pkg/vcs: refactor bisection support

In preparation for syz-ci bisection:
- move bisection function into a separate interface
  they look out of place in vcs.Repo because most OSes
  don't implement it and most users don't case
- extract author name and more CC emails for commits
- move linux-specific PreviousReleaseTags into linux.go
- fix inconclusive bisection (more than 1 potential commits)
- add tests fr bisection
- add maintainers returned from get_maintainers.pl for commits
  that don't have enough emails (e.g. only author email)

Update #501

10 files changed, 404 insertions, 145 deletions

diff --git a/pkg/vcs/akaros.go b/pkg/vcs/akaros.go
index 8d8d640e6..0d3e701fb 100644
--- a/pkg/vcs/akaros.go
+++ b/pkg/vcs/akaros.go
@@ -4,8 +4,6 @@
 package vcs
 
 import (
-	"fmt"
-	"io"
 	"path/filepath"
 )
 
@@ -16,8 +14,8 @@ type akaros struct {
 
 func newAkaros(vm, dir string) *akaros {
 	return &akaros{
-		git:      newGit(dir),
-		dropbear: newGit(filepath.Join(dir, "dropbear")),
+		git:      newGit(dir, nil),
+		dropbear: newGit(filepath.Join(dir, "dropbear"), nil),
 	}
 }
 
@@ -27,15 +25,3 @@ func (ctx *akaros) Poll(repo, branch string) (*Commit, error) {
 	}
 	return ctx.git.Poll(repo, branch)
 }
-
-func (ctx *akaros) ExtractFixTagsFromCommits(baseCommit, email string) ([]*Commit, error) {
-	return ctx.git.ExtractFixTagsFromCommits(baseCommit, email)
-}
-
-func (ctx *akaros) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error) {
-	return nil, fmt.Errorf("not implemented for akaros")
-}
-
-func (ctx *akaros) PreviousReleaseTags(commit string) ([]string, error) {
-	return nil, fmt.Errorf("not implemented for akaros")
-}
diff --git a/pkg/vcs/freebsd.go b/pkg/vcs/freebsd.go
index 6ef7858ce..f007ab69f 100644
--- a/pkg/vcs/freebsd.go
+++ b/pkg/vcs/freebsd.go
@@ -14,7 +14,7 @@ type freebsd struct {
 
 func newFreeBSD(vm, dir string) *freebsd {
 	return &freebsd{
-		git: newGit(dir),
+		git: newGit(dir, nil),
 	}
 }
 
diff --git a/pkg/vcs/fuchsia.go b/pkg/vcs/fuchsia.go
index 07626cd5e..c04404416 100644
--- a/pkg/vcs/fuchsia.go
+++ b/pkg/vcs/fuchsia.go
@@ -22,7 +22,7 @@ func newFuchsia(vm, dir string) *fuchsia {
 	return &fuchsia{
 		vm:     vm,
 		dir:    dir,
-		zircon: newGit(filepath.Join(dir, "zircon")),
+		zircon: newGit(filepath.Join(dir, "zircon"), nil),
 	}
 }
 
@@ -91,10 +91,7 @@ func (ctx *fuchsia) ExtractFixTagsFromCommits(baseCommit, email string) ([]*Comm
 	return ctx.zircon.ExtractFixTagsFromCommits(baseCommit, email)
 }
 
-func (ctx *fuchsia) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error) {
-	return nil, fmt.Errorf("not implemented for fuchsia")
-}
-
-func (ctx *fuchsia) PreviousReleaseTags(commit string) ([]string, error) {
-	return nil, fmt.Errorf("not implemented for fuchsia")
+func (ctx *fuchsia) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, interface{}, error)) (
+	*Commit, interface{}, error) {
+	return nil, nil, fmt.Errorf("not implemented for fuchsia")
 }
diff --git a/pkg/vcs/git.go b/pkg/vcs/git.go
index 4f23bb16c..210c5b154 100644
--- a/pkg/vcs/git.go
+++ b/pkg/vcs/git.go
@@ -11,22 +11,25 @@ import (
 	"net/mail"
 	"os"
 	"os/exec"
+	"regexp"
 	"sort"
-	"strconv"
 	"strings"
 	"time"
 
