EH: tag matching seems broken

[yamt]

the current logic decides exception matching (ie. which catch clause to use) by comparing tag indexes.
it seems wrong because, if i read the spec correctly, it's allowed for a module to import the same tag multiple times.

[ermler]

@yamt
a good question. we looked at "try-catch.wast" that was present when implementing. The files shows a test, where a tag is imported from a module and the catch-block aims at tagindex after importing.

See, how "test.throw" in external module throws "test.e0"
https://github.com/WebAssembly/exception-handling/blob/cfe863826484d7d8a630324f1839f7ed3afaffc9/test/core/try_catch.wast#L5

Module imports "test.e0" as "imported-e0"
https://github.com/WebAssembly/exception-handling/blob/cfe863826484d7d8a630324f1839f7ed3afaffc9/test/core/try_catch.wast#L11

and the testcase "catch-imported" calls "test.throw" and catches the "test.e0" exception as tagindex "imported-e0":
https://github.com/WebAssembly/exception-handling/blob/cfe863826484d7d8a630324f1839f7ed3afaffc9/test/core/try_catch.wast#L136

we did our implementation to behave like this and wrote wamr code that looks up and replaces tagindex after returning from the external call.

wasm-micro-runtime/core/iwasm/interpreter/wasm_interp_classic.c

Line 6488 in e8c2952

#if WASM_ENABLE_EXCE_HANDLING != 0

but anyhow, it is a good question, which behavior is expected, if the same tag is imported twice and so has multiple catchblocks in the importing module....

[yamt]

i submitted a test case. WebAssembly/exception-handling#326
(it's for the latest version of the proposal though.)

[ermler]

i submitted a test case. WebAssembly/exception-handling#326 (it's for the latest version of the proposal though.)

thanks for clarification, that test case explains the idea.