227 lines
7.4 KiB
Go
227 lines
7.4 KiB
Go
package wasmdebug
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import (
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"debug/dwarf"
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"errors"
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"fmt"
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"io"
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"sort"
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"strings"
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"sync"
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)
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// DWARFLines is used to retrieve source code line information from the DWARF data.
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type DWARFLines struct {
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// d is created by DWARF custom sections.
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d *dwarf.Data
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// linesPerEntry maps dwarf.Offset for dwarf.Entry to the list of lines contained by the entry.
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// The value is sorted in the increasing order by the address.
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linesPerEntry map[dwarf.Offset][]line
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mux sync.Mutex
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}
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type line struct {
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addr uint64
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pos dwarf.LineReaderPos
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}
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// NewDWARFLines returns DWARFLines for the given *dwarf.Data.
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func NewDWARFLines(d *dwarf.Data) *DWARFLines {
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if d == nil {
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return nil
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}
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return &DWARFLines{d: d, linesPerEntry: map[dwarf.Offset][]line{}}
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}
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// isTombstoneAddr returns true if the given address is invalid a.k.a tombstone address which was made no longer valid
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// by linker. According to the DWARF spec[1], the value is encoded as 0xffffffff for Wasm (as 32-bit target),
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// but some tools encode it either in -1, -2 [2] or 1<<32 (This might not be by tools, but by debug/dwarf package's bug).
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//
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// [1] https://dwarfstd.org/issues/200609.1.html
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// [2] https://github.com/WebAssembly/binaryen/blob/97178d08d4a20d2a5e3a6be813fc6a7079ef86e1/src/wasm/wasm-debug.cpp#L651-L660
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// [3] https://reviews.llvm.org/D81784
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func isTombstoneAddr(addr uint64) bool {
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addr32 := int32(addr)
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return addr32 == -1 || addr32 == -2 ||
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addr32 == 0 // This covers 1 <<32.
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}
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// Line returns the line information for the given instructionOffset which is an offset in
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// the code section of the original Wasm binary. Returns empty string if the info is not found.
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func (d *DWARFLines) Line(instructionOffset uint64) (ret []string) {
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if d == nil {
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return
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}
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// DWARFLines is created per Wasm binary, so there's a possibility that multiple instances
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// created from a same binary face runtime error at the same time, and that results in
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// concurrent access to this function.
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d.mux.Lock()
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defer d.mux.Unlock()
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r := d.d.Reader()
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var inlinedRoutines []*dwarf.Entry
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var cu *dwarf.Entry
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var inlinedDone bool
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entry:
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for {
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ent, err := r.Next()
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if err != nil || ent == nil {
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break
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}
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// If we already found the compilation unit and relevant inlined routines, we can stop searching entries.
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if cu != nil && inlinedDone {
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break
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}
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switch ent.Tag {
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case dwarf.TagCompileUnit, dwarf.TagInlinedSubroutine:
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default:
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// Only CompileUnit and InlinedSubroutines are relevant.
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continue
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}
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// Check if the entry spans the range which contains the target instruction.
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ranges, err := d.d.Ranges(ent)
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if err != nil {
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continue
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}
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for _, pcs := range ranges {
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start, end := pcs[0], pcs[1]
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if isTombstoneAddr(start) || isTombstoneAddr(end) {
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continue
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}
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if start <= instructionOffset && instructionOffset < end {
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switch ent.Tag {
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case dwarf.TagCompileUnit:
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cu = ent
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case dwarf.TagInlinedSubroutine:
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inlinedRoutines = append(inlinedRoutines, ent)
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// Search inlined subroutines until all the children.
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inlinedDone = !ent.Children
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// Not that "children" in the DWARF spec is defined as the next entry to this entry.
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// See "2.3 Relationship of Debugging Information Entries" in https://dwarfstd.org/doc/DWARF4.pdf
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}
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continue entry
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}
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}
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}
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// If the relevant compilation unit is not found, nothing we can do with this DWARF info.
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if cu == nil {
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return
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}
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lineReader, err := d.d.LineReader(cu)
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if err != nil || lineReader == nil {
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return
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}
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var lines []line
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var ok bool
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var le dwarf.LineEntry
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// Get the lines inside the entry.
