use binary search to optimize performance

Signed-off-by: Changsheng Huang <1984737645@qq.com>
Signed-off-by: Lancelot <1984737645@qq.com>

pkg/ksyms/ksyms.go

@@ -146,18 +146,25 @@ func (k *Ksyms) GetFnOffset(addr uint64) (*FnOffset, error) {
 
 // GetFnOffset -- retruns the FnOffset for a given address
 func (k *Ksyms) getFnOffset(addr uint64) (*FnOffset, error) {
-
-	// TODO: we can do binary search here if we care about performance
-	i := 0
-	for k.table[i].addr < addr {
-		i++
+	// address is before first symbol
+	if k.table[0].addr > addr {
+		return nil, fmt.Errorf("address %d is before first symbol %s@%d", addr, k.table[0].name, k.table[0].addr)
 	}
 
-	if i == 0 {
-		return nil, fmt.Errorf("address %d is before first sumbol %s@%d", addr, k.table[0].name, k.table[0].addr)
+	// binary search
+	l, r := 0, len(k.table)-1
+
+	for l < r {
+		// prevents overflow
+		m := l + ((r - l + 1) >> 1)
+		if k.table[m].addr < addr {
+			l = m
+		} else {
+			r = m - 1
+		}
 	}
 
-	sym := k.table[i-1]
+	sym := k.table[l]
 	if !sym.isFunction() {
 		return nil, fmt.Errorf("Unable to find function for addr 0x%x", addr)
 	}

pkg/ksyms/ksyms_test.go

@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+package ksyms
+
+import (
+	"testing"
+)
+
+func TestGetFnOffset(t *testing.T) {
+	ksyms := &Ksyms{
+		table: []ksym{
+			{addr: 0x100, name: "addr1", ty: "t"},
+			{addr: 0x200, name: "addr2", ty: "t"},
+			{addr: 0x300, name: "addr3", ty: "w"},
+			{addr: 0x400, name: "addr4", ty: "t"},
+			{addr: 0x500, name: "addr5", ty: "t"},
+			{addr: 0x600, name: "addr6", ty: "t"},
+			{addr: 0x700, name: "addr7", ty: "t"},
+			{addr: 0x800, name: "addr8", ty: "t"},
+			{addr: 0x900, name: "addr9", ty: "t"},
+			{addr: 0xa00, name: "addr10", ty: "t"},
+		},
+	}
+
+	tests := []struct {
+		name    string
+		addr    uint64
+		wantErr bool
+		want    FnOffset
+	}{
+		{
+			name: "valid first address",
+			addr: 0x100,
+			want: FnOffset{SymName: "addr1", Offset: 0},
+		},
+		{
+			name: "addr 0x110",
+			addr: 0x110,
+			want: FnOffset{SymName: "addr1", Offset: 0x10},
+		},
+		{
+			name: "addr 0x410",
+			addr: 0x410,
+			want: FnOffset{SymName: "addr4", Offset: 0x10},
+		},
+		{
+			name: "addr 0x50f",
+			addr: 0x50f,
+			want: FnOffset{SymName: "addr5", Offset: 0xf},
+		},
+		{
+			name: "addr 0x550",
+			addr: 0x550,
+			want: FnOffset{SymName: "addr5", Offset: 0x050},
+		},
+		{
+			name: "addr 0x900",
+			addr: 0x900,
+			want: FnOffset{SymName: "addr8", Offset: 0x100},
+		},
+		{
+			name:    "address is before first symbol",
+			addr:    0x090,
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ksyms.getFnOffset(tt.addr)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("Unexpected error: %v", err)
+			}
+			if tt.wantErr {
+				if err == nil {
+					t.Fatalf("expected error: %v", err)
+				}
+				return
+			}
+			if got.SymName != tt.want.SymName {
+				t.Fatalf("Symbol name (%v) did not match expected value (%v) for %v", got.SymName, tt.want.SymName, tt.name)
+			}
+			if got.Offset != tt.want.Offset {
+				t.Fatalf("Symbol offset (%x) did not match expected value (%x) for %v", got.Offset, tt.want.Offset, tt.name)
+			}
+		})
+	}
+}