 	"github.com/google/syzkaller/pkg/hash"
+	"github.com/google/syzkaller/pkg/log"
 	"github.com/google/syzkaller/pkg/osutil"
 )
 
 type git struct {
-	dir string
+	dir      string
+	ignoreCC map[string]bool
 }
 
-func newGit(dir string) *git {
+func newGit(dir string, ignoreCC map[string]bool) *git {
 	return &git{
-		dir: dir,
+		dir:      dir,
+		ignoreCC: ignoreCC,
 	}
 }
 
@@ -66,7 +69,7 @@ func (git *git) CheckoutBranch(repo, branch string) (*Commit, error) {
 	dir := git.dir
 	runSandboxed(dir, "git", "bisect", "reset")
 	if _, err := runSandboxed(dir, "git", "reset", "--hard"); err != nil {
-		if err := git.initRepo(); err != nil {
+		if err := git.initRepo(err); err != nil {
 			return nil, err
 		}
 	}
@@ -84,7 +87,7 @@ func (git *git) CheckoutCommit(repo, commit string) (*Commit, error) {
 	dir := git.dir
 	runSandboxed(dir, "git", "bisect", "reset")
 	if _, err := runSandboxed(dir, "git", "reset", "--hard"); err != nil {
-		if err := git.initRepo(); err != nil {
+		if err := git.initRepo(err); err != nil {
 			return nil, err
 		}
 	}
@@ -111,7 +114,7 @@ func (git *git) SwitchCommit(commit string) (*Commit, error) {
 }
 
 func (git *git) clone(repo, branch string) error {
-	if err := git.initRepo(); err != nil {
+	if err := git.initRepo(nil); err != nil {
 		return err
 	}
 	if _, err := runSandboxed(git.dir, "git", "remote", "add", "origin", repo); err != nil {
@@ -123,7 +126,10 @@ func (git *git) clone(repo, branch string) error {
 	return nil
 }
 
-func (git *git) initRepo() error {
+func (git *git) initRepo(reason error) error {
+	if reason != nil {
+		log.Logf(1, "git: initializing repo at %v: %v", git.dir, reason)
+	}
 	if err := os.RemoveAll(git.dir); err != nil {
 		return fmt.Errorf("failed to remove repo dir: %v", err)
 	}
@@ -144,27 +150,27 @@ func (git *git) HeadCommit() (*Commit, error) {
 }
 
 func (git *git) getCommit(commit string) (*Commit, error) {
-	output, err := runSandboxed(git.dir, "git", "log", "--format=%H%n%s%n%ae%n%ad%n%b", "-n", "1", commit)
+	output, err := runSandboxed(git.dir, "git", "log", "--format=%H%n%s%n%ae%n%an%n%ad%n%b", "-n", "1", commit)
 	if err != nil {
 		return nil, err
 	}
-	return gitParseCommit(output, nil, nil)
+	return gitParseCommit(output, nil, nil, git.ignoreCC)
 }
 
-func gitParseCommit(output, user, domain []byte) (*Commit, error) {
+func gitParseCommit(output, user, domain []byte, ignoreCC map[string]bool) (*Commit, error) {
 	lines := bytes.Split(output, []byte{'\n'})
 	if len(lines) < 4 || len(lines[0]) != 40 {
 		return nil, fmt.Errorf("unexpected git log output: %q", output)
 	}
 	const dateFormat = "Mon Jan 2 15:04:05 2006 -0700"
-	date, err := time.Parse(dateFormat, string(lines[3]))
+	date, err := time.Parse(dateFormat, string(lines[4]))
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse date in git log output: %v\n%q", err, output)
 	}
 	cc := make(map[string]bool)
 	cc[strings.ToLower(string(lines[2]))] = true
 	var tags []string
-	for _, line := range lines[4:] {
+	for _, line := range lines[5:] {
 		if user != nil {
 			userPos := bytes.Index(line, user)
 			if userPos != -1 {
@@ -195,7 +201,11 @@ func gitParseCommit(output, user, domain []byte) (*Commit, error) {
 			if err != nil {
 				break
 			}
-			cc[strings.ToLower(addr.Address)] = true
+			email := strings.ToLower(addr.Address)
+			if ignoreCC[email] {
+				continue
+			}
+			cc[email] = true
 			break
 		}
 	}
@@ -205,12 +215,13 @@ func gitParseCommit(output, user, domain []byte) (*Commit, error) {
 	}
 	sort.Strings(sortedCC)
 	com := &Commit{
-		Hash:   string(lines[0]),
-		Title:  string(lines[1]),
-		Author: string(lines[2]),
-		CC:     sortedCC,
-		Tags:   tags,
-		Date:   date,
+		Hash:       string(lines[0]),
+		Title:      string(lines[1]),
+		Author:     string(lines[2]),
+		AuthorName: string(lines[3]),
+		CC:         sortedCC,
+		Tags:       tags,
+		Date:       date,
 	}
 	return com, nil
 }
@@ -276,7 +287,7 @@ func (git *git) ExtractFixTagsFromCommits(baseCommit, email string) ([]*Commit,
 
