support thin strings

[joyeecheung]

Looks like in Node.js v8.3.0 (with v8 6.0) thin strings are enabled by default, since they are not recognized by llnode, when inspecting those strings the output is broken. e.g. when viewing the backtrace of test/inspect-scenario.js, script names that are thin strings will be displayed as "no script" (since llnode cannot do String::ToString() on them) and frames with functions containing thin string arguments would be empty:

 * thread #1: tid = 0x5bac78, 0x0000000100bc8412 node`v8::base::OS::Abort() at platform-posix.cc:261, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  * frame #0: 0x0000000100bc8412 node`v8::base::OS::Abort() at platform-posix.cc:261 [opt]
    frame #1: 0x00000001008a777b node`v8::internal::Runtime_Throw(int, v8::internal::Object**, v8::internal::Isolate*) [inlined] v8::internal::__RT_impl_Runtime_Throw(v8::internal::Arguments, v8::internal::Isolate*) at runtime-internal.cc:74 [opt]
    frame #2: 0x00000001008a775a node`v8::internal::Runtime_Throw(args_length=<unavailable>, args_object=<unavailable>, isolate=0x00000001030492e0) at runtime-internal.cc:71 [opt]
    frame #3: 0x000038d5094040dd <exit>
    frame #4: 0x000038d50950523a
    frame #5: 0x000038d509412f12 method(this=0x000012a70245bda1:<Object: Class>) at (no script):20:43 fn=0x00001a7c7fb0dbe1
    frame #6: 0x000038d5094f35e9
    frame #7: 0x000038d509412f12 closure(this=0x00001fb4b3602241:<undefined>) at (no script):11:17 fn=0x000012a702405879
    frame #8: 0x000038d5094f3fa1
    frame #9: 0x000038d509412f12
    frame #10: 0x000038d5094f2cc8
    frame #11: 0x000038d509412f12
    frame #12: 0x000038d5094f38aa
    frame #13: 0x000038d509412f12
    frame #14: 0x000038d5094f38aa
    frame #15: 0x000038d509412f12
    frame #16: 0x000038d5094f373c
    frame #17: 0x000038d509412f12
    frame #18: 0x000038d5094f4242
    frame #19: 0x000038d509412f12 Module._load(this=0x00003d76f5bbb379:<function: Module at module.js:55:16>, 0x00003d76f5bc7039:<String: "/Users/joyee/pro...">, 0x00001fb4b3602211:<null>, 0x00001fb4b36022c1:<true>) at module.js:434:24 fn=0x000011003aec1319
    frame #20: 0x000038d5094f2cc8
    frame #21: 0x000038d509412f12 Module.runMain(this=0x00003d76f5bbb379:<function: Module at module.js:55:16>) at module.js:607:26 fn=0x000011003aec1589
    frame #22: 0x000038d509513c29
    frame #23: 0x000038d509412f12 startup(this=0x00001fb4b3602241:<undefined>) at bootstrap_node.js:1:10 fn=0x0000278695a7df51
    frame #24: 0x000038d5094f3fa1
    frame #25: 0x000038d509412f12 (anonymous)(this=0x00001fb4b3602211:<null>, 0x0000278695a7dfd1:<Object: process>) at bootstrap_node.js:1:10 fn=0x0000278695a7e021
    frame #26: 0x000038d509410650 <internal>
    frame #27: 0x000038d5094e4ead <entry>
    frame #28: 0x00000001005dbe21 node`v8::internal::(anonymous namespace)::Invoke(isolate=0x0000000000000049, is_construct=<unavailable>, target=<unavailable>, receiver=<unavailable>, argc=1, args=<unavailable>, new_target=<unavailable>, message_handling=<unavailable>) at execution.cc:145 [opt]
    frame #29: 0x00000001005dbb09 node`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>*) [inlined] v8::internal::(anonymous namespace)::CallInternal(message_handling=kReport) at execution.cc:181 [opt]
    frame #30: 0x00000001005dba80 node`v8::internal::Execution::Call(isolate=0x0000000103000c00, callable=Handle<v8::internal::Object> @ r12, receiver=<unavailable>, argc=1, argv=<unavailable>) at execution.cc:191 [opt]
    frame #31: 0x0000000100205158 node`v8::Function::Call(this=0x0000000103049238, context=<unavailable>, recv=<unavailable>, argc=1, argv=0x00007fff5fbfe190) at api.cc:5287 [opt]
    frame #32: 0x0000000100a523e3 node`node::LoadEnvironment(env=0x00007fff5fbfe240) at node.cc:3628 [opt]
    frame #33: 0x0000000100a59231 node`node::Start(isolate=0x0000000103000c00, isolate_data=<unavailable>, argc=2, argv=<unavailable>, exec_argc=1, exec_argv=0x0000000102703c80) at node.cc:4553 [opt]
    frame #34: 0x0000000100a53d6e node`node::Start(event_loop=0x0000000101763818, argc=2, argv=0x00000001027043b0, exec_argc=<unavailable>, exec_argv=<unavailable>) at node.cc:4639 [opt]
    frame #35: 0x0000000100a539fb node`node::Start(argc=<unavailable>, argv=0x00000001027043b0) at node.cc:4701 [opt]
    frame #36: 0x0000000100001534 node`start + 52

