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Isolate command

Isolate guess​

Locate the v8::internal::Isolate structure.

v8::internal::Isolate is the core data structure of the V8 engine, which represents a V8 virtual machine, which has its own Heap (heap), GC (garbage collection), etc. Many analysis tools of andb need to be based on this data structure, so generally debugging Corefile should first locate Isolate.

  • isolate guess page
  • isolate guess stack

andb currently provides 2 methods to quickly locate Isolate,

  1. By page

The V8 engine maintains memory page management by itself, and each page also has a page header fixed for each version, through which the V8::internal::Heap structure can be found. The Heap structure is part of Isolate, so it is possible to find the first address of Isolate.

  1. By stack

Node.js keeps the data of the V8 engine in the local variables of Node::Run(), which are stored on the call stack of the main thread, The first address of Isolate can be obtained from the main thread stack memory.

(gdb) isolate guess page
(v8::internal::Isolate *) $isolate = 0x5f93c70
(gdb) isolate guess stack
(v8::internal::Isolate *) $isolate = 0x5f93c70

Variables prefixed with "\$" are called Convenience variables. In the above example, you can access the v8 virtual machine through "\$isolate"

(gdb) p $isolate->heap_.new_space_
$2 = (v8::internal::NewSpace *) 0x60296f0

(gdb) p $isolate->heap_.new_space_.to_space_
$5 = {
  <v8::internal::Space> = {
    <v8::internal::Malloced> = {<No data fields>},
    members of v8::internal::Space:
    _vptr.Space = 0x23d3890 <vtable for v8::internal::SemiSpace+16>,
    allocation_observers_ = std::vector of length 0, capacity 0,
    memory_chunk_list_ = {
      front_ = 0x667900000,
      back_ = 0x159131e80000
    },
    external_backing_store_bytes_ = 0x6029a20,
    allocation_observers_paused_ = false,
    heap_ = 0x5f9d1b8,
    id_ = v8::internal::NEW_SPACE,
    committed_ = {
      <std::__atomic_base<unsigned long>> = {
        static _S_alignment = 8,
        _M_i = 1048576
      }, <No data fields>},
    max_committed_ = 2097152,
    free_list_ = std::unique_ptr<v8::internal::FreeList> = {
      get() = 0x6029980
    }
  },
  members of v8::internal::SemiSpace:
  current_capacity_ = 1048576,
  maximum_capacity_ = 16777216,
  minimum_capacity_ = 1048576,
  age_mark_ = 27507487032,
  committed_ = true,
  id_ = v8::internal::kToSpace,
  current_page_ = 0x10d414980000,
  pages_used_ = 2
}

Currently andb only supports a single Isolate.