cgo: handle versioned ELF symbols

Fixes issue 1397.

R=iant
CC=golang-dev
http://codereview.appspot.com/4444064

2 files changed, 166 insertions, 48 deletions

diff --git a/src/pkg/debug/elf/elf.go b/src/pkg/debug/elf/elf.go
index 74e979986..5d45b2486 100644
--- a/src/pkg/debug/elf/elf.go
+++ b/src/pkg/debug/elf/elf.go
@@ -330,29 +330,35 @@ func (i SectionIndex) GoString() string { return stringName(uint32(i), shnString
 type SectionType uint32
 
 const (
-	SHT_NULL          SectionType = 0          /* inactive */
-	SHT_PROGBITS      SectionType = 1          /* program defined information */
-	SHT_SYMTAB        SectionType = 2          /* symbol table section */
-	SHT_STRTAB        SectionType = 3          /* string table section */
-	SHT_RELA          SectionType = 4          /* relocation section with addends */
-	SHT_HASH          SectionType = 5          /* symbol hash table section */
-	SHT_DYNAMIC       SectionType = 6          /* dynamic section */
-	SHT_NOTE          SectionType = 7          /* note section */
-	SHT_NOBITS        SectionType = 8          /* no space section */
-	SHT_REL           SectionType = 9          /* relocation section - no addends */
-	SHT_SHLIB         SectionType = 10         /* reserved - purpose unknown */
-	SHT_DYNSYM        SectionType = 11         /* dynamic symbol table section */
-	SHT_INIT_ARRAY    SectionType = 14         /* Initialization function pointers. */
-	SHT_FINI_ARRAY    SectionType = 15         /* Termination function pointers. */
-	SHT_PREINIT_ARRAY SectionType = 16         /* Pre-initialization function ptrs. */
-	SHT_GROUP         SectionType = 17         /* Section group. */
-	SHT_SYMTAB_SHNDX  SectionType = 18         /* Section indexes (see SHN_XINDEX). */
-	SHT_LOOS          SectionType = 0x60000000 /* First of OS specific semantics */
-	SHT_HIOS          SectionType = 0x6fffffff /* Last of OS specific semantics */
-	SHT_LOPROC        SectionType = 0x70000000 /* reserved range for processor */
-	SHT_HIPROC        SectionType = 0x7fffffff /* specific section header types */
-	SHT_LOUSER        SectionType = 0x80000000 /* reserved range for application */
-	SHT_HIUSER        SectionType = 0xffffffff /* specific indexes */
+	SHT_NULL           SectionType = 0          /* inactive */
+	SHT_PROGBITS       SectionType = 1          /* program defined information */
+	SHT_SYMTAB         SectionType = 2          /* symbol table section */
+	SHT_STRTAB         SectionType = 3          /* string table section */
+	SHT_RELA           SectionType = 4          /* relocation section with addends */
+	SHT_HASH           SectionType = 5          /* symbol hash table section */
+	SHT_DYNAMIC        SectionType = 6          /* dynamic section */
+	SHT_NOTE           SectionType = 7          /* note section */
+	SHT_NOBITS         SectionType = 8          /* no space section */
+	SHT_REL            SectionType = 9          /* relocation section - no addends */
+	SHT_SHLIB          SectionType = 10         /* reserved - purpose unknown */
+	SHT_DYNSYM         SectionType = 11         /* dynamic symbol table section */
+	SHT_INIT_ARRAY     SectionType = 14         /* Initialization function pointers. */
+	SHT_FINI_ARRAY     SectionType = 15         /* Termination function pointers. */
+	SHT_PREINIT_ARRAY  SectionType = 16         /* Pre-initialization function ptrs. */
+	SHT_GROUP          SectionType = 17         /* Section group. */
+	SHT_SYMTAB_SHNDX   SectionType = 18         /* Section indexes (see SHN_XINDEX). */
+	SHT_LOOS           SectionType = 0x60000000 /* First of OS specific semantics */
+	SHT_GNU_ATTRIBUTES SectionType = 0x6ffffff5 /* GNU object attributes */
+	SHT_GNU_HASH       SectionType = 0x6ffffff6 /* GNU hash table */
+	SHT_GNU_LIBLIST    SectionType = 0x6ffffff7 /* GNU prelink library list */
+	SHT_GNU_VERDEF     SectionType = 0x6ffffffd /* GNU version definition section */
+	SHT_GNU_VERNEED    SectionType = 0x6ffffffe /* GNU version needs section */
+	SHT_GNU_VERSYM     SectionType = 0x6fffffff /* GNU version symbol table */
+	SHT_HIOS           SectionType = 0x6fffffff /* Last of OS specific semantics */
+	SHT_LOPROC         SectionType = 0x70000000 /* reserved range for processor */
+	SHT_HIPROC         SectionType = 0x7fffffff /* specific section header types */
+	SHT_LOUSER         SectionType = 0x80000000 /* reserved range for application */
+	SHT_HIUSER         SectionType = 0xffffffff /* specific indexes */
 )
 
