cmd/link: on wasm, number of functions limited to 2^16

[HarikrishnanBalagopal]

Overview

It seems to me that the size of a WASM function is limited to 2^16 = 65536 bytes?

go/src/cmd/link/internal/wasm/asm.go

Line 90 in 649671b

ldr.SetSymValue(s, int64(funcValueOffset+va/ld.MINFUNC)<<16) // va starts at zero

This leads to a bunch of errors whenever using more than a few libraries in our WASM app
The code for our app is available in this branch https://github.com/konveyor/move2kube/blob/wasm/go.mod
The code is able to build using the official Go compiler WASIP1 support
https://github.com/konveyor/move2kube/blob/dec9d8da6e5f8882aacb46a8e5f784b96b42a3c6/Makefile#L45C2-L45C100

Issue

When we try to add the https://pkg.go.dev/go.starlark.net/starlark library then we get a bunch of compile errors

type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).ModTime is too big: 0x100c40000
type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).ModTime is too big: 0x100c40000
type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).Mode is too big: 0x100c60000
type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).Mode is too big: 0x100c60000
type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).Name is too big: 0x100c70000
type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).Name is too big: 0x100c70000
type:*github.com/mholt/archiver/v3.FileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*FileInfo).Size is too big: 0x100c90000
/usr/local/go/pkg/tool/linux_amd64/link: too many errors
make: *** [Makefile:45: build] Error 1

Fix

Please remove this arbitrary limit on function size or at least provide a way to work around it. This is a severe limit on any real world app that will use many different libraries to implement various features.

The WASM page size is 65536 bytes https://developer.mozilla.org/en-US/docs/WebAssembly/JavaScript_interface/Memory/Memory which is 2^16 and can be addressed with 16 bits. That might explain where this particular limit came from but it doesn't explain why a single function has to fit all inside of one WASM page. Especially since WASM functions live is a completely separate address space than the WASM linear memory.

Also see these comments:

• Function body maximum size WebAssembly/design#1138 (comment)
• Function body maximum size WebAssembly/design#1138 (comment)
• Function body maximum size WebAssembly/design#1138 (comment)

Related

https://stackoverflow.com/questions/67294859/why-golang-limit-the-symbol-number-to-65535-while-compile-wasm-target
#7769
#7980
WebAssembly/design#1138

[mauri870]

/cc @golang/wasm

[mauri870]

Looking at the limits for other implementations I see no issue bumping the function size in Go, unless that has to do with some internal implementation detail on our side that I'm not aware of. For instance, Webkit and V8 use 7654321, we might as well just ride the same train.

[mauri870]

After some investigation this appears to be a bug with 1.22. I'm able to compile this without any errors with go 1.21.

It happens for both js and wasip1 here. Since there are unrelated failures I was only able to bisect to a certain range 4346ba3...8be8bfe (113 commits).

This error prevents the compilation of large wasm programs with Go 1.22 without a workaround.

/cc @golang/release

[HarikrishnanBalagopal]

After some investigation this appears to be a bug with 1.22. I'm able to compile this without any errors with go 1.21.

It happens for both js and wasip1 here. Since there are unrelated failures I was only able to bisect to a certain range 4346ba3...8be8bfe (113 commits).

This error prevents the compilation of large wasm programs with Go 1.22 without a workaround.

/cc @golang/release

@mauri870 I don't think the bug is only in v1.22 because we have not tried v1.22 yet. The errors we saw are all with Go v1.21

The line I linked in the first post is still there in the master branch

go/src/cmd/link/internal/wasm/asm.go

Line 157 in 2184a39

ldr.SetSymValue(s, int64(funcValueOffset+va/ld.MINFUNC)<<16) // va starts at zero

The git blame shows that line has been there from the beginning when WASM got added f41dc71#diff-b189a5a4d6f377939c502fb248c71ab0f1febe60a54f283eaca1dad73c196604R85

Working

Building the wasm branch https://github.com/konveyor/move2kube/tree/wasm works correctly:

$ go version
go version go1.21.0 darwin/arm64
$ make build
mkdir -p "./bin"
CGO_ENABLED=0 GOOS=wasip1 GOARCH=wasm go build -ldflags ' -X github.com/konveyor/move2kube-wasm/types/info.buildmetadata=unreleased -X github.com/konveyor/move2kube-wasm/types/info.gitCommit=dec9d8da6e5f8882aacb46a8e5f784b96b42a3c6 -X github.com/konveyor/move2kube-wasm/types/info.gitTreeState=clean' -o "./bin/move2kube.wasm" .
gzip -f "./bin/move2kube.wasm"
# We have to put require github.com/sirupsen/logrus v1.9.4-0.20230606125235-dd1b4c2e81af
# in order for logrus to work. See https://github.com/HarikrishnanBalagopal/test-wasi-fs-browser/tree/main
# CGO_ENABLED=0 tinygo build -o "./bin/move2kube.wasm" -target=wasi .
$ echo $?
0

Non-working

After adding the go.starlark.net v0.0.0-20200306205701-8dd3e2ee1dd5 library, building this branch https://github.com/HarikrishnanBalagopal/move2kube/tree/feat/starlark with Golang v1.21.0 gives errors:

