// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build linux
// +build 386 amd64
package runtime
import "unsafe"
// Look up symbols in the Linux vDSO.
// This code was originally based on the sample Linux vDSO parser at
// https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/vDSO/parse_vdso.c
// This implements the ELF dynamic linking spec at
// http://sco.com/developers/gabi/latest/ch5.dynamic.html
// The version section is documented at
// http://refspecs.linuxfoundation.org/LSB_3.2.0/LSB-Core-generic/LSB-Core-generic/symversion.html
const (
_AT_SYSINFO_EHDR = 33
_PT_LOAD = 1 /* Loadable program segment */
_PT_DYNAMIC = 2 /* Dynamic linking information */
_DT_NULL = 0 /* Marks end of dynamic section */
_DT_HASH = 4 /* Dynamic symbol hash table */
_DT_STRTAB = 5 /* Address of string table */
_DT_SYMTAB = 6 /* Address of symbol table */
_DT_GNU_HASH = 0x6ffffef5 /* GNU-style dynamic symbol hash table */
_DT_VERSYM = 0x6ffffff0
_DT_VERDEF = 0x6ffffffc
_VER_FLG_BASE = 0x1 /* Version definition of file itself */
_SHN_UNDEF = 0 /* Undefined section */
_SHT_DYNSYM = 11 /* Dynamic linker symbol table */
_STT_FUNC = 2 /* Symbol is a code object */
_STB_GLOBAL = 1 /* Global symbol */
_STB_WEAK = 2 /* Weak symbol */
_EI_NIDENT = 16
// Maximum indices for the array types used when traversing the vDSO ELF structures.
// Computed from architecture-specific max provided by vdso_linux_*.go
vdsoSymTabSize = vdsoArrayMax / unsafe.Sizeof(elfSym{})
vdsoDynSize = vdsoArrayMax / unsafe.Sizeof(elfDyn{})
vdsoSymStringsSize = vdsoArrayMax // byte
vdsoVerSymSize = vdsoArrayMax / 2 // uint16
vdsoHashSize = vdsoArrayMax / 4 // uint32
// vdsoBloomSizeScale is a scaling factor for gnuhash tables which are uint32 indexed,
// but contain uintptrs
vdsoBloomSizeScale = unsafe.Sizeof(uintptr(0)) / 4 // uint32
)
/* How to extract and insert information held in the st_info field. */
func _ELF_ST_BIND(val byte) byte { return val >> 4 }
func _ELF_ST_TYPE(val byte) byte { return val & 0xf }
type symbol_key struct {
name string
sym_hash uint32
gnu_hash uint32
ptr *uintptr
}
type version_key struct {
version string
ver_hash uint32
}
type vdso_info struct {
valid bool
/* Load information */
load_addr uintptr
load_offset uintptr /* load_addr - recorded vaddr */
/* Symbol table */
symtab *[vdsoSymTabSize]elfSym
symstrings *[vdsoSymStringsSize]byte
chain []uint32
bucket []uint32
symOff uint32
isGNUHash bool
/* Version table */
versym *[vdsoVerSymSize]uint16
verdef *elfVerdef
}
var linux26 = version_key{"LINUX_2.6", 0x3ae75f6}
// see vdso_linux_*.go for sym_keys[] and __vdso_* vars
func vdso_init_from_sysinfo_ehdr(info *vdso_info, hdr *elfEhdr) {
info.valid = false
info.load_addr = uintptr(unsafe.Pointer(hdr))
pt := unsafe.Pointer(info.load_addr + uintptr(hdr.e_phoff))
// We need two things from the segment table: the load offset
// and the dynamic table.
var found_vaddr bool
var dyn *[vdsoDynSize]elfDyn
for i := uint16(0); i < hdr.e_phnum; i++ {
pt := (*elfPhdr)(add(pt, uintptr(i)*unsafe.Sizeof(elfPhdr{})))
switch pt.p_type {
case _PT_LOAD:
if !found_vaddr {
found_vaddr = true
info.load_offset = info.load_addr + uintptr(pt.p_offset-pt.p_vaddr)
}
case _PT_DYNAMIC:
dyn = (*[vdsoDynSize]elfDyn)(unsafe.Pointer(info.load_addr + uintptr(pt.p_offset)))
}
}
if !found_vaddr || dyn == nil {
return // Failed
}
// Fish out the useful bits of the dynamic table.