 var shtStrings = []intName{
@@ -374,7 +380,12 @@ var shtStrings = []intName{
 	{17, "SHT_GROUP"},
 	{18, "SHT_SYMTAB_SHNDX"},
 	{0x60000000, "SHT_LOOS"},
-	{0x6fffffff, "SHT_HIOS"},
+	{0x6ffffff5, "SHT_GNU_ATTRIBUTES"},
+	{0x6ffffff6, "SHT_GNU_HASH"},
+	{0x6ffffff7, "SHT_GNU_LIBLIST"},
+	{0x6ffffffd, "SHT_GNU_VERDEF"},
+	{0x6ffffffe, "SHT_GNU_VERNEED"},
+	{0x6fffffff, "SHT_GNU_VERSYM"},
 	{0x70000000, "SHT_LOPROC"},
 	{0x7fffffff, "SHT_HIPROC"},
 	{0x80000000, "SHT_LOUSER"},
@@ -518,6 +529,9 @@ const (
 	DT_PREINIT_ARRAYSZ DynTag = 33         /* Size in bytes of the array of pre-initialization functions. */
 	DT_LOOS            DynTag = 0x6000000d /* First OS-specific */
 	DT_HIOS            DynTag = 0x6ffff000 /* Last OS-specific */
+	DT_VERSYM          DynTag = 0x6ffffff0
+	DT_VERNEED         DynTag = 0x6ffffffe
+	DT_VERNEEDNUM      DynTag = 0x6fffffff
 	DT_LOPROC          DynTag = 0x70000000 /* First processor-specific type. */
 	DT_HIPROC          DynTag = 0x7fffffff /* Last processor-specific type. */
 )
@@ -559,6 +573,9 @@ var dtStrings = []intName{
 	{33, "DT_PREINIT_ARRAYSZ"},
 	{0x6000000d, "DT_LOOS"},
 	{0x6ffff000, "DT_HIOS"},
+	{0x6ffffff0, "DT_VERSYM"},
+	{0x6ffffffe, "DT_VERNEED"},
+	{0x6fffffff, "DT_VERNEEDNUM"},
 	{0x70000000, "DT_LOPROC"},
 	{0x7fffffff, "DT_HIPROC"},
 }
diff --git a/src/pkg/debug/elf/file.go b/src/pkg/debug/elf/file.go
index 6fdcda6d4..9ae8b413d 100644
--- a/src/pkg/debug/elf/file.go
+++ b/src/pkg/debug/elf/file.go
@@ -35,9 +35,11 @@ type FileHeader struct {
 // A File represents an open ELF file.
 type File struct {
 	FileHeader
-	Sections []*Section
-	Progs    []*Prog
-	closer   io.Closer
+	Sections  []*Section
+	Progs     []*Prog
+	closer    io.Closer
+	gnuNeed   []verneed
+	gnuVersym []byte
 }
 
 // A SectionHeader represents a single ELF section header.
@@ -329,8 +331,8 @@ func NewFile(r io.ReaderAt) (*File, os.Error) {
 }
 
