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>

8 files changed, 23 insertions, 60 deletions

diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index 5935011e19..87238cc74f 100644
--- a/src/cmd/dist/test.go
+++ b/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
diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 9d8c321307..685ccac826 100644
--- a/src/cmd/go/alldocs.go
+++ b/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.
diff --git a/src/cmd/go/internal/help/helpdoc.go b/src/cmd/go/internal/help/helpdoc.go
index 035235fe1b..2bb3584eba 100644
--- a/src/cmd/go/internal/help/helpdoc.go
+++ b/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.
diff --git a/src/cmd/go/internal/list/list.go b/src/cmd/go/internal/list/list.go
index 8c85ddcf21..f23fbe5fea 100644
--- a/src/cmd/go/internal/list/list.go
+++ b/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?
diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 9d0ad27f0d..e39ffcbd50 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/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
diff --git a/src/cmd/go/internal/work/init.go b/src/cmd/go/internal/work/init.go
index 4dbbd2a13f..b2ee00d53c 100644
--- a/src/cmd/go/internal/work/init.go
+++ b/src/cmd/go/internal/work/init.go
@@ -246,16 +246,20 @@ func buildModeInit() {
 		}
 		ldBuildmode = "pie"
 	case "shared":
-		pkgsFilter = pkgsNotMain
-		if gccgo {
-			codegenArg = "-fPIC"
-		} else {
-			codegenArg = "-dynlink"
-		}
-		if cfg.BuildO != "" {
-			base.Fatalf("-buildmode=shared and -o not supported together")
+		if cfg.Goos == "linux" {
+			switch cfg.Goarch {
+			case "386", "amd64", "arm", "arm64", "ppc64le", "s390x":
+				// -buildmode=shared was supported on these platforms at one point, but
+				// 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.)
+			}
 		}
-		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)
 		}
diff --git a/src/cmd/go/testdata/script/list_linkshared.txt b/src/cmd/go/testdata/script/list_linkshared.txt
deleted file mode 100644
index baae1e2be8..0000000000
--- a/src/cmd/go/testdata/script/list_linkshared.txt
+++ /dev/null
@@ -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
diff --git a/src/cmd/internal/sys/supported.go b/src/cmd/internal/sys/supported.go
index e6c56fbc56..473e390587 100644
--- a/src/cmd/internal/sys/supported.go
+++ b/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",