Allow pushing an "extra" value in Frame in padding

host/host.go

@@ -38,6 +38,7 @@ type Frame struct {
 	File          FileID
 	Lineno        libpf.AddressOrLineno
 	Type          libpf.FrameType
+	Extra         libpf.AddressOrLineno
 	ReturnAddress bool
 }
 

support/ebpf/tracemgmt.h

@@ -328,27 +328,32 @@ static inline EBPF_INLINE bool unwinder_unwind_frame_pointer(UnwindState *state)
 //       calc_line). This should probably be renamed to something like "frame type
 //       specific data".
 static inline EBPF_INLINE ErrorCode _push_with_max_frames(
-  Trace *trace, u64 file, u64 line, u8 frame_type, u8 return_address, u32 max_frames)
+  Trace *trace, u64 file, u64 line, u64 extra, u8 frame_type, u8 return_address, u32 max_frames)
 {
   if (trace->stack_len >= max_frames) {
     DEBUG_PRINT("unable to push frame: stack is full");
     increment_metric(metricID_UnwindErrStackLengthExceeded);
     return ERR_STACK_LENGTH_EXCEEDED;
   }
 
+  u64 extra_addr = (u64)extra & 0x0000FFFFFFFFFFFFULL;
 #ifdef TESTING_COREDUMP
   // tools/coredump uses CGO to build the eBPF code. This dispatches
   // the frame information directly to helper implemented in ebpfhelpers.go.
-  int __push_frame(u64, u64, u64, u8, u8);
+  int __push_frame(u64, u64, u64, u64, u8, u8);
   trace->stack_len++;
-  return __push_frame(__cgo_ctx->id, file, line, frame_type, return_address);
+  return __push_frame(__cgo_ctx->id, file, line, extra_addr, frame_type, return_address);
 #else
-  trace->frames[trace->stack_len++] = (Frame){
+  Frame frame = {
     .file_id        = file,
     .addr_or_line   = line,
     .kind           = frame_type,
     .return_address = return_address,
   };
+  if (extra_addr != 0) {
+    __builtin_memcpy(frame.pad, &extra_addr, 6);
+  }
+  trace->frames[trace->stack_len++] = frame;
 
   return ERR_OK;
 #endif
@@ -359,19 +364,27 @@ static inline EBPF_INLINE ErrorCode
 _push_with_return_address(Trace *trace, u64 file, u64 line, u8 frame_type, bool return_address)
 {
   return _push_with_max_frames(
-    trace, file, line, frame_type, return_address, MAX_NON_ERROR_FRAME_UNWINDS);
+    trace, file, line, 0, frame_type, return_address, MAX_NON_ERROR_FRAME_UNWINDS);
 }
 
 // Push the file ID, line number and frame type into FrameList
 static inline EBPF_INLINE ErrorCode _push(Trace *trace, u64 file, u64 line, u8 frame_type)
 {
-  return _push_with_max_frames(trace, file, line, frame_type, 0, MAX_NON_ERROR_FRAME_UNWINDS);
+  return _push_with_max_frames(trace, file, line, 0, frame_type, 0, MAX_NON_ERROR_FRAME_UNWINDS);
+}
+
+// Push the file ID, line number and frame type with an extra address into FrameList
+static inline EBPF_INLINE ErrorCode
+_push_with_extra(Trace *trace, u64 file, u64 line, u64 extra, u8 frame_type)
+{
+  return _push_with_max_frames(
+    trace, file, line, extra, frame_type, 0, MAX_NON_ERROR_FRAME_UNWINDS);
 }
 
 // Push a critical error frame.
 static inline EBPF_INLINE ErrorCode push_error(Trace *trace, ErrorCode error)
 {
-  return _push_with_max_frames(trace, 0, error, FRAME_MARKER_ABORT, 0, MAX_FRAME_UNWINDS);
+  return _push_with_max_frames(trace, 0, error, 0, FRAME_MARKER_ABORT, 0, MAX_FRAME_UNWINDS);
 }
 
 // Send a trace to user-land via the `trace_events` perf event buffer.

tools/coredump/ebpfhelpers.go

@@ -36,13 +36,14 @@ func __bpf_log(buf unsafe.Pointer, sz C.int) {
 }
 
 //export __push_frame
-func __push_frame(id, file, line C.u64, frameType, returnAddress C.uchar) C.int {
+func __push_frame(id, file, line, extra C.u64, frameType, returnAddress C.uchar) C.int {
 	ctx := ebpfContextMap[id]
 
 	ctx.trace.Frames = append(ctx.trace.Frames, host.Frame{
 		File:          host.FileID(file),
 		Lineno:        libpf.AddressOrLineno(line),
 		Type:          libpf.FrameType(frameType),
+		Extra:         libpf.AddressOrLineno(extra),
 		ReturnAddress: returnAddress != 0,
 	})
 

tracer/tracer.go

@@ -8,6 +8,7 @@ import (
 	"bufio"
 	"bytes"
 	"context"
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"math"
@@ -857,6 +858,13 @@ func (t *Tracer) eBPFMetricsCollector(
 	return metricsUpdates
 }
 
+func reconstruct48BitAddress(bytes [6]uint8) uint64 {
+	// Pad to 8 bytes for binary.LittleEndian
+	padded := [8]uint8{}
+	copy(padded[:], bytes[:])
+	return binary.LittleEndian.Uint64(padded[:])
+}
+
 // loadBpfTrace parses a raw BPF trace into a `host.Trace` instance.
 //
 // If the raw trace contains a kernel stack ID, the kernel stack is also
@@ -930,6 +938,10 @@ func (t *Tracer) loadBpfTrace(raw []byte, cpu int) *host.Trace {
 			Type:          libpf.FrameType(rawFrame.Kind),
 			ReturnAddress: rawFrame.Return_address != 0,
 		}
+		// If there is additional data in the padding, append it as an extra value
+		if rawFrame.Pad[0] != 0 {
+			trace.Frames[i].Extra = libpf.AddressOrLineno(reconstruct48BitAddress(rawFrame.Pad))
+		}
 	}
 	return trace
 }