 func (git *git) fetchCommits(since, base, user, domain string, greps []string, fixedStrings bool) ([]*Commit, error) {
 	const commitSeparator = "---===syzkaller-commit-separator===---"
-	args := []string{"log", "--since", since, "--format=%H%n%s%n%ae%n%ad%n%b%n" + commitSeparator}
+	args := []string{"log", "--since", since, "--format=%H%n%s%n%ae%n%an%n%ad%n%b%n" + commitSeparator}
 	if fixedStrings {
 		args = append(args, "--fixed-strings")
 	}
@@ -314,7 +325,7 @@ func (git *git) fetchCommits(since, base, user, domain string, greps []string, f
 			buf.WriteByte('\n')
 			continue
 		}
-		com, err := gitParseCommit(buf.Bytes(), userBytes, domainBytes)
+		com, err := gitParseCommit(buf.Bytes(), userBytes, domainBytes, git.ignoreCC)
 		if err != nil {
 			return nil, err
 		}
@@ -343,7 +354,7 @@ func splitEmail(email string) (user, domain string, err error) {
 	return
 }
 
-func (git *git) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error) {
+func (git *git) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) ([]*Commit, error) {
 	dir := git.dir
 	runSandboxed(dir, "git", "bisect", "reset")
 	runSandboxed(dir, "git", "reset", "--hard")
@@ -375,59 +386,44 @@ func (git *git) Bisect(bad, good string, trace io.Writer, pred func() (BisectRes
 			firstBad = current
 		}
 		output, err = runSandboxed(dir, "git", "bisect", bisectTerms[res])
+		fmt.Fprintf(trace, "# git bisect %v %v\n%s", bisectTerms[res], current.Hash, output)
 		if err != nil {
+			if bytes.Contains(output, []byte("There are only 'skip'ped commits left to test")) {
+				return git.bisectInconclusive(output)
+			}
 			return nil, err
 		}
-		fmt.Fprintf(trace, "# git bisect %v %v\n%s", bisectTerms[res], current.Hash, output)
 		next, err := git.HeadCommit()
 		if err != nil {
 			return nil, err
 		}
 		if current.Hash == next.Hash {
-			return firstBad, nil
+			return []*Commit{firstBad}, nil
 		}
 		current = next
 	}
 }
 
