From 19e60d98644908b93a82bd57fc05597102a76bac Mon Sep 17 00:00:00 2001
From: Rangi <sylvie.oukaour+rangi42@gmail.com>
Date: Tue, 14 Jul 2026 00:42:42 -0400
Subject: [PATCH] Fix large `ds` in linker script overflowing the PC

---
 src/link/layout.cpp             | 4 +++-
 test/link/script-ds/a.asm       | 2 ++
 test/link/script-ds/b.asm       | 2 ++
 test/link/script-ds/out.err     | 3 +++
 test/link/script-ds/script.link | 5 +++++
 test/link/test.sh               | 9 +++++++++
 6 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 test/link/script-ds/a.asm
 create mode 100644 test/link/script-ds/b.asm
 create mode 100644 test/link/script-ds/out.err
 create mode 100644 test/link/script-ds/script.link

diff --git a/src/link/layout.cpp b/src/link/layout.cpp
index 89b51465..750e22fe 100644
--- a/src/link/layout.cpp
+++ b/src/link/layout.cpp
@@ -204,7 +204,9 @@ void layout_Pad(uint32_t length) {
 	uint16_t &pc = curAddr[activeType][activeBankIdx];
 
 	assume(pc >= typeInfo.startAddr);
-	if (uint16_t offset = pc - typeInfo.startAddr; length + offset > typeInfo.size) {
+	// `length + offset` can overflow `uint32_t`, so check just `length` first
+	if (uint16_t offset = pc - typeInfo.startAddr;
+	    length > typeInfo.size || length + offset > typeInfo.size) {
 		scriptError(
 		    "Cannot increase the current address by %u bytes: only %u bytes to $%04" PRIx16,
 		    length,
diff --git a/test/link/script-ds/a.asm b/test/link/script-ds/a.asm
new file mode 100644
index 00000000..1c186445
--- /dev/null
+++ b/test/link/script-ds/a.asm
@@ -0,0 +1,2 @@
+section "foo", rom0
+Foo:: dw Foo
diff --git a/test/link/script-ds/b.asm b/test/link/script-ds/b.asm
new file mode 100644
index 00000000..a4820cdb
--- /dev/null
+++ b/test/link/script-ds/b.asm
@@ -0,0 +1,2 @@
+section "bar", rom0
+Bar:: dw Bar
diff --git a/test/link/script-ds/out.err b/test/link/script-ds/out.err
new file mode 100644
index 00000000..0324b18a
--- /dev/null
+++ b/test/link/script-ds/out.err
@@ -0,0 +1,3 @@
+error: Cannot increase the current address by 4294967280 bytes: only 12286 bytes to $4000
+    at script-ds/script.link(4)
+Linking failed with 1 error
diff --git a/test/link/script-ds/script.link b/test/link/script-ds/script.link
new file mode 100644
index 00000000..ef46c75d
--- /dev/null
+++ b/test/link/script-ds/script.link
@@ -0,0 +1,5 @@
+ROM0
+	org $1000
+	"foo"
+	ds $ffff_fff0
+	"bar"
diff --git a/test/link/test.sh b/test/link/test.sh
index d82c77e6..760b136f 100755
--- a/test/link/test.sh
+++ b/test/link/test.sh
@@ -322,6 +322,15 @@ tryDiff "$test"/out.err "$outtemp"
 tryCmp "$test"/out.gb "$gbtemp"
 evaluateTest
 
+test="script-ds"
+startTest
+"$RGBASM" -o "$otemp" "$test"/a.asm
+"$RGBASM" -o "$gbtemp2" "$test"/b.asm
+continueTest
+rgblinkQuiet -o "$gbtemp" -l "$test"/script.link "$otemp" "$gbtemp2" 2>"$outtemp"
+tryDiff "$test"/out.err "$outtemp"
+evaluateTest
+
 test="script-include"
 startTest
 "$RGBASM" -o "$otemp" "$test"/a.asm