Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Update JS API to better specify opaqueData exception identity #250

Open
wants to merge 4 commits into
base: main
Choose a base branch
from
Open

Update JS API to better specify opaqueData exception identity #250

Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
b87068d
Update JS API to better specify opaqueData exception identity
dschuff Feb 15, 2023
af87b72
review
dschuff Feb 16, 2023
b6df4c2
clarify language about null identity from wasm throw
dschuff Mar 3, 2023
38bbc27
fix typo
dschuff Mar 16, 2023
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
20 changes: 13 additions & 7 deletions document/js-api/index.bs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -798,7 +798,7 @@ Each {{Table}} object has a \[[Table]] internal slot, which is a [=table address
The <dfn constructor for="Table">Table(|descriptor|, |value|)</dfn> constructor, when invoked, performs the following steps:
1. Let |elementType| be [=ToValueType=](|descriptor|["element"]).
1. If |elementType| is not a [=reftype=],
1. [=Throw=] a {{TypeError}} exception.
1. Throw a {{TypeError}} exception.
aheejin marked this conversation as resolved.
Show resolved Hide resolved
1. Let |initial| be |descriptor|["initial"].
1. If |descriptor|["maximum"] [=map/exists=], let |maximum| be |descriptor|["maximum"]; otherwise, let |maximum| be empty.
1. If |maximum| is not empty and |maximum| &lt; |initial|, throw a {{RangeError}} exception.
Expand Down Expand Up @@ -1044,10 +1044,12 @@ This slot holds a [=function address=] relative to the [=surrounding agent=]'s [
1. [=list/Append=] [=ToWebAssemblyValue=](|arg|, |t|) to |args|.
1. Set |i| to |i| + 1.
1. Let (|store|, |ret|) be the result of [=func_invoke=](|store|, |funcaddr|, |args|).
1. Note: The expectation is that [=func_invoke=] will be updated to return (|store|, <var ignore>val</var>* | [=error=] | (exception |exntag| |payload| |opaqueData|)).
1. Note: The expectation is that [=func_invoke=] will be updated to return (|store|, <var ignore>val</var>* | [=error=] | (exception |exntag| |payload|)). XXX (we still need to update document/core/appendix/embedding.rst for this)

1. Set the [=surrounding agent=]'s [=associated store=] to |store|.
1. If |ret| is [=error=], throw an exception. This exception should be a WebAssembly {{RuntimeError}} exception, unless otherwise indicated by <a href="#errors">the WebAssembly error mapping</a>.
1. If |ret| is exception |exntag| |payload| |opaqueData|, then
1. If |ret| is exception |exntag| |payload|, then
1. Let |opaqueData| be the [=externref=] associated with the returned exception.
1. If |opaqueData| is not [=ref.null=] [=externref=],
1. Let « [=ref.extern=] |externaddr| » be |opaqueData|.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Does this (preexisting) line mean we have the reverse mapping from opaqueData (or object) to externaddr..?

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

My interpretation of the preexisting line is that the core spec was expected to be updated to say that func_invoke (from the core spec) returns the opaqueData (and is also expected to say where opaqueData comes from). There is no need for a reverse mapping because opaqueData is the externaddr and is passed directly into this step. I think of this like as basically just being a cast from opaqueData (a construct that was to be defined in the core spec) to externaddr (a construct that is used in this spec as a key in the map).

1. Throw the result of [=retrieving an extern value=] from |externaddr|.
Expand Down Expand Up @@ -1081,7 +1083,7 @@ Note: Exported Functions do not have a \[[Construct]] method and thus it is not
1. Otherwise, if |resultsSize| is 1, return « [=?=] [=ToWebAssemblyValue=](|ret|, |results|[0]) ».
1. Otherwise,
1. Let |method| be [=?=] [=GetMethod=](|ret|, [=@@iterator=]).
1. If |method| is undefined, [=throw=] a {{TypeError}}.
1. If |method| is undefined, throw a {{TypeError}}.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why?

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Same reason as above.

1. Let |values| be [=?=] [=IterableToList=](|ret|, |method|).
1. Let |wasmValues| be a new, empty [=list=].
1. If |values|'s [=list/size=] is not |resultsSize|, throw a {{TypeError}} exception.
Expand Down Expand Up @@ -1113,7 +1115,7 @@ Note: Exported Functions do not have a \[[Construct]] method and thus it is not
1. Let |type| be the [=JavaScript exception tag=].
1. Let |payload| be « ».
1. Let |opaqueData| be [=ToWebAssemblyValue=](|v|, [=externref=])
1. [=WebAssembly/Throw=] with |type|, |payload| and |opaqueData|.
1. [=WebAssembly/Throw=] with |type|, |payload|, and |opaqueData|.
1. Otherwise, return |result|.\[[Value]].
1. Let |store| be the [=surrounding agent=]'s [=associated store=].
1. Let (|store|, |funcaddr|) be [=func_alloc=](|store|, |functype|, |hostfunc|).
Expand Down Expand Up @@ -1361,10 +1363,14 @@ For any [=associated store=] |store|, the result of

To <dfn for=WebAssembly>throw</dfn> with a [=tag address=] |type|, a matching [=list=] of WebAssembly values |payload|, and an [=externref=] |opaqueData|, perform the following steps:
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is the tag address referred to as a "type" here?

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We'll fix the tag/type wording in a separate change.


1. Associate |opaqueData| with the identity of the thrown exception.
1. Unwind the stack until reaching the *catching try block* given |type|.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This seems to assume that there is a catch block to handle it, but of course that does not need to be the case, and it is not when the exception actually escapes to JS.

Copy link
Member Author

@dschuff dschuff Mar 3, 2023 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Indeed. Ideally this text should probably say something like "create an exception and unwind the stack" according to the language of the core spec, and "do whatever the core spec says should be done with exceptions"; i.e. unwind until the exception is caught or propagate it back to the embedder. Is there a particular spot in the core spec that defines that creation?

Copy link
Member Author

@dschuff dschuff Mar 3, 2023 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Maybe what we actually need to do is define some kind of interface in the embedding appendix for that (that appendix at least needs to be updated to say what happens when an invoked function raises/propagates an exception). The question still remains though, since that interface will itself need to say what happens.

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

#268 is the beginning of what I meant by the above comment; although I noticed that it doesn't say anything about calls from the instance into the embedder, so there may not be anything relevant to the case we're talking about here.

1. Invoke the catch block with |payload| and |opaqueData|.
1. Invoke the catch block with |payload|.

Note: This algorithm is expected to be moved into the core specification.
Note: The identity represented by |opaqueData| is not exposed to core wasm code, but remains with the exception as it propagates through the wasm frames on the stack.
If the exception propagates back to JavaScript (by returning from [=func_invoke=]), the same |opaqueData| is returned with it.
If the exception is caught and rethrown with the rethrow instruction, the identity remains the same.
Exceptions that originate from core WebAssembly (using the WebAssembly throw instruction) have a |ref.null| identity associated with them.

</div>

Expand Down