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[dev.link] cmd/link: use fingerprint as package hash

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Now the compiler-generated fingerprint is a hash of the export
data. We don't need to hash it ourselves in the linker. And the
linker doesn't need to read export data at all.

Fixes #33820.

Change-Id: I54bf3ebfd0f0c72aa43a352d7b2e0575dd62970d
Reviewed-on: https://go-review.googlesource.com/c/go/+/236119
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Cherry Zhang 2020-06-01 19:36:16 -04:00
parent 7795523910
commit 7bc3b6e5e4
4 changed files with 5 additions and 79 deletions
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72
src/cmd/link/internal/ld/lib.go
View file

@ -48,7 +48,6 @@ import (
"debug/macho"
"encoding/base64"
"encoding/binary"
"encoding/hex"
"fmt"
"io"
"io/ioutil"
@ -785,16 +784,6 @@ func (ctxt *Link) linksetup() {
ctxt.loader.SetAttrReachable(moduledata, true)
ctxt.Moduledata = moduledata
// If package versioning is required, generate a hash of the
// packages used in the link.
if ctxt.BuildMode == BuildModeShared || ctxt.BuildMode == BuildModePlugin || ctxt.CanUsePlugins() {
for _, lib := range ctxt.Library {
if lib.Shlib == "" {
genhash(ctxt, lib)
}
}
}
if ctxt.Arch == sys.Arch386 && ctxt.HeadType != objabi.Hwindows {
if (ctxt.BuildMode == BuildModeCArchive && ctxt.IsELF) || ctxt.BuildMode == BuildModeCShared || ctxt.BuildMode == BuildModePIE || ctxt.DynlinkingGo() {
got := ctxt.loader.LookupOrCreateSym("_GLOBAL_OFFSET_TABLE_", 0)
@ -919,67 +908,6 @@ func nextar(bp *bio.Reader, off int64, a *ArHdr) int64 {
return arsize + SAR_HDR
}
func genhash(ctxt *Link, lib *sym.Library) {
f, err := bio.Open(lib.File)
if err != nil {
Errorf(nil, "cannot open file %s for hash generation: %v", lib.File, err)
return
}
defer f.Close()
var magbuf [len(ARMAG)]byte
if _, err := io.ReadFull(f, magbuf[:]); err != nil {
Exitf("file %s too short", lib.File)
}
if string(magbuf[:]) != ARMAG {
Exitf("%s is not an archive file", lib.File)
}
var arhdr ArHdr
l := nextar(f, f.Offset(), &arhdr)
if l <= 0 {
Errorf(nil, "%s: short read on archive file symbol header", lib.File)
return
}
if arhdr.name != pkgdef {
Errorf(nil, "%s: missing package data entry", lib.File)
return
}
h := sha1.New()
// To compute the hash of a package, we hash the first line of
// __.PKGDEF (which contains the toolchain version and any
// GOEXPERIMENT flags) and the export data (which is between
// the first two occurrences of "\n$$").
pkgDefBytes := make([]byte, atolwhex(arhdr.size))
_, err = io.ReadFull(f, pkgDefBytes)
if err != nil {
Errorf(nil, "%s: error reading package data: %v", lib.File, err)
return
}
firstEOL := bytes.IndexByte(pkgDefBytes, '\n')
if firstEOL < 0 {
Errorf(nil, "cannot parse package data of %s for hash generation, no newline found", lib.File)
return
}
firstDoubleDollar := bytes.Index(pkgDefBytes, []byte("\n$$"))
if firstDoubleDollar < 0 {
Errorf(nil, "cannot parse package data of %s for hash generation, no \\n$$ found", lib.File)
return
}
secondDoubleDollar := bytes.Index(pkgDefBytes[firstDoubleDollar+1:], []byte("\n$$"))
if secondDoubleDollar < 0 {
Errorf(nil, "cannot parse package data of %s for hash generation, only one \\n$$ found", lib.File)
return
}
h.Write(pkgDefBytes[0:firstEOL])
h.Write(pkgDefBytes[firstDoubleDollar : firstDoubleDollar+secondDoubleDollar])
lib.Hash = hex.EncodeToString(h.Sum(nil))
}
func loadobjfile(ctxt *Link, lib *sym.Library) {
pkg := objabi.PathToPrefix(lib.Pkg)