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if lines, ok = d.linesPerEntry[cu.Offset]; !ok {
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// If not found, we create the list of lines by reading all the LineEntries in the Entry.
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//
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// Note that the dwarf.LineEntry.SeekPC API shouldn't be used because the Go's dwarf package assumes that
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// all the line entries in an Entry are sorted in increasing order which *might not* be true
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// for some languages. Such order requirement is not a part of DWARF specification,
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// and in fact Zig language tends to emit interleaved line information.
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//
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// Thus, here we read all line entries here, and sort them in the increasing order wrt addresses.
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for {
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pos := lineReader.Tell()
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err = lineReader.Next(&le)
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if errors.Is(err, io.EOF) {
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break
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} else if err != nil {
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return
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}
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// TODO: Maybe we should ignore tombstone addresses by using isTombstoneAddr,
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// but not sure if that would be an issue in practice.
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lines = append(lines, line{addr: le.Address, pos: pos})
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}
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sort.Slice(lines, func(i, j int) bool { return lines[i].addr < lines[j].addr })
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d.linesPerEntry[cu.Offset] = lines // Caches for the future inquiries for the same Entry.
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}
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// Now we have the lines for this entry. We can find the corresponding source line for instructionOffset
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// via binary search on the list.
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n := len(lines)
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index := sort.Search(n, func(i int) bool { return lines[i].addr >= instructionOffset })
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if index == n { // This case the address is not found. See the doc sort.Search.
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return
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}
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ln := lines[index]
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if ln.addr != instructionOffset {
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// If the address doesn't match exactly, the previous entry is the one that contains the instruction.
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// That can happen anytime as the DWARF spec allows it, and other tools can handle it in this way conventionally
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// https://github.com/gimli-rs/addr2line/blob/3a2dbaf84551a06a429f26e9c96071bb409b371f/src/lib.rs#L236-L242
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// https://github.com/kateinoigakukun/wasminspect/blob/f29f052f1b03104da9f702508ac0c1bbc3530ae4/crates/debugger/src/dwarf/mod.rs#L453-L459
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if index-1 < 0 {
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return
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}
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ln = lines[index-1]
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}
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// Advance the line reader for the found position.
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lineReader.Seek(ln.pos)
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err = lineReader.Next(&le)
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if err != nil {
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// If we reach this block, that means there's a bug in the []line creation logic above.
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panic("BUG: stored dwarf.LineReaderPos is invalid")
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}
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// In the inlined case, the line info is the innermost inlined function call.
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inlined := len(inlinedRoutines) != 0
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prefix := fmt.Sprintf("%#x: ", instructionOffset)
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ret = append(ret, formatLine(prefix, le.File.Name, int64(le.Line), int64(le.Column), inlined))
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if inlined {
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prefix = strings.Repeat(" ", len(prefix))
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files := lineReader.Files()
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// inlinedRoutines contain the inlined call information in the reverse order (children is higher than parent),
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// so we traverse the reverse order and emit the inlined calls.
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for i := len(inlinedRoutines) - 1; i >= 0; i-- {
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inlined := inlinedRoutines[i]
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fileIndex, ok := inlined.Val(dwarf.AttrCallFile).(int64)
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if !ok {
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return
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} else if fileIndex >= int64(len(files)) {
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// This in theory shouldn't happen according to the spec, but guard against ill-formed DWARF info.
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return
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}
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fileName := files[fileIndex]
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line, _ := inlined.Val(dwarf.AttrCallLine).(int64)
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col, _ := inlined.Val(dwarf.AttrCallColumn).(int64)
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ret = append(ret, formatLine(prefix, fileName.Name, line, col,
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// Last one is the origin of the inlined function calls.
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i != 0))
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}
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}
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return
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}
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func formatLine(prefix, fileName string, line, col int64, inlined bool) string {
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builder := strings.Builder{}
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builder.WriteString(prefix)
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builder.WriteString(fileName)
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if line != 0 {
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builder.WriteString(fmt.Sprintf(":%d", line))
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if col != 0 {
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builder.WriteString(fmt.Sprintf(":%d", col))
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}
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}
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if inlined {
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builder.WriteString(" (inlined)")
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}
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return builder.String()
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}
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