cmd/go: remove support for -buildmode=shared

It never worked in module mode (or with a read-only GOROOT).
A proposal to drop it was filed (and approved) in
https://golang.org/issue/47788.

Fixes #47788

Change-Id: I0c12f38eb0c5dfe9384fbdb49ed202301fa4273d
Reviewed-on: https://go-review.googlesource.com/c/go/+/359096
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

doc/go1.18.html

@@ -89,6 +89,13 @@ Do not send CLs removing the interior tags from such phrases.
   package.
 </p>
 
+<p><!-- golang.org/issue/47788 -->
+  The <code>go</code> command no longer supports <code>-linkshared</code>
+  and <code>-buildmode=shared</code>.
+  (<code>shared<code> building and linking has never worked in module mode or
+  when <code>GOROOT</code> is not writable.)
+<p>
+
 <p>
   TODO: complete this section, or delete if not needed
 </p>

misc/cgo/testshared/overlaydir_test.go

@@ -1,78 +0,0 @@
-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package shared_test
-
-import (
-	"io"
-	"os"
-	"path/filepath"
-	"strings"
-)
-
-// overlayDir makes a minimal-overhead copy of srcRoot in which new files may be added.
-//
-// TODO: Once we no longer need to support the misc module in GOPATH mode,
-// factor this function out into a package to reduce duplication.
-func overlayDir(dstRoot, srcRoot string) error {
-	dstRoot = filepath.Clean(dstRoot)
-	if err := os.MkdirAll(dstRoot, 0777); err != nil {
-		return err
-	}
-
-	srcRoot, err := filepath.Abs(srcRoot)
-	if err != nil {
-		return err
-	}
-
-	return filepath.Walk(srcRoot, func(srcPath string, info os.FileInfo, err error) error {
-		if err != nil || srcPath == srcRoot {
-			return err
-		}
-
-		suffix := strings.TrimPrefix(srcPath, srcRoot)
-		for len(suffix) > 0 && suffix[0] == filepath.Separator {
-			suffix = suffix[1:]
-		}
-		dstPath := filepath.Join(dstRoot, suffix)
-
-		perm := info.Mode() & os.ModePerm
-		if info.Mode()&os.ModeSymlink != 0 {
-			info, err = os.Stat(srcPath)
-			if err != nil {
-				return err
-			}
-			perm = info.Mode() & os.ModePerm
-		}
-
-		// Always copy directories (don't symlink them).
-		// If we add a file in the overlay, we don't want to add it in the original.
-		if info.IsDir() {
-			return os.MkdirAll(dstPath, perm|0200)
-		}
-
-		// If the OS supports symlinks, use them instead of copying bytes.
-		if err := os.Symlink(srcPath, dstPath); err == nil {
-			return nil
-		}
-
-		// Otherwise, copy the bytes.
-		src, err := os.Open(srcPath)
-		if err != nil {
-			return err
-		}
-		defer src.Close()
-
-		dst, err := os.OpenFile(dstPath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
-		if err != nil {
-			return err
-		}
-
-		_, err = io.Copy(dst, src)
-		if closeErr := dst.Close(); err == nil {
-			err = closeErr
-		}
-		return err
-	})
-}

misc/cgo/testshared/testdata/dep2/dep2.go

@@ -1,15 +0,0 @@
-package dep2
-
-import "testshared/depBase"
-
-var W int = 1
-
-var hasProg depBase.HasProg
-
-type Dep2 struct {
-	depBase.Dep
-}
-
-func G() int {
-	return depBase.F() + 1
-}

misc/cgo/testshared/testdata/dep3/dep3.go

@@ -1,22 +0,0 @@
-package dep3
-
-// The point of this test file is that it references a type from
-// depBase that is also referenced in dep2, but dep2 is loaded by the
-// linker before depBase (because it is earlier in the import list).
-// There was a bug in the linker where it would not correctly read out
-// the type data in this case and later crash.
-
-import (
-	"testshared/dep2"
-	"testshared/depBase"
-)
-
-type Dep3 struct {
-	dep  depBase.Dep
-	dep2 dep2.Dep2
-}
-
-func D3() int {
-	var x Dep3
-	return x.dep.X + x.dep2.X
-}

