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diff --git a/src/util/check_arg.h b/src/util/check_arg.h
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+++ b/src/util/check_arg.h
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+#ifndef _CHECK_ARG_INCLUDED_
+#define _CHECK_ARG_INCLUDED_
+
+/*++
+/* NAME
+/*	check_arg 3h
+/* SUMMARY
+/*	type checking/narrowing/widening for unprototyped arguments
+/* SYNOPSIS
+/*	#include <check_arg.h>
+/*
+/*	/* Example checking infrastructure for int, int *, const int *. */
+/*	CHECK_VAL_HELPER_DCL(tag, int);
+/*	CHECK_PTR_HELPER_DCL(tag, int);
+/*	CHECK_CPTR_HELPER_DCL(tag, int);
+/*
+/*	/* Example variables with type int, int *, const int *. */
+/*	int int_val;
+/*	int *int_ptr;
+/*	const int *int_cptr;
+/*
+/*	/* Example variadic function with type-flag arguments. */
+/*	func(FLAG_INT_VAL, CHECK_VAL(tag, int, int_val),
+/*	     FLAG_INT_PTR, CHECK_PTR(tag, int, int_ptr),
+/*	     FLAG_INT_CPTR, CHECK_CPTR(tag, int, int_cptr)
+/*	     FLAG_END);
+/* DESCRIPTION
+/*	This module implements wrappers for unprototyped function
+/*	arguments, to enable the same type checking, type narrowing,
+/*	and type widening as for prototyped function arguments. The
+/*	wrappers may also be useful in other contexts.
+/*
+/*	Typically, these wrappers are hidden away in a per-module
+/*	header file that is read by the consumers of that module.
+/*	To protect consumers against name collisions between wrappers
+/*	in different header files, wrappers should be called with
+/*	a distinct per-module tag value.  The tag syntax is that
+/*	of a C identifier.
+/*
+/*	Use CHECK_VAL(tag, type, argument) for arguments with a
+/*	basic type: int, long, etc., and types defined with "typedef"
+/*	where indirection is built into the type itself (for example,
+/*	the result of "typedef int *foo" or function pointer
+/*	typedefs).
+/*
+/*	Use CHECK_PTR(tag, type, argument) for non-const pointer
+/*	arguments, CHECK_CPTR(tag, type, argument) for const pointer
+/*	arguments, and CHECK_PPTR(tag, type, argument) for pointer-
+/*	to-pointer arguments.
+/*
+/*	Use CHECK_*_HELPER_DCL(tag, type) to provide the
+/*	checking infrastructure for all CHECK_*(tag, type, ...)
+/*	instances with the same *, tag and type. Depending on
+/*	the compilation environment, the infrastructure consists
+/*	of an inline function definition or a dummy assignment
+/*	target declaration.
+/*
+/*	The compiler should report the following problems:
+/* .IP \(bu
+/*	Const pointer argument where a non-const pointer is expected.
+/* .IP \(bu
+/*	Pointer argument where a non-pointer is expected and
+/*	vice-versa.
+/* .IP \(bu
+/*	Pointer/pointer type mismatches except void/non-void pointers.
+/*	Just like function prototypes, all CHECK_*PTR() wrappers
+/*	cast their result to the desired type.
+/* .IP \(bu
+/*	Non-constant non-pointer argument where a pointer is expected.
+/*. PP
+/*	Just like function prototypes, the CHECK_*PTR() wrappers
+/*	handle "bare" numerical constants by casting their argument
+/*	to the desired pointer type.
+/*
+/*	Just like function prototypes, the CHECK_VAL() wrapper
+/*	cannot force the caller to specify a particular non-pointer
+/*	type and casts its argument value to the desired type which
+/*	may wider or narrower than the argument value.
+/* IMPLEMENTATION
+
+ /*
+  * Choose between an implementation based on inline functions (standardized
+  * with C99) or conditional assignment (portable to older compilers, with
+  * some caveats as discussed below).
+  */
+#ifndef NO_INLINE
+
+ /*
+  * Parameter checks expand into inline helper function calls.
+  */
+#define CHECK_VAL(tag, type, v) check_val_##tag##type(v)
+#define CHECK_PTR(tag, type, v) check_ptr_##tag##type(v)
+#define CHECK_CPTR(tag, type, v) check_cptr_##tag##type(v)
+#define CHECK_PPTR(tag, type, v) check_pptr_##tag##type(v)
+
+ /*
+  * Macros to instantiate the inline helper functions.
+  */
+#define CHECK_VAL_HELPER_DCL(tag, type) \
+	static inline type check_val_##tag##type(type v) { return v; }
+#define CHECK_PTR_HELPER_DCL(tag, type) \
+	static inline type *check_ptr_##tag##type(type *v) { return v; }
+#define CHECK_CPTR_HELPER_DCL(tag, type) \
+	static inline const type *check_cptr_##tag##type(const type *v) \
+	    { return v; }
+#define CHECK_PPTR_HELPER_DCL(tag, type) \
+	static inline type **check_pptr_##tag##type(type **v) { return v; }
+
+#else					/* NO_INLINE */
+
+ /*
+  * Parameter checks expand into unreachable conditional assignments.
+  * Inspired by OpenSSL's verified pointer check, our implementation also
+  * detects const/non-const pointer conflicts, and it also supports
+  * non-pointer expressions.
+  */
+#define CHECK_VAL(tag, type, v) ((type) (1 ? (v) : (CHECK_VAL_DUMMY(type) = (v))))
+#define CHECK_PTR(tag, type, v) ((type *) (1 ? (v) : (CHECK_PTR_DUMMY(type) = (v))))
+#define CHECK_CPTR(tag, type, v) \
+	((const type *) (1 ? (v) : (CHECK_CPTR_DUMMY(type) = (v))))
+#define CHECK_PPTR(tag, type, v) ((type **) (1 ? (v) : (CHECK_PPTR_DUMMY(type) = (v))))
+
+ /*
+  * These macros instantiate assignment target declarations. Since the
+  * assignment is made in unreachable code, the compiler "should" not emit
+  * any references to those assignment targets. We use the "extern" class so
+  * that gcc will not complain about unused variables. Using "extern" breaks
+  * when a compiler does emit references to unreachable assignment targets.
+  * Hopefully, those cases will be rare.
+  */
+#define CHECK_VAL_HELPER_DCL(tag, type) extern type CHECK_VAL_DUMMY(type)
+#define CHECK_PTR_HELPER_DCL(tag, type) extern type *CHECK_PTR_DUMMY(type)
+#define CHECK_CPTR_HELPER_DCL(tag, type) extern const type *CHECK_CPTR_DUMMY(type)
+#define CHECK_PPTR_HELPER_DCL(tag, type) extern type **CHECK_PPTR_DUMMY(type)
+
+ /*
+  * The actual dummy assignment target names.
+  */
+#define CHECK_VAL_DUMMY(type) check_val_dummy_##type
+#define CHECK_PTR_DUMMY(type) check_ptr_dummy_##type
+#define CHECK_CPTR_DUMMY(type) check_cptr_dummy_##type
+#define CHECK_PPTR_DUMMY(type) check_pptr_dummy_##type
+
+#endif					/* NO_INLINE */
+
+/* LICENSE
+/* .ad
+/* .fi
+/*	The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/*	Wietse Venema
+/*	IBM T.J. Watson Research
+/*	P.O. Box 704
+/*	Yorktown Heights, NY 10598, USA
+/*--*/
+
+#endif