Exported WebAssembly function cabi_realloc

[elewis787]

Are there details on why the export tags for cabi_realloc were removed in 88cdc52

This still seems relevant when targeting wasip1 and using the wasi adapters ( such as the reactor adapter ) to build a component. I have tested this by adding my own cabi_realloc function and using the export tags, then converting to a wasip2 component using the wasmtime adapters.

GOOS=wasip1 GOARCH=wasm go build -o main.wasm main.go

wasm-tools component embed --world word ./wit/lex.wit main.wasm -o main.embed.wasm
wasm-tools component new -o main.component.wasm --adapt wasi_snapshot_preview1=wasi_snapshot_preview1.reactor.wasm main.embed.wasm

experimenting here https://github.com/elewis787/lex

I believe this relates to the work at tinygo-org/tinygo#4451 and golang/go#65199 but hope for some details.

My goal is to use the wit bindings for exported functions and build a wasip2 reactor component in tinygo or go.

[ydnar]

The affected code is not used in the current TinyGo implementation.

In suppose we could make this work in Go, but not TinyGo.

[elewis787]

I could see it being helpful for go.

Using go 1.24, I was able to use it and then convert a wasip1 module to a component with the adapters. There are likely edge cases I haven't run into.

Mainly just wanted to see if there was more context that I wasn't thinking of 😄.

Calling out that I did use this in a wasmtime-go host implementation when executing an exported function in a module compiled in both go and tiny-go targeting wasip1.

[ydnar]

Have you had any luck just using go:linkname with this package, or reimplementing it in your own package?

[elewis787]

Reimplementing it in my own package worked. I will look into the go:linkname.

[ydnar]

This issue still valid?

[sd2k]

Using go 1.24, I was able to use it and then convert a wasip1 module to a component with the adapters. There are likely edge cases I haven't run into.

Hey @elewis787, I'm curious, how did you manage to get this working in big Go? I'm trying to do something similar: compile a module with Go using:

GOOS=wasip1 GOARCH=wasm go build -buildmode=c-shared -o simple.wasm
wasm-tools component embed --world simple world.wit simple.wasm -o simple.embedded.wasm
wasm-tools component new -o simple.component.wasm --adapt wasi_snapshot_preview1.reactor.wasm simple.embedded.wasm

and run it with wasmtime.

Depending on the types in the wit, I run into one of two issues:

• if the wit just contains simple types like u32s, the commands above work fine, but instantiating the module gives an error like this:

assertion failed at adapter line 2745Error: Failed to instantiate world

Caused by:
    0: error while executing at wasm backtrace:
           0: 0x18c034 - wit-component:adapter:wasi_snapshot_preview1!wasi_snapshot_preview1::macros::assert_fail::hc9f2f4814700df55
           1: 0x18c6d2 - wit-component:adapter:wasi_snapshot_preview1!args_sizes_get
           2: 0x18fe6c - wit-component:shim!adapt-wasi_snapshot_preview1-args_sizes_get
           3: 0x7267d - <unknown>!runtime.args_sizes_get
           4: 0x72c71 - <unknown>!runtime.goenvs
           5: 0x80f06 - <unknown>!runtime.schedinit
           6: 0xf1298 - <unknown>!runtime.rt0_go
           7: 0xf19ff - <unknown>!_rt0_wasm_wasip1
           8: 0xf1a0b - <unknown>!_rt0_wasm_wasip1_lib
    1: wasm trap: wasm `unreachable` instruction executed

(which points to this line of the adapter and I think is related to memory corruption, probably because GOARCH=wasm is wasm64)

• if the wit contains more complex types, wasm-tools component new fails with:

error: failed to encode a component from module

Caused by:
    0: module does not export a function named `cabi_realloc`

If I copy the realloc code mentioned in this issue and export with //go:wasmexport cabi_realloc, the wasm-tools commands work but I get an enormous stack trace trying to instantiate the module:

         13655: 0xf14cc - <unknown>!runtime.systemstack
         13656: 0xebe87 - <unknown>!runtime.throw
         13657: 0x73e2c - <unknown>!runtime.sigpanic
         13658: 0x210a1 - <unknown>!runtime.mallocgcTiny
         13659: 0xe9d3d - <unknown>!runtime.mallocgc
         13660: 0xed8d9 - <unknown>!runtime.makeslice
         13661: 0xf5a8c - <unknown>!main.alloc
         13662: 0xf54e4 - <unknown>!main.Realloc
         13663: 0xf5bc0 - <unknown>!cabi_realloc
         13664: 0x18fd20 - wit-component:adapter:wasi_snapshot_preview1!allocate_stack
         13665: 0x18e1d0 - wit-component:adapter:wasi_snapshot_preview1!clock_time_get
         13666: 0x191605 - wit-component:shim!adapt-wasi_snapshot_preview1-clock_time_get
         13667: 0x726c4 - <unknown>!runtime.clock_time_get
         13668: 0x73af4 - <unknown>!runtime.nanotime1
         13669: 0xa5912 - <unknown>!runtime.__ticksType_.init
         13670: 0x80c1a - <unknown>!runtime.schedinit
         13671: 0xf12a8 - <unknown>!runtime.rt0_go
         13672: 0xf1a0f - <unknown>!_rt0_wasm_wasip1
         13673: 0xf1a1b - <unknown>!_rt0_wasm_wasip1_lib
    1: wasm trap: call stack exhausted

---

All this to say, it feels like the adapters are incompatible with big Go right now but I'm intrigued if you managed to get things working!

[elewis787]

@sd2k with dev updates I am afraid I can't reproduce the above. However, most of the work can be found in https://github.com/elewis787/lex. I'll go back through my notes and get refamiliarized with the steps I took to get something close.

Another issue I have run into is duplicate imports outlined in golang/go#60525 - I believe this is still a problem when attempting to use the adapters with big go.

I haven't had a chance to circle back to testing this out more, but I came to the same conclusion: big Go has compatibility issues. I believe it boils down to memory allocation and wasm binary format.

I still have it on my list to dig into it more and see what can be done to help push things forward in getting big Go to be adaptable into a wasip2 component.

[elewis787]

This issue still valid?

@ydnar, I think we can close this. Sorry for the delay; I missed the notification.