misc/cgo/testshared/testdata/depBase/asm.s

@@ -1,10 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build gc
-
-#include "textflag.h"
-
-TEXT ·ImplementedInAsm(SB),NOSPLIT,$0-0
-       RET

misc/cgo/testshared/testdata/depBase/dep.go

@@ -1,37 +0,0 @@
-// Copyright 2016 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package depBase
-
-import (
-	"os"
-	"reflect"
-)
-
-var SlicePtr interface{} = &[]int{}
-
-var V int = 1
-
-var HasMask []string = []string{"hi"}
-
-type HasProg struct {
-	array [1024]*byte
-}
-
-type Dep struct {
-	X int
-}
-
-func (d *Dep) Method() int {
-	// This code below causes various go.itab.* symbols to be generated in
-	// the shared library. Similar code in ../exe/exe.go results in
-	// exercising https://golang.org/issues/17594
-	reflect.TypeOf(os.Stdout).Elem()
-	return 10
-}
-
-func F() int {
-	defer func() {}()
-	return V
-}

misc/cgo/testshared/testdata/depBase/gccgo.go

@@ -1,9 +0,0 @@
-// Copyright 2016 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build gccgo
-
-package depBase
-
-func ImplementedInAsm() {}

misc/cgo/testshared/testdata/depBase/stubs.go

@@ -1,9 +0,0 @@
-// Copyright 2016 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build gc
-
-package depBase
-
-func ImplementedInAsm()

misc/cgo/testshared/testdata/division/division.go

@@ -1,17 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-//go:noinline
-func div(x, y uint32) uint32 {
-	return x / y
-}
-
-func main() {
-	a := div(97, 11)
-	if a != 8 {
-		panic("FAIL")
-	}
-}

misc/cgo/testshared/testdata/exe/exe.go

@@ -1,45 +0,0 @@
-package main
-
-import (
-	"os"
-	"reflect"
-	"runtime"
-
-	"testshared/depBase"
-)
-
-// Having a function declared in the main package triggered
-// golang.org/issue/18250
-func DeclaredInMain() {
-}
-
-type C struct {
-}
-
-func F() *C {
-	return nil
-}
-
-var slicePtr interface{} = &[]int{}
-
-func main() {
-	defer depBase.ImplementedInAsm()
-	// This code below causes various go.itab.* symbols to be generated in
-	// the executable. Similar code in ../depBase/dep.go results in
-	// exercising https://golang.org/issues/17594
-	reflect.TypeOf(os.Stdout).Elem()
-	runtime.GC()
-	depBase.V = depBase.F() + 1
-
-	var c *C
-	if reflect.TypeOf(F).Out(0) != reflect.TypeOf(c) {
-		panic("bad reflection results, see golang.org/issue/18252")
-	}
-
-	sp := reflect.New(reflect.TypeOf(slicePtr).Elem())
-	s := sp.Interface()
-
-	if reflect.TypeOf(s) != reflect.TypeOf(slicePtr) {
-		panic("bad reflection results, see golang.org/issue/18729")
-	}
-}

misc/cgo/testshared/testdata/exe2/exe2.go

@@ -1,8 +0,0 @@
-package main
-
-import "testshared/dep2"
-
-func main() {
-	d := &dep2.Dep2{}
-	dep2.W = dep2.G() + 1 + d.Method()
-}

misc/cgo/testshared/testdata/exe3/exe3.go

@@ -1,7 +0,0 @@
-package main
-
-import "testshared/dep3"
-
-func main() {
-	dep3.D3()
-}

misc/cgo/testshared/testdata/execgo/exe.go

@@ -1,8 +0,0 @@
-package main
-
-/*
- */
-import "C"
-
-func main() {
-}

misc/cgo/testshared/testdata/explicit/explicit.go

@@ -1,9 +0,0 @@
-package explicit
-
-import (
-	"testshared/implicit"
-)
-
-func E() int {
-	return implicit.I()
-}