-// Note: linux-specific.
-func (git *git) PreviousReleaseTags(commit string) ([]string, error) {
-	output, err := runSandboxed(git.dir, "git", "tag", "--no-contains", commit, "--merged", commit, "v*.*")
-	if err != nil {
-		return nil, err
-	}
-	return gitParseReleaseTags(output)
-}
-
-func gitParseReleaseTags(output []byte) ([]string, error) {
-	var tags []string
-	for _, tag := range bytes.Split(output, []byte{'\n'}) {
-		if releaseTagRe.Match(tag) && gitReleaseTagToInt(string(tag)) != 0 {
-			tags = append(tags, string(tag))
-		}
-	}
-	sort.Slice(tags, func(i, j int) bool {
-		return gitReleaseTagToInt(tags[i]) > gitReleaseTagToInt(tags[j])
-	})
-	return tags, nil
-}
-
-func gitReleaseTagToInt(tag string) uint64 {
-	matches := releaseTagRe.FindStringSubmatchIndex(tag)
-	v1, err := strconv.ParseUint(tag[matches[2]:matches[3]], 10, 64)
-	if err != nil {
-		return 0
-	}
-	v2, err := strconv.ParseUint(tag[matches[4]:matches[5]], 10, 64)
-	if err != nil {
-		return 0
-	}
-	var v3 uint64
-	if matches[6] != -1 {
-		v3, err = strconv.ParseUint(tag[matches[6]:matches[7]], 10, 64)
+func (git *git) bisectInconclusive(output []byte) ([]*Commit, error) {
+	// For inconclusive bisection git prints the following message:
+	//
+	//	There are only 'skip'ped commits left to test.
+	//	The first bad commit could be any of:
+	//	1f43f400a2cbb02f3d34de8fe30075c070254816
+	//	4d96e13ee9cd1f7f801e8c7f4b12f09d1da4a5d8
+	//	5cd856a5ef9aa189df757c322be34ad735a5b17f
+	//	We cannot bisect more!
+	//
+	// For conclusive bisection:
+	//
+	//	7c3850adbcccc2c6c9e7ab23a7dcbc4926ee5b96 is the first bad commit
+	var commits []*Commit
+	for _, hash := range regexp.MustCompile("[a-f0-9]{40}").FindAll(output, -1) {
+		com, err := git.getCommit(string(hash))
 		if err != nil {
-			return 0
+			return nil, err
 		}
+		commits = append(commits, com)
 	}
-	return v1*1e6 + v2*1e3 + v3
+	return commits, nil
 }
diff --git a/pkg/vcs/git_repo_test.go b/pkg/vcs/git_repo_test.go
index f60bfc737..6e8018dfc 100644
--- a/pkg/vcs/git_repo_test.go
+++ b/pkg/vcs/git_repo_test.go
@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sort"
 	"testing"
 	"time"
 
@@ -22,6 +23,7 @@ func init() {
 
 const (
 	userEmail           = `test@syzkaller.com`
+	userName            = `Test Syzkaller`
 	extractFixTagsEmail = `"syzbot" <syzbot@my.mail.com>`
 )
 
@@ -34,7 +36,7 @@ func TestGitRepo(t *testing.T) {
 	defer os.RemoveAll(baseDir)
 	repo1 := createTestRepo(t, baseDir, "repo1")
 	repo2 := createTestRepo(t, baseDir, "repo2")
-	repo := newGit(filepath.Join(baseDir, "repo"))
+	repo := newGit(filepath.Join(baseDir, "repo"), nil)
 	{
 		com, err := repo.Poll(repo1.dir, "master")
 		if err != nil {
@@ -165,6 +167,9 @@ func checkCommit(t *testing.T, idx int, test testCommit, com *Commit, checkTags
 	if test.author != com.Author {
 		t.Errorf("#%v: want author %q, got %q", idx, test.author, com.Author)
 	}
+	if userName != com.AuthorName {
+		t.Errorf("#%v: want author name %q, got %q", idx, userName, com.Author)
+	}
 	if diff := cmp.Diff(test.cc, com.CC); diff != "" {
 		t.Logf("%#v", com.CC)
 		t.Error(diff)
@@ -273,11 +278,142 @@ Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 `,
 		title:  "USB: fix usbmon BUG trigger",
 		author: userEmail,
-		cc:     []string{userEmail},
+		cc:     []string{"gregkh@linuxfoundation.org", userEmail, "zaitcev@redhat.com"},
 		tags:   []string{"f9831b881b3e849829fc"},
 	},
 }
 
