Check for unsatisfiable alignment constraints

Fixes #493

src/asm/section.c

@@ -108,6 +108,9 @@ static struct Section *getSection(char const *pzName, enum SectionType type,
 				yyerror("Section \"%s\"'s fixed address doesn't match its alignment",
 					pzName);
 			alignment = 1; /* Ignore it if it's satisfied */
+		} else if (startaddr[type] & mask) {
+			yyerror("Section \"%s\"'s alignment cannot be attained in %s",
+				pzName, typeNames[type]);
 		}
 	}
 

src/link/section.c

@@ -161,6 +161,13 @@ static void doSanityChecks(struct Section *section, void *ptr)
 	if (section->isAlignFixed && section->alignMask == 1)
 		section->isAlignFixed = false;
 
+	/* Too large an alignment may not be satisfiable */
+	if (section->isAlignFixed
+	 && (section->alignMask & startaddr[section->type]))
+		fail("%s: %s sections cannot be aligned to $%x bytes",
+		     section->name, typeNames[section->type],
+		     section->alignMask + 1);
+
 	uint32_t minbank = bankranges[section->type][0],
 		 maxbank = bankranges[section->type][1];