misc/cgo/testshared/testdata/gcdata/main/main.go

@@ -1,37 +0,0 @@
-// Copyright 2020 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Test that GC data is generated correctly for global
-// variables with types defined in a shared library.
-// See issue 39927.
-
-// This test run under GODEBUG=clobberfree=1. The check
-// *x[i] == 12345 depends on this debug mode to clobber
-// the value if the object is freed prematurely.
-
-package main
-
-import (
-	"fmt"
-	"runtime"
-	"testshared/gcdata/p"
-)
-
-var x p.T
-
-func main() {
-	for i := range x {
-		x[i] = new(int)
-		*x[i] = 12345
-	}
-	runtime.GC()
-	runtime.GC()
-	runtime.GC()
-	for i := range x {
-		if *x[i] != 12345 {
-			fmt.Printf("x[%d] == %d, want 12345\n", i, *x[i])
-			panic("FAIL")
-		}
-	}
-}

misc/cgo/testshared/testdata/gcdata/p/p.go

@@ -1,7 +0,0 @@
-// Copyright 2020 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package p
-
-type T [10]*int

misc/cgo/testshared/testdata/global/main.go

@@ -1,71 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-import (
-	"testshared/globallib"
-)
-
-//go:noinline
-func testLoop() {
-	for i, s := range globallib.Data {
-		if s != int64(i) {
-			panic("testLoop: mismatch")
-		}
-	}
-}
-
-//go:noinline
-func ptrData() *[1<<20 + 10]int64 {
-	return &globallib.Data
-}
-
-//go:noinline
-func testMediumOffset() {
-	for i, s := range globallib.Data[1<<16-2:] {
-		if s != int64(i)+1<<16-2 {
-			panic("testMediumOffset: index mismatch")
-		}
-	}
-
-	x := globallib.Data[1<<16-1]
-	if x != 1<<16-1 {
-		panic("testMediumOffset: direct mismatch")
-	}
-
-	y := &globallib.Data[1<<16-3]
-	if y != &ptrData()[1<<16-3] {
-		panic("testMediumOffset: address mismatch")
-	}
-}
-
-//go:noinline
-func testLargeOffset() {
-	for i, s := range globallib.Data[1<<20:] {
-		if s != int64(i)+1<<20 {
-			panic("testLargeOffset: index mismatch")
-		}
-	}
-
-	x := globallib.Data[1<<20+1]
-	if x != 1<<20+1 {
-		panic("testLargeOffset: direct mismatch")
-	}
-
-	y := &globallib.Data[1<<20+2]
-	if y != &ptrData()[1<<20+2] {
-		panic("testLargeOffset: address mismatch")
-	}
-}
-
-func main() {
-	testLoop()
-
-	// SSA rules commonly merge offsets into addresses. These
-	// tests access global data in different ways to try
-	// and exercise different SSA rules.
-	testMediumOffset()
-	testLargeOffset()
-}

misc/cgo/testshared/testdata/globallib/global.go

@@ -1,17 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package globallib
-
-// Data is large enough to that offsets into it do not fit into
-// 16-bit or 20-bit immediates. Ideally we'd also try and overrun
-// 32-bit immediates, but that requires the test machine to have
-// too much memory.
-var Data [1<<20 + 10]int64
-
-func init() {
-	for i := range Data {
-		Data[i] = int64(i)
-	}
-}

misc/cgo/testshared/testdata/iface/main.go

@@ -1,17 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-import "testshared/iface_a"
-import "testshared/iface_b"
-
-func main() {
-	if iface_a.F() != iface_b.F() {
-		panic("empty interfaces not equal")
-	}
-	if iface_a.G() != iface_b.G() {
-		panic("non-empty interfaces not equal")
-	}
-}

misc/cgo/testshared/testdata/iface_a/a.go

@@ -1,17 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package iface_a
-
-import "testshared/iface_i"
-
-//go:noinline
-func F() interface{} {
-	return (*iface_i.T)(nil)
-}
-
-//go:noinline
-func G() iface_i.I {
-	return (*iface_i.T)(nil)
-}