+func TestBisect(t *testing.T) {
+	t.Parallel()
+	repoDir, err := ioutil.TempDir("", "syz-git-test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(repoDir)
+	repo := makeTestRepo(t, repoDir)
+	var commits []string
+	for i := 0; i < 5; i++ {
+		repo.commitChange(fmt.Sprintf("commit %v", i))
+		com, err := repo.repo.HeadCommit()
+		if err != nil {
+			t.Fatal(err)
+		}
+		commits = append(commits, com.Hash)
+		t.Logf("%v %v", com.Hash, com.Title)
+	}
+	type Test struct {
+		pred   func() (BisectResult, error)
+		result []string
+	}
+	tests := []Test{
+		{
+			// All are bad.
+			func() (BisectResult, error) {
+				return BisectBad, nil
+			},
+			[]string{commits[1]},
+		},
+		{
+			// All are good.
+			func() (BisectResult, error) {
+				return BisectGood, nil
+			},
+			[]string{commits[4]},
+		},
+		{
+			// All are skipped.
+			func() (BisectResult, error) {
+				return BisectSkip, nil
+			},
+			[]string{commits[1], commits[2], commits[3], commits[4]},
+		},
+		{
+			// Some are skipped.
+			func() (BisectResult, error) {
+				current, err := repo.repo.HeadCommit()
+				if err != nil {
+					t.Fatal(err)
+				}
+				switch current.Hash {
+				case commits[1]:
+					return BisectSkip, nil
+				case commits[2]:
+					return BisectSkip, nil
+				case commits[3]:
+					return BisectGood, nil
+				default:
+					return 0, fmt.Errorf("unknown commit %v", current.Hash)
+				}
+			},
+			[]string{commits[4]},
+		},
+		{
+			// Some are skipped.
+			func() (BisectResult, error) {
+				current, err := repo.repo.HeadCommit()
+				if err != nil {
+					t.Fatal(err)
+				}
+				switch current.Hash {
+				case commits[1]:
+					return BisectGood, nil
+				case commits[2]:
+					return BisectSkip, nil
+				case commits[3]:
+					return BisectBad, nil
+				default:
+					return 0, fmt.Errorf("unknown commit %v", current.Hash)
+				}
+			},
+			[]string{commits[2], commits[3]},
+		},
+		{
+			// Some are skipped.
+			func() (BisectResult, error) {
+				current, err := repo.repo.HeadCommit()
+				if err != nil {
+					t.Fatal(err)
+				}
+				switch current.Hash {
+				case commits[1]:
+					return BisectSkip, nil
+				case commits[2]:
+					return BisectSkip, nil
+				case commits[3]:
+					return BisectGood, nil
+				default:
+					return 0, fmt.Errorf("unknown commit %v", current.Hash)
+				}
+			},
+			[]string{commits[4]},
+		},
+	}
+	for i, test := range tests {
+		t.Logf("TEST %v", i)
+		result, err := repo.repo.Bisect(commits[4], commits[0], (*testWriter)(t), test.pred)
+		if err != nil {
+			t.Fatal(err)
+		}
+		var got []string
+		for _, com := range result {
+			got = append(got, com.Hash)
+		}
+		sort.Strings(got) // git result order is non-deterministic (wat)
+		sort.Strings(test.result)
+		if diff := cmp.Diff(test.result, got); diff != "" {
+			t.Logf("result: %+v", got)
+			t.Fatal(diff)
+		}
+	}
+}
+
+type testWriter testing.T
+
+func (t *testWriter) Write(data []byte) (int, error) {
+	(*testing.T)(t).Log(string(data))
+	return len(data), nil
+}
+
 func createTestRepo(t *testing.T, baseDir, name string) *testRepo {
 	repo := makeTestRepo(t, filepath.Join(baseDir, name))
 	repo.git("checkout", "-b", "master")
@@ -304,16 +440,19 @@ func makeTestRepo(t *testing.T, dir string) *testRepo {
 	if err := osutil.MkdirAll(dir); err != nil {
 		t.Fatal(err)
 	}
+	ignoreCC := map[string]bool{
+		"stable@vger.kernel.org": true,
+	}
 	repo := &testRepo{
 		t:       t,
 		dir:     dir,
 		name:    filepath.Base(dir),
 		commits: make(map[string]map[string]*Commit),
-		repo:    newGit(dir),
+		repo:    newGit(dir, ignoreCC),
 	}
 	repo.git("init")
 	repo.git("config", "--add", "user.email", userEmail)
-	repo.git("config", "--add", "user.name", "Test Syzkaller")
+	repo.git("config", "--add", "user.name", userName)
 	return repo
 }
 
