wasip1: add `//go:wasmexport` support #4451

aykevl · 2024-09-01T17:18:19Z

This adds support for the //go:wasmexport pragma as proposed here: golang/go#65199

It is currently implemented only for wasip1, but it is certainly possible to extend it to other targets like GOOS=js, -target=wasm-unknown, or -target=wasip2. ~~It is also currently limited to -buildmode=c-shared, this is a limitation that could easily be lifted in the future.~~

WIP: this needs tests, but I'm not entirely sure how to test this (I've tested it by using the --invoke flag to wasmtime).

This will likely replace #4082.

If you want fast calls into the binary, I'd recommend to disable the scheduler (-scheduler=none). That should give a significant speedup since lots of complexity is avoided. Though there are also some possible optimizations that I haven't implemented yet (like caching stacks).

github-actions · 2024-09-01T17:41:18Z

Size difference with the dev branch:

Binary size difference

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 103296  103296      0   0.00%    9816    9816      0   0.00% tinygo build -size short -o ./build/test.hex -target=metro-m4-airlift -stack-size 8kb ./examples/net/socket/
 336880  336880      0   0.00%   15732   15732      0   0.00% tinygo build -size short -o ./build/test.hex -target=matrixportal-m4 -stack-size 8kb ./examples/net/webstatic/
 111372  111372      0   0.00%    7756    7756      0   0.00% tinygo build -size short -o ./build/test.hex -target=arduino-mkrwifi1010 -stack-size 8kb ./examples/net/tlsclient/
 154024  154024      0   0.00%    6524    6524      0   0.00% tinygo build -size short -o ./build/test.hex -target=nano-rp2040 -stack-size 8kb ./examples/net/mqttclient/natiu/
 116892  116892      0   0.00%   13116   13116      0   0.00% tinygo build -size short -o ./build/test.hex -target=wioterminal -stack-size 8kb ./examples/net/webclient/
 284592  284592      0   0.00%   18156   18156      0   0.00% tinygo build -size short -o ./build/test.hex -target=wioterminal -stack-size 8kb ./examples/net/webserver/
 285624  285624      0   0.00%   17228   17228      0   0.00% tinygo build -size short -o ./build/test.hex -target=wioterminal -stack-size 8kb ./examples/net/mqttclient/paho/
5248664 5248664      0   0.00%  781946  781946      0   0.00%

compiler/symbol.go

ydnar · 2024-09-01T21:45:53Z

builder/build.go

@@ -649,6 +650,13 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	result.Binary = result.Executable // final file
 	ldflags := append(config.LDFlags(), "-o", result.Executable)

+	if config.Options.BuildMode == "c-shared" {
+		if config.GOOS() != "wasip1" {


I think we’ll quickly relax this, perhaps better to check the triple or GOARCH for a wasm prefix?

I’m fairly certain that @deadprogram will want to use this for unknown.

Yes. But to avoid too much complexity in this PR I've left it out. I tried to do it all at once but it became a bit more complex than I liked. Better to get it working for wasip1 first and then expand support to other targets (which should be relatively easy).

ydnar · 2024-09-01T21:48:00Z

compileopts/config.go

+		// Use reactor mode, which means the application is initialized in
+		// _initialize and main.main is not called by default. See for example:
+		// https://github.com/WebAssembly/WASI/blob/main/legacy/application-abi.md
+		tags = append(tags, "tinygo_wasm_reactor")


Proposal: rename tinygo_wasm_reactor to tinygo.buildmode.c_shared

I guess we can do that, but tinygo_wasm_reactor seemed a bit more explicit. We can always change it later (I hope, if no external packages suddenly start depending on the build tag).

Context: I think mapping the tag to the flag eases the developer experience, both for TinyGo developers and end users.

I have fixed this by removing the tag altogether and selecting between entry points inside the compiler. (This is similar to how big Go does it).

ydnar · 2024-09-01T21:50:14Z

compileopts/options.go

@@ -26,6 +27,7 @@ type Options struct {
 	GOMIPS          string // environment variable (only used with GOARCH=mips and GOARCH=mipsle)
 	Directory       string // working dir, leave it unset to use the current working dir
 	Target          string


Worth adding BuildMode to TargetSpec as well, so wasm-unknown and wasip2 can set build mode to c-shared by default?

We can do that in the PR that adds //go:wasmexport to wasm-unknown :)
This kind of complexity is why I kept //go:wasmexport to wasip1 for the initial version.

Ok. I'll make a follow up PR for wasip2 and unknown.

ydnar · 2024-09-01T21:53:16Z

compiler/symbol.go

+					continue
+				}
+				name := parts[1]
+				if name == "_start" || name == "_initialize" {


So //export remains for exports like _start and _initialize that don’t get the goroutine / scheduler dance?

