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dwarf_expression.go
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dwarf_expression.go
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// Copyright 2022-2024 The Parca Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
package unwind
import (
"debug/elf"
"github.com/parca-dev/parca-agent/internal/dwarf/frame"
)
type DWARFExpressionID int16
const (
ExpressionUnknown DWARFExpressionID = iota
ExpressionPlt1
ExpressionPlt2
)
// DWARF expressions that we recognize.
// Plt1 is equivalent to: sp + 8 + ((((ip & 15) >= 11)) << 3.
var Plt1 = [...]byte{
frame.DW_OP_breg7,
frame.DW_OP_const1u,
frame.DW_OP_breg16,
frame.DW_OP_lit15,
frame.DW_OP_and,
frame.DW_OP_lit11,
frame.DW_OP_ge,
frame.DW_OP_lit3,
frame.DW_OP_shl,
frame.DW_OP_plus,
}
// Plt2 is quivalent to: sp + 8 + ((((ip & 15) >= 10)) << 3.
var Plt2 = [...]byte{
frame.DW_OP_breg7,
frame.DW_OP_const1u,
frame.DW_OP_breg16,
frame.DW_OP_lit15,
frame.DW_OP_and,
frame.DW_OP_lit10,
frame.DW_OP_ge,
frame.DW_OP_lit3,
frame.DW_OP_shl,
frame.DW_OP_plus,
}
// equalBytes checks whether two byte slices are equal.
func equalBytes(a, b []byte) bool {
if len(a) != len(b) {
return false
}
for i := range a {
if a[i] != b[i] {
return false
}
}
return true
}
// ExpressionIdentifier returns the identifier for recognized
// DWARF expressions.
func ExpressionIdentifier(expression []byte, arch elf.Machine) DWARFExpressionID {
if arch == elf.EM_X86_64 {
cleanedExpression := make([]byte, 0, len(expression))
for _, opcode := range expression {
if opcode == 0x0 {
continue
}
cleanedExpression = append(cleanedExpression, opcode)
}
if equalBytes(Plt1[:], cleanedExpression) {
return ExpressionPlt1
}
if equalBytes(Plt2[:], cleanedExpression) {
return ExpressionPlt2
}
}
return ExpressionUnknown
}