diff --git a/pkg/vcs/git_test.go b/pkg/vcs/git_test.go
index a22835a69..b2ad32b6b 100644
--- a/pkg/vcs/git_test.go
+++ b/pkg/vcs/git_test.go
@@ -7,6 +7,8 @@ import (
 	"reflect"
 	"testing"
 	"time"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 func TestGitParseCommit(t *testing.T) {
@@ -14,6 +16,7 @@ func TestGitParseCommit(t *testing.T) {
 		`2075b16e32c26e4031b9fd3cbe26c54676a8fcb5
 rbtree: include rcu.h
 foobar@foobar.de
+Foo Bar
 Fri May 11 16:02:14 2018 -0700
 Since commit c1adf20052d8 ("Introduce rb_replace_node_rcu()")
 rbtree_augmented.h uses RCU related data structures but does not include
@@ -30,14 +33,18 @@ Reported-and-Tested-by: Name-name <name@name.com>
 Tested-by: Must be correct <mustbe@correct.com>
 Signed-off-by: Linux Master <linux@linux-foundation.org>
 `: {
-			Hash:   "2075b16e32c26e4031b9fd3cbe26c54676a8fcb5",
-			Title:  "rbtree: include rcu.h",
-			Author: "foobar@foobar.de",
+			Hash:       "2075b16e32c26e4031b9fd3cbe26c54676a8fcb5",
+			Title:      "rbtree: include rcu.h",
+			Author:     "foobar@foobar.de",
+			AuthorName: "Foo Bar",
 			CC: []string{
 				"and@me.com",
+				"another@email.de",
 				"foobar@foobar.de",
+				"linux@linux-foundation.org",
 				"mustbe@correct.com",
 				"name@name.com",
+				"somewhere@email.com",
 				"subsystem@reviewer.com",
 				"yetanother@email.org",
 			},
@@ -45,7 +52,7 @@ Signed-off-by: Linux Master <linux@linux-foundation.org>
 		},
 	}
 	for input, com := range tests {
-		res, err := gitParseCommit([]byte(input), nil, nil)
+		res, err := gitParseCommit([]byte(input), nil, nil, nil)
 		if err != nil && com != nil {
 			t.Fatalf("want %+v, got error: %v", com, err)
 		}
@@ -64,8 +71,8 @@ Signed-off-by: Linux Master <linux@linux-foundation.org>
 		if com.Author != res.Author {
 			t.Fatalf("want author %q, got %q", com.Author, res.Author)
 		}
-		if !reflect.DeepEqual(com.CC, res.CC) {
-			t.Fatalf("want CC %q, got %q", com.CC, res.CC)
+		if diff := cmp.Diff(com.CC, res.CC); diff != "" {
+			t.Fatalf("bad CC: %v", diff)
 		}
 		if !com.Date.Equal(res.Date) {
 			t.Fatalf("want date %v, got %v", com.Date, res.Date)
diff --git a/pkg/vcs/linux.go b/pkg/vcs/linux.go
new file mode 100644
index 000000000..f8d97d60e
--- /dev/null
+++ b/pkg/vcs/linux.go
@@ -0,0 +1,154 @@
+// Copyright 2019 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package vcs
+
+import (
+	"bytes"
+	"io"
+	"net/mail"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/google/syzkaller/pkg/email"
+	"github.com/google/syzkaller/pkg/osutil"
+)
+
+type linux struct {
+	*git
+}
+
+func newLinux(dir string) *linux {
+	ignoreCC := map[string]bool{
+		"stable@vger.kernel.org": true,
+	}
+	return &linux{
+		git: newGit(dir, ignoreCC),
+	}
+}
+
+func (ctx *linux) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) ([]*Commit, error) {
+	commits, err := ctx.git.Bisect(bad, good, trace, pred)
+	if len(commits) == 1 {
+		ctx.addMaintainers(commits[0])
+	}
+	return commits, err
+}
+
+func (ctx *linux) addMaintainers(com *Commit) {
+	if len(com.CC) > 3 {
