Added assert.h, with assert() defined (almost) as per POSIX, and

linker_assert() defined as gPXE-specific.

src/include/assert.h

+#ifndef _ASSERT_H
+#define _ASSERT_H
+
+/** @file
+ *
+ * Assertions
+ *
+ * This file provides two assertion macros: assert() (for run-time
+ * assertions) and linker_assert() (for link-time assertions).
+ *
+ */
+
+/**
+ * Assert a condition at run-time.
+ *
+ * If the condition is not true, a debug message will be printed.
+ * Assertions only take effect in debug-enabled builds (see DBG()).
+ *
+ * @todo Make an assertion failure abort the program
+ *
+ */
+#define assert( condition ) 						   \
+	do { 								   \
+		if ( ! (condition) ) { 					   \
+			printf ( "assert(%s) failed at %s line %d [%s]\n", \
+				 #condition, __FILE__, __LINE__,	   \
+				 __FUNCTION__ );			   \
+		} 							   \
+	} while ( 0 )
+
+/**
+ * Assert a condition at link-time.
+ *
+ * If the condition is not true, the link will fail with an unresolved
+ * symbol (error_symbol).
+ *
+ * This macro is gPXE-specific.  Do not use this macro in code
+ * intended to be portable.
+ *
+ */
+#define linker_assert( condition, error_symbol )	\
+        if ( ! (condition) ) {				\
+                extern void error_symbol ( void );	\
+                error_symbol();				\
+        }
+
+#ifdef NDEBUG
+#undef assert
+#define assert(x) do {} while ( 0 )
+
+#endif /* _ASSERT_H */