Before (output in v8.2.1)

 * thread #1: tid = 0x5b416b, 0x0000000100bf7e32 node`v8::base::OS::Abort() + 18, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  * frame #0: 0x0000000100bf7e32 node`v8::base::OS::Abort() + 18
    frame #1: 0x000000010068579a node`v8::internal::Isolate::Throw(v8::internal::Object*, v8::internal::MessageLocation*) + 842
    frame #2: 0x000000010083a50b node`v8::internal::Runtime_Throw(int, v8::internal::Object**, v8::internal::Isolate*) + 59
    frame #3: 0x000026abe7b040bd <exit>
    frame #4: 0x000026abe7c874b4 method(this=0x000002fc27a4f989:<Object: Class>) at /Users/joyee/projects/llnode/test/fixtures/inspect-scenario.js:20:43 fn=0x0000368fab67ed41
    frame #5: 0x000026abe7c7c9ef closure(this=0x00003b8295902241:<undefined>) at /Users/joyee/projects/llnode/test/fixtures/inspect-scenario.js:11:17 fn=0x0000019a5b7f5589
    frame #6: 0x000026abe7c6a585 (anonymous)(this=0x0000019a5b7f3419:<Object: Object>, 0x0000019a5b7f3419:<Object: Object>, 0x0000019a5b7f5141:<function: require at internal/module.js:8:19>, 0x0000019a5b7f3359:<Object: Module>, 0x0000019a5b7f2769:<String: "/Users/joyee/pro...">, 0x0000019a5b7f50d9:<String: "/Users/joyee/pro...">) at /Users/joyee/projects/llnode/test/fixtures/inspect-scenario.js:1:10 fn=0x0000019a5b7f5091
    frame #7: 0x000026abe7c69b90 Module._compile(this=0x0000019a5b7f3359:<Object: Module>, 0x0000019a5b7f4279:<String: "'use strict';

