From 9d23975d89e6cc3df4f2156b2ae0df5d2cef16fb Mon Sep 17 00:00:00 2001 From: "Bryan C. Mills" Date: Thu, 17 Jan 2019 14:39:31 -0500 Subject: [PATCH] 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 Reviewed-by: Brad Fitzpatrick Reviewed-by: Russ Cox --- src/cmd/go/internal/modload/build.go | 11 ++- src/cmd/go/testdata/script/mod_modinfo.txt | 85 +++++++++++++++++----- 2 files changed, 77 insertions(+), 19 deletions(-) diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go index 10bea15fa3..2a8be90b78 100644 --- a/src/cmd/go/internal/modload/build.go +++ b/src/cmd/go/internal/modload/build.go @@ -252,10 +252,19 @@ func findModule(target, path string) module.Version { 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 f8ad18f136..fb31f9e43b 100644 --- a/src/cmd/go/testdata/script/mod_modinfo.txt +++ b/src/cmd/go/testdata/script/mod_modinfo.txt @@ -7,34 +7,83 @@ cd x 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()) - - 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) - } - } + println(quote.Hello()) +} + +-- 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") } -- 2.50.0