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coredump: Add gosym sub command #234

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2 changes: 1 addition & 1 deletion README.md
Original file line number Diff line number Diff line change
Expand Up @@ -476,7 +476,7 @@ The host agent code is tested with three test suites:
tests. This works great for the user-land portion of the agent, but is unable
to test any of the unwinding logic and BPF interaction.
- **coredump test suite**\
The coredump test suite (`utils/coredump`) we compile the whole BPF unwinder
The coredump test suite (`tools/coredump`) we compile the whole BPF unwinder
code into a user-mode executable, then use the information from a coredump to
simulate a realistic environment to test the unwinder code in. The coredump
suite essentially implements all required BPF helper functions in user-space,
Expand Down
38 changes: 34 additions & 4 deletions tools/coredump/coredump.go
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,8 @@ import (
"fmt"
"os"
"runtime"
"strconv"
"strings"
"time"
"unsafe"

Expand Down Expand Up @@ -114,16 +116,44 @@ func (c *symbolizationCache) symbolize(ty libpf.FrameType, fileID libpf.FileID,
}

if data, ok := c.symbols[libpf.NewFrameID(fileID, lineNumber)]; ok {
return fmt.Sprintf("%s+%d in %s:%d",
data.FunctionName, data.FunctionOffset,
data.SourceFile, data.SourceLine), nil
return formatSymbolizedFrame(data, true), nil
}

sourceFile, ok := c.files[fileID]
if !ok {
sourceFile = fmt.Sprintf("%08x", fileID)
}
return fmt.Sprintf("%s+0x%x", sourceFile, lineNumber), nil
return formatUnsymbolizedFrame(sourceFile, lineNumber), nil
}

func formatSymbolizedFrame(frame *reporter.FrameMetadataArgs, functionOffsets bool) string {
var funcOffset string
if functionOffsets {
funcOffset = "+" + strconv.Itoa(int(frame.FunctionOffset))
}
return fmt.Sprintf("%s%s in %s:%d",
frame.FunctionName, funcOffset,
frame.SourceFile, frame.SourceLine)
}

func formatUnsymbolizedFrame(file string, addr libpf.AddressOrLineno) string {
return fmt.Sprintf("%s+0x%x", file, addr)
}

func parseUnsymbolizedFrame(frame string) (file string, addr libpf.AddressOrLineno, err error) {
fileS, addrS, found := strings.Cut(frame, "+0x")
if !found {
err = fmt.Errorf("bad frame string: %q", frame)
return
}
file = fileS
var addrU uint64
addrU, err = strconv.ParseUint(addrS, 16, 64)
if err != nil {
return
}
addr = libpf.AddressOrLineno(addrU)
return
}

func ExtractTraces(ctx context.Context, pr process.Process, debug bool,
Expand Down
137 changes: 137 additions & 0 deletions tools/coredump/gosym.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,137 @@
package main

import (
"context"
"debug/elf"
"debug/gosym"
"errors"
"flag"
"fmt"
"os"
"path/filepath"

"github.com/peterbourgon/ff/v3/ffcli"
"go.opentelemetry.io/ebpf-profiler/libpf"
"go.opentelemetry.io/ebpf-profiler/reporter"
"go.opentelemetry.io/ebpf-profiler/tools/coredump/modulestore"
)

type gosymCmd struct {
store *modulestore.Store
casePath string
}

func newGosymCmd(store *modulestore.Store) *ffcli.Command {
args := &gosymCmd{store: store}

set := flag.NewFlagSet("gosym", flag.ExitOnError)
set.StringVar(&args.casePath, "case", "", "Path of the test case to debug")

return &ffcli.Command{
Name: "gosym",
Exec: args.exec,
ShortUsage: "gosym",
ShortHelp: "Symbolize go test case",
FlagSet: set,
}
}

func (cmd *gosymCmd) exec(context.Context, []string) (err error) {
// Validate arguments.
if cmd.casePath == "" {
return errors.New("please specify `-case`")
}

