[v24.x] deps: V8: backport 0b94a9fd23ba - #65753

Backport of v8/v8@0b94a9f ("[leaptiering] Fix BaselineOutOfLinePrologue builtin") to the V8 13.6 in v24.x. Applies cleanly to deps/v8; v8_embedder_string bumped to -node.54.

Fixes: #62393

What crashes

A register that nothing guarantees, pushed on the stack as if it were a tagged pointer, then read by the GC:

sequenceDiagram
    participant M as JS caller (Sparkplug code)
    participant CL as CompileLazy (TurboFan/CSA-generated)
    participant P as BaselineOutOfLinePrologue (hand-written asm)
    participant GC as mark-compact
    M->>CL: first call of f()
    Note over CL: x4 is NOT part of the JS linkage here<br/>(V8_JS_LINKAGE_INCLUDES_DISPATCH_HANDLE undefined)<br/>register allocator uses x4 as scratch → x4 = 0x7
    CL->>P: tail call into freshly compiled baseline code
    Note over P: stack guard slow path:<br/>Push(x4, new_target)  // "dispatch handles always look like Smis"
    P->>GC: Runtime_StackGuardWithGap → CollectGarbage
    Note over GC: InternalFrame::Iterate → ClearStaleLeftTrimmedPointerVisitor<br/>IsHeapObject(0x7) is true (low bit set)<br/>reads map_word at 0x7 - 1
    GC--xGC: SIGSEGV, KERN_INVALID_ADDRESS at 0x6

Node.js builds V8 with leaptiering on and the sandbox off. In that configuration V8_JS_LINKAGE_INCLUDES_DISPATCH_HANDLE is not defined (src/common/globals.h), so kJavaScriptCallDispatchHandleRegister (x4 on arm64, r15 on x64) is not carried by JS calls. Two hand-written builtins still gated the push on V8_ENABLE_LEAPTIERING_BOOL. The upstream commit message says it directly: "This issue triggered only on non-sandbox configuration with enabled leaptiering."

Why only v24: ClearStaleLeftTrimmedPointerVisitor started visiting stack roots in V8 12.6 (v8/v8@22c404b8bbbb, 2024-05). Node 22 ships V8 12.4, so the same stale slot was never dereferenced there. The fix landed in V8 main after the 13.6 branch cut and is present in Node 25/26.

Evidence

Instrumented v24.20.0 (macOS arm64) logging every non-Smi, non-pointer value in INTERNAL frame slots right before the GC visitor ran. Three independent crashes, identical frame:

builtin = BaselineOutOfLinePrologue   code_offset = 116   INTERNAL frame, 6 slots from sp:

[0] 0x7000000000    SmiTag(frame_size)              ok
[1] 0x0             padreg (PushArgument)           ok
[2] 0x10b697280011  new_target                      ok, valid HeapObject
[3] 0x7             kJavaScriptCallDispatchHandleRegister   <-- stale; callee's real dispatch_handle was 0x143c900
[4] 0x0             padreg (EnterFrame)             ok
[5] 0x2e            INTERNAL frame marker (23 << 1) ok

Matching crash report for the same worker: EXC_BAD_ACCESS / KERN_INVALID_ADDRESS at 0x0000000000000006 in ClearStaleLeftTrimmedPointerVisitor::VisitRootPointers ← InternalFrame::Iterate.

Stack walk at that point (callee = first call of a small module-level helper, i.e. the CompileLazy path):

 0  EXIT      CEntry_Return1_ArgvOnStack_NoBuiltinExit
 1  INTERNAL  BaselineOutOfLinePrologue                          <-- bad slot here
 2  BASELINE  forEach            (axios.cjs)   dispatch_handle 0x143c900
 3  BASELINE  <module wrapper>   (axios.cjs)   dispatch_handle 0x143c400
 4  TURBOFAN  _execModule        (jest-runtime)

A temporary check at the builtin entry (x4 == closure.dispatch_handle, abort otherwise) fires even for:

node --always-sparkplug -e 'function f(a,b){return a+b}; f(1,2)'

so this is not memory corruption: in this configuration the register simply never holds the handle.

The fix (same as upstream, all ports)

 deps/v8/src/builtins/arm64/builtins-arm64.cc          Generate_BaselineOutOfLinePrologue
 deps/v8/src/codegen/arm64/macro-assembler-arm64.cc    GenerateTailCallToReturnedCode
-    Register maybe_dispatch_handle = V8_ENABLE_LEAPTIERING_BOOL
+    Register maybe_dispatch_handle = V8_JS_LINKAGE_INCLUDES_DISPATCH_HANDLE_BOOL
                                          ? kJavaScriptCallDispatchHandleRegister
                                          : padreg;
     static_assert(kJSDispatchHandleShift > 0);
+    __ AssertSmi(maybe_dispatch_handle);
     __ Push(maybe_dispatch_handle, new_target);

With the linkage macro undefined the slot now receives padreg (xzr, i.e. Smi 0) instead of whatever was in x4. Same change on x64 (#ifdef V8_JS_LINKAGE_INCLUDES_DISPATCH_HANDLE around the push/pop), loong64, mips64 and riscv.

Verification

Same jest suite (322 suites / 5184 tests), 4 workers, --no-maglev --always-sparkplug --max-old-space-size=512, macOS arm64:

The last column matters more than the crash count: the instrumentation logged any non-pointer tagged value in an INTERNAL frame slot whether or not a GC happened to hit it.

I have not run V8 CI / make test-v8; please trigger it.

Refs: v8/v8@0b94a9f