DTV info detection improvements per feedback

- Move DTVInfo struct definition into C
- Make DTVInfo struct members mirror TSDInfo names
- Rename IsPotentialTSDDSO

Author: dalehamel

libc/libc.go

@@ -15,6 +15,7 @@ import (
 )
 
 type TSDInfo = support.TSDInfo
+type DTVInfo = support.DTVInfo
 
 // LibcInfo contains introspection information extracted from the C-library
 type LibcInfo struct {
@@ -24,15 +25,31 @@ type LibcInfo struct {
 	DTVInfo DTVInfo
 }
 
+var (
+	// regex for the libc
+	libcRegex = regexp.MustCompile(`.*/(ld-musl|ld-linux|libc|libpthread)([-.].*)?\.so`)
+)
 
-// TODO comment
-type DTVInfo struct {
-	// Offset is the offset of DTV from FS base (or from thread pointer)
-	Offset     int64
-	// EntryWidth is the size of each DTV entry in bytes
-	EntryWidth uint32 
-	// Indirect is 0 if DTV is at FS+offset, 1 if at [FS+0]+offset
-	Indirect   uint8
+// IsPotentialLibcDSO determines if the DSO filename potentially contains libc code
+func IsPotentialLibcDSO(filename string) bool {
+	return libcRegex.MatchString(filename)
+}
+
+func ExtractLibcInfo(ef *pfelf.File) (*LibcInfo, error) {
+	tsdinfo, err := extractTSDInfo(ef)
+	if err != nil {
+		return nil, err
+	}
+
+	dtvinfo, err := extractDTVInfo(ef)
+	if err != nil {
+		return &LibcInfo{}, err
+	}
+
+	return &LibcInfo{
+		TSDInfo: tsdinfo,
+		DTVInfo: dtvinfo,
+	}, nil
 }
 
 // This code analyzes the C-library provided POSIX defined function which is used
@@ -80,33 +97,6 @@ type DTVInfo struct {
 //
 // Reading the value is basically "return self->specific_1stblock[key].data;"
 
-var (
-	// regex for the libc
-	libcRegex = regexp.MustCompile(`.*/(ld-musl|libc|libpthread)([-.].*)?\.so`)
-)
-
-// IsPotentialTSDDSO determines if the DSO filename potentially contains pthread code
-func IsPotentialTSDDSO(filename string) bool {
-	return libcRegex.MatchString(filename)
-}
-
-func ExtractLibcInfo(ef *pfelf.File) (*LibcInfo, error) {
-	tsdinfo, err := extractTSDInfo(ef)
-	if err != nil {
-		return nil, err
-	}
-
-	dtvinfo, err := extractDTVInfo(ef)
-	if err != nil {
-		return &LibcInfo{}, err
-	}
-
-	return &LibcInfo{
-		TSDInfo: tsdinfo,
-		DTVInfo: dtvinfo,
-	}, nil
-}
-
 // extractTSDInfo extracts the introspection data for pthread thread specific data.
 func extractTSDInfo(ef *pfelf.File) (TSDInfo, error) {
 	_, code, err := ef.SymbolData("__pthread_getspecific", 2048)

libc/libc_aarch64.go

@@ -332,8 +332,8 @@ func extractDTVInfoARM(code []byte) (DTVInfo, error) {
 	}
 
 	return DTVInfo{
-		Offset:     dtvOffset,
-		EntryWidth: entryWidth,
+		Offset:     int16(dtvOffset),
+		Multiplier: uint8(entryWidth),
 		Indirect:   1,
 	}, nil
 }

libc/libc_x86.go

@@ -120,8 +120,8 @@ func extractDTVInfoX86(code []byte) (DTVInfo, error) {
 
 	if result.Match(expected) {
 		return DTVInfo{
-			Offset:     int64(dtvOffset.CapturedValue()),
-			EntryWidth: uint32(entryWidth.CapturedValue()),
+			Offset:     int16(dtvOffset.CapturedValue()),
+			Multiplier: uint8(entryWidth.CapturedValue()),
 			Indirect:   0,
 		}, nil
 	}
@@ -143,8 +143,8 @@ func extractDTVInfoX86(code []byte) (DTVInfo, error) {
 
 	if result.Match(expected) {
 		return DTVInfo{
-			Offset:     int64(dtvOffset.CapturedValue()),
-			EntryWidth: uint32(entryWidth.CapturedValue()),
+			Offset:     int16(dtvOffset.CapturedValue()),
+			Multiplier: uint8(entryWidth.CapturedValue()),
 			Indirect:   1,
 		}, nil
 	}
@@ -162,8 +162,8 @@ func extractDTVInfoX86(code []byte) (DTVInfo, error) {
 
 	if result.Match(expected) {
 		return DTVInfo{
-			Offset:     int64(dtvOffset.CapturedValue()),
-			EntryWidth: uint32(entryWidth.CapturedValue()),
+			Offset:     int16(dtvOffset.CapturedValue()),
+			Multiplier: uint8(entryWidth.CapturedValue()),
 			Indirect:   1,
 		}, nil
 	}
@@ -182,8 +182,8 @@ func extractDTVInfoX86(code []byte) (DTVInfo, error) {
 
 	if result.Match(expected) {
 		return DTVInfo{
-			Offset:     int64(dtvOffset.CapturedValue()),
-			EntryWidth: uint32(entryWidth.CapturedValue()),
+			Offset:     int16(dtvOffset.CapturedValue()),
+			Multiplier: uint8(entryWidth.CapturedValue()),
 			Indirect:   1,
 		}, nil
 	}

processmanager/execinfomanager/manager.go

@@ -194,8 +194,8 @@ func (mgr *ExecutableInfoManager) AddOrIncRef(fileID host.FileID,
 		intervalData = synthesizeIntervalData(ef)
 	}
 
-	// Also gather TSD info if applicable.
-	if libc.IsPotentialTSDDSO(elfRef.FileName()) {
+	// Also gather Libc info if applicable.
+	if libc.IsPotentialLibcDSO(elfRef.FileName()) {
 		if ef, errx := elfRef.GetELF(); errx == nil {
 			libcInfo, _ = libc.ExtractLibcInfo(ef)
 		}

support/ebpf/types.h

@@ -406,6 +406,18 @@ typedef struct TSDInfo {
   u8 indirect;
 } TSDInfo;
 
+// DTVInfo contains data needed to read Thread Local Storage (TLS) values, which
+// are located using the Dynamic Thread Vector (DTV)
+typedef struct DTVInfo {
+  // Offset is the offset of DTV from FS base (or from thread pointer)
+  s16 offset;
+  // Multiplier is the size of each DTV entry in bytes
+  // Typically 8 bytes on 64bit musl and 16 bytes on 64bit glibc
+  u8 multiplier;
+  // Indirect is 0 if DTV is at FS+offset, 1 if at [FS+0]+offset
+  u8 indirect;
+} DTVInfo;
+
 // DotnetProcInfo is a container for the data needed to build stack trace for a dotnet process.
 typedef struct DotnetProcInfo {
   u32 version;

support/types.go

@@ -119,6 +119,7 @@ type StackDeltaPageInfo C.StackDeltaPageInfo
 type StackDeltaPageKey C.StackDeltaPageKey
 type SystemAnalysis C.SystemAnalysis
 type TSDInfo C.TSDInfo
+type DTVInfo C.DTVInfo
 type Trace C.Trace
 type UnwindInfo C.UnwindInfo