1 files changed, 68 insertions, 0 deletions
diff --git a/pkg/rpcserver/last_executing.go b/pkg/rpcserver/last_executing.go
new file mode 100644
index 000000000..341ae6534
--- /dev/null
+++ b/pkg/rpcserver/last_executing.go
@@ -0,0 +1,68 @@
+// Copyright 2024 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package rpcserver
+
+import (
+	"sort"
+	"time"
+)
+
+// LastExecuting keeps the given number of last executed programs
+// for each proc in a VM, and allows to query this set after a crash.
+type LastExecuting struct {
+	count     int
+	procs     []ExecRecord
+	positions []int
+}
+
+type ExecRecord struct {
+	ID   int
+	Proc int
+	Prog []byte
+	Time time.Duration
+}
+
+func MakeLastExecuting(procs, count int) *LastExecuting {
+	return &LastExecuting{
+		count:     count,
+		procs:     make([]ExecRecord, procs*count),
+		positions: make([]int, procs),
+	}
+}
+
+// Note execution of the 'prog' on 'proc' at time 'now'.
+func (last *LastExecuting) Note(id, proc int, prog []byte, now time.Duration) {
+	pos := &last.positions[proc]
+	last.procs[proc*last.count+*pos] = ExecRecord{
+		ID:   id,
+		Proc: proc,
+		Prog: prog,
+		Time: now,
+	}
+	*pos++
+	if *pos == last.count {
+		*pos = 0
+	}
+}
+
+// Returns a sorted set of last executing programs.
+// The records are sorted by time in ascending order.
+// ExecRecord.Time is the difference in start executing time between this
+// program and the program that started executing last.
+func (last *LastExecuting) Collect() []ExecRecord {
+	procs := last.procs
+	last.procs = nil // The type must not be used after this.
+	sort.Slice(procs, func(i, j int) bool {
+		return procs[i].Time < procs[j].Time
+	})
+	max := procs[len(procs)-1].Time
+	for i := len(procs) - 1; i >= 0; i-- {
+		if procs[i].Time == 0 {
+			procs = procs[i+1:]
+			break
+		}
+		procs[i].Time = max - procs[i].Time
+	}
+	return procs
+}