInfo   *flinfo = (FmgrInfo *) arg;
+	const FmgrInfo   *flinfo = (const FmgrInfo *) arg;
 	SQLFunctionCachePtr fcache = (SQLFunctionCachePtr) flinfo->fn_extra;
 	int			syntaxerrposition;
 
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 38767ae..6a5beea 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -63,7 +63,7 @@ static ParamListInfo _SPI_convert_params(int nargs, Oid *argtypes,
 
 static int	_SPI_pquery(QueryDesc *queryDesc, bool fire_triggers, uint64 tcount);
 
-static void _SPI_error_callback(void *arg);
+static void _SPI_error_callback(const void *arg);
 
 static void _SPI_cursor_operation(Portal portal,
 					  FetchDirection direction, long count,
@@ -1265,7 +1265,7 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
 	 * throws an error.
 	 */
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = (void *) plansource->query_string;
+	spierrcontext.arg = (const void *) plansource->query_string;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -1693,7 +1693,7 @@ SPI_plan_get_cached_plan(SPIPlanPtr plan)
 
 	/* Setup error traceback support for ereport() */
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = (void *) plansource->query_string;
+	spierrcontext.arg = (const void *) plansource->query_string;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -1835,7 +1835,7 @@ _SPI_prepare_plan(const char *src, SPIPlanPtr plan)
 	 * Setup error traceback support for ereport()
 	 */
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = (void *) src;
+	spierrcontext.arg = (const void *) src;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -1938,7 +1938,7 @@ _SPI_prepare_oneshot_plan(const char *src, SPIPlanPtr plan)
 	 * Setup error traceback support for ereport()
 	 */
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = (void *) src;
+	spierrcontext.arg = (const void *) src;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -2047,7 +2047,7 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 		List	   *stmt_list;
 		ListCell   *lc2;
 
-		spierrcontext.arg = (void *) plansource->query_string;
+		spierrcontext.arg = (const void *) plansource->query_string;
 
 		/*
 		 * If this is a one-shot plan, we still need to do parse analysis.
@@ -2439,7 +2439,7 @@ _SPI_pquery(QueryDesc *queryDesc, bool fire_triggers, uint64 tcount)
  * Add context information when a query invoked via SPI fails
  */
 static void
-_SPI_error_callback(void *arg)
+_SPI_error_callback(const void *arg)
 {
 	const char *query = (const char *) arg;
 	int			syntaxerrposition;
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 663ffe0..f39cfad 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -148,7 +148,7 @@ static Node *substitute_actual_parameters(Node *expr, int nargs, List *args,
 							 int *usecounts);
 static Node *substitute_actual_parameters_mutator(Node *node,
 							  substitute_actual_parameters_context *context);
-static void sql_inline_error_callback(void *arg);
+static void sql_inline_error_callback(const void *arg);
 static Expr *evaluate_expr(Expr *expr, Oid result_type, int32 result_typmod,
 			  Oid result_collation);
 static Query *substitute_actual_srf_parameters(Query *expr,
@@ -4671,9 +4671,9 @@ substitute_actual_parameters_mutator(Node *node,
  * error context callback to let us supply a call-stack traceback
  */
 static void
-sql_inline_error_callback(void *arg)
+sql_inline_error_callback(const void *arg)
 {
-	inline_error_callback_arg *callback_arg = (inline_error_callback_arg *) arg;
+	const inline_error_callback_arg *callback_arg = (const inline_error_callback_arg *) arg;
 	int			syntaxerrposition;
 
 	/* If it's a syntax error, convert to internal syntax error report */
diff --git a/src/backend/parser/parse_node.c b/src/backend/parser/parse_node.c
index 62d2f71..ba6ccd0 100644
--- a/src/backend/parser/parse_node.c
+++ b/src/backend/parser/parse_node.c
@@ -31,7 +31,7 @@
 #include "utils/varbit.h"
 
 
-static void pcb_error_callback(void *arg);
+static void pcb_error_callback(const void *arg);
 
