syz-manager: properly calculate previous instruction PC

We used to subtract 5 which is length of call instruction on amd64.
Do proper per-arch calculation.

2 files changed, 27 insertions, 8 deletions

diff --git a/syz-manager/cover.go b/syz-manager/cover.go
index a2663314f..dde9ef93a 100644
--- a/syz-manager/cover.go
+++ b/syz-manager/cover.go
@@ -60,10 +60,6 @@ var (
 	vmOffsets       = make(map[string]uint32)
 )
 
-const (
-	callLen = 5 // length of a call instruction, x86-ism
-)
-
 func initAllCover(os, arch, vmlinux string) {
 	// Running objdump on vmlinux takes 20-30 seconds, so we do it asynchronously on start.
 	// Running nm on vmlinux may takes 200 microsecond and being called during symbolization of every crash,
@@ -91,7 +87,7 @@ func initAllCover(os, arch, vmlinux string) {
 	}()
 }
 
-func generateCoverHTML(w io.Writer, vmlinux string, cov cover.Cover) error {
+func generateCoverHTML(w io.Writer, vmlinux, arch string, cov cover.Cover) error {
 	if len(cov) == 0 {
 		return fmt.Errorf("No coverage data available")
 	}
@@ -102,7 +98,9 @@ func generateCoverHTML(w io.Writer, vmlinux string, cov cover.Cover) error {
 	}
 	pcs := make([]uint64, 0, len(cov))
 	for pc := range cov {
-		pcs = append(pcs, cover.RestorePC(pc, base)-callLen)
+		fullPC := cover.RestorePC(pc, base)
+		prevPC := previousInstructionPC(arch, fullPC)
+		pcs = append(pcs, prevPC)
 	}
 	uncovered, err := uncoveredPcsInFuncs(vmlinux, pcs)
 	if err != nil {
@@ -393,6 +391,25 @@ func symbolize(vmlinux string, pcs []uint64) ([]symbolizer.Frame, string, error)
 	return frames, prefix, nil
 }
 
+func previousInstructionPC(arch string, pc uint64) uint64 {
+	switch arch {
+	case "amd64":
+		return pc - 5
+	case "386":
+		return pc - 1
+	case "arm64":
+		return pc - 4
+	case "arm":
+		// THUMB instructions are 2 or 4 bytes with low bit set.
+		// ARM instructions are always 4 bytes.
+		return (pc - 3) & ^uint64(1)
+	case "ppc64le":
+		return pc - 4
+	default:
+		panic("unknown arch")
+	}
+}
+
 type templateData struct {
 	Files []*templateFile
 }
diff --git a/syz-manager/html.go b/syz-manager/html.go
index 08a91ea8e..126ec715a 100644
--- a/syz-manager/html.go
+++ b/syz-manager/html.go
@@ -211,7 +211,7 @@ func (mgr *Manager) httpCover(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	if err := generateCoverHTML(w, mgr.cfg.Vmlinux, cov); err != nil {
+	if err := generateCoverHTML(w, mgr.cfg.Vmlinux, mgr.cfg.TargetVMArch, cov); err != nil {
 		http.Error(w, fmt.Sprintf("failed to generate coverage profile: %v", err), http.StatusInternalServerError)
 		return
 	}
@@ -322,7 +322,9 @@ func (mgr *Manager) httpRawCover(w http.ResponseWriter, r *http.Request) {
 	}
 	pcs := make([]uint64, 0, len(cov))
 	for pc := range cov {
-		pcs = append(pcs, cover.RestorePC(pc, base)-callLen)
+		fullPC := cover.RestorePC(pc, base)
+		prevPC := previousInstructionPC(mgr.cfg.TargetVMArch, fullPC)
+		pcs = append(pcs, prevPC)
 	}
 	sort.Slice(pcs, func(i, j int) bool {
 		return pcs[i] < pcs[j]