From 211c350aee530ff43771ddc1f49c013e7183f507 Mon Sep 17 00:00:00 2001
From: NeilBrown <neil@brown.name>
Date: Tue, 16 Nov 2021 08:23:06 +1100
Subject: [PATCH] oceani: pass a destination buffer into interp_exec to receive
 large result.

To handle assignment from large objects - particularly a structure
returned by a function - we cannot just pass back a 'struct value'.
Instead we need to pass in a sufficiently large buffer, and have
the value producer copy into it.

This patch passes in a 'dest' and 'dtype' for this purpose.  It is not
yet used to full potential.

Signed-off-by: NeilBrown <neil@brown.name>
---
 csrc/oceani.mdc | 63 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 42 insertions(+), 21 deletions(-)

diff --git a/csrc/oceani.mdc b/csrc/oceani.mdc
index 12beeb2..f375db6 100644
--- a/csrc/oceani.mdc
+++ b/csrc/oceani.mdc
@@ -1642,12 +1642,16 @@ in `rval`.
 		struct value rval, *lval;
 	};
 
-	static struct lrval _interp_exec(struct parse_context *c, struct exec *e);
+	/* If dest is passed, dtype must give the expected type, and
+	 * result can go there, in which case type is returned as NULL.
+	 */
+	static struct lrval _interp_exec(struct parse_context *c, struct exec *e,
+					 struct value *dest, struct type *dtype);
 
 	static struct value interp_exec(struct parse_context *c, struct exec *e,
 					struct type **typeret)
 	{
-		struct lrval ret = _interp_exec(c, e);
+		struct lrval ret = _interp_exec(c, e, NULL, NULL);
 
 		if (!ret.type) abort();
 		if (typeret)
@@ -1660,8 +1664,9 @@ in `rval`.
 	static struct value *linterp_exec(struct parse_context *c, struct exec *e,
 					  struct type **typeret)
 	{
-		struct lrval ret = _interp_exec(c, e);
+		struct lrval ret = _interp_exec(c, e, NULL, NULL);
 
+		if (!ret.type) abort();
 		if (ret.lval)
 			*typeret = ret.type;
 		else
@@ -1669,8 +1674,28 @@ in `rval`.
 		return ret.lval;
 	}
 
-	static struct lrval _interp_exec(struct parse_context *c, struct exec *e)
+	/* dinterp_exec is used when the destination type is certain and
+	 * the value has a place to go.
+	 */
+	static void dinterp_exec(struct parse_context *c, struct exec *e,
+				 struct value *dest, struct type *dtype,
+				 int need_free)
+	{
+		struct lrval ret = _interp_exec(c, e, dest, dtype);
+		if (!ret.type)
+			return;	// NOTEST
+		if (need_free)
+			free_value(dtype, dest);
+		if (ret.lval)
+			dup_value(dtype, ret.lval, dest);
+		else
+			memcpy(dest, &ret.rval, dtype->size);
+	}
+
+	static struct lrval _interp_exec(struct parse_context *c, struct exec *e,
+					 struct value *dest, struct type *dtype)
 	{
+		/* If the result is copied to dest, ret.type is set to NULL */
 		struct lrval ret;
 		struct value rv = {}, *lrv = NULL;
 		struct type *rvtype;
@@ -1698,9 +1723,11 @@ in `rval`.
 		}
 		## interp exec cases
 		}
-		ret.lval = lrv;
-		ret.rval = rv;
-		ret.type = rvtype;
+		if (rvtype) {
+			ret.lval = lrv;
+			ret.rval = rv;
+			ret.type = rvtype;
+		}
 		## interp exec cleanup
 		return ret;
 	}
@@ -1992,7 +2019,7 @@ with a const size by whether they are prepared at parse time or not.
 		if (i >= 0 && i < ltype->array.size)
 			lrv = ptr + i * rvtype->size;
 		else
-			val_init(ltype->array.member, &rv);
+			val_init(ltype->array.member, &rv); // UNSAFE
 		ltype = NULL;
 		break;
 	}
@@ -3999,12 +4026,9 @@ it is declared, and error will be raised as the name is created as
 
 	case Assign:
 		lleft = linterp_exec(c, b->left, &ltype);
-		right = interp_exec(c, b->right, &rtype);
-		if (lleft) {
-			free_value(ltype, lleft);
-			dup_value(ltype, &right, lleft);
-			ltype = NULL;
-		}
+		if (lleft)
+			dinterp_exec(c, b->right, lleft, ltype, 1);
+		ltype = Tnone;
 		break;
 
 	case Declare:
@@ -4015,13 +4039,10 @@ it is declared, and error will be raised as the name is created as
 		val = var_value(c, v);
 		if (v->type->prepare_type)
 			v->type->prepare_type(c, v->type, 0);
-		if (b->right) {
-			right = interp_exec(c, b->right, &rtype);
-			memcpy(val, &right, rtype->size);
-			rtype = Tnone;
-		} else {
+		if (b->right)
+			dinterp_exec(c, b->right, val, v->type, 0);
+		else
 			val_init(v->type, val);
-		}
 		break;
 	}
 
@@ -4533,7 +4554,7 @@ casepart` to track a list of case parts.
 		rv = interp_exec(c, b->left, &rvtype);
 		if (rvtype == Tnone ||
 		    (rvtype == Tbool && rv.bool != 0))
-			// cnd is Tnone or Tbool, doesn't need to be freed
+			// rvtype is Tnone or Tbool, doesn't need to be freed
 			interp_exec(c, b->right, NULL);
 		break;
 
-- 
2.43.0