$ go version
go version go1.21.0 darwin/arm64
$ make build
mkdir -p "./bin"
CGO_ENABLED=0 GOOS=wasip1 GOARCH=wasm go build -ldflags ' -X github.com/konveyor/move2kube-wasm/types/info.buildmetadata=unreleased -X github.com/konveyor/move2kube-wasm/types/info.gitCommit=6d72f91783749e697f9fa38c17f8b4d892c9d102 -X github.com/konveyor/move2kube-wasm/types/info.gitTreeState=clean' -o "./bin/move2kube.wasm" .
# github.com/konveyor/move2kube-wasm
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).IsDir is too big: 0x100240000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).IsDir is too big: 0x100240000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).ModTime is too big: 0x100250000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).ModTime is too big: 0x100250000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Mode is too big: 0x100260000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Mode is too big: 0x100260000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Name is too big: 0x100270000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Name is too big: 0x100270000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Size is too big: 0x100280000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Size is too big: 0x100280000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Sys is too big: 0x100290000
type:*github.com/mholt/archiver/v3.rarFileInfo: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*rarFileInfo).Sys is too big: 0x100290000
type:*github.com/mholt/archiver/v3.TarLz4: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarLz4).Match is too big: 0x100010000
type:*github.com/mholt/archiver/v3.TarLz4: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarLz4).Match is too big: 0x100010000
type:*github.com/mholt/archiver/v3.TarLz4: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarLz4).Read is too big: 0x100030000
type:*github.com/mholt/archiver/v3.TarLz4: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarLz4).Read is too big: 0x100030000
type:*github.com/mholt/archiver/v3.TarLz4: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarLz4).Write is too big: 0x100050000
type:*github.com/mholt/archiver/v3.TarLz4: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarLz4).Write is too big: 0x100050000
type:*github.com/mholt/archiver/v3.TarSz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarSz).CheckPath is too big: 0x100070000
type:*github.com/mholt/archiver/v3.TarSz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarSz).CheckPath is too big: 0x100070000
type:*github.com/mholt/archiver/v3.TarSz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarSz).Close is too big: 0x100090000
/opt/homebrew/Cellar/go/1.21.0/libexec/pkg/tool/darwin_arm64/link: too many errors
make: *** [build] Error 1

Difference

The difference is that we added the starlark-go library and a file that uses it https://github.com/HarikrishnanBalagopal/move2kube/blob/feat/starlark/transformer/external/starlarktransformer.go

$ git checkout feat/starlark 
Switched to branch 'feat/starlark'
Your branch is up to date with 'origin/feat/starlark'.
$ git status
On branch feat/starlark
Your branch is up to date with 'origin/feat/starlark'.

nothing to commit, working tree clean
$ git diff wasm --name-status 
M       go.mod
M       go.sum
A       transformer/external/starlarktransformer.go
$ git diff wasm go.mod
diff --git a/go.mod b/go.mod
index 8fdc019..e8de3ed 100644
--- a/go.mod
+++ b/go.mod
@@ -28,6 +28,7 @@ require (
        github.com/spf13/cobra v1.7.0
        github.com/spf13/viper v1.16.0
        github.com/whilp/git-urls v1.0.0
+       go.starlark.net v0.0.0-20200306205701-8dd3e2ee1dd5
        golang.org/x/crypto v0.12.0
        golang.org/x/mod v0.10.0
        golang.org/x/text v0.12.0
$ git diff wasm go.sum
diff --git a/go.sum b/go.sum
index 6fe3536..0caf20c 100644
--- a/go.sum
+++ b/go.sum
@@ -1702,6 +1702,7 @@ go.opentelemetry.io/otel/trace v0.20.0/go.mod h1:6GjCW8zgDjwGHGa6GkyeB8+/5vjT16g
 go.opentelemetry.io/otel/trace v1.0.0-RC1/go.mod h1:86UHmyHWFEtWjfWPSbu0+d0Pf9Q6e1U+3ViBOc+NXAg=
 go.opentelemetry.io/proto/otlp v0.7.0/go.mod h1:PqfVotwruBrMGOCsRd/89rSnXhoiJIqeYNgFYFoEGnI=
 go.opentelemetry.io/proto/otlp v0.9.0/go.mod h1:1vKfU9rv61e9EVGthD1zNvUbiwPcimSsOPU9brfSHJg=
+go.starlark.net v0.0.0-20200306205701-8dd3e2ee1dd5 h1:+FNtrFTmVw0YZGpBGX56XDee331t6JAXeK2bcyhLOOc=
 go.starlark.net v0.0.0-20200306205701-8dd3e2ee1dd5/go.mod h1:nmDLcffg48OtT/PSW0Hg7FvpRQsQh5OSqIylirxKC7o=
 go.uber.org/atomic v1.3.2/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
 go.uber.org/atomic v1.4.0/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=

[mauri870]

Thanks, but I still can't reproduce on 1.21 for some reason

$ CGO_ENABLED=0 GOOS=wasip1 GOARCH=wasm go1.21.5 build
$ CGO_ENABLED=0 GOOS=wasip1 GOARCH=wasm gotip build
# github.com/konveyor/move2kube-wasm
type:*github.com/mholt/archiver/v3.TarGz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarGz).Match is too big: 0x100010000
type:*github.com/mholt/archiver/v3.TarGz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarGz).Match is too big: 0x100010000
type:*github.com/mholt/archiver/v3.TarGz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarGz).Read is too big: 0x100030000 
# ...

[HarikrishnanBalagopal]

type:*github.com/mholt/archiver/v3.TarGz: non-pc-relative relocation address for github.com/mholt/archiver/v3.(*TarGz).Match is too big: 0x100010000

I might be confused but the output you have shown includes the compile error. Are you trying to reproduce something else?

[mauri870]

Sorry, I think I was not clear enough. With 1.21.5 it built just fine, the error you see is for gotip(1.22).