From 73d1044beced0168e8f18043924f8053730af7b5 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Mon, 11 Sep 2023 22:54:41 +0900
Subject: [PATCH] [qfcc] Support offset aliases of values

But explicitly not for pointers (even an offset of 0 breaks the pointer
relocation).
---
 tools/qfcc/include/value.h     |  2 ++
 tools/qfcc/source/statements.c | 16 +++++++++++++---
 tools/qfcc/source/value.c      | 16 ++++++++++++++++
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/tools/qfcc/include/value.h b/tools/qfcc/include/value.h
index 74aa179d6..5ffc9c3ac 100644
--- a/tools/qfcc/include/value.h
+++ b/tools/qfcc/include/value.h
@@ -67,6 +67,8 @@ void value_store (pr_type_t *dst, const struct type_s *dstType,
 				  const struct expr_s *src);
 const char *get_value_string (const struct ex_value_s *value);
 
+struct ex_value_s *offset_alias_value (struct ex_value_s *value,
+									   struct type_s *type, int offset);
 struct ex_value_s *alias_value (struct ex_value_s *value, struct type_s *type);
 struct def_s *emit_value (struct ex_value_s *value, struct def_s *def);
 struct def_s *emit_value_core (struct ex_value_s *value, struct def_s *def,
diff --git a/tools/qfcc/source/statements.c b/tools/qfcc/source/statements.c
index b09d0fad2..dd1a995a5 100644
--- a/tools/qfcc/source/statements.c
+++ b/tools/qfcc/source/statements.c
@@ -154,7 +154,7 @@ _print_operand (operand_t *op)
 			printf ("%s", op->def->name);
 			break;
 		case op_value:
-			printf ("(%s) %s", pr_type_name[op->type->type],
+			printf ("(%s) %s", get_type_string (op->type),
 					get_value_string (op->value));
 			break;
 		case op_label:
@@ -514,8 +514,18 @@ offset_alias_operand (type_t *type, int offset, operand_t *aop, expr_t *expr)
 			def = def->alias;
 		return def_operand (alias_def (def, type, offset), 0, expr);
 	} else if (aop->op_type == op_value) {
-		top = value_operand (aop->value, expr);
-		top->type = type;
+		if (!is_ptr (aop->value->type)) {
+			auto value = offset_alias_value (aop->value, type, offset);
+			top = value_operand (value, expr);
+		} else {
+			// even an offset of 0 will break a pointer value because of
+			// relocations
+			if (offset) {
+				internal_error (expr, "offset alias of pointer value operand");
+			}
+			top = value_operand (aop->value, expr);
+			top->type = type;
+		}
 		return top;
 	} else {
 		internal_error (expr, "invalid alias target: %s: %s",
diff --git a/tools/qfcc/source/value.c b/tools/qfcc/source/value.c
index e6f85c402..bf4a3a676 100644
--- a/tools/qfcc/source/value.c
+++ b/tools/qfcc/source/value.c
@@ -531,6 +531,22 @@ ReuseString (const char *str)
 	return strpool_addstr (pr.strings, str);
 }
 
+ex_value_t *
+offset_alias_value (ex_value_t *value, type_t *type, int offset)
+{
+	if (type_size (type) > type_size (value->type)) {
+		error (0, "unable to alias to a larger sized value");
+		return value;
+	}
+	if (offset < 0 || offset + type_size (type) > type_size (value->type)) {
+		error (0, "invalid offset");
+		return value;
+	}
+	pr_type_t   data[type_size (value->type)];
+	memcpy (data, &value->v, sizeof (pr_type_t) * type_size (value->type));
+	return new_type_value (type, data + offset);
+}
+
 ex_value_t *
 alias_value (ex_value_t *value, type_t *type)
 {