 
 /*
@@ -169,9 +169,9 @@ cancel_parser_errposition_callback(ParseCallbackState *pcbstate)
  * if the error is a query cancel --- are there any other important cases?
  */
 static void
-pcb_error_callback(void *arg)
+pcb_error_callback(const void *arg)
 {
-	ParseCallbackState *pcbstate = (ParseCallbackState *) arg;
+	const ParseCallbackState *pcbstate = (const ParseCallbackState *) arg;
 
 	if (geterrcode() != ERRCODE_QUERY_CANCELED)
 		(void) parser_errposition(pcbstate->pstate, pcbstate->location);
diff --git a/src/backend/parser/parse_type.c b/src/backend/parser/parse_type.c
index a8bb472..e7f9152 100644
--- a/src/backend/parser/parse_type.c
+++ b/src/backend/parser/parse_type.c
@@ -664,7 +664,7 @@ typeidTypeRelid(Oid type_id)
  * error context callback for parse failure during parseTypeString()
  */
 static void
-pts_error_callback(void *arg)
+pts_error_callback(const void *arg)
 {
 	const char *str = (const char *) arg;
 
@@ -706,7 +706,7 @@ typeStringToTypeName(const char *str)
 	 * Setup error traceback support in case of ereport() during parse
 	 */
 	ptserrcontext.callback = pts_error_callback;
-	ptserrcontext.arg = (void *) str;
+	ptserrcontext.arg = (const void *) str;
 	ptserrcontext.previous = error_context_stack;
 	error_context_stack = &ptserrcontext;
 
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 1512be5..f978e68 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -53,7 +53,7 @@ typedef struct LogicalErrorCallbackState
 } LogicalErrorCallbackState;
 
 /* wrappers around output plugin callbacks */
-static void output_plugin_error_callback(void *arg);
+static void output_plugin_error_callback(const void *arg);
 static void startup_cb_wrapper(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 				   bool is_init);
 static void shutdown_cb_wrapper(LogicalDecodingContext *ctx);
@@ -518,9 +518,9 @@ LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin)
 }
 
 static void
-output_plugin_error_callback(void *arg)
+output_plugin_error_callback(const void *arg)
 {
-	LogicalErrorCallbackState *state = (LogicalErrorCallbackState *) arg;
+	const LogicalErrorCallbackState *state = (const LogicalErrorCallbackState *) arg;
 
 	/* not all callbacks have an associated LSN  */
 	if (state->report_location != InvalidXLogRecPtr)
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 90804a3..29dd558 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -442,8 +442,8 @@ static void WaitIO(BufferDesc *buf);
 static bool StartBufferIO(BufferDesc *buf, bool forInput);
 static void TerminateBufferIO(BufferDesc *buf, bool clear_dirty,
 				  uint32 set_flag_bits);
-static void shared_buffer_write_error_callback(void *arg);
-static void local_buffer_write_error_callback(void *arg);
+static void shared_buffer_write_error_callback(const void *arg);
+static void local_buffer_write_error_callback(const void *arg);
 static BufferDesc *BufferAlloc(SMgrRelation smgr,
 			char relpersistence,
 			ForkNumber forkNum,
@@ -2665,7 +2665,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln)
 
 	/* Setup error traceback support for ereport() */
 	errcallback.callback = shared_buffer_write_error_callback;
-	errcallback.arg = (void *) buf;
+	errcallback.arg = (const void *) buf;
 	errcallback.previous = error_context_stack;
 	error_context_stack = &errcallback;
 
@@ -3154,7 +3154,7 @@ FlushRelationBuffers(Relation rel)
 
 				/* Setup error traceback support for ereport() */
 				errcallback.callback = local_buffer_write_error_callback;
-				errcallback.arg = (void *) bufHdr;
+				errcallback.arg = (const void *) bufHdr;
 				errcallback.previous = error_context_stack;
 				error_context_stack = &errcallback;
 
@@ -3963,9 +3963,9 @@ AbortBufferIO(void)
  * Error context callback for errors occurring during shared buffer writes.
  */
 static void
-shared_buffer_write_error_callback(void *arg)
+shared_buffer_write_error_callback(const void *arg)
 {
-	BufferDesc *bufHdr = (BufferDesc *) arg;
+	const BufferDesc *bufHdr = (const BufferDesc *) arg;
 
