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cmd/compile: go:linkname does not work with dot in importpath #67361

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jiping-s opened this issue May 14, 2024 · 4 comments
Closed

cmd/compile: go:linkname does not work with dot in importpath #67361

jiping-s opened this issue May 14, 2024 · 4 comments
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compiler/runtime Issues related to the Go compiler and/or runtime.

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@jiping-s
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jiping-s commented May 14, 2024

Go version

go1.22.1 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/myname/Library/Caches/go-build'
GOENV='/Users/myname/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/myname/.go/pkg/mod'
GONOPROXY='*'
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/myname/.go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.1'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/myname/.go/pkg/mod/gopkg.in/yaml.v3@v3.0.1/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/n3/rjz31n_50516xs92p6gswgsr0000gp/T/go-build174368253=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Use go linkname with gopkg.in/yaml.v3 or gopkg.in/yaml.v2

playground: https://go.dev/play/p/1yYtFVvGnfn

package main

import (
	"fmt"
	_ "unsafe"

	_ "gopkg.in/yaml.v2"
)

//go:linkname newEncoder gopkg.in/yaml.v2.newEncoder
func newEncoder() any

func main() {
	newEncoder()
}

What did you see happen?

relocation target gopkg.in/yaml.v2.newEncoder not defined

What did you expect to see?

The symbol is imported and can be called.

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label May 14, 2024
jiping-s added a commit to relex/slog-agent that referenced this issue May 14, 2024
@mauri870
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The go:linkname directive is not part of the language and its use in user code is highly discouraged. It can break at any time without warning. From what I see in your example you can just import the package as-is, there is no need to use linkname, plus I'm not sure if it even works with external packages, I have mainly seen its use with internal Go libraries.

@seankhliao
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see #63846 (comment)

@seankhliao seankhliao closed this as not planned Won't fix, can't repro, duplicate, stale May 14, 2024
@jiping-s
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jiping-s commented May 15, 2024

From what I see in your example you can just import the package as-is, there is no need to use linkname, plus I'm not sure if it even works with external packages, I have mainly seen its use with internal Go libraries.

  • linkname is needed to access the internal decoder, not the public one (we're using yaml.Node.Decode with no public way to config.)
  • It does work with external packages and we use it on production system for other packages. Here is one working example:
//go:linkname DBBeforeQuery github.com/uptrace/bun.(*DB).beforeQuery
func DBBeforeQuery(
	instance *bun.DB,
	ctx context.Context,
	iquery bun.Query,
	queryTemplate string,
	queryArgs []interface{},
	query string,
	model bun.Model,
) (context.Context, *bun.QueryEvent)

@jiping-s
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Hi! I found the actual symbol name by go tool compile. "." in the last part of package name is encoded:

// gopkg.in/yaml.v2 => gopkg.in/yaml%2ev2

//go:linkname newEncoder2 gopkg.in/yaml%2ev2.newEncoder
func newEncoder2() any

jiping-s added a commit to relex/slog-agent that referenced this issue May 17, 2024
…ut secret (#58)

* accessing internal yaml v3 methods, see golang/go#67361
* added tests for client worker's connection opening

since the YAML change, all practically optional fields in config can be turned optional by removing the value checks.
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