debug/gosym: report different line number than cmd/addr2line

[zdyj3170101136]

What version of Go are you using (go version)?

$ go version
go1.18.8

What operating system and processor architecture are you using (go env)?

go env

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE=""
GOPROXY="https://goproxy.cn"
GOROOT="/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.18.8"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/root/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4192850700=/tmp/go-build -gno-record-gcc-switches"

What did you do?

get pprof:

curl pprof 127.0.0.1:8887/debug/pprof/profile?seconds=1

open it with pprof raw:

  793: 0x410ab7 M=1 runtime.nextFreeFast /usr/local/go1.18/go/src/runtime/malloc.go:850 s=0
             runtime.mallocgc /usr/local/go1.18/go/src/runtime/malloc.go:1083 s=0
Mappings
1: 0x400000/0x99c2000/0x0 /home/data/server/otel-collector/data/otelcol-contrib 0bfdbe13c5603e284aed96d5ad62f47eea0cb692 [FN]

use debug/gosym to get funcname and line:

func parse(file string, f *elf.File) (*elf.File, *gosym.Table) {
	pclndat, err := f.Section(".gopclntab").Data()
	if err != nil {
		f.Close()
		log.Fatalf("reading %s gopclntab: %v", file, err)
	}

	pcln := gosym.NewLineTable(pclndat, f.Section(".text").Addr)
	tab, err := gosym.NewTable(nil, pcln)
	if err != nil {
		f.Close()
		log.Fatalf("parsing %s gosymtab: %v", file, err)
	}

	return f, tab
}

What did you expect to see?

with same address, the debug/gosym should have same line number compared with go tool addr2line.

use go tool addr2line to get funcname and line:

[root@plat-sh-infra-prod-jaeger-collector003 ~]#  /go/bin/go tool addr2line /home/data/server/otel-collector/data/otelcol-contrib
410ab7
runtime.mallocgc
/usr/local/go1.18/go/src/runtime/malloc.go:850

What did you see instead?

the debug/gosym have different line number compared with go tool addr2line.

debug/gosym:

/usr/local/go1.18/go/src/runtime/malloc.go 1117

it's line number is 1117, not 850.

[cherrymui]

The line numbers from the addr2line and pprof commands both look reasonable. Could you share your complete code about how you get the line number with the debug/gosym package? (The code snippet above only includes loading the table, not getting the line number.) Thanks,

[zdyj3170101136]

来自 addr2line 和 pprof 命令的行号看起来都很合理。您能否分享有关如何获取debug/gosym包行号的完整代码？（上面的代码片段只包括加载表格，而不是获取行号。）谢谢，

code:

package main

import (
	"debug/elf"
	"debug/gosym"
	"log"
	"os"
	"strconv"
)

func main() {
	if len(os.Args) >= 3 {
		_, tab := crack(os.Args[1])
		pc, _ := strconv.ParseUint(os.Args[2], 16, 64)
		log.Println(tab.PCToLine(pc))
	}
}

func crack(file string) (*elf.File, *gosym.Table) {
	// Open self
	f, err := elf.Open(file)
	if err != nil {
		log.Fatal(err)
	}
	return parse(file, f)
}

func parse(file string, f *elf.File) (*elf.File, *gosym.Table) {
	pclndat, err := f.Section(".gopclntab").Data()
	if err != nil {
		f.Close()
		log.Fatalf("reading %s gopclntab: %v", file, err)
	}

	pcln := gosym.NewLineTable(pclndat, f.Section(".text").Addr)
	tab, err := gosym.NewTable(nil, pcln)
	if err != nil {
		f.Close()
		log.Fatalf("parsing %s gosymtab: %v", file, err)
	}

	return f, tab
}

command:

[root@plat-sh-infra-prod-jaeger-collector003 ~]# /go/bin/go build main.go && ./main /home/data/server/otel-collector/data/otelcol-contrib 410ab7
2022/11/22 10:12:41 /usr/local/go1.18/go/src/runtime/malloc.go 1117 &{4261280 0xc0047d0730 4263648 [] [] 0 0xc0000c4000 <nil>}