 // getSymbols returns a slice of Symbols from parsing the symbol table
-// with the given type.
-func (f *File) getSymbols(typ SectionType) ([]Symbol, os.Error) {
+// with the given type, along with the associated string table.
+func (f *File) getSymbols(typ SectionType) ([]Symbol, []byte, os.Error) {
 	switch f.Class {
 	case ELFCLASS64:
 		return f.getSymbols64(typ)
@@ -339,27 +341,27 @@ func (f *File) getSymbols(typ SectionType) ([]Symbol, os.Error) {
 		return f.getSymbols32(typ)
 	}
 
-	return nil, os.ErrorString("not implemented")
+	return nil, nil, os.ErrorString("not implemented")
 }
 
-func (f *File) getSymbols32(typ SectionType) ([]Symbol, os.Error) {
+func (f *File) getSymbols32(typ SectionType) ([]Symbol, []byte, os.Error) {
 	symtabSection := f.SectionByType(typ)
 	if symtabSection == nil {
-		return nil, os.ErrorString("no symbol section")
+		return nil, nil, os.ErrorString("no symbol section")
 	}
 
 	data, err := symtabSection.Data()
 	if err != nil {
-		return nil, os.ErrorString("cannot load symbol section")
+		return nil, nil, os.ErrorString("cannot load symbol section")
 	}
 	symtab := bytes.NewBuffer(data)
 	if symtab.Len()%Sym32Size != 0 {
-		return nil, os.ErrorString("length of symbol section is not a multiple of SymSize")
+		return nil, nil, os.ErrorString("length of symbol section is not a multiple of SymSize")
 	}
 
 	strdata, err := f.stringTable(symtabSection.Link)
 	if err != nil {
-		return nil, os.ErrorString("cannot load string table section")
+		return nil, nil, os.ErrorString("cannot load string table section")
 	}
 
 	// The first entry is all zeros.
@@ -382,27 +384,27 @@ func (f *File) getSymbols32(typ SectionType) ([]Symbol, os.Error) {
 		i++
 	}
 
-	return symbols, nil
+	return symbols, strdata, nil
 }
 
-func (f *File) getSymbols64(typ SectionType) ([]Symbol, os.Error) {
+func (f *File) getSymbols64(typ SectionType) ([]Symbol, []byte, os.Error) {
 	symtabSection := f.SectionByType(typ)
 	if symtabSection == nil {
-		return nil, os.ErrorString("no symbol section")
+		return nil, nil, os.ErrorString("no symbol section")
 	}
 
 	data, err := symtabSection.Data()
 	if err != nil {
-		return nil, os.ErrorString("cannot load symbol section")
+		return nil, nil, os.ErrorString("cannot load symbol section")
 	}
 	symtab := bytes.NewBuffer(data)
 	if symtab.Len()%Sym64Size != 0 {
-		return nil, os.ErrorString("length of symbol section is not a multiple of Sym64Size")
+		return nil, nil, os.ErrorString("length of symbol section is not a multiple of Sym64Size")
 	}
 
 	strdata, err := f.stringTable(symtabSection.Link)
 	if err != nil {
-		return nil, os.ErrorString("cannot load string table section")
+		return nil, nil, os.ErrorString("cannot load string table section")
 	}
 
 	// The first entry is all zeros.
@@ -425,7 +427,7 @@ func (f *File) getSymbols64(typ SectionType) ([]Symbol, os.Error) {
 		i++
 	}
 
-	return symbols, nil
+	return symbols, strdata, nil
 }
 
 // getString extracts a string from an ELF string table.
@@ -468,7 +470,7 @@ func (f *File) applyRelocationsAMD64(dst []byte, rels []byte) os.Error {
 		return os.ErrorString("length of relocation section is not a multiple of Sym64Size")
 	}
 
-	symbols, err := f.getSymbols(SHT_SYMTAB)
+	symbols, _, err := f.getSymbols(SHT_SYMTAB)
 	if err != nil {
 		return err
 	}
@@ -544,24 +546,123 @@ func (f *File) DWARF() (*dwarf.Data, os.Error) {
 	return dwarf.New(abbrev, nil, nil, info, nil, nil, nil, str)
 }
 
