From 0c2f512a9c2a98d00046ede2e1e665cd6e38052e Mon Sep 17 00:00:00 2001
From: fatadel <afatkhutdinov@mozilla.com>
Date: Wed, 18 Feb 2026 14:49:51 +0100
Subject: [PATCH 1/3] fix crash when nativeSymbol index is out of bounds in
 assembly view

---
 src/selectors/url-state.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/selectors/url-state.ts b/src/selectors/url-state.ts
index 3045882da5..a584925126 100644
--- a/src/selectors/url-state.ts
+++ b/src/selectors/url-state.ts
@@ -88,7 +88,7 @@ export const getAssemblyViewNativeSymbol: Selector<NativeSymbolInfo | null> = (
   const { nativeSymbols, currentNativeSymbol } =
     getProfileSpecificState(state).assemblyView;
   return currentNativeSymbol !== null
-    ? nativeSymbols[currentNativeSymbol]
+    ? (nativeSymbols[currentNativeSymbol] ?? null)
     : null;
 };
 export const getAssemblyViewCurrentNativeSymbolEntryIndex: Selector<

From 109f4256a8b24c60edab252911578f18cecdb62e Mon Sep 17 00:00:00 2001
From: fatadel <afatkhutdinov@mozilla.com>
Date: Wed, 18 Feb 2026 15:09:58 +0100
Subject: [PATCH 2/3] add test

---
 src/test/store/bottom-box.test.ts | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/src/test/store/bottom-box.test.ts b/src/test/store/bottom-box.test.ts
index f410ee3a3c..32a6e1c1a4 100644
--- a/src/test/store/bottom-box.test.ts
+++ b/src/test/store/bottom-box.test.ts
@@ -345,6 +345,29 @@ describe('bottom box', function () {
     ).toBeOneOf([0x40, 0x45]);
   });
 
+  it('returns null for getAssemblyViewNativeSymbol when nativeSymbols is empty but initialNativeSymbol is 0', function () {
+    // initialNativeSymbol = 0, even when nativeSymbols is empty
+    // (e.g., when the frame has no native symbol).
+    // The selector must return null (not undefined)
+    // to avoid a crash when downstream code accesses .libIndex on it.
+    const { dispatch, getState } = setup();
+
+    dispatch(
+      updateBottomBoxContentsAndMaybeOpen('calltree', {
+        libIndex: null,
+        sourceIndex: null,
+        nativeSymbols: [],
+        initialNativeSymbol: 0,
+        highlightedLineNumber: null,
+        highlightedInstructionAddress: null,
+      })
+    );
+
+    expect(
+      UrlStateSelectors.getAssemblyViewNativeSymbol(getState())
+    ).toBeNull();
+  });
+
   // Further ideas for tests:
   //
   // - A test with multiple threads: Open the assembly view for a symbol, switch

From e09282ca25238fb796463a800c6f5526e8b6412c Mon Sep 17 00:00:00 2001
From: fatadel <afatkhutdinov@mozilla.com>
Date: Wed, 18 Feb 2026 15:37:02 +0100
Subject: [PATCH 3/3] incorporate feedback

---
 src/reducers/url-state.ts  | 11 ++++++++++-
 src/selectors/url-state.ts |  2 +-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/reducers/url-state.ts b/src/reducers/url-state.ts
index 8903ea34b2..d307ce0b6e 100644
--- a/src/reducers/url-state.ts
+++ b/src/reducers/url-state.ts
@@ -606,12 +606,21 @@ const assemblyView: Reducer<AssemblyViewState> = (
       const { nativeSymbols, currentNativeSymbol, shouldOpenAssemblyView } =
         action;
       const shouldScroll = action.scrollToInstructionAddress !== undefined;
+
+      // Clamp currentNativeSymbol to null if it is out of bounds, so that
+      // "currentNativeSymbol is always in-bounds or null" holds.
+      const clampedNativeSymbol =
+        currentNativeSymbol !== null &&
+        currentNativeSymbol < nativeSymbols.length
+          ? currentNativeSymbol
+          : null;
+
       return {
         scrollGeneration: shouldScroll
           ? state.scrollGeneration + 1
           : state.scrollGeneration,
         nativeSymbols,
-        currentNativeSymbol,
+        currentNativeSymbol: clampedNativeSymbol,
         isOpen: state.isOpen || shouldOpenAssemblyView,
         scrollToInstructionAddress: action.scrollToInstructionAddress,
         highlightedInstruction: action.highlightedInstructionAddress,
diff --git a/src/selectors/url-state.ts b/src/selectors/url-state.ts
index a584925126..3045882da5 100644
--- a/src/selectors/url-state.ts
+++ b/src/selectors/url-state.ts
@@ -88,7 +88,7 @@ export const getAssemblyViewNativeSymbol: Selector<NativeSymbolInfo | null> = (
   const { nativeSymbols, currentNativeSymbol } =
     getProfileSpecificState(state).assemblyView;
   return currentNativeSymbol !== null
-    ? (nativeSymbols[currentNativeSymbol] ?? null)
+    ? nativeSymbols[currentNativeSymbol]
     : null;
 };
 export const getAssemblyViewCurrentNativeSymbolEntryIndex: Selector<