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- // Copyright 2018 Google Inc. All Rights Reserved.
- //
- // 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.
-
- // +build linux
-
- package server
-
- import (
- "errors"
- "fmt"
-
- "cloud.google.com/go/cmd/go-cloud-debug-agent/internal/debug/dwarf"
- )
-
- func (s *Server) functionStartAddress(name string) (uint64, error) {
- entry, err := s.dwarfData.LookupFunction(name)
- if err != nil {
- return 0, err
- }
- addrAttr := entry.Val(dwarf.AttrLowpc)
- if addrAttr == nil {
- return 0, fmt.Errorf("symbol %q has no LowPC attribute", name)
- }
- addr, ok := addrAttr.(uint64)
- if !ok {
- return 0, fmt.Errorf("symbol %q has non-uint64 LowPC attribute", name)
- }
- return addr, nil
- }
-
- // evalLocation parses a DWARF location description encoded in v. It works for
- // cases where the variable is stored at an offset from the Canonical Frame
- // Address. The return value is this offset.
- // TODO: a more general location-description-parsing function.
- func evalLocation(v []uint8) (int64, error) {
- // Some DWARF constants.
- const (
- opConsts = 0x11
- opPlus = 0x22
- opCallFrameCFA = 0x9C
- )
- if len(v) == 0 {
- return 0, errors.New("empty location specifier")
- }
- if v[0] != opCallFrameCFA {
- return 0, errors.New("unsupported location specifier")
- }
- if len(v) == 1 {
- // The location description was just DW_OP_call_frame_cfa, so the location is exactly the CFA.
- return 0, nil
- }
- if v[1] != opConsts {
- return 0, errors.New("unsupported location specifier")
- }
- offset, v, err := sleb128(v[2:])
- if err != nil {
- return 0, err
- }
- if len(v) == 1 && v[0] == opPlus {
- // The location description was DW_OP_call_frame_cfa, DW_OP_consts <offset>, DW_OP_plus.
- // So return the offset.
- return offset, nil
- }
- return 0, errors.New("unsupported location specifier")
- }
-
- func uleb128(v []uint8) (u uint64) {
- var shift uint
- for _, x := range v {
- u |= (uint64(x) & 0x7F) << shift
- shift += 7
- if x&0x80 == 0 {
- break
- }
- }
- return u
- }
-
- // sleb128 parses a signed integer encoded with sleb128 at the start of v, and
- // returns the integer and the remainder of v.
- func sleb128(v []uint8) (s int64, rest []uint8, err error) {
- var shift uint
- var sign int64 = -1
- var i int
- var x uint8
- for i, x = range v {
- s |= (int64(x) & 0x7F) << shift
- shift += 7
- sign <<= 7
- if x&0x80 == 0 {
- if x&0x40 != 0 {
- s |= sign
- }
- break
- }
- }
- if i == len(v) {
- return 0, nil, errors.New("truncated sleb128")
- }
- return s, v[i+1:], nil
- }
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