From: Xiangdong Ji <xiangdong.ji@gmail.com>
Date: Sun, 18 Oct 2020 18:43:23 +0000 (-0700)
Subject: cmd/go: use the last -linkmode flag to determine external linking
X-Git-Tag: go1.16beta1~603
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=61313dab524f2c82add8442e15d87fca5b7103de;p=gostls13.git

cmd/go: use the last -linkmode flag to determine external linking

Current linkmode checking in determining package dependencies doesn't
take multiple -linkmode options into consideration, may lead to redundant
dependency on 'runtime/cgo'.

Fixes the problem and adds a testcase.

Change-Id: Iac5ea9fb3ca5ef931201afd0f3441f41f946c919
Reviewed-on: https://go-review.googlesource.com/c/go/+/263497
Trust: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
---

diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index c9665265e9..f07bd3e075 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -1978,16 +1978,20 @@ func externalLinkingForced(p *Package) bool {
 	// external linking mode, as of course does
 	// -ldflags=-linkmode=external. External linking mode forces
 	// an import of runtime/cgo.
+	// If there are multiple -linkmode options, the last one wins.
 	pieCgo := cfg.BuildBuildmode == "pie" && !sys.InternalLinkPIESupported(cfg.BuildContext.GOOS, cfg.BuildContext.GOARCH)
 	linkmodeExternal := false
 	if p != nil {
 		ldflags := BuildLdflags.For(p)
-		for i, a := range ldflags {
-			if a == "-linkmode=external" {
-				linkmodeExternal = true
-			}
-			if a == "-linkmode" && i+1 < len(ldflags) && ldflags[i+1] == "external" {
+		for i := len(ldflags) - 1; i >= 0; i-- {
+			a := ldflags[i]
+			if a == "-linkmode=external" ||
+				a == "-linkmode" && i+1 < len(ldflags) && ldflags[i+1] == "external" {
 				linkmodeExternal = true
+				break
+			} else if a == "-linkmode=internal" ||
+				a == "-linkmode" && i+1 < len(ldflags) && ldflags[i+1] == "internal" {
+				break
 			}
 		}
 	}
diff --git a/src/cmd/go/testdata/script/gcflags_patterns.txt b/src/cmd/go/testdata/script/gcflags_patterns.txt
index 5374493a43..f23cecefd3 100644
--- a/src/cmd/go/testdata/script/gcflags_patterns.txt
+++ b/src/cmd/go/testdata/script/gcflags_patterns.txt
@@ -63,6 +63,10 @@ stderr 'link.* -X=math.pi=3'
 go build -n -ldflags=-X=math.pi=3
 stderr 'link.* -X=math.pi=3'
 
+# cgo.a should not be a dependency of internally-linked go package
+go build -ldflags='-linkmode=external -linkmode=internal' -n prog.go
+! stderr 'packagefile .*runtime/cgo.a'
+
 -- z1/z.go --
 package z1
 import _ "y"