Yes, but it's an implementation detail. Eventually I'd like to make //export work as it does on every other architecture (that is, it makes the function available to the linker but doesn't export it on a wasm level) - but that will probably require a deprecation period so people have time to switch to //go:wasmexport.

ydnar · 2024-09-01T21:53:47Z

compiler/symbol.go

+					continue
+				}
+				if c.BuildMode != "c-shared" && f.RelString(nil) == "main.main" {
+					c.addError(f.Pos(), fmt.Sprintf("//go:wasmexport does not allow main.main to be exported with -buildmode=%s", c.BuildMode))


Does big Go blow up if main.main is declared with -buildmode=c-shared?

Yes. This is what the proposal says:

When the -buildmode flag is unset, the _start function and any exported functions will be exported to the host. Using //go:wasmexport on the main function in this mode will result in a compilation error. In this mode, only _start will initialize the runtime, and so must be the first export called from the host. Any other exported functions may only be called through calling into host functions that call other exports during the execution of the _start function. Once the _start function has returned, no other exports may be called on the same instance.

I think the proposal allows main.main, and wasmexport on it, when -buildmode=c-shared:

When using -buildmode=c-shared, the resulting Wasm binary will not contain a _start function, and will only contain the _initialize function and any exported functions. The Go main function will not be exported to the host. The user can choose to export it like any other function using the //go:wasmexport directive. The _initialize function will not automatically call main. The main function will not initialize the runtime.

Ah, I missed the ! in the line. My mistake!

ydnar · 2024-09-01T21:55:05Z

Looks like big Go supports go:wasmexport under js and with main.main: golang/go#65199 (comment)

ydnar · 2024-09-29T20:34:19Z

For backwards compatibility, if both //export and //go:wasmexport are found, only implement go:wasmexport?

ydnar · 2024-09-29T21:04:18Z

For tests, we could implement wasip1, wasip2, and unknown tests.

For wasip2, we can implement both worlds: wasi:cli/command and wasi:http/proxy, verifying:

Goroutines started during init run during the reactor call (wasi:cli/command#run and wasi:http/incoming-handler#handle).
The expected reactor function is called, by verifying output to either stdout/stderr or the HTTP response.

For wasip1 and unknown, using wasmtime with --invoke should be sufficient.

aykevl

This PR still needs tests, that's what's needed to make this mergeable.

Looks like big Go supports go:wasmexport under js and with main.main: golang/go#65199 (comment)

Yes, I've intentionally left that out of the first PR. Focusing on wasip1 first made the PR a lot simpler.
(And to be clear, the comment does not say that main.main can be exported, just that if you call an imported function that imported function can then call back into an exported function. Which is exactly what I've implemented for wasip1 here).

For backwards compatibility, if both //export and //go:wasmexport are found, only implement go:wasmexport?

I guess we can do this. I don't see any obvious problems with that, as far as I can think the external ABI is the same (though of course //go:wasmexport has clearly defined semantics and //export does not). I would like to remove the ability for //export to produce wasm exported functions at some point though, because it's a non-standard TinyGo extension.

aykevl · 2024-10-02T09:29:15Z

compiler/symbol.go

+					continue
+				}
+				name := parts[1]
+				if name == "_start" || name == "_initialize" {


Yes, but it's an implementation detail. Eventually I'd like to make //export work as it does on every other architecture (that is, it makes the function available to the linker but doesn't export it on a wasm level) - but that will probably require a deprecation period so people have time to switch to //go:wasmexport.

aykevl · 2024-10-02T09:30:42Z

builder/build.go

@@ -649,6 +650,13 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	result.Binary = result.Executable // final file
 	ldflags := append(config.LDFlags(), "-o", result.Executable)

+	if config.Options.BuildMode == "c-shared" {
+		if config.GOOS() != "wasip1" {


Yes. But to avoid too much complexity in this PR I've left it out. I tried to do it all at once but it became a bit more complex than I liked. Better to get it working for wasip1 first and then expand support to other targets (which should be relatively easy).

aykevl · 2024-10-02T09:33:34Z

compileopts/config.go

+		// Use reactor mode, which means the application is initialized in
+		// _initialize and main.main is not called by default. See for example:
+		// https://github.com/WebAssembly/WASI/blob/main/legacy/application-abi.md
+		tags = append(tags, "tinygo_wasm_reactor")


I guess we can do that, but tinygo_wasm_reactor seemed a bit more explicit. We can always change it later (I hope, if no external packages suddenly start depending on the build tag).

aykevl · 2024-10-02T09:34:25Z

compileopts/options.go

@@ -26,6 +27,7 @@ type Options struct {
 	GOMIPS          string // environment variable (only used with GOARCH=mips and GOARCH=mipsle)
 	Directory       string // working dir, leave it unset to use the current working dir
 	Target          string


