Rework VDSO synthetic deltas to be less special

processmanager/execinfomanager/manager.go

@@ -191,6 +191,13 @@ func (mgr *ExecutableInfoManager) AddOrIncRef(fileID host.FileID,
 		}
 		return ExecutableInfo{}, fmt.Errorf("failed to extract interval data: %w", err)
 	}
+	if len(intervalData.Deltas) == 0 {
+		ef, errx := elfRef.GetELF()
+		if errx != nil {
+			return ExecutableInfo{}, errx
+		}
+		intervalData = synthesizeIntervalData(ef)
+	}
 
 	// Also gather TSD info if applicable.
 	if tpbase.IsPotentialTSDDSO(elfRef.FileName()) {
@@ -232,33 +239,6 @@ func (mgr *ExecutableInfoManager) AddOrIncRef(fileID host.FileID,
 	return info.ExecutableInfo, nil
 }
 
-// AddSynthIntervalData should only be called once for a given file ID. It will error if it or
-// AddOrIncRef has been previously called for the same file ID. Interpreter detection is skipped.
-func (mgr *ExecutableInfoManager) AddSynthIntervalData(
-	fileID host.FileID,
-	data sdtypes.IntervalData,
-) error {
-	state := mgr.state.WLock()
-	defer mgr.state.WUnlock(&state)
-
-	if _, exists := state.executables[fileID]; exists {
-		return errors.New("AddSynthIntervalData: mapping already exists")
-	}
-
-	ref, _, err := state.loadDeltas(fileID, data.Deltas)
-	if err != nil {
-		return fmt.Errorf("failed to load deltas: %w", err)
-	}
-
-	state.executables[fileID] = &entry{
-		ExecutableInfo: ExecutableInfo{Data: nil},
-		mapRef:         ref,
-		rc:             1,
-	}
-
-	return nil
-}
-
 // RemoveOrDecRef decrements the reference counter of the executable being tracked. Once the RC
 // reaches zero, information about the file is removed from the manager and the corresponding
 // BPF maps.

processmanager/synthdeltas.go → processmanager/execinfomanager/synthdeltas.go

@@ -1,9 +1,10 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package processmanager // import "go.opentelemetry.io/ebpf-profiler/processmanager"
+package execinfomanager // import "go.opentelemetry.io/ebpf-profiler/processmanager/execinfomanager"
 
 import (
+	"debug/elf"
 	"sort"
 
 	aa "golang.org/x/arch/arm64/arm64asm"
@@ -21,9 +22,15 @@ const regFP = 29
 // regLR is the arm64 link register (x30) number
 const regLR = 30
 
-// createVDSOSyntheticRecordNone returns no synthetic deltas when the kernel vDSO
-// is known to have valid unwind information.
-func createVDSOSyntheticRecordNone(_ *pfelf.File) sdtypes.IntervalData {
+// synthesizeIntervalData creates synthetic stack deltas if possible.
+// Currently supported for ARM64 vDSO only.
+func synthesizeIntervalData(ef *pfelf.File) sdtypes.IntervalData {
+	if ef.Machine == elf.EM_AARCH64 {
+		soname, err := ef.DynString(elf.DT_SONAME)
+		if err == nil && soname[0] == "linux-vdso.so.1" {
+			return createVDSOSyntheticRecordArm64(ef)
+		}
+	}
 	return sdtypes.IntervalData{}
 }
 

processmanager/synthdeltas_test.go → processmanager/execinfomanager/synthdeltas_test.go

@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package processmanager // import "go.opentelemetry.io/ebpf-profiler/processmanager"
+package execinfomanager // import "go.opentelemetry.io/ebpf-profiler/processmanager/execinfomanager"
 
 import (
 	"testing"

processmanager/manager.go

@@ -22,7 +22,6 @@ import (
 	"go.opentelemetry.io/ebpf-profiler/lpm"
 	"go.opentelemetry.io/ebpf-profiler/metrics"
 	"go.opentelemetry.io/ebpf-profiler/nativeunwind"
-	sdtypes "go.opentelemetry.io/ebpf-profiler/nativeunwind/stackdeltatypes"
 	"go.opentelemetry.io/ebpf-profiler/periodiccaller"
 	pmebpf "go.opentelemetry.io/ebpf-profiler/processmanager/ebpf"
 	eim "go.opentelemetry.io/ebpf-profiler/processmanager/execinfomanager"
@@ -332,13 +331,3 @@ func (pm *ProcessManager) MaybeNotifyAPMAgent(
 
 	return serviceName
 }
-
-// AddSynthIntervalData adds synthetic stack deltas to the manager. This is useful for cases where
-// populating the information via the stack delta provider isn't viable, for example because the
-// `.eh_frame` section for a binary is broken. If `AddSynthIntervalData` was called for a given
-// file ID, the stack delta provider will not be consulted and the manually added stack deltas take
-// precedence.
-func (pm *ProcessManager) AddSynthIntervalData(fileID host.FileID,
-	data sdtypes.IntervalData) error {
-	return pm.eim.AddSynthIntervalData(fileID, data)
-}

processmanager/processinfo.go

@@ -352,19 +352,7 @@ func (pm *ProcessManager) getELFInfo(pr process.Process, mapping *process.Mappin
 	hostFileID := host.FileIDFromLibpf(fileID)
 	info.fileID = hostFileID
 	info.addressMapper = ef.GetAddressMapper()
-	if mapping.IsVDSO() {
-		intervals := createVDSOSyntheticRecord(ef)
-		if intervals.Deltas != nil {
-			if err := pm.AddSynthIntervalData(hostFileID, intervals); err != nil {
-				info.err = fmt.Errorf("failed to add synthetic deltas: %w", err)
-			}
-		}
-	}
-	// Do not cache the entry if synthetic stack delta loading failed,
-	// so next encounter of the VDSO will retry loading them.
-	if info.err == nil {
-		pm.elfInfoCache.Add(key, info)
-	}
+	pm.elfInfoCache.Add(key, info)
 	pm.FileIDMapper.Set(hostFileID, fileID)
 
 	if pm.reporter.ExecutableKnown(fileID) {