DCHECK prevents debug build from starting

[targos]

Can be reproduced with https://github.com/nodejs/node/tree/canary-base in its current state.

➤ out/Debug/node


#
# Fatal error
# Debug check failed: count <= JSObject::kMaxEmbedderFields (7 vs. 6).
#
#
#
#FailureMessage Object: 0x16b32dbf8
----- Native stack trace -----

 1: 0x104bef964 node::DumpNativeBacktrace(__sFILE*) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 2: 0x104eab458 node::NodePlatform::GetStackTracePrinter()::$_0::operator()() const [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 3: 0x104eab414 node::NodePlatform::GetStackTracePrinter()::$_0::__invoke() [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 4: 0x107fb7618 V8_Fatal(char const*, ...) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 5: 0x107fb6edc v8::base::SetFatalFunction(void (*)(char const*, int, char const*)) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 6: 0x1099a913c v8::ObjectTemplate::SetInternalFieldCount(int) (.cold.1) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 7: 0x1051e1cf4 v8::ObjectTemplate::SetInternalFieldCount(int) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 8: 0x104d9b100 node::fs::CreatePerIsolateProperties(node::IsolateData*, v8::Local<v8::ObjectTemplate>) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
 9: 0x104d99fd4 _register_isolate_fs(node::IsolateData*, v8::Local<v8::ObjectTemplate>) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
10: 0x104ce43a4 node::binding::CreateInternalBindingTemplates(node::IsolateData*) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
11: 0x104c319c0 node::IsolateData::CreateProperties() [/Users/mzasso/git/nodejs/canary/out/Debug/node]
12: 0x104c339a8 node::IsolateData::IsolateData(v8::Isolate*, uv_loop_s*, node::MultiIsolatePlatform*, node::ArrayBufferAllocator*, node::SnapshotData const*, std::__1::shared_ptr<node::PerIsolateOptions>) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
13: 0x104c31d08 node::IsolateData::IsolateData(v8::Isolate*, uv_loop_s*, node::MultiIsolatePlatform*, node::ArrayBufferAllocator*, node::SnapshotData const*, std::__1::shared_ptr<node::PerIsolateOptions>) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
14: 0x104c31b34 node::IsolateData::CreateIsolateData(v8::Isolate*, uv_loop_s*, node::MultiIsolatePlatform*, node::ArrayBufferAllocator*, node::EmbedderSnapshotData const*, std::__1::shared_ptr<node::PerIsolateOptions>) [/Users/mzasso/git/nodejs/canary/out/Debug/node]
15: 0x104b44db4 node::CreateIsolateData(v8::Isolate*, uv_loop_s*, node::MultiIsolatePlatform*, node::ArrayBufferAllocator*, node::EmbedderSnapshotData const*) [/Users/mzasso/git/nodejs/canary/out/Debug/node]

[joyeecheung]

This was caused by https://chromium-review.googlesource.com/c/v8/v8/+/8190376 which ended up halving the kMaxEmbedderFields (to 6) in builds without pointer compression. This is tricky - the easiest (?) fix I can think of is to squeeze some fields out of the binding objects (currently we have FileHandle and ModuleWrap with 7 fields) somehow. Or maybe we can figure out a way to find some more wiggle room in the V8 layout?

[joyeecheung]

Note: another impact of that change is that now all promises will be 8 bytes bigger, all array buffers and typed arrays will be 16 bytes bigger, and other Node.js objects will receive various size increases depending on number of slots (every slot has doubled in size). It's currently also problematic in release build to some non-trivial extent, every time the object uses the 7th slot it's actually getting corrupted, just that we only have FileHandle and ModuleWrap with 7 slots and maybe the corruption was somewhat tolerated in the simple tests (but after a GC or when other in-object properties override the corrupted slots it would show as bad crashes)

[joyeecheung]

Uploaded https://chromium-review.googlesource.com/c/v8/v8/+/8250427 as a potential fix to increase the limit of embedder fields to 14 (bumping kFirstInobjectPropertyOffsetBitCount further would increase the limit to 30, but in Node.js we only need 7 anyway). Will need to check with the V8 team to see if it's safe/acceptable.