 	/* Buffer is pinned, so we can read the tag without locking the spinlock */
 	if (bufHdr != NULL)
@@ -3982,9 +3982,9 @@ shared_buffer_write_error_callback(void *arg)
  * Error context callback for errors occurring during local buffer writes.
  */
 static void
-local_buffer_write_error_callback(void *arg)
+local_buffer_write_error_callback(const void *arg)
 {
-	BufferDesc *bufHdr = (BufferDesc *) arg;
+	const BufferDesc *bufHdr = (const BufferDesc *) arg;
 
 	if (bufHdr != NULL)
 	{
diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c
index cbee20e..483c24b 100644
--- a/src/backend/storage/lmgr/lmgr.c
+++ b/src/backend/storage/lmgr/lmgr.c
@@ -56,7 +56,7 @@ typedef struct XactLockTableWaitInfo
 	ItemPointer ctid;
 } XactLockTableWaitInfo;
 
-static void XactLockTableWaitErrorCb(void *arg);
+static void XactLockTableWaitErrorCb(const void *arg);
 
 /*
  * RelationInitLockInfo
@@ -700,9 +700,9 @@ SpeculativeInsertionWait(TransactionId xid, uint32 token)
  *		Error context callback for transaction lock waits.
  */
 static void
-XactLockTableWaitErrorCb(void *arg)
+XactLockTableWaitErrorCb(const void *arg)
 {
-	XactLockTableWaitInfo *info = (XactLockTableWaitInfo *) arg;
+	const XactLockTableWaitInfo *info = (const XactLockTableWaitInfo *) arg;
 
 	/*
 	 * We would like to print schema name too, but that would require a
diff --git a/src/backend/tsearch/ts_locale.c b/src/backend/tsearch/ts_locale.c
index 85e1cd0..65ba6b0 100644
--- a/src/backend/tsearch/ts_locale.c
+++ b/src/backend/tsearch/ts_locale.c
@@ -18,7 +18,7 @@
 #include "tsearch/ts_locale.h"
 #include "tsearch/ts_public.h"
 
-static void tsearch_readline_callback(void *arg);
+static void tsearch_readline_callback(const void *arg);
 
 
 #ifdef USE_WIDE_UPPER_LOWER
@@ -162,9 +162,9 @@ tsearch_readline_end(tsearch_readline_state *stp)
  * configuration file.
  */
 static void
-tsearch_readline_callback(void *arg)
+tsearch_readline_callback(const void *arg)
 {
-	tsearch_readline_state *stp = (tsearch_readline_state *) arg;
+	const tsearch_readline_state *stp = (const tsearch_readline_state *) arg;
 
 	/*
 	 * We can't include the text of the config line for errors that occur
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 65eb347..379a0ee 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -33,7 +33,7 @@ extern bool NextCopyFrom(CopyState cstate, ExprContext *econtext,
 			 Datum *values, bool *nulls, Oid *tupleOid);
 extern bool NextCopyFromRawFields(CopyState cstate,
 					  char ***fields, int *nfields);
-extern void CopyFromErrorCallback(void *arg);
+extern void CopyFromErrorCallback(const void *arg);
 
 extern DestReceiver *CreateCopyDestReceiver(void);
 
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 70dc365..1e73c46 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -236,8 +236,8 @@ extern char *format_elog_string(const char *fmt,...) pg_attribute_printf(1, 2);
 typedef struct ErrorContextCallback
 {
 	struct ErrorContextCallback *previous;
-	void		(*callback) (void *arg);
-	void	   *arg;
+	void		(*callback) (const void *arg);
+	const void  *arg;
 } ErrorContextCallback;
 