misc/cgo/testshared/testdata/iface_b/b.go

@@ -1,17 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package iface_b
-
-import "testshared/iface_i"
-
-//go:noinline
-func F() interface{} {
-	return (*iface_i.T)(nil)
-}
-
-//go:noinline
-func G() iface_i.I {
-	return (*iface_i.T)(nil)
-}

misc/cgo/testshared/testdata/iface_i/i.go

@@ -1,17 +0,0 @@
-// Copyright 2017 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package iface_i
-
-type I interface {
-	M()
-}
-
-type T struct {
-}
-
-func (t *T) M() {
-}
-
-// *T implements I

misc/cgo/testshared/testdata/implicit/implicit.go

@@ -1,5 +0,0 @@
-package implicit
-
-func I() int {
-	return 42
-}

misc/cgo/testshared/testdata/implicitcmd/implicitcmd.go

@@ -1,10 +0,0 @@
-package main
-
-import (
-	"testshared/explicit"
-	"testshared/implicit"
-)
-
-func main() {
-	println(implicit.I() + explicit.E())
-}

misc/cgo/testshared/testdata/issue25065/a.go

@@ -1,20 +0,0 @@
-// Copyright 2018 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Package issue25065 has a type with a method that is
-//  1) referenced in a method expression
-//  2) not called
-//  3) not converted to an interface
-//  4) is a value method but the reference is to the pointer method
-// These cases avoid the call to makefuncsym from typecheckfunc, but we
-// still need to call makefuncsym somehow or the symbol will not be defined.
-package issue25065
-
-type T int
-
-func (t T) M() {}
-
-func F() func(*T) {
-	return (*T).M
-}

misc/cgo/testshared/testdata/issue30768/issue30768lib/lib.go

@@ -1,11 +0,0 @@
-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package issue30768lib
-
-// S is a struct that requires a generated hash function.
-type S struct {
-	A string
-	B int
-}

misc/cgo/testshared/testdata/issue30768/x_test.go

@@ -1,22 +0,0 @@
-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package issue30768_test
-
-import (
-	"testing"
-
-	"testshared/issue30768/issue30768lib"
-)
-
-type s struct {
-	s issue30768lib.S
-}
-
-func Test30768(t *testing.T) {
-	// Calling t.Log will convert S to an empty interface,
-	// which will force a reference to the generated hash function,
-	// defined in the shared library.
-	t.Log(s{})
-}

misc/cgo/testshared/testdata/issue39777/a/a.go

@@ -1,9 +0,0 @@
-// Copyright 2020 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package a
-
-import "testshared/issue39777/b"
-
-func F() { b.F() }

misc/cgo/testshared/testdata/issue39777/b/b.go

@@ -1,7 +0,0 @@
-// Copyright 2020 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package b
-
-func F() {}

misc/cgo/testshared/testdata/issue44031/a/a.go

@@ -1,9 +0,0 @@
-// Copyright 2021 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package a
-
-type ATypeWithALoooooongName interface { // a long name, so the type descriptor symbol name is mangled
-	M()
-}

misc/cgo/testshared/testdata/issue44031/b/b.go

@@ -1,17 +0,0 @@
-// Copyright 2021 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package b
-
-import "testshared/issue44031/a"
-
-type T int
-
-func (T) M() {}
-
-var i = a.ATypeWithALoooooongName(T(0))
-
-func F() {
-	i.M()
-}

misc/cgo/testshared/testdata/issue44031/main/main.go

@@ -1,20 +0,0 @@
-// Copyright 2021 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-import "testshared/issue44031/b"
-
-type t int
-
-func (t) m() {}
-
-type i interface{ m() } // test that unexported method is correctly marked
-
-var v interface{} = t(0)
-
-func main() {
-	b.F()
-	v.(i).m()
-}