+		return
+	}
+	list := ctx.getMaintainers(com.Hash, false)
+	if len(list) < 3 {
+		list = ctx.getMaintainers(com.Hash, true)
+	}
+	com.CC = email.MergeEmailLists(com.CC, list)
+}
+
+func (ctx *linux) getMaintainers(hash string, blame bool) []string {
+	args := "git show " + hash + " | " +
+		filepath.FromSlash("scripts/get_maintainer.pl") + " --no-n --no-rolestats"
+	if blame {
+		args += " --git-blame"
+	}
+	output, err := osutil.RunCmd(time.Minute, ctx.git.dir, "bash", "-c", args)
+	if err != nil {
+		return nil
+	}
+	var list []string
+	for _, line := range strings.Split(string(output), "\n") {
+		addr, err := mail.ParseAddress(line)
+		if err != nil {
+			continue
+		}
+		list = append(list, strings.ToLower(addr.Address))
+	}
+	return list
+}
+
+func (ctx *linux) PreviousReleaseTags(commit string) ([]string, error) {
+	output, err := runSandboxed(ctx.dir, "git", "tag", "--no-contains", commit, "--merged", commit, "v*.*")
+	if err != nil {
+		return nil, err
+	}
+	tags, err := gitParseReleaseTags(output)
+	if err != nil {
+		return nil, err
+	}
+	for i, tag := range tags {
+		if tag == "v3.8" {
+			// v3.8 does not work with modern perl, and as we go further in history
+			// make stops to work, then binutils, glibc, etc. So we stop at v3.8.
+			// Up to that point we only need an ancient gcc.
+			tags = tags[:i]
+			break
+		}
+	}
+	return tags, nil
+}
+
+func gitParseReleaseTags(output []byte) ([]string, error) {
+	var tags []string
+	for _, tag := range bytes.Split(output, []byte{'\n'}) {
+		if releaseTagRe.Match(tag) && gitReleaseTagToInt(string(tag)) != 0 {
+			tags = append(tags, string(tag))
+		}
+	}
+	sort.Slice(tags, func(i, j int) bool {
+		return gitReleaseTagToInt(tags[i]) > gitReleaseTagToInt(tags[j])
+	})
+	return tags, nil
+}
+
+func gitReleaseTagToInt(tag string) uint64 {
+	matches := releaseTagRe.FindStringSubmatchIndex(tag)
+	v1, err := strconv.ParseUint(tag[matches[2]:matches[3]], 10, 64)
+	if err != nil {
+		return 0
+	}
+	v2, err := strconv.ParseUint(tag[matches[4]:matches[5]], 10, 64)
+	if err != nil {
+		return 0
+	}
+	var v3 uint64
+	if matches[6] != -1 {
+		v3, err = strconv.ParseUint(tag[matches[6]:matches[7]], 10, 64)
+		if err != nil {
+			return 0
+		}
+	}
+	return v1*1e6 + v2*1e3 + v3
+}
+
+func (ctx *linux) EnvForCommit(commit string, kernelConfig []byte) (*BisectEnv, error) {
+	tagList, err := ctx.PreviousReleaseTags(commit)
+	if err != nil {
+		return nil, err
+	}
+	tags := make(map[string]bool)
+	for _, tag := range tagList {
+		tags[tag] = true
+	}
+	env := &BisectEnv{
+		Compiler:     "gcc-" + linuxCompilerVersion(tags),
+		KernelConfig: kernelConfig,
+	}
+	return env, nil
+}
+
+func linuxCompilerVersion(tags map[string]bool) string {
+	switch {
+	case tags["v4.12"]:
+		return "8.1.0"
+	case tags["v4.11"]:
+		return "7.3.0"
+	case tags["v3.19"]:
+		return "5.5.0"
+	default:
+		return "4.9.4"
+	}
+}
diff --git a/pkg/vcs/netbsd.go b/pkg/vcs/netbsd.go
index b43523756..6b710f4ca 100644
--- a/pkg/vcs/netbsd.go
+++ b/pkg/vcs/netbsd.go
@@ -3,29 +3,12 @@
 
