Stream: wasm

Topic: "new" Import/Export Name Rules

Robin Brown (Jun 23 2023 at 22:32):

I'm trying to update my template compiler project and its tests to the latest versions of wasmtime and wasm-tools. However, after resolving some WIT syntax and minor API changes, I'm getting stuck on the new export validation naming rules (as seen here).

(component
  ...
  (type (;0;) (record))
  (type (;1;) (func (param "params" 0) (result string)))
  (func (;0;) (type 1) (canon lift (core func 1) string-encoding=utf8 (memory 0) (realloc 0)))
  (export (;1;) "apply" (func 0))
)
Error: failed to parse WebAssembly module

Caused by:
    func not valid to be used as export (at offset 0x40b)

From what I'm reading, I think I need to export the record type holding my parameters (in this case there are no params, it has no fields). However, when I add that logic and an additional export before the function export the problem doesn't go away.

(component
  ...
  (type (;0;) (record))
  (type (;1;) (func (param "params" 0) (result string)))
  (func (;0;) (type 1) (canon lift (core func 1) string-encoding=utf8 (memory 0) (realloc 0)))
  (export (;2;) "params" (type 0))
  (export (;1;) "apply" (func 0))
)
Error: failed to parse WebAssembly module

Caused by:
    func not valid to be used as export (at offset 0x416)

What does the component need to look like for this to work?

Robin Brown (Jun 23 2023 at 22:37):

I've also tried splitting up the export sections to match the tests more closely but get an even more confusing error.

(component
  ...
  (type (;0;) (record))
  (export (;1;) "params" (type 0))
  (type (;2;) (func (param "params" 0) (result string)))
  (func (;0;) (type 1) (canon lift (core func 1) string-encoding=utf8 (memory 0) (realloc 0)))
  (export (;1;) "apply" (func 0))
)
Error: failed to parse WebAssembly module

Caused by:
    type index 1 is not a function type (at offset 0x40f)

Robin Brown (Jun 23 2023 at 22:38):

I'm also don't understand why wasmprinter is labeling the indices the way it does and why splitting sections up behaves so strangely.

Alex Crichton (Jun 23 2023 at 23:10):

it's subtle, but the fix here is to change (param "params" 0) to (param "params" 1)

Alex Crichton (Jun 23 2023 at 23:11):

indices in comments like (;0;) mean that the item is introducing and defining index 0, and those comments can in theory be replaced with $foo for human-readability

Alex Crichton (Jun 23 2023 at 23:11):

indicies like (type 1) are referring to the index 1

Alex Crichton (Jun 23 2023 at 23:12):

as for sections, at least for now in components the seconds are often interspersed and occur frequently, often with 1 element in them, which is why everything looks jumbled up

Alex Crichton (Jun 23 2023 at 23:12):

the text format preserves the order in the original binary

Robin Brown (Jun 27 2023 at 15:37):

Do exports introduce new indices in their respective index spaces? If so, I think that's the concept/detail I was missing.

Robin Brown (Jun 27 2023 at 15:38):

Thanks for your help! The upgrade was successful with the index change you suggested.
https://github.com/Kylebrown9/template-compiler/pull/2

Last updated: Nov 22 2024 at 16:03 UTC