misc/cgo/testshared/testdata/issue47837/a/a.go

@@ -1,19 +0,0 @@
-// Copyright 2021 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package a
-
-type A interface {
-	M()
-}
-
-//go:noinline
-func TheFuncWithArgA(a A) {
-	a.M()
-}
-
-type ImplA struct{}
-
-//go:noinline
-func (A *ImplA) M() {}

misc/cgo/testshared/testdata/issue47837/main/main.go

@@ -1,14 +0,0 @@
-// Copyright 2021 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-import (
-	"testshared/issue47837/a"
-)
-
-func main() {
-	var vara a.ImplA
-	a.TheFuncWithArgA(&vara)
-}

misc/cgo/testshared/testdata/trivial/trivial.go

@@ -1,9 +0,0 @@
-package main
-
-func main() {
-	// This is enough to make sure that the executable references
-	// a type descriptor, which was the cause of
-	// https://golang.org/issue/25970.
-	c := make(chan int)
-	_ = c
-}

src/cmd/dist/test.go

@@ -762,9 +762,6 @@ func (t *tester) registerTests() {
 		if t.supportedBuildmode("c-shared") {
 			t.registerHostTest("testcshared", "../misc/cgo/testcshared", "misc/cgo/testcshared", ".")
 		}
-		if t.supportedBuildmode("shared") {
-			t.registerTest("testshared", "../misc/cgo/testshared", t.goTest(), t.timeout(600), ".")
-		}
 		if t.supportedBuildmode("plugin") {
 			t.registerTest("testplugin", "../misc/cgo/testplugin", t.goTest(), t.timeout(600), ".")
 		}
@@ -1047,12 +1044,6 @@ func (t *tester) supportedBuildmode(mode string) bool {
 			return true
 		}
 		return false
-	case "shared":
-		switch pair {
-		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le", "linux-s390x":
-			return true
-		}
-		return false
 	case "plugin":
 		// linux-arm64 is missing because it causes the external linker
 		// to crash, see https://golang.org/issue/17138

src/cmd/go/alldocs.go

@@ -162,9 +162,6 @@
 // 		flags has a similar effect.
 // 	-ldflags '[pattern=]arg list'
 // 		arguments to pass on each go tool link invocation.
-// 	-linkshared
-// 		build code that will be linked against shared libraries previously
-// 		created with -buildmode=shared.
 // 	-mod mode
 // 		module download mode to use: readonly, vendor, or mod.
 // 		By default, if a vendor directory is present and the go version in go.mod
@@ -778,7 +775,6 @@
 //         Name          string   // package name
 //         Doc           string   // package documentation string
 //         Target        string   // install path
-//         Shlib         string   // the shared library that contains this package (only set when -linkshared)
 //         Goroot        bool     // is this package in the Go root?
 //         Standard      bool     // is this package part of the standard Go library?
 //         Stale         bool     // would 'go install' do anything for this package?
@@ -1799,11 +1795,6 @@
 // 		non-main packages are built into .a files (the default
 // 		behavior).
 //
-// 	-buildmode=shared
-// 		Combine all the listed non-main packages into a single shared
-// 		library that will be used when building with the -linkshared
-// 		option. Packages named main are ignored.
-//
 // 	-buildmode=exe
 // 		Build the listed main packages and everything they import into
 // 		executables. Packages not named main are ignored.

src/cmd/go/internal/help/helpdoc.go

@@ -726,11 +726,6 @@ are:
 		non-main packages are built into .a files (the default
 		behavior).
 
-	-buildmode=shared
-		Combine all the listed non-main packages into a single shared
-		library that will be used when building with the -linkshared
-		option. Packages named main are ignored.
-
 	-buildmode=exe
 		Build the listed main packages and everything they import into
 		executables. Packages not named main are ignored.