c...">, 0x0000019a5b7f2769:<String: "/Users/joyee/pro...">) at module.js:526:37 fn=0x0000368fab636f19
    frame #8: 0x000026abe7c639a3 Module._extensions..js(this=0x0000019a5b7ef779:<Object: Object>, 0x0000019a5b7f3359:<Object: Module>, 0x0000019a5b7f2769:<String: "/Users/joyee/pro...">) at module.js:578:37 fn=0x0000368fab636f61
    frame #9: 0x000026abe7c6242a Module.load(this=0x0000019a5b7f3359:<Object: Module>, 0x0000019a5b7f2769:<String: "/Users/joyee/pro...">) at module.js:494:33 fn=0x0000368fab636e89
    frame #10: 0x000026abe7be014b
    frame #11: 0x000026abe7b12759 tryModuleLoad(this=0x00003b8295902241:<undefined>, 0x0000019a5b7f3359:<Object: Module>, 0x0000019a5b7f2769:<String: "/Users/joyee/pro...">) at module.js:463:23 fn=0x0000019a5b7be7b1
    frame #12: 0x000026abe7c5b7f6 Module._load(this=0x0000019a5b7be601:<function: Module at module.js:50:16>, 0x0000019a5b7c9e89:<String: "/Users/joyee/pro...">, 0x00003b8295902211:<null>, 0x00003b82959022c1:<true>) at module.js:432:24 fn=0x0000368fab636dc9
    frame #13: 0x000026abe7c5b27e Module.runMain(this=0x0000019a5b7be601:<function: Module at module.js:50:16>) at module.js:603:26 fn=0x0000368fab637039
    frame #14: 0x000026abe7c303b8 startup(this=0x00003b8295902241:<undefined>) at bootstrap_node.js:1:10 fn=0x00002b4165c07b31
    frame #15: 0x000026abe7c2e5cb (anonymous)(this=0x00003b8295902211:<null>, 0x00002b4165c07859:<Object: process>) at bootstrap_node.js:1:10 fn=0x00002b4165c07be9
    frame #16: 0x000026abe7b10290 <internal>
    frame #17: 0x000026abe7bd646d <entry>
    frame #18: 0x0000000100559626 node`v8::internal::(anonymous namespace)::Invoke(v8::internal::Isolate*, bool, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Object>, int, v8::internal::Handle<v8::internal::Object>*, v8::internal::Handle<v8::internal::Object>, v8::internal::Execution::MessageHandling) + 742
    frame #19: 0x0000000100559283 node`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>*) + 179
    frame #20: 0x00000001001619ef node`v8::Function::Call(v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*) + 559
    frame #21: 0x0000000100a7d703 node`node::LoadEnvironment(node::Environment*) + 591
    frame #22: 0x0000000100a846e6 node`node::Start(v8::Isolate*, node::IsolateData*, int, char const* const*, int, char const* const*) + 426
    frame #23: 0x0000000100a7f7c1 node`node::Start(uv_loop_s*, int, char const* const*, int, char const* const*) + 462
    frame #24: 0x0000000100a7edb5 node`node::Start(int, char**) + 331
    frame #25: 0x0000000100000e34 node`start + 52

[joyeecheung]

BTW I am working on this, still trying to figure out why LoadConstant("ThinStringTag") is giving me -1 though...(it's supposed to be 5)

[bnoordhuis]

@joyeecheung Does this (node) patch help?

diff --git a/deps/v8/tools/gen-postmortem-metadata.py b/deps/v8/tools/gen-postmortem-metadata.py
index e793a91865..9e0b7c8a0c 100644
--- a/deps/v8/tools/gen-postmortem-metadata.py
+++ b/deps/v8/tools/gen-postmortem-metadata.py
@@ -72,6 +72,7 @@ consts_misc = [
     { 'name': 'ConsStringTag',          'value': 'kConsStringTag' },
     { 'name': 'ExternalStringTag',      'value': 'kExternalStringTag' },
     { 'name': 'SlicedStringTag',        'value': 'kSlicedStringTag' },
+    { 'name': 'ThinStringTag',          'value': 'kThinStringTag' },
 
     { 'name': 'HeapObjectTag',          'value': 'kHeapObjectTag' },
     { 'name': 'HeapObjectTagMask',      'value': 'kHeapObjectTagMask' },

[joyeecheung]

@bnoordhuis Yes, that's what I need, thanks!

I've got the thin string support working but then discovered the frame test was failing because Turbofan now puts stub frames on the stack in that scenario. I will open a PR fixing these two issues.

[joyeecheung]

@bnoordhuis BTW have you opened a CL to the V8 upstream yet?

[bnoordhuis]

I have now: https://chromium-review.googlesource.com/c/618986