1// Copyright 2021 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package decodemeta
6
7// This package contains APIs and helpers for decoding a single package's
8// meta data "blob" emitted by the compiler when coverage instrumentation
9// is turned on.
10
11import (
12	"encoding/binary"
13	"fmt"
14	"internal/coverage"
15	"internal/coverage/slicereader"
16	"internal/coverage/stringtab"
17	"io"
18	"os"
19)
20
21// See comments in the encodecovmeta package for details on the format.
22
23type CoverageMetaDataDecoder struct {
24	r      *slicereader.Reader
25	hdr    coverage.MetaSymbolHeader
26	strtab *stringtab.Reader
27	tmp    []byte
28	debug  bool
29}
30
31func NewCoverageMetaDataDecoder(b []byte, readonly bool) (*CoverageMetaDataDecoder, error) {
32	slr := slicereader.NewReader(b, readonly)
33	x := &CoverageMetaDataDecoder{
34		r:   slr,
35		tmp: make([]byte, 0, 256),
36	}
37	if err := x.readHeader(); err != nil {
38		return nil, err
39	}
40	if err := x.readStringTable(); err != nil {
41		return nil, err
42	}
43	return x, nil
44}
45
46func (d *CoverageMetaDataDecoder) readHeader() error {
47	if err := binary.Read(d.r, binary.LittleEndian, &d.hdr); err != nil {
48		return err
49	}
50	if d.debug {
51		fmt.Fprintf(os.Stderr, "=-= after readHeader: %+v\n", d.hdr)
52	}
53	return nil
54}
55
56func (d *CoverageMetaDataDecoder) readStringTable() error {
57	// Seek to the correct location to read the string table.
58	stringTableLocation := int64(coverage.CovMetaHeaderSize + 4*d.hdr.NumFuncs)
59	if _, err := d.r.Seek(stringTableLocation, io.SeekStart); err != nil {
60		return err
61	}
62
63	// Read the table itself.
64	d.strtab = stringtab.NewReader(d.r)
65	d.strtab.Read()
66	return nil
67}
68
69func (d *CoverageMetaDataDecoder) PackagePath() string {
70	return d.strtab.Get(d.hdr.PkgPath)
71}
72
73func (d *CoverageMetaDataDecoder) PackageName() string {
74	return d.strtab.Get(d.hdr.PkgName)
75}
76
77func (d *CoverageMetaDataDecoder) ModulePath() string {
78	return d.strtab.Get(d.hdr.ModulePath)
79}
80
81func (d *CoverageMetaDataDecoder) NumFuncs() uint32 {
82	return d.hdr.NumFuncs
83}
84
85// ReadFunc reads the coverage meta-data for the function with index
86// 'findex', filling it into the FuncDesc pointed to by 'f'.
87func (d *CoverageMetaDataDecoder) ReadFunc(fidx uint32, f *coverage.FuncDesc) error {
88	if fidx >= d.hdr.NumFuncs {
89		return fmt.Errorf("illegal function index")
90	}
91
92	// Seek to the correct location to read the function offset and read it.
93	funcOffsetLocation := int64(coverage.CovMetaHeaderSize + 4*fidx)
94	if _, err := d.r.Seek(funcOffsetLocation, io.SeekStart); err != nil {
95		return err
96	}
97	foff := d.r.ReadUint32()
98
99	// Check assumptions
100	if foff < uint32(funcOffsetLocation) || foff > d.hdr.Length {
101		return fmt.Errorf("malformed func offset %d", foff)
102	}
103
104	// Seek to the correct location to read the function.
105	floc := int64(foff)
106	if _, err := d.r.Seek(floc, io.SeekStart); err != nil {
107		return err
108	}
109
110	// Preamble containing number of units, file, and function.
111	numUnits := uint32(d.r.ReadULEB128())
112	fnameidx := uint32(d.r.ReadULEB128())
113	fileidx := uint32(d.r.ReadULEB128())
114
115	f.Srcfile = d.strtab.Get(fileidx)
116	f.Funcname = d.strtab.Get(fnameidx)
117
118	// Now the units
119	f.Units = f.Units[:0]
120	if cap(f.Units) < int(numUnits) {
121		f.Units = make([]coverage.CoverableUnit, 0, numUnits)
122	}
123	for k := uint32(0); k < numUnits; k++ {
124		f.Units = append(f.Units,
125			coverage.CoverableUnit{
126				StLine:  uint32(d.r.ReadULEB128()),
127				StCol:   uint32(d.r.ReadULEB128()),
128				EnLine:  uint32(d.r.ReadULEB128()),
129				EnCol:   uint32(d.r.ReadULEB128()),
130				NxStmts: uint32(d.r.ReadULEB128()),
131			})
132	}
133	lit := d.r.ReadULEB128()
134	f.Lit = lit != 0
135	return nil
136}
137