 package vcs
 
-import (
-	"fmt"
-	"io"
-)
-
 type netbsd struct {
 	*git
 }
 
 func newNetBSD(vm, dir string) *netbsd {
 	return &netbsd{
-		git: newGit(dir),
+		git: newGit(dir, nil),
 	}
 }
-
-func (ctx *netbsd) ExtractFixTagsFromCommits(baseCommit, email string) ([]*Commit, error) {
-	return ctx.git.ExtractFixTagsFromCommits(baseCommit, email)
-}
-
-func (ctx *netbsd) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error) {
-	return nil, fmt.Errorf("not implemented for netbsd")
-}
-
-func (ctx *netbsd) PreviousReleaseTags(commit string) ([]string, error) {
-	return nil, fmt.Errorf("not implemented for netbsd")
-}
diff --git a/pkg/vcs/openbsd.go b/pkg/vcs/openbsd.go
index 3998ce58a..f97290f99 100644
--- a/pkg/vcs/openbsd.go
+++ b/pkg/vcs/openbsd.go
@@ -3,29 +3,12 @@
 
 package vcs
 
-import (
-	"fmt"
-	"io"
-)
-
 type openbsd struct {
 	*git
 }
 
 func newOpenBSD(vm, dir string) *openbsd {
 	return &openbsd{
-		git: newGit(dir),
+		git: newGit(dir, nil),
 	}
 }
-
-func (ctx *openbsd) ExtractFixTagsFromCommits(baseCommit, email string) ([]*Commit, error) {
-	return ctx.git.ExtractFixTagsFromCommits(baseCommit, email)
-}
-
-func (ctx *openbsd) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error) {
-	return nil, fmt.Errorf("not implemented for openbsd")
-}
-
-func (ctx *openbsd) PreviousReleaseTags(commit string) ([]string, error) {
-	return nil, fmt.Errorf("not implemented for openbsd")
-}
diff --git a/pkg/vcs/vcs.go b/pkg/vcs/vcs.go
index 9d779410f..8026bbfd5 100644
--- a/pkg/vcs/vcs.go
+++ b/pkg/vcs/vcs.go
@@ -49,25 +49,32 @@ type Repo interface {
 	// Given email = "user@domain.com", it searches for tags of the form "user+tag@domain.com"
 	// and returns commits with these tags.
 	ExtractFixTagsFromCommits(baseCommit, email string) ([]*Commit, error)
+}
 
-	// PreviousReleaseTags returns list of preceding release tags that are reachable from the given commit.
-	PreviousReleaseTags(commit string) ([]string, error)
-
+// Bisecter may be optionally implemented by Repo.
+type Bisecter interface {
 	// Bisect bisects good..bad commit range against the provided predicate (wrapper around git bisect).
 	// The predicate should return an error only if there is no way to proceed
 	// (it will abort the process), if possible it should prefer to return BisectSkip.
 	// Progress of the process is streamed to the provided trace.
-	// Returns the first commit on which the predicate returns BisectBad.
-	Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error)
+	// Returns the first commit on which the predicate returns BisectBad,
+	// or multiple commits if bisection is inconclusive due to BisectSkip.
+	Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) ([]*Commit, error)
+
+	// PreviousReleaseTags returns list of preceding release tags that are reachable from the given commit.
+	PreviousReleaseTags(commit string) ([]string, error)
+
+	EnvForCommit(commit string, kernelConfig []byte) (*BisectEnv, error)
 }
 
 type Commit struct {
-	Hash   string
-	Title  string
-	Author string
-	CC     []string
-	Tags   []string
-	Date   time.Time
+	Hash       string
+	Title      string
+	Author     string
+	AuthorName string
+	CC         []string
+	Tags       []string
+	Date       time.Time
 }
 
 type BisectResult int
@@ -78,10 +85,15 @@ const (
 	BisectSkip
 )
 
+type BisectEnv struct {
+	Compiler     string
+	KernelConfig []byte
+}
+
 func NewRepo(os, vm, dir string) (Repo, error) {
 	switch os {
 	case "linux":
-		return newGit(dir), nil
+		return newLinux(dir), nil
 	case "akaros":
 		return newAkaros(vm, dir), nil
 	case "fuchsia":
@@ -97,7 +109,7 @@ func NewRepo(os, vm, dir string) (Repo, error) {
 }
 
 func NewSyzkallerRepo(dir string) Repo {
-	return newGit(dir)
+	return newGit(dir, nil)
 }
 
 func Patch(dir string, patch []byte) error {
@@ -171,6 +183,8 @@ var (
 		regexp.MustCompile(`^[A-Za-z-]+\-and\-[Aa]cked\-.*: (.*)$`),
 		regexp.MustCompile(`^Tested\-.*: (.*)$`),
 		regexp.MustCompile(`^[A-Za-z-]+\-and\-[Tt]ested\-.*: (.*)$`),
+		regexp.MustCompile(`^Signed-off-by: (.*)$`),
+		regexp.MustCompile(`^C[Cc]: (.*)$`),
 	}
 )