We can do that in the PR that adds //go:wasmexport to wasm-unknown :)
This kind of complexity is why I kept //go:wasmexport to wasip1 for the initial version.

aykevl · 2024-10-02T09:37:15Z

compiler/symbol.go

+					continue
+				}
+				if c.BuildMode != "c-shared" && f.RelString(nil) == "main.main" {
+					c.addError(f.Pos(), fmt.Sprintf("//go:wasmexport does not allow main.main to be exported with -buildmode=%s", c.BuildMode))


Yes. This is what the proposal says:

When the -buildmode flag is unset, the _start function and any exported functions will be exported to the host. Using //go:wasmexport on the main function in this mode will result in a compilation error. In this mode, only _start will initialize the runtime, and so must be the first export called from the host. Any other exported functions may only be called through calling into host functions that call other exports during the execution of the _start function. Once the _start function has returned, no other exports may be called on the same instance.

aykevl · 2024-10-02T16:04:32Z

Added some light testing
Removed the tinygo_wasm_reactor build tag.
Added runtime asserts to check that //go:wasmexport functions aren't being called at a time that it is not allowed.
Added support for //go:wasmexport with -buildmode=default (though I couldn't really test this: it's impossible to test through wasmtime --invoke).

This is now ready for review.

main_test.go

src/runtime/runtime_wasip1.go

aykevl · 2024-10-03T14:08:05Z

Added -target=wasm-unknown. Defaulting to -buildmode=c-shared but -buildmode=default can also be used to make _start the entry point.
Added some more testing for different configurations.

I looked into wasip2 support, but that's a bit harder to test because wazero doesn't support wasm components (and wasip2) yet.

This adds support for the `//go:wasmexport` pragma as proposed here: golang/go#65199 It is currently implemented only for wasip1 and wasm-unknown, but it is certainly possible to extend it to other targets like GOOS=js and wasip2.

ydnar · 2024-10-03T21:15:51Z

compiler/goroutine.go

+// it needs to start a new goroutine each time the exported function is called.
+func (b *builder) createWasmExport() {
+	pos := b.info.wasmExportPos
+	if b.info.exported {


Is it possible to flip this so //export is ignored if //go:wasmexport is present?

(and maybe warn?)

ydnar · 2024-10-04T22:33:39Z

Merging per @aykevl’s message in Slack: https://gophers.slack.com/archives/CN4R2DQV7/p1728076418126569?thread_ts=1727844162.259119&cid=CN4R2DQV7

Yes, the wasmexport PR is ready from my POV.

aykevl force-pushed the wasip1-c-shared branch from af59cff to 829f62e Compare September 1, 2024 17:25

aykevl mentioned this pull request Sep 1, 2024

WASI reactor mode #2735

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ydnar reviewed Sep 1, 2024

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elewis787 mentioned this pull request Oct 1, 2024

Exported WebAssembly function cabi_realloc bytecodealliance/go-modules#184

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aykevl commented Oct 2, 2024

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aykevl force-pushed the wasip1-c-shared branch from 829f62e to 2752ff2 Compare October 2, 2024 16:00

aykevl marked this pull request as ready for review October 2, 2024 16:02

ydnar reviewed Oct 2, 2024

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aykevl force-pushed the wasip1-c-shared branch 5 times, most recently from 801f81d to 407ab0f Compare October 3, 2024 14:07

wasm: add //go:wasmexport support

c79d817

This adds support for the `//go:wasmexport` pragma as proposed here: golang/go#65199 It is currently implemented only for wasip1 and wasm-unknown, but it is certainly possible to extend it to other targets like GOOS=js and wasip2.

aykevl force-pushed the wasip1-c-shared branch from 407ab0f to c79d817 Compare October 3, 2024 14:39

aykevl mentioned this pull request Oct 3, 2024

wasm: add //go:wasmexport support to js/wasm #4494

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compiler, runtime: enable go:wasmexport for wasip2 #4496

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ydnar merged commit 9da8b5c into dev Oct 4, 2024
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ydnar deleted the wasip1-c-shared branch October 4, 2024 22:33

ydnar mentioned this pull request Oct 4, 2024

compiler, runtime: enable go:wasmexport for wasip2 #4499

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Can I use go1.21 to compile plugins? knqyf263/go-plugin#58

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fix: use tinygo reactor module dylibso/xtp-go-bindgen#30

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wasm-unknown: cannot build binaries without main #4670

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wasip1: add `//go:wasmexport` support #4451

wasip1: add `//go:wasmexport` support #4451

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wasip1: add //go:wasmexport support #4451

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wasip1: add `//go:wasmexport` support #4451

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