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Source file src/debug/dwarf/unit.go

Documentation: debug/dwarf

     1  // Copyright 2009 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  
     5  package dwarf
     6  
     7  import (
     8  	"sort"
     9  	"strconv"
    10  )
    11  
    12  // DWARF debug info is split into a sequence of compilation units.
    13  // Each unit has its own abbreviation table and address size.
    14  
    15  type unit struct {
    16  	base   Offset // byte offset of header within the aggregate info
    17  	off    Offset // byte offset of data within the aggregate info
    18  	data   []byte
    19  	atable abbrevTable
    20  	asize  int
    21  	vers   int
    22  	utype  uint8 // DWARF 5 unit type
    23  	is64   bool  // True for 64-bit DWARF format
    24  }
    25  
    26  // Implement the dataFormat interface.
    27  
    28  func (u *unit) version() int {
    29  	return u.vers
    30  }
    31  
    32  func (u *unit) dwarf64() (bool, bool) {
    33  	return u.is64, true
    34  }
    35  
    36  func (u *unit) addrsize() int {
    37  	return u.asize
    38  }
    39  
    40  func (d *Data) parseUnits() ([]unit, error) {
    41  	// Count units.
    42  	nunit := 0
    43  	b := makeBuf(d, unknownFormat{}, "info", 0, d.info)
    44  	for len(b.data) > 0 {
    45  		len, _ := b.unitLength()
    46  		if len != Offset(uint32(len)) {
    47  			b.error("unit length overflow")
    48  			break
    49  		}
    50  		b.skip(int(len))
    51  		nunit++
    52  	}
    53  	if b.err != nil {
    54  		return nil, b.err
    55  	}
    56  
    57  	// Again, this time writing them down.
    58  	b = makeBuf(d, unknownFormat{}, "info", 0, d.info)
    59  	units := make([]unit, nunit)
    60  	for i := range units {
    61  		u := &units[i]
    62  		u.base = b.off
    63  		var n Offset
    64  		n, u.is64 = b.unitLength()
    65  		dataOff := b.off
    66  		vers := b.uint16()
    67  		if vers < 2 || vers > 5 {
    68  			b.error("unsupported DWARF version " + strconv.Itoa(int(vers)))
    69  			break
    70  		}
    71  		u.vers = int(vers)
    72  		if vers >= 5 {
    73  			u.utype = b.uint8()
    74  			u.asize = int(b.uint8())
    75  		}
    76  		var abbrevOff uint64
    77  		if u.is64 {
    78  			abbrevOff = b.uint64()
    79  		} else {
    80  			abbrevOff = uint64(b.uint32())
    81  		}
    82  		atable, err := d.parseAbbrev(abbrevOff, u.vers)
    83  		if err != nil {
    84  			if b.err == nil {
    85  				b.err = err
    86  			}
    87  			break
    88  		}
    89  		u.atable = atable
    90  		if vers < 5 {
    91  			u.asize = int(b.uint8())
    92  		}
    93  
    94  		switch u.utype {
    95  		case utSkeleton, utSplitCompile:
    96  			b.uint64() // unit ID
    97  		case utType, utSplitType:
    98  			b.uint64()  // type signature
    99  			if u.is64 { // type offset
   100  				b.uint64()
   101  			} else {
   102  				b.uint32()
   103  			}
   104  		}
   105  
   106  		u.off = b.off
   107  		u.data = b.bytes(int(n - (b.off - dataOff)))
   108  	}
   109  	if b.err != nil {
   110  		return nil, b.err
   111  	}
   112  	return units, nil
   113  }
   114  
   115  // offsetToUnit returns the index of the unit containing offset off.
   116  // It returns -1 if no unit contains this offset.
   117  func (d *Data) offsetToUnit(off Offset) int {
   118  	// Find the unit after off
   119  	next := sort.Search(len(d.unit), func(i int) bool {
   120  		return d.unit[i].off > off
   121  	})
   122  	if next == 0 {
   123  		return -1
   124  	}
   125  	u := &d.unit[next-1]
   126  	if u.off <= off && off < u.off+Offset(len(u.data)) {
   127  		return next - 1
   128  	}
   129  	return -1
   130  }
   131  

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