tetragon

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// SPDX-License-Identifier: Apache-2.0
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// Copyright Authors of Tetragon
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package sensors
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import (
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	"fmt"
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	"github.com/cilium/ebpf"
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	"github.com/cilium/ebpf/asm"
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)
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func UpdateStatsMap(m *ebpf.Map, val int64) error {
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	if m.KeySize() != uint32(4) || m.ValueSize() != uint32(8) {
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		return fmt.Errorf("Wrong key/value size")
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	}
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	if m.Type() != ebpf.PerCPUArray {
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		return fmt.Errorf("Wrong map type")
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	}
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	prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
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		Type: ebpf.SocketFilter,
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		Instructions: asm.Instructions{
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			// map fd into r1
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			asm.LoadMapPtr(asm.R1, m.FD()),
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			// 0 into &FP[-4]
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			asm.LoadImm(asm.R2, 0, asm.DWord),
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			asm.StoreMem(asm.RFP, -4, asm.R2, asm.Word),
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			// &FP[-4] into r2
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			asm.Mov.Reg(asm.R2, asm.RFP),
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			asm.Add.Imm(asm.R2, -4),
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			asm.FnMapLookupElem.Call(),
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			// NULL ptr, jump to error
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			asm.JEq.Imm(asm.R0, 0, "error"),
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			// add 'val' to the elem value
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			asm.LoadImm(asm.R1, val, asm.DWord),
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			asm.StoreXAdd(asm.R0, asm.R1, asm.DWord),
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			// return 0
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			asm.LoadImm(asm.R0, 0, asm.DWord),
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			asm.Return(),
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			// return 1
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			asm.LoadImm(asm.R0, 1, asm.DWord).WithSymbol("error"),
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			asm.Return(),
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		},
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		License: "GPL",
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	})
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	if err != nil {
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		return err
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	}
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	defer prog.Close()
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	// not used, but needed to pass program test run
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	in := make([]byte, 20)
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	var ret uint32
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	opts := ebpf.RunOptions{Data: in}
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	ret, err = prog.Run(&opts)
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	// executed, but failed in bpf program above
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	if err == nil && ret != 0 {
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		err = fmt.Errorf("Failed to update map value")
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	}
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	return err
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}
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