var test *CoredumpTestCase
test, err = readTestCase(cmd.casePath)
if err != nil {
return fmt.Errorf("failed to read test case: %w", err)
}

symTable, addrs, err := goModuleAddrs(cmd.store, test)
if err != nil {
return fmt.Errorf("failed to find go module addresses: %w", err)
}

for addr, originFrames := range addrs {
file, line, fn := symTable.PCToLine(uint64(addr))
for _, originFrame := range originFrames {
frame := reporter.FrameMetadataArgs{
FunctionName: fn.Name,
SourceFile: file,
SourceLine: libpf.SourceLineno(line),
}
*originFrame = formatSymbolizedFrame(&frame, false) + " (" + *originFrame + ")"
}
}

return writeTestCaseJSON(os.Stdout, test)
}

// goModuleAddrs returns the symtable for the go module of test case and the
// addresses to symbolize for it mapped to pointers to the frames in the test
// case that reference them.
func goModuleAddrs(store *modulestore.Store, c *CoredumpTestCase) (
*gosym.Table, map[libpf.AddressOrLineno][]*string, error,
) {
var symTable *gosym.Table
var module *ModuleInfo
for i := range c.Modules {
table, err := gosymTable(store, &c.Modules[i])
if err != nil {
continue
} else if symTable != nil {
return nil, nil, errors.New("multiple go modules found")
}
symTable = table
module = &c.Modules[i]
}

addrs := map[libpf.AddressOrLineno][]*string{}
moduleName := filepath.Base(module.LocalPath)
for _, thread := range c.Threads {
for i, frame := range thread.Frames {
frameModuleName, addr, err := parseUnsymbolizedFrame(frame)
if err != nil {
continue
}

if frameModuleName != moduleName {
continue
}

addrs[addr] = append(addrs[addr], &thread.Frames[i])
}
}
return symTable, addrs, nil
}

func gosymTable(store *modulestore.Store, module *ModuleInfo) (*gosym.Table, error) {
reader, err := store.OpenReadAt(module.Ref)
if err != nil {
return nil, fmt.Errorf("failed to open module: %w", err)
}
defer reader.Close()

exe, err := elf.NewFile(reader)
if err != nil {
return nil, err
}

textSection := exe.Section(".text")
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if textSection == nil {
return nil, errors.New("missing .text section")
}

pclntab := exe.Section(".gopclntab")
if pclntab == nil {
return nil, errors.New("missing .gopclntab section")
}

lineTableData, err := pclntab.Data()
if err != nil {
return nil, err
}
lineTable := gosym.NewLineTable(lineTableData, textSection.Addr)
return gosym.NewTable(nil, lineTable)
}
9 changes: 7 additions & 2 deletions tools/coredump/json.go
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ package main
import (
"encoding/json"
"fmt"
"io"
"os"
"path/filepath"
"runtime"
Expand Down Expand Up @@ -73,13 +74,17 @@ func writeTestCase(path string, c *CoredumpTestCase, allowOverwrite bool) error
return fmt.Errorf("failed to create JSON file: %w", err)
}

enc := json.NewEncoder(jsonFile)
return writeTestCaseJSON(jsonFile, c)
}

// writeTestCaseJSON writes a test case to the given writer as JSON.
func writeTestCaseJSON(w io.Writer, c *CoredumpTestCase) error {
enc := json.NewEncoder(w)
enc.SetIndent("", " ")
enc.SetEscapeHTML(false)
if err := enc.Encode(c); err != nil {
return fmt.Errorf("JSON Marshall failed: %w", err)
}

return nil
}

Expand Down
1 change: 1 addition & 0 deletions tools/coredump/main.go
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@ func main() {
newRebaseCmd(store),
newUploadCmd(store),
newGdbCmd(store),
newGosymCmd(store),
},
Exec: func(context.Context, []string) error {
return flag.ErrHelp
Expand Down