From 42ca44494c6ca94c6a1f433e61bc5d95d51b2222 Mon Sep 17 00:00:00 2001
From: Matthew Dempsky <mdempsky@google.com>
Date: Wed, 23 Mar 2022 12:10:02 -0700
Subject: [PATCH] internal/pkgbits: add fingerprints to unified IR export
 format

So far unified IR has been relying on the backwards-compat iexport
data to supply package fingerprints for imports. To be able to drop
the iexport data and natively use unified IR everywhere.

This CL applies basically the same idea that iexport used: simply
hash all of the export data as it's being written out, and then tack
on an 8-byte hash at the end.

Change-Id: Iaca5fbfd7443088bc7f422a1c58be3e762c29014
Reviewed-on: https://go-review.googlesource.com/c/go/+/396196
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
---
 src/go/build/deps_test.go       | 10 +++++-----
 src/internal/pkgbits/decoder.go | 10 ++++++++--
 src/internal/pkgbits/encoder.go | 12 +++++++++++-
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index d541f0926de..5794e3d25e9 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -310,11 +310,6 @@ var depsRules = `
 	go/build/constraint, go/doc, go/parser, internal/buildcfg, internal/goroot, internal/goversion
 	< go/build;
 
-	DEBUG, go/build, go/types, text/scanner
-  < internal/pkgbits
-	< go/internal/gcimporter, go/internal/gccgoimporter, go/internal/srcimporter
-	< go/importer;
-
 	# databases
 	FMT
 	< database/sql/internal
@@ -449,6 +444,11 @@ var depsRules = `
 
 	# crypto-aware packages
 
+	CRYPTO, DEBUG, go/build, go/types, text/scanner
+	< internal/pkgbits
+	< go/internal/gcimporter, go/internal/gccgoimporter, go/internal/srcimporter
+	< go/importer;
+
 	NET, crypto/rand, mime/quotedprintable
 	< mime/multipart;
 
diff --git a/src/internal/pkgbits/decoder.go b/src/internal/pkgbits/decoder.go
index 9c8ad446ca4..5b4e8f69aff 100644
--- a/src/internal/pkgbits/decoder.go
+++ b/src/internal/pkgbits/decoder.go
@@ -22,7 +22,7 @@ type PkgDecoder struct {
 
 	elemEndsEnds [numRelocs]uint32
 	elemEnds     []uint32
-	elemData     string
+	elemData     string // last 8 bytes are fingerprint
 }
 
 func (pr *PkgDecoder) PkgPath() string { return pr.pkgPath }
@@ -50,7 +50,7 @@ func NewPkgDecoder(pkgPath, input string) PkgDecoder {
 	assert(err == nil)
 
 	pr.elemData = input[pos:]
-	assert(len(pr.elemData) == int(pr.elemEnds[len(pr.elemEnds)-1]))
+	assert(len(pr.elemData)-8 == int(pr.elemEnds[len(pr.elemEnds)-1]))
 
 	return pr
 }
@@ -67,6 +67,12 @@ func (pr *PkgDecoder) TotalElems() int {
 	return len(pr.elemEnds)
 }
 
+func (pr *PkgDecoder) Fingerprint() [8]byte {
+	var fp [8]byte
+	copy(fp[:], pr.elemData[len(pr.elemData)-8:])
+	return fp
+}
+
 func (pr *PkgDecoder) AbsIdx(k RelocKind, idx int) int {
 	absIdx := idx
 	if k > 0 {
diff --git a/src/internal/pkgbits/encoder.go b/src/internal/pkgbits/encoder.go
index 820c707940a..4780f01c392 100644
--- a/src/internal/pkgbits/encoder.go
+++ b/src/internal/pkgbits/encoder.go
@@ -8,6 +8,7 @@ package pkgbits
 
 import (
 	"bytes"
+	"crypto/md5"
 	"encoding/binary"
 	"go/constant"
 	"io"
@@ -30,7 +31,10 @@ func NewPkgEncoder(syncFrames int) PkgEncoder {
 	}
 }
 
-func (pw *PkgEncoder) DumpTo(out io.Writer) {
+func (pw *PkgEncoder) DumpTo(out0 io.Writer) (fingerprint [8]byte) {
+	h := md5.New()
+	out := io.MultiWriter(out0, h)
+
 	writeUint32 := func(x uint32) {
 		assert(binary.Write(out, binary.LittleEndian, x) == nil)
 	}
@@ -57,6 +61,12 @@ func (pw *PkgEncoder) DumpTo(out io.Writer) {
 			assert(err == nil)
 		}
 	}
+
+	copy(fingerprint[:], h.Sum(nil))
+	_, err := out0.Write(fingerprint[:])
+	assert(err == nil)
+
+	return
 }
 
 func (pw *PkgEncoder) StringIdx(s string) int {