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runtime: support DT_GNU_HASH in VDSO

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Currently we only support finding symbols in the VDSO using the old
DT_HASH. These days everything uses DT_GNU_HASH instead. To keep up
with the times and future-proof against DT_HASH disappearing from the
VDSO in the future, this commit adds support for DT_GNU_HASH and
prefers it over DT_HASH.

Tested by making sure it found a DT_GNU_HASH section and all of the
expected symbols in it, and then disabling the DT_GNU_HASH path and
making sure the old DT_HASH path still found all of the symbols.

Fixes #19649.

Change-Id: I508c8b35a019330d2c32f04f3833b69cb2686f13
Reviewed-on: https://go-review.googlesource.com/45511
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Austin Clements 2017-06-13 08:52:53 -04:00
parent 816deacc70
commit 9065c3bf34
1 changed files with 79 additions and 33 deletions
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112
src/runtime/vdso_linux_amd64.go
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@ -23,12 +23,13 @@ const (
_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_VERSYM = 0x6ffffff0
_DT_VERDEF = 0x6ffffffc
_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 */
@ -126,6 +127,7 @@ type elf64Auxv struct {
type symbol_key struct {
name string
sym_hash uint32
gnu_hash uint32
ptr *uintptr
}
@ -146,6 +148,8 @@ type vdso_info struct {
symstrings *[1 << 32]byte
chain []uint32
bucket []uint32
symOff uint32
isGNUHash bool
/* Version table */
versym *[1 << 32]uint16
@ -155,9 +159,9 @@ type vdso_info struct {
var linux26 = version_key{"LINUX_2.6", 0x3ae75f6}
var sym_keys = []symbol_key{
{"__vdso_time", 0xa33c485, &__vdso_time_sym},
{"__vdso_gettimeofday", 0x315ca59, &__vdso_gettimeofday_sym},
{"__vdso_clock_gettime", 0xd35ec75, &__vdso_clock_gettime_sym},
{"__vdso_time", 0xa33c485, 0x821e8e0d, &__vdso_time_sym},
{"__vdso_gettimeofday", 0x315ca59, 0xb01bca00, &__vdso_gettimeofday_sym},
{"__vdso_clock_gettime", 0xd35ec75, 0x6e43a318, &__vdso_clock_gettime_sym},
}
// initialize with vsyscall fallbacks
@ -197,8 +201,7 @@ func vdso_init_from_sysinfo_ehdr(info *vdso_info, hdr *elf64Ehdr) {
// Fish out the useful bits of the dynamic table.
var hash *[1 << 30]uint32
hash = nil
var hash, gnuhash *[1 << 30]uint32
info.symstrings = nil
info.symtab = nil
info.versym = nil
@ -213,6 +216,8 @@ func vdso_init_from_sysinfo_ehdr(info *vdso_info, hdr *elf64Ehdr) {
info.symtab = (*[1 << 32]elf64Sym)(unsafe.Pointer(p))
case _DT_HASH:
hash = (*[1 << 30]uint32)(unsafe.Pointer(p))
case _DT_GNU_HASH:
gnuhash = (*[1 << 30]uint32)(unsafe.Pointer(p))
case _DT_VERSYM:
info.versym = (*[1 << 32]uint16)(unsafe.Pointer(p))
case _DT_VERDEF:
@ -220,7 +225,7 @@ func vdso_init_from_sysinfo_ehdr(info *vdso_info, hdr *elf64Ehdr) {
}
}
if info.symstrings == nil || info.symtab == nil || hash == nil {
if info.symstrings == nil || info.symtab == nil || (hash == nil && gnuhash == nil) {
return // Failed
}
@ -228,11 +233,21 @@ func vdso_init_from_sysinfo_ehdr(info *vdso_info, hdr *elf64Ehdr) {
info.versym = nil
}
// 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]
if gnuhash != nil {
// Parse the GNU hash table header.
nbucket := gnuhash[0]
info.symOff = gnuhash[1]
bloomSize := gnuhash[2]
info.bucket = gnuhash[4+bloomSize*2:][:nbucket]
info.chain = gnuhash[4+bloomSize*2+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
@ -266,25 +281,56 @@ func vdso_parse_symbols(info *vdso_info, version int32) {
return
}
apply := func(symIndex uint32, k symbol_key) bool {
sym := &info.symtab[symIndex]
typ := _ELF64_ST_TYPE(sym.st_info)
bind := _ELF64_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 {
for chain := info.bucket[k.sym_hash%uint32(len(info.bucket))]; chain != 0; chain = info.chain[chain] {
sym := &info.symtab[chain]
typ := _ELF64_ST_TYPE(sym.st_info)
bind := _ELF64_ST_BIND(sym.st_info)
if typ != _STT_FUNC || bind != _STB_GLOBAL && bind != _STB_WEAK || sym.st_shndx == _SHN_UNDEF {
continue
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 k.name != gostringnocopy(&info.symstrings[sym.st_name]) {
continue
if hash&1 != 0 {
// End of chain.
break
}
// Check symbol version.
if info.versym != nil && version != 0 && int32(info.versym[chain]&0x7fff) != version {
continue
}
*k.ptr = info.load_offset + uintptr(sym.st_value)
break
}
}
}