cmd/go/internal/modload: ensure that __debug_modinfo__ is not discarded during linking
Fixes #28753
Updates #29628
Change-Id: I4a561be7d491a0d088e656b00151ae1bdbd16a84
Reviewed-on: https://go-review.googlesource.com/c/158357
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index 10bea15..2a8be90 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -252,10 +252,19 @@
func ModInfoProg(info string) []byte {
// Inject a variable with the debug information as runtime/debug.modinfo,
// but compile it in package main so that it is specific to the binary.
- // No need to populate it in an init func; it will still work with go:linkname.
+ //
+ // The variable must be a literal so that it will have the correct value
+ // before the initializer for package main runs.
+ //
+ // We also want the value to be present even if runtime/debug.modinfo is
+ // otherwise unused in the rest of the program. Reading it in an init function
+ // suffices for now.
+
return []byte(fmt.Sprintf(`package main
import _ "unsafe"
//go:linkname __debug_modinfo__ runtime/debug.modinfo
var __debug_modinfo__ = %q
+var keepalive_modinfo = __debug_modinfo__
+func init() { keepalive_modinfo = __debug_modinfo__ }
`, string(infoStart)+info+string(infoEnd)))
}
diff --git a/src/cmd/go/testdata/script/mod_modinfo.txt b/src/cmd/go/testdata/script/mod_modinfo.txt
index f8ad18f..fb31f9e 100644
--- a/src/cmd/go/testdata/script/mod_modinfo.txt
+++ b/src/cmd/go/testdata/script/mod_modinfo.txt
@@ -7,34 +7,83 @@
go mod edit -require=rsc.io/quote@v1.5.2
go mod edit -replace=rsc.io/quote@v1.5.2=rsc.io/quote@v1.0.0
-go run main.go
-
-stderr 'Hello, world.'
+# Build a binary and ensure that it can output its own debug info.
+# The debug info should be accessible before main starts (golang.org/issue/29628).
+go build
+exec ./x$GOEXE
stderr 'mod\s+x\s+\(devel\)'
stderr 'dep\s+rsc.io/quote\s+v1.5.2\s+'
stderr '=>\s+rsc.io/quote\s+v1.0.0\s+h1:'
+stderr 'Hello, world.'
+
+[short] skip
+
+# Build a binary that accesses its debug info by reading the binary directly
+# (rather than through debug.ReadBuildInfo).
+# The debug info should still be present (golang.org/issue/28753).
+cd unused
+go build
+exec ./unused$GOEXE
-- x/go.mod --
module x
+-- x/lib/lib.go --
+// Package lib accesses runtime/debug.modinfo before package main's init
+// functions have run.
+package lib
+
+import "runtime/debug"
+
+func init() {
+ m, ok := debug.ReadBuildInfo()
+ if !ok {
+ panic("failed debug.ReadBuildInfo")
+ }
+ println("mod", m.Main.Path, m.Main.Version)
+ for _, d := range m.Deps {
+ println("dep", d.Path, d.Version, d.Sum)
+ if r := d.Replace; r != nil {
+ println("=>", r.Path, r.Version, r.Sum)
+ }
+ }
+}
+
-- x/main.go --
package main
-import "runtime/debug"
-import "rsc.io/quote"
+import (
+ "rsc.io/quote"
+ _ "x/lib"
+)
func main() {
- println(quote.Hello())
+ println(quote.Hello())
+}
- m, ok := debug.ReadBuildInfo()
- if !ok {
- panic("failed debug.ReadBuildInfo")
- }
- println("mod", m.Main.Path, m.Main.Version)
- for _, d := range m.Deps {
- println("dep", d.Path, d.Version, d.Sum)
- if r := d.Replace; r != nil {
- println("=>", r.Path, r.Version, r.Sum)
- }
- }
+-- x/unused/main.go --
+// The unused binary does not access runtime/debug.modinfo.
+package main
+
+import (
+ "bytes"
+ "encoding/hex"
+ "io/ioutil"
+ "log"
+ "os"
+
+ _ "rsc.io/quote"
+)
+
+func main() {
+ b, err := ioutil.ReadFile(os.Args[0])
+ if err != nil {
+ log.Fatal(err)
+ }
+
+ infoStart, _ := hex.DecodeString("3077af0c9274080241e1c107e6d618e6")
+ if !bytes.Contains(b, infoStart) {
+ log.Fatal("infoStart not found in binary")
+ }
+ log.Println("ok")
}
