Creating isolate segfaults when no natives_blob.bin present

[xax...@gmail.com]

I saw a thread from earlier this year, but I wanted to say it's still happening:

https://groups.google.com/forum/#!topic/v8-dev/LxKgBbEHLCE

If I run the sample code from here 

https://developers.google.com/v8/get_started

and don't copy natives_blob.bin to the current directory, I get the following crash when creating an isolate:

* thread #1: tid = 0xb1c49, 0x0000000100724b6e h2`v8::internal::NativesCollection<(v8::internal::NativeType)0>::GetScriptSource(int) [inlined] v8::internal::List<v8::internal::Vector<char const>, v8::internal::FreeStoreAllocationPolicy>::operator[](i=3) const + 3 at list.h:69, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x20)

  * frame #0: 0x0000000100724b6e h2`v8::internal::NativesCollection<(v8::internal::NativeType)0>::GetScriptSource(int) [inlined] v8::internal::List<v8::internal::Vector<char const>, v8::internal::FreeStoreAllocationPolicy>::operator[](i=3) const + 3 at list.h:69

    frame #1: 0x0000000100724b6b h2`v8::internal::NativesCollection<(v8::internal::NativeType)0>::GetScriptSource(int) [inlined] v8::internal::NativesStore::GetScriptSource(this=0x0000000000000000, index=3) at natives-external.cc:41

    frame #2: 0x0000000100724b6b h2`v8::internal::NativesCollection<(v8::internal::NativeType)0>::GetScriptSource(index=3) + 11 at natives-external.cc:213

    frame #3: 0x00000001004d3bc2 h2`v8::internal::Deserializer::ReadData(this=0x00007fff5fbff7a8, current=<unavailable>, limit=0x000034e592019710, source_space=1, current_object_address="\x89R") + 4802 at serialize.cc:1157

    frame #4: 0x00000001004d4b97 h2`v8::internal::Deserializer::ReadObject(this=0x00007fff5fbff7a8, space_number=1, write_back=0x000034e592019610) + 423 at serialize.cc:825

    frame #5: 0x00000001004d2bf0 h2`v8::internal::Deserializer::ReadData(this=0x00007fff5fbff7a8, current=<unavailable>, limit=0x000034e5920196e8, source_space=1, current_object_address="\tB") + 752 at serialize.cc:1028

    frame #6: 0x00000001004d4b97 h2`v8::internal::Deserializer::ReadObject(this=0x00007fff5fbff7a8, space_number=1, write_back=0x0000000102801420) + 423 at serialize.cc:825

    frame #7: 0x00000001004d2bf0 h2`v8::internal::Deserializer::ReadData(this=0x00007fff5fbff7a8, current=<unavailable>, limit=0x0000000102801ae8, source_space=0, current_object_address=0x0000000000000000) + 752 at serialize.cc:1028

    frame #8: 0x00000001002c2219 h2`v8::internal::Heap::IterateStrongRoots(this=0x0000000102801020, v=0x00007fff5fbff7a8, mode=VISIT_ONLY_STRONG) + 41 at heap.cc:4569

    frame #9: 0x00000001004d204d h2`v8::internal::Deserializer::Deserialize(this=0x00007fff5fbff7a8, isolate=<unavailable>) + 253 at serialize.cc:532

    frame #10: 0x000000010034cf66 h2`v8::internal::Isolate::Init(this=0x0000000102801000, des=0x00007fff5fbff7a8) + 4390 at isolate.cc:2201

    frame #11: 0x00000001004dd0e5 h2`v8::internal::Snapshot::Initialize(isolate=0x0000000102801000) + 549 at snapshot-common.cc:58

    frame #12: 0x0000000100029a24 h2`v8::Isolate::New(params=<unavailable>) + 308 at api.cc:7139

    frame #13: 0x000000010000172d h2`main + 157

    frame #14: 0x00007fff95ffd5ad libdyld.dylib`start + 1

    frame #15: 0x00007fff95ffd5ad libdyld.dylib`start + 1

Copy in the one file and everything works fine.   

This is on a completely bog standard build of 4.9.0.0 on os x 10.11.1.

[Daniel Vogelheim]

Hi,

V8 really, really needs its 'natives', so crashing if it doesn't have them is the expected result. The 'natives' are the built-in JS libraries and V8 cannot execute without them. Note that the 'Get started' guide explicitly tells you to copy the natives file. (Step 4 in 'Run the Example').

What used to be different is that by default the 'natives' were linked into the library, so there was no separate file to take care. You can return to this state by compiling with v8_use_external_startup_data=0.

If you build with the default settings - 'natives' in an external file - then the embedder is expected to hand the natives to V8, via v8::V8::SetNativesDataBlob. The 'hello world' example does this in the simplest possible way, by telling V8 to load them from the path of the executable (line "V8::InitializeExternalStartupData(argv[0]);"). Presumably a more sophisticated embedder would use a more sophisticated mechanism.

Daniel

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[Zac Hansen]

It just seems odd that there's no way to detect them being missing and throw an exception that actually gives some information about the problem or even regenerate the contents of the file at the cost of startup speed.

--Zac

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[Yang Guo]

I agree that we could handle this case more gracefully, but then again, d8's purpose is testing V8, not for production usage.

The content of the natives file cannot be generated by d8. You are confusing it with the startup snapshot.

Yang

[Zac Hansen]

What is d8?  Am I on the wrong list?

[nexus226]

Hi,

d8 is for running v8 engine in command line mode. You can find it in v8/out/{arch}/d8 after v8 build is completed.

Thanks,

Honggyu