src/cmd/go/internal/list/list.go

@@ -23,8 +23,8 @@ import (
 	"cmd/go/internal/load"
 	"cmd/go/internal/modinfo"
 	"cmd/go/internal/modload"
-	"cmd/go/internal/work"
 	"cmd/go/internal/str"
+	"cmd/go/internal/work"
 )
 
 var CmdList = &base.Command{
@@ -56,7 +56,6 @@ to -f '{{.ImportPath}}'. The struct being passed to the template is:
         Name          string   // package name
         Doc           string   // package documentation string
         Target        string   // install path
-        Shlib         string   // the shared library that contains this package (only set when -linkshared)
         Goroot        bool     // is this package in the Go root?
         Standard      bool     // is this package part of the standard Go library?
         Stale         bool     // would 'go install' do anything for this package?

src/cmd/go/internal/work/build.go

@@ -116,9 +116,6 @@ and test commands:
 		flags has a similar effect.
 	-ldflags '[pattern=]arg list'
 		arguments to pass on each go tool link invocation.
-	-linkshared
-		build code that will be linked against shared libraries previously
-		created with -buildmode=shared.
 	-mod mode
 		module download mode to use: readonly, vendor, or mod.
 		By default, if a vendor directory is present and the go version in go.mod

src/cmd/go/internal/work/init.go

@@ -246,16 +246,20 @@ func buildModeInit() {
 		}
 		ldBuildmode = "pie"
 	case "shared":
-		pkgsFilter = pkgsNotMain
+		if cfg.Goos == "linux" {
-		if gccgo {
+			switch cfg.Goarch {
-			codegenArg = "-fPIC"
+			case "386", "amd64", "arm", "arm64", "ppc64le", "s390x":
-		} else {
+				// -buildmode=shared was supported on these platforms at one point, but
-			codegenArg = "-dynlink"
+				// never really worked in module mode.
+				// Support was officially dropped as of Go 1.18.
+				// (See https://golang.org/issue/47788.)
+				base.Fatalf("-buildmode=shared no longer supported as of Go 1.18")
+
+				// TODO(#47788): Remove supporting code for -buildmode=shared.
+				// (For the Go 1.18 release, we will keep most of the code around but
+				// disabled to avoid merge conflicts in case we need to revert quickly.)
 			}
-		if cfg.BuildO != "" {
-			base.Fatalf("-buildmode=shared and -o not supported together")
 		}
-		ldBuildmode = "shared"
 	case "plugin":
 		pkgsFilter = oneMainPkg
 		if gccgo {
@@ -274,6 +278,15 @@ func buildModeInit() {
 	}
 
 	if cfg.BuildLinkshared {
+		if cfg.Goos == "linux" {
+			switch cfg.Goarch {
+			case "386", "amd64", "arm", "arm64", "ppc64le", "s390x":
+				base.Fatalf("-linkshared no longer supported as of Go 1.18")
+				// TODO(#47788): Remove supporting code for linkshared.
+				// (For the Go 1.18 release, we will keep most of the code around but
+				// disabled to avoid merge conflicts in case we need to revert quickly.)
+			}
+		}
 		if !sys.BuildModeSupported(cfg.BuildToolchainName, "shared", cfg.Goos, cfg.Goarch) {
 			base.Fatalf("-linkshared not supported on %s/%s\n", cfg.Goos, cfg.Goarch)
 		}

src/cmd/go/testdata/script/list_linkshared.txt

@@ -1,16 +0,0 @@
-env GO111MODULE=on
-
-# golang.org/issue/35759: 'go list -linkshared'
-# panicked if invoked on a test-only package.
-
-[!buildmode:shared] skip
-
-go list -f '{{.ImportPath}}: {{.Target}} {{.Shlib}}' -linkshared .
-stdout '^example.com:  $'
-
--- go.mod --
-module example.com
-
-go 1.14
--- x.go --
-package x

src/cmd/internal/sys/supported.go

@@ -109,13 +109,6 @@ func BuildModeSupported(compiler, buildmode, goos, goarch string) bool {
 		}
 		return false
 
-	case "shared":
-		switch platform {
-		case "linux/386", "linux/amd64", "linux/arm", "linux/arm64", "linux/ppc64le", "linux/s390x":
-			return true
-		}
-		return false
-
 	case "plugin":
 		switch platform {
 		case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/s390x", "linux/ppc64le",