From a1ee817906deec24c5d3a5033c97d63bc9d372f9 Mon Sep 17 00:00:00 2001
From: Hojun-Cho <ghwns6743@gmail.com>
Date: Wed, 20 May 2026 19:28:59 +0900
Subject: [PATCH] =?UTF-8?q?selfhost/cmd/ww/main.ww:=203=C3=97=20".\0"=20am?=
 =?UTF-8?q?alloc=20=E2=86=92=20stack=20[2]u8?=
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dobuild/dorun/dotest each allocated a 2-byte heap "." prefix buffer via
amalloc, set dot[0]='.'; dot[1]=0; passed dot as *u8 to a callee, then
let the arena chunk live forever. The dot pointer never escapes the
function — every callee chain (resolvemodule, cstrendswithlit,
rundirtests/runsingletest) byte-copies its input into a fresh arena
allocation before returning, never storing the original pointer.

Replace with `let dot: [2]u8 = ['.': u8, 0u8]; ... &dot[0]`. Both
stages allocate a fresh frame slot per let at function-frame entry
(localoff cstage / localadd wwstage), so the slot lives across the
synchronous callee.

Verified 132/132 + 995_self_rebuild byte-identity.
---
 selfhost/cmd/ww/main.combined.ww | 15 ++++++---------
 selfhost/cmd/ww/main.ww          | 15 ++++++---------
 2 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/selfhost/cmd/ww/main.combined.ww b/selfhost/cmd/ww/main.combined.ww
index db84b3d4..03d6fe1d 100644
--- a/selfhost/cmd/ww/main.combined.ww
+++ b/selfhost/cmd/ww/main.combined.ww
@@ -2038,9 +2038,8 @@ fn dobuild(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 
 	if (src == nil) {
 		// default to cwd module
-		let dot: *u8 = amalloc(a, 2u64): *u8;
-		dot[0] = 46u8; dot[1] = 0u8;
-		src = dot;
+		let dot: [2]u8 = ['.': u8, 0u8];
+		src = &dot[0];
 	};
 	let isdir: i32 = 0;
 	let resolved: *u8 = resolvemodule(a, selfdir, src, incs, &isdir);
@@ -2193,9 +2192,8 @@ fn dorun(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	};
 
 	if (src == nil) {
-		let dot: *u8 = amalloc(a, 2u64): *u8;
-		dot[0] = 46u8; dot[1] = 0u8;
-		src = dot;
+		let dot: [2]u8 = ['.': u8, 0u8];
+		src = &dot[0];
 	};
 	let isdir: i32 = 0;
 	let resolved: *u8 = resolvemodule(a, selfdir, src, incs, &isdir);
@@ -2331,9 +2329,8 @@ fn dotest(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	let a: *arena = newarena();
 	let target: *u8;
 	if (start >= argc) {
-		let dot: *u8 = amalloc(a, 2u64): *u8;
-		dot[0] = 46u8; dot[1] = 0u8;
-		target = dot;
+		let dot: [2]u8 = ['.': u8, 0u8];
+		target = &dot[0];
 	} else {
 		target = argv[start];
 	};
diff --git a/selfhost/cmd/ww/main.ww b/selfhost/cmd/ww/main.ww
index d17955c4..af5ff430 100644
--- a/selfhost/cmd/ww/main.ww
+++ b/selfhost/cmd/ww/main.ww
@@ -1178,9 +1178,8 @@ fn dobuild(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 
 	if (src == nil) {
 		// default to cwd module
-		let dot: *u8 = amalloc(a, 2u64): *u8;
-		dot[0] = 46u8; dot[1] = 0u8;
-		src = dot;
+		let dot: [2]u8 = ['.': u8, 0u8];
+		src = &dot[0];
 	};
 	let isdir: i32 = 0;
 	let resolved: *u8 = resolvemodule(a, selfdir, src, incs, &isdir);
@@ -1333,9 +1332,8 @@ fn dorun(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	};
 
 	if (src == nil) {
-		let dot: *u8 = amalloc(a, 2u64): *u8;
-		dot[0] = 46u8; dot[1] = 0u8;
-		src = dot;
+		let dot: [2]u8 = ['.': u8, 0u8];
+		src = &dot[0];
 	};
 	let isdir: i32 = 0;
 	let resolved: *u8 = resolvemodule(a, selfdir, src, incs, &isdir);
@@ -1471,9 +1469,8 @@ fn dotest(selfdir: *u8, argv: **u8, argc: i32, start: i32) i32 = {
 	let a: *arena = newarena();
 	let target: *u8;
 	if (start >= argc) {
-		let dot: *u8 = amalloc(a, 2u64): *u8;
-		dot[0] = 46u8; dot[1] = 0u8;
-		target = dot;
+		let dot: [2]u8 = ['.': u8, 0u8];
+		target = &dot[0];
 	} else {
 		target = argv[start];
 	};