pkg/build: support debug tracing

Add ability to trace build process and save debug artefacts.
Add tracing of ELF signature calculation.
Useful for debugging of #2297.

4 files changed, 22 insertions, 6 deletions

diff --git a/pkg/build/android.go b/pkg/build/android.go
index 5f5472724..352f4739e 100644
--- a/pkg/build/android.go
+++ b/pkg/build/android.go
@@ -122,7 +122,7 @@ func (a android) build(params Params) (ImageDetails, error) {
 		return details, err
 	}
 
-	details.Signature, err = elfBinarySignature(vmlinux)
+	details.Signature, err = elfBinarySignature(vmlinux, params.Tracer)
 	if err != nil {
 		return details, fmt.Errorf("failed to generate signature: %s", err)
 	}
diff --git a/pkg/build/build.go b/pkg/build/build.go
index d72fe9072..025de57c3 100644
--- a/pkg/build/build.go
+++ b/pkg/build/build.go
@@ -13,6 +13,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/google/syzkaller/pkg/debugtracer"
 	"github.com/google/syzkaller/pkg/osutil"
 	"github.com/google/syzkaller/pkg/report"
 	"github.com/google/syzkaller/pkg/vcs"
@@ -32,6 +33,7 @@ type Params struct {
 	CmdlineFile  string
 	SysctlFile   string
 	Config       []byte
+	Tracer       debugtracer.DebugTracer
 }
 
 // Information that is returned from the Image function.
@@ -61,6 +63,9 @@ type ImageDetails struct {
 // the version of the compiler/toolchain that was used to build the kernel.
 // The CompilerID field is not guaranteed to be non-empty.
 func Image(params Params) (details ImageDetails, err error) {
+	if params.Tracer == nil {
+		params.Tracer = &debugtracer.NullTracer{}
+	}
 	var builder builder
 	builder, err = getBuilder(params.TargetOS, params.TargetArch, params.VMType)
 	if err != nil {
diff --git a/pkg/build/linux.go b/pkg/build/linux.go
index 775991664..be9a38377 100644
--- a/pkg/build/linux.go
+++ b/pkg/build/linux.go
@@ -10,7 +10,6 @@ import (
 	"debug/elf"
 	"encoding/hex"
 	"fmt"
-	"io"
 	"io/ioutil"
 	"os"
 	"path"
@@ -19,6 +18,7 @@ import (
 	"runtime"
 	"time"
 
+	"github.com/google/syzkaller/pkg/debugtracer"
 	"github.com/google/syzkaller/pkg/osutil"
 	"github.com/google/syzkaller/sys/targets"
 )
@@ -58,7 +58,8 @@ func (linux linux) build(params Params) (ImageDetails, error) {
 	} else if err := embedLinuxKernel(params, kernelPath); err != nil {
 		return details, err
 	}
-	details.Signature, err = elfBinarySignature(filepath.Join(params.OutputDir, "obj", "vmlinux"))
+	vmlinux := filepath.Join(params.OutputDir, "obj", "vmlinux")
+	details.Signature, err = elfBinarySignature(vmlinux, params.Tracer)
 	return details, err
 }
 
@@ -243,7 +244,7 @@ func queryLinuxCompiler(kernelDir string) (string, error) {
 
 // elfBinarySignature calculates signature of an elf binary aiming at runtime behavior
 // (text/data, debug info is ignored).
-func elfBinarySignature(bin string) (string, error) {
+func elfBinarySignature(bin string, tracer debugtracer.DebugTracer) (string, error) {
 	f, err := os.Open(bin)
 	if err != nil {
 		return "", fmt.Errorf("failed to open binary for signature: %v", err)
@@ -262,7 +263,16 @@ func elfBinarySignature(bin string) (string, error) {
 		if sec.Flags&elf.SHF_ALLOC == 0 || sec.Type == elf.SHT_NOBITS || sec.Type == elf.SHT_NOTE {
 			continue
 		}
-		io.Copy(hasher, sec.Open())
+		data, err := sec.Data()
+		if err != nil {
+			return "", fmt.Errorf("failed to read ELF section %v: %v", sec.Name, err)
+		}
+		hasher1 := sha256.New()
+		hasher1.Write(data)
+		hash := hasher1.Sum(nil)
+		hasher.Write(hash)
+		tracer.Log("section %v: size %v signature %v", sec.Name, len(data), hex.EncodeToString(hash[:8]))
+		tracer.SaveFile(sec.Name, data)
 	}
 	return hex.EncodeToString(hasher.Sum(nil)), nil
 }
diff --git a/pkg/build/linux_test.go b/pkg/build/linux_test.go
index 63614e023..af719427c 100644
--- a/pkg/build/linux_test.go
+++ b/pkg/build/linux_test.go
@@ -14,6 +14,7 @@ import (
 	"testing"
 	"text/template"
 
+	"github.com/google/syzkaller/pkg/debugtracer"
 	"github.com/google/syzkaller/pkg/osutil"
 )
 
@@ -86,7 +87,7 @@ func sign(t *testing.T, flags []string, changed, comment bool) string {
 	if err != nil {
 		t.Fatalf("compiler failed: %v\n%s\n\n%s", err, src, out)
 	}
-	sign, err := elfBinarySignature(bin)
+	sign, err := elfBinarySignature(bin, &debugtracer.TestTracer{T: t})
 	if err != nil {
 		t.Fatal(err)
 	}