Reproducible BUILD_PATH_PREFIX_MAP

Make builds reproducible by honoring BUILD_PATH_PREFIX_MAP
Upstream has rejected the patch in this form and promised to implement an
alternative they are happy with instead. That hasn't happened yet though.

Bug: https://github.com/golang/go/issues/22491, https://github.com/golang/go/issues/16860
Forwarded: https://golang.org/cl/73291 (rejected upstream though)

Gbp-Pq: Name 0001-Reproducible-BUILD_PATH_PREFIX_MAP.patch

diff --git a/src/cmd/go/internal/work/gc.go b/src/cmd/go/internal/work/gc.go
index 3d09f69fcc3e43698dbb8182695bb4f4746247f9..91965dff87e0d5dccf8b4f7e10a5a57425215129 100644 (file)
--- a/src/cmd/go/internal/work/gc.go
+++ b/src/cmd/go/internal/work/gc.go
@@ -560,7 +560,10 @@ func (gcToolchain) ld(b *Builder, root *Action, out, importcfg, mainpkg string)
                dir, out = filepath.Split(out)
        }
 
-       return b.run(root, dir, root.Package.ImportPath, nil, cfg.BuildToolexec, base.Tool("link"), "-o", out, "-importcfg", importcfg, ldflags, mainpkg)
+       // Apply the rewrite of $WORK to /tmp/go-build also to DWARF file tables:
+       env := []string{"BUILD_PATH_PREFIX_MAP=/tmp/go-build=" + b.WorkDir + ":" + os.Getenv("BUILD_PATH_PREFIX_MAP")}
+
+       return b.run(root, dir, root.Package.ImportPath, env, cfg.BuildToolexec, base.Tool("link"), "-o", out, "-importcfg", importcfg, ldflags, mainpkg)
 }
 
 func (gcToolchain) ldShared(b *Builder, root *Action, toplevelactions []*Action, out, importcfg string, allactions []*Action) error {

diff --git a/src/cmd/link/internal/ld/buildpathprefix.go b/src/cmd/link/internal/ld/buildpathprefix.go
new file mode 100644 (file)
index 0000000..8cda8a5
--- /dev/null
+++ b/src/cmd/link/internal/ld/buildpathprefix.go
@@ -0,0 +1,56 @@
+// Copyright 2010 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 ld
+
+import (
+       "log"
+       "os"
+       "strings"
+       "sync"
+)
+
+func decode(s string) string {
+       s = strings.Replace(s, "%.", ":", -1)
+       s = strings.Replace(s, "%+", "=", -1)
+       s = strings.Replace(s, "%#", "%", -1)
+       return s
+}
+
+type prefixMapEntry struct {
+       target string
+       source string
+}
+
+var (
+       buildPathPrefixMap     []prefixMapEntry
+       buildPathPrefixMapOnce sync.Once
+)
+
+// See https://reproducible-builds.org/specs/build-path-prefix-map/
+func applyBuildPathPrefixMap(dir string) string {
+       // Parse the BUILD_PATH_PREFIX_MAP only once; this function gets called for
+       // every compiled file.
+       buildPathPrefixMapOnce.Do(func() {
+               for _, item := range strings.Split(os.Getenv("BUILD_PATH_PREFIX_MAP"), ":") {
+                       if strings.TrimSpace(item) == "" {
+                               continue
+                       }
+                       parts := strings.Split(item, "=")
+                       if got, want := len(parts), 2; got != want {
+                               log.Fatalf("parsing BUILD_PATH_PREFIX_MAP: incorrect number of = separators in item %q: got %d, want %d", item, got-1, want-1)
+                       }
+                       buildPathPrefixMap = append(buildPathPrefixMap, prefixMapEntry{
+                               target: decode(parts[0]),
+                               source: decode(parts[1]),
+                       })
+               }
+       })
+       for _, e := range buildPathPrefixMap {
+               if strings.HasPrefix(dir, e.source) {
+                       return e.target + strings.TrimPrefix(dir, e.source)
+               }
+       }
+       return dir
+}

diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index a150306df9174dc8dd9f9ddf18cb62254d673baf..b4d605025b291c21dd0496651dcedf45c111b598 100644 (file)
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -1173,7 +1173,7 @@ func writelines(ctxt *Link, unit *compilationUnit, ls *sym.Symbol) {
                        }
                        // File indexes are 1-based.
                        fileNums[int(f.Value)] = len(fileNums) + 1
-                       Addstring(ls, f.Name)
+                       Addstring(ls, applyBuildPathPrefixMap(f.Name))
                        ls.AddUint8(0)
                        ls.AddUint8(0)
                        ls.AddUint8(0)
@@ -1752,7 +1752,7 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
                unit.dwinfo = newdie(ctxt, &dwroot, dwarf.DW_ABRV_COMPUNIT, unit.lib.Pkg, 0)
                newattr(unit.dwinfo, dwarf.DW_AT_language, dwarf.DW_CLS_CONSTANT, int64(dwarf.DW_LANG_Go), 0)
                // OS X linker requires compilation dir or absolute path in comp unit name to output debug info.
-               compDir := getCompilationDir()
+               compDir := applyBuildPathPrefixMap(getCompilationDir())
                // TODO: Make this be the actual compilation directory, not
                // the linker directory. If we move CU construction into the
                // compiler, this should happen naturally.

diff --git a/src/cmd/link/internal/ld/pcln.go b/src/cmd/link/internal/ld/pcln.go
index b42e510f571269b47b4960b733a1c2bba9665cff..41fa7eb83343e565f20d210bbabecd4094b7dccd 100644 (file)
--- a/src/cmd/link/internal/ld/pcln.go
+++ b/src/cmd/link/internal/ld/pcln.go
@@ -302,7 +302,7 @@ func (ctxt *Link) pclntab() {
                off = int32(ftab.SetAddr(ctxt.Arch, int64(off), s))
 
                // name int32
-               nameoff := nameToOffset(s.Name)
+               nameoff := nameToOffset(applyBuildPathPrefixMap(s.Name))
                off = int32(ftab.SetUint32(ctxt.Arch, int64(off), uint32(nameoff)))
 
                // args int32
@@ -449,7 +449,7 @@ func (ctxt *Link) pclntab() {
        ftab.SetUint32(ctxt.Arch, int64(start), uint32(len(ctxt.Filesyms)+1))
        for i := len(ctxt.Filesyms) - 1; i >= 0; i-- {
                s := ctxt.Filesyms[i]
-               ftab.SetUint32(ctxt.Arch, int64(start)+s.Value*4, uint32(ftabaddstring(ctxt, ftab, s.Name)))
+               ftab.SetUint32(ctxt.Arch, int64(start)+s.Value*4, uint32(ftabaddstring(ctxt, ftab, applyBuildPathPrefixMap(s.Name))))
        }
 
        ftab.Size = int64(len(ftab.P))