var hash, gnuhash *[vdsoHashSize]uint32
info.symstrings = nil
info.symtab = nil
info.versym = nil
info.verdef = nil
for i := 0; dyn[i].d_tag != _DT_NULL; i++ {
dt := &dyn[i]
p := info.load_offset + uintptr(dt.d_val)
switch dt.d_tag {
case _DT_STRTAB:
info.symstrings = (*[vdsoSymStringsSize]byte)(unsafe.Pointer(p))
case _DT_SYMTAB:
info.symtab = (*[vdsoSymTabSize]elfSym)(unsafe.Pointer(p))
case _DT_HASH:
hash = (*[vdsoHashSize]uint32)(unsafe.Pointer(p))
case _DT_GNU_HASH:
gnuhash = (*[vdsoHashSize]uint32)(unsafe.Pointer(p))
case _DT_VERSYM:
info.versym = (*[vdsoVerSymSize]uint16)(unsafe.Pointer(p))
case _DT_VERDEF:
info.verdef = (*elfVerdef)(unsafe.Pointer(p))
}
}
if info.symstrings == nil || info.symtab == nil || (hash == nil && gnuhash == nil) {
return // Failed
}
if info.verdef == nil {
info.versym = nil
}
if gnuhash != nil {
// Parse the GNU hash table header.
nbucket := gnuhash[0]
info.symOff = gnuhash[1]
bloomSize := gnuhash[2]
info.bucket = gnuhash[4+bloomSize*uint32(vdsoBloomSizeScale):][:nbucket]
info.chain = gnuhash[4+bloomSize*uint32(vdsoBloomSizeScale)+nbucket:]
info.isGNUHash = true
} else {
// Parse the hash table header.
nbucket := hash[0]
nchain := hash[1]
info.bucket = hash[2 : 2+nbucket]
info.chain = hash[2+nbucket : 2+nbucket+nchain]
}
// That's all we need.
info.valid = true
}
func vdso_find_version(info *vdso_info, ver *version_key) int32 {
if !info.valid {
return 0
}
def := info.verdef
for {
if def.vd_flags&_VER_FLG_BASE == 0 {
aux := (*elfVerdaux)(add(unsafe.Pointer(def), uintptr(def.vd_aux)))
if def.vd_hash == ver.ver_hash && ver.version == gostringnocopy(&info.symstrings[aux.vda_name]) {
return int32(def.vd_ndx & 0x7fff)
}
}
if def.vd_next == 0 {
break
}
def = (*elfVerdef)(add(unsafe.Pointer(def), uintptr(def.vd_next)))
}
return -1 // cannot match any version
}
func vdso_parse_symbols(info *vdso_info, version int32) {
if !info.valid {
return
}
apply := func(symIndex uint32, k symbol_key) bool {
sym := &info.symtab[symIndex]
typ := _ELF_ST_TYPE(sym.st_info)
bind := _ELF_ST_BIND(sym.st_info)
if typ != _STT_FUNC || bind != _STB_GLOBAL && bind != _STB_WEAK || sym.st_shndx == _SHN_UNDEF {
return false
}
if k.name != gostringnocopy(&info.symstrings[sym.st_name]) {
return false
}
// Check symbol version.
if info.versym != nil && version != 0 && int32(info.versym[symIndex]&0x7fff) != version {
return false
}
*k.ptr = info.load_offset + uintptr(sym.st_value)
return true
}
if !info.isGNUHash {
// Old-style DT_HASH table.
for _, k := range sym_keys {
for chain := info.bucket[k.sym_hash%uint32(len(info.bucket))]; chain != 0; chain = info.chain[chain] {
if apply(chain, k) {
break
}
}
}
return
}
// New-style DT_GNU_HASH table.
for _, k := range sym_keys {
symIndex := info.bucket[k.gnu_hash%uint32(len(info.bucket))]
if symIndex < info.symOff {
continue
}
for ; ; symIndex++ {
hash := info.chain[symIndex-info.symOff]
if hash|1 == k.gnu_hash|1 {
// Found a hash match.
if apply(symIndex, k) {
break
}
}
if hash&1 != 0 {
// End of chain.
break
}
}
}
}
func archauxv(tag, val uintptr) {
switch tag {
case _AT_SYSINFO_EHDR:
if val == 0 {
// Something went wrong
return
}
var info vdso_info
// TODO(rsc): I don't understand why the compiler thinks info escapes
// when passed to the three functions below.
info1 := (*vdso_info)(noescape(unsafe.Pointer(&info)))
vdso_init_from_sysinfo_ehdr(info1, (*elfEhdr)(unsafe.Pointer(val)))
vdso_parse_symbols(info1, vdso_find_version(info1, &linux26))
}
}