+type ImportedSymbol struct {
+	Name    string
+	Version string
+	Library string
+}
+
 // ImportedSymbols returns the names of all symbols
 // referred to by the binary f that are expected to be
 // satisfied by other libraries at dynamic load time.
 // It does not return weak symbols.
-func (f *File) ImportedSymbols() ([]string, os.Error) {
-	sym, err := f.getSymbols(SHT_DYNSYM)
+func (f *File) ImportedSymbols() ([]ImportedSymbol, os.Error) {
+	sym, str, err := f.getSymbols(SHT_DYNSYM)
 	if err != nil {
 		return nil, err
 	}
-	var all []string
-	for _, s := range sym {
+	f.gnuVersionInit(str)
+	var all []ImportedSymbol
+	for i, s := range sym {
 		if ST_BIND(s.Info) == STB_GLOBAL && s.Section == SHN_UNDEF {
-			all = append(all, s.Name)
+			all = append(all, ImportedSymbol{Name: s.Name})
+			f.gnuVersion(i, &all[len(all)-1])
 		}
 	}
 	return all, nil
 }
 
+type verneed struct {
+	File string
+	Name string
+}
+
+// gnuVersionInit parses the GNU version tables
+// for use by calls to gnuVersion.
+func (f *File) gnuVersionInit(str []byte) {
+	// Accumulate verneed information.
+	vn := f.SectionByType(SHT_GNU_VERNEED)
+	if vn == nil {
+		return
+	}
+	d, _ := vn.Data()
+
+	var need []verneed
+	i := 0
+	for {
+		if i+16 > len(d) {
+			break
+		}
+		vers := f.ByteOrder.Uint16(d[i : i+2])
+		if vers != 1 {
+			break
+		}
+		cnt := f.ByteOrder.Uint16(d[i+2 : i+4])
+		fileoff := f.ByteOrder.Uint32(d[i+4 : i+8])
+		aux := f.ByteOrder.Uint32(d[i+8 : i+12])
+		next := f.ByteOrder.Uint32(d[i+12 : i+16])
+		file, _ := getString(str, int(fileoff))
+
+		var name string
+		j := i + int(aux)
+		for c := 0; c < int(cnt); c++ {
+			if j+16 > len(d) {
+				break
+			}
+			// hash := f.ByteOrder.Uint32(d[j:j+4])
+			// flags := f.ByteOrder.Uint16(d[j+4:j+6])
+			other := f.ByteOrder.Uint16(d[j+6 : j+8])
+			nameoff := f.ByteOrder.Uint32(d[j+8 : j+12])
+			next := f.ByteOrder.Uint32(d[j+12 : j+16])
+			name, _ = getString(str, int(nameoff))
+			ndx := int(other)
+			if ndx >= len(need) {
+				a := make([]verneed, 2*(ndx+1))
+				copy(a, need)
+				need = a
+			}
+
+			need[ndx] = verneed{file, name}
+			if next == 0 {
+				break
+			}
+			j += int(next)
+		}
+
+		if next == 0 {
+			break
+		}
+		i += int(next)
+	}
+
+	// Versym parallels symbol table, indexing into verneed.
+	vs := f.SectionByType(SHT_GNU_VERSYM)
+	if vs == nil {
+		return
+	}
+	d, _ = vs.Data()
+
+	f.gnuNeed = need
+	f.gnuVersym = d
+}
+
+// gnuVersion adds Library and Version information to sym,
+// which came from offset i of the symbol table.
+func (f *File) gnuVersion(i int, sym *ImportedSymbol) {
+	// Each entry is two bytes; skip undef entry at beginning.
+	i = (i + 1) * 2
+	if i >= len(f.gnuVersym) {
+		return
+	}
+	j := int(f.ByteOrder.Uint16(f.gnuVersym[i:]))
+	if j < 2 || j >= len(f.gnuNeed) {
+		return
+	}
+	n := &f.gnuNeed[j]
+	sym.Library = n.File
+	sym.Version = n.Name
+}
+
 // ImportedLibraries returns the names of all libraries
 // referred to by the binary f that are expected to be
 // linked with the binary at dynamic link time.