Skip to main content

v8 command

v8 version​

Displays the version information of the current V8 engine.

  • v8 version
(gdb) v8 version
8.4.371.23
8.4.371.23-node.85

v8 inspect / object​

Similar to d8 to display detailed parsing information for an object.

  • v8 inspect [tagging]
  • v8 object [address]

Tagging Pointer is the object pointer of the V8 engine, similar to the c/c++ pointer. When V8 allocates objects, it will always align the address according to the word width, so the lowest 2 bits of the pointer are always zero, so it is used to identify additional information . The lowest bit is 1 for a Tagging Pointer, and 0 for a Smi. The next lowest bit is the Strong/Weak reference flag.

            |----- 32 bits -----|----- 32 bits -----|
Pointer:    |________________address______________w1|
Smi:        |____int32_value____|0000000000000000000|

The difference between the v8 inspect and v8 object command lines is whether the argument is a Tagging Pointer or the memory address of the object.

(gdb) v8 i 0xe953aa7729
[JSObject 0xe953aa7729]
- Properties:
 - variables: <JsObject 0xe953ab2389>
 - target_defaults: <JsObject 0xe953ab2349>
- Elements: []
[Map 0x2048032e79a9]
- InstanceSizeInWords: 5
- InobjectPropertiesStartOrConstructorFunctionIndex: 3
- UsedOrUnusedInstanceSizeInWords: 5
- VisitorId: 25
- InstanceType: JS_OBJECT_TYPE (1057)
- BitField: 0x0
[MapBitFields1 0x0]
- HasNonInstancePrototype: 0
- IsCallable: 0
- HasNamedInterceptor: 0
- HasIndexedInterceptor: 0
- IsUndetectable: 0
- IsAccessCheckNeeded: 0
- IsConstructor: 0
- HasPrototypeSlot: 0
- BitField2: 0x19
[MapBitFields2 0x19]
- NewTargetIsBase: 1
- IsImmutablePrototype: 0
- Unused: 0
- ElementsKind: HOLEY_ELEMENTS (3)
- BitField3: 0x8400bff
[MapBitFields3 0x8400bff]
- EnumLength: 1023
- NumberOfOwnDescriptors: 2
- IsPrototypeMap: 0
- IsDictionaryMap: 0
- OwnsDescriptors: 1
- IsInRetainedMapList: 0
- IsDeprecated: 0
- IsUnstable: 0
- IsMigrationTarget: 0
- IsExtensible: 1
- MayHaveIntrestingSymbols: 0
- ConstructionCounter: 0
- Prototype: <JsObject 0x11eb600c0931>
- ConstructorOrBackPointerOrNativeContext: <Map 0x2048032e7961>
- InstanceDescriptors: <DescriptorArray 0x368e672facf1>
- DependentCode: <WeakFixedArray 0xb6f27200289>
- PrototypeValidityCell: <Cell 0x2d2cd9700661>
- TransitionsOrPrototypeInfo: <Smi 0 0x0>
[HeapObject]
 - MapWord: 0x2048032e79a9
 - Size: 40
 - Page: 0xe953a80000
   - NextObject: 0xe953aa7751

v8 bt​

Display the v8 call stack.

  • v8 bt
(gdb) v8 bt
#0  0x00000e5ce6f04010 home(this=<JsObject 0x620f5fe24e9>) at /disks/banana/zlei/alibaba/andb/test/backtrace/deadloop/dist/controller/home.controller.js:0
#1  0x0000000001462119 <arguments_adaptor>()
#2  0x00000000014681e2 (anonymous)(this=<Oddball 0x5d12f880471>, arg0=<JsObject 0x620f5fc8421>, arg1=<JsBoundFunction 0x620f5fe1c39>) at /disks/banana/zlei/alibaba/andb/test/backtrace/deadloop/node_modules/@midwayjs/core/dist/common/webGenerator.js:0
#3  0x0000000001494db0 (anonymous)(this=<JsGlobalProxy 0x12b3e36823e1>, arg0=<JsObject 0x620f5fe24e9>) at undefined:1489
#4  0x00000000015110ee <stub>()
#5  0x0000000001487eda <stub>()
#6  0x0000000001465e58 <entry>()
#7  0x0000000000d2863b v8::internal::(anonymous namespace)::Invoke(v8::internal::Isolate*, v8::internal::(anonymous namespace)::InvokeParams const&)()
#8  0x0000000000d29553 v8::internal::Execution::TryRunMicrotasks(v8::internal::Isolate*, v8::internal::MicrotaskQueue*, v8::internal::MaybeHandle<v8::internal::Object>*)()
#9  0x0000000000d52be1 v8::internal::MicrotaskQueue::RunMicrotasks(v8::internal::Isolate*)()
#10 0x0000000000d52fc1 v8::internal::MicrotaskQueue::PerformCheckpoint(v8::Isolate*)()
#11 0x0000000000c38261 v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<false>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments)()
#12 0x0000000000c39eff v8::internal::Builtin_HandleApiCall(int, unsigned long*, v8::internal::Isolate*)()
#13 0x00000000014cf459 <builtin_exit>()
#14 0x00000000014681e2 processTicksAndRejections(this=<JsApiObject 0x12b3e3681d81>) at internal/process/task_queues.js:0
#15 0x0000000001465efa <internal>()
#16 0x0000000001465cd8 <entry>()
#17 0x0000000000d281e1 v8::internal::(anonymous namespace)::Invoke(v8::internal::Isolate*, v8::internal::(anonymous namespace)::InvokeParams const&)()
#18 0x0000000000d2900f v8::internal::Execution::Call(v8::internal::Isolate*, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Object>, int, v8::internal::Handle<v8::internal::Object>*)()
#19 0x0000000000bd4879 v8::Function::Call(v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*)()
#20 0x000000000098af6e node::InternalCallbackScope::Close()()
#21 0x000000000098c172 node::InternalMakeCallback(node::Environment*, v8::Local<v8::Object>, v8::Local<v8::Object>, v8::Local<v8::Function>, int, v8::Local<v8::Value>*, node::async_context)()
#22 0x000000000099ae06 node::AsyncWrap::MakeCallback(v8::Local<v8::Function>, int, v8::Local<v8::Value>*)()
#23 0x0000000000a473cd non-virtual thunk to node::(anonymous namespace)::Parser::OnStreamRead(long, uv_buf_t const&)()
#24 0x0000000000b0fcbc node::LibuvStreamWrap::ReadStart()::{lambda(uv_stream_s*, long, uv_buf_t const*)#2}::_FUN(uv_stream_s*, long, uv_buf_t const*)()
#25 0x00000000014551d2 uv__read(stream=<optimized out>) at ../deps/uv/src/unix/stream.c:1259
#26 0x00000000014558d8 uv__stream_io(loop=<optimized out>, w=<optimized out>, events=<optimized out>) at ../deps/uv/src/unix/stream.c:1326
#27 0x000000000145c2e5 uv__io_poll(loop=<optimized out>, timeout=<optimized out>) at ../deps/uv/src/unix/linux-core.c:472
#28 0x0000000001449595 uv_run(loop=<optimized out>, mode=<optimized out>) at ../deps/uv/src/unix/core.c:394
#29 0x0000000000a6fef5 node::NodeMainInstance::Run()()
#30 0x00000000009f7c41 node::Start(int, char**)()
#31 0x00007f71ae0fe445 __libc_start_main(main=0x9885b0 <main>, argc=2, argv=0x7fff155e5378, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fff155e5368) at ../csu/libc-start.c:266
#32 0x0000000000989c5d _start()