 extern PGDLLIMPORT ErrorContextCallback *error_context_stack;
diff --git a/src/pl/plpgsql/src/pl_comp.c b/src/pl/plpgsql/src/pl_comp.c
index 18948c8..63ad31c 100644
--- a/src/pl/plpgsql/src/pl_comp.c
+++ b/src/pl/plpgsql/src/pl_comp.c
@@ -92,7 +92,7 @@ static PLpgSQL_function *do_compile(FunctionCallInfo fcinfo,
 		   PLpgSQL_function *function,
 		   PLpgSQL_func_hashkey *hashkey,
 		   bool forValidator);
-static void plpgsql_compile_error_callback(void *arg);
+static void plpgsql_compile_error_callback(const void *arg);
 static void add_parameter_name(PLpgSQL_nsitem_type itemtype, int itemno, const char *name);
 static void add_dummy_return(PLpgSQL_function *function);
 static Node *plpgsql_pre_column_ref(ParseState *pstate, ColumnRef *cref);
@@ -919,7 +919,7 @@ plpgsql_compile_inline(char *proc_source)
  * source text is passed as an argument.
  */
 static void
-plpgsql_compile_error_callback(void *arg)
+plpgsql_compile_error_callback(const void *arg)
 {
 	if (arg)
 	{
diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 470cf93..03dc187 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -155,7 +155,7 @@ static HTAB *shared_cast_hash = NULL;
 /************************************************************
  * Local function forward declarations
  ************************************************************/
-static void plpgsql_exec_error_callback(void *arg);
+static void plpgsql_exec_error_callback(const void *arg);
 static PLpgSQL_datum *copy_plpgsql_datum(PLpgSQL_datum *datum);
 static MemoryContext get_stmt_mcontext(PLpgSQL_execstate *estate);
 static void push_stmt_mcontext(PLpgSQL_execstate *estate);
@@ -966,9 +966,9 @@ plpgsql_exec_event_trigger(PLpgSQL_function *func, EventTriggerData *trigdata)
  * error context callback to let us supply a call-stack traceback
  */
 static void
-plpgsql_exec_error_callback(void *arg)
+plpgsql_exec_error_callback(const void *arg)
 {
-	PLpgSQL_execstate *estate = (PLpgSQL_execstate *) arg;
+	const PLpgSQL_execstate *estate = (const PLpgSQL_execstate *) arg;
 
 	if (estate->err_text != NULL)
 	{
diff --git a/src/pl/plpgsql/src/pl_gram.y b/src/pl/plpgsql/src/pl_gram.y
index 0b41e3a..4a2d865 100644
--- a/src/pl/plpgsql/src/pl_gram.y
+++ b/src/pl/plpgsql/src/pl_gram.y
@@ -98,7 +98,7 @@ static	PLpgSQL_row		*make_scalar_list1(char *initial_name,
 										   int lineno, int location);
 static	void			 check_sql_expr(const char *stmt, int location,
 										int leaderlen);
-static	void			 plpgsql_sql_error_callback(void *arg);
+static	void			 plpgsql_sql_error_callback(const void *arg);
 static	PLpgSQL_type	*parse_datatype(const char *string, int location);
 static	void			 check_labels(const char *start_label,
 									  const char *end_label,
@@ -3556,9 +3556,9 @@ check_sql_expr(const char *stmt, int location, int leaderlen)
 }
 
 static void
-plpgsql_sql_error_callback(void *arg)
+plpgsql_sql_error_callback(const void *arg)
 {
-	sql_error_callback_arg *cbarg = (sql_error_callback_arg *) arg;
+	const sql_error_callback_arg *cbarg = (const sql_error_callback_arg *) arg;
 	int			errpos;
 
 	/*
diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index c84a97b..f83b109 100644
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -976,7 +976,7 @@ typedef struct PLpgSQL_plugin
 	void		(*stmt_end) (PLpgSQL_execstate *estate, PLpgSQL_stmt *stmt);
 
 	/* Function pointers set by PL/pgSQL itself */
-	void		(*error_callback) (void *arg);
+	void		(*error_callback) (const void *arg);
 	void		(*assign_expr) (PLpgSQL_execstate *estate, PLpgSQL_datum *target,
 											PLpgSQL_expr *expr);
 } PLpgSQL_plugin;