From d9c0d37fd52481304c345fa9537bec6a5302d4c5 Mon Sep 17 00:00:00 2001
From: Rangi <sylvie.oukaour+rangi42@gmail.com>
Date: Mon, 20 Jul 2026 19:12:54 -0400
Subject: [PATCH] Explicitly allow `JR` offsets to wrap around in RGBLINK

This reverts commit f27a8132d993fc48df27410c0660fde14c0aaccd.
---
 src/link/patch.cpp                  |   6 ++++--
 test/link/jr-wraparound/a.asm       |   3 +++
 test/link/jr-wraparound/b.asm       |   4 ++++
 test/link/jr-wraparound/ref.out.bin | Bin 0 -> 16384 bytes
 test/link/jr-wraparound/ref.out.sym |   5 +++++
 test/link/test.sh                   |  10 ++++++++++
 6 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 test/link/jr-wraparound/a.asm
 create mode 100644 test/link/jr-wraparound/b.asm
 create mode 100644 test/link/jr-wraparound/ref.out.bin
 create mode 100644 test/link/jr-wraparound/ref.out.sym

diff --git a/src/link/patch.cpp b/src/link/patch.cpp
index e16befd6..8a0e43f7 100644
--- a/src/link/patch.cpp
+++ b/src/link/patch.cpp
@@ -588,12 +588,14 @@ static void applyFilePatches(Section &section, Section &dataSection) {
 				// Offset is relative to the byte *after* the operand
 				// PC as operand to `jr` is lower than reference PC by 2
 				uint16_t address = patch.pcSection->org + patch.pcOffset + 2;
-				int32_t jumpOffset = value - address;
+				// The truncation of `value - address` is intentional, since
+				// a low ROM0 address may `jr` to a high HRAM one.
+				int16_t jumpOffset = value - address;
 
 				if (jumpOffset < -128 || jumpOffset > 127) {
 					firstErrorAt(
 					    patch,
-					    "`JR` target must be between -128 and 127 bytes away, not %" PRId32
+					    "`JR` target must be between -128 and 127 bytes away, not %" PRId16
 					    "; use `JP` instead",
 					    jumpOffset
 					);
diff --git a/test/link/jr-wraparound/a.asm b/test/link/jr-wraparound/a.asm
new file mode 100644
index 00000000..796baf67
--- /dev/null
+++ b/test/link/jr-wraparound/a.asm
@@ -0,0 +1,3 @@
+SECTION "low", ROM0[$0048]
+LCDInterrupt:
+	jr hLCDInterruptHandler
diff --git a/test/link/jr-wraparound/b.asm b/test/link/jr-wraparound/b.asm
new file mode 100644
index 00000000..df368750
--- /dev/null
+++ b/test/link/jr-wraparound/b.asm
@@ -0,0 +1,4 @@
+SECTION "high", HRAM[$FFE0]
+hLCDInterruptHandler::
+.jp: db ; should be $c3 (jp)
+.address: dw
diff --git a/test/link/jr-wraparound/ref.out.bin b/test/link/jr-wraparound/ref.out.bin
new file mode 100644
index 0000000000000000000000000000000000000000..801fd75fe6aa2783bd40eb11d8caefb25c4a72b4
GIT binary patch
literal 16384
zcmeIuF#!Mo2*a?+KskCbv5!<hk0hODJ0BMU1PBlyK!5-N0t5&UAV7cs0RjXF5FkK+
y009C72oNAZfB*pk1PBlyK!5-N0t5&UAV7cs0RjXF5FkK+009C72oNCfQQ!cO{{XK5

literal 0
HcmV?d00001

diff --git a/test/link/jr-wraparound/ref.out.sym b/test/link/jr-wraparound/ref.out.sym
new file mode 100644
index 00000000..b63e8648
--- /dev/null
+++ b/test/link/jr-wraparound/ref.out.sym
@@ -0,0 +1,5 @@
+; File generated by rgblink
+00:0048 LCDInterrupt
+00:ffe0 hLCDInterruptHandler
+00:ffe0 hLCDInterruptHandler.jp
+00:ffe1 hLCDInterruptHandler.address
diff --git a/test/link/test.sh b/test/link/test.sh
index 760b136f..cb30efc3 100755
--- a/test/link/test.sh
+++ b/test/link/test.sh
@@ -191,6 +191,16 @@ tryDiff "$test"/ref.out.map "$outtemp"
 tryDiff "$test"/ref.out.sym "$outtemp2"
 evaluateTest
 
+test="jr-wraparound"
+startTest
+"$RGBASM" -o "$otemp" "$test"/a.asm
+"$RGBASM" -o "$outtemp" "$test"/b.asm
+continueTest
+rgblinkQuiet -o "$gbtemp" -n "$outtemp2" "$otemp" "$outtemp"
+tryCmpRom "$test"/ref.out.bin
+tryDiff "$test"/ref.out.sym "$outtemp2"
+evaluateTest
+
 test="high-low"
 startTest
 "$RGBASM" -o "$otemp" "$test"/a.asm