1 files changed, 295 insertions, 0 deletions
diff --git a/src/runtime/vdso_linux.go b/src/runtime/vdso_linux.go
new file mode 100644
index 0000000..4523615
--- /dev/null
+++ b/src/runtime/vdso_linux.go
@@ -0,0 +1,295 @@
+// 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.
+
+//go:build linux && (386 || amd64 || arm || arm64 || loong64 || mips64 || mips64le || ppc64 || ppc64le || riscv64 || s390x)
+
+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
+// https://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 */
+
+	_STT_NOTYPE = 0 /* Symbol type is not specified */
+
+	_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 vdsoSymbolKey struct {
+	name    string
+	symHash uint32
+	gnuHash uint32
+	ptr     *uintptr
+}
+
+type vdsoVersionKey struct {
+	version string
+	verHash uint32
+}
+
+type vdsoInfo struct {
+	valid bool
+
+	/* Load information */
+	loadAddr   uintptr
+	loadOffset uintptr /* loadAddr - 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
+}
+
+// see vdso_linux_*.go for vdsoSymbolKeys[] and vdso*Sym vars
+
+func vdsoInitFromSysinfoEhdr(info *vdsoInfo, hdr *elfEhdr) {
+	info.valid = false
+	info.loadAddr = uintptr(unsafe.Pointer(hdr))
+
+	pt := unsafe.Pointer(info.loadAddr + uintptr(hdr.e_phoff))
+
+	// We need two things from the segment table: the load offset
+	// and the dynamic table.
+	var foundVaddr 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 !foundVaddr {
+				foundVaddr = true
+				info.loadOffset = info.loadAddr + uintptr(pt.p_offset-pt.p_vaddr)
+			}
+
+		case _PT_DYNAMIC:
+			dyn = (*[vdsoDynSize]elfDyn)(unsafe.Pointer(info.loadAddr + uintptr(pt.p_offset)))
+		}
+	}
+
+	if !foundVaddr || 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.loadOffset + 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 vdsoFindVersion(info *vdsoInfo, ver *vdsoVersionKey) 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.verHash && 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 vdsoParseSymbols(info *vdsoInfo, version int32) {
+	if !info.valid {
+		return
+	}
+
+	apply := func(symIndex uint32, k vdsoSymbolKey) bool {
+		sym := &info.symtab[symIndex]
+		typ := _ELF_ST_TYPE(sym.st_info)
+		bind := _ELF_ST_BIND(sym.st_info)
+		// On ppc64x, VDSO functions are of type _STT_NOTYPE.
+		if typ != _STT_FUNC && typ != _STT_NOTYPE || 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.loadOffset + uintptr(sym.st_value)
+		return true
+	}
+
+	if !info.isGNUHash {
+		// Old-style DT_HASH table.
+		for _, k := range vdsoSymbolKeys {
+			if len(info.bucket) > 0 {
+				for chain := info.bucket[k.symHash%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 vdsoSymbolKeys {
+		symIndex := info.bucket[k.gnuHash%uint32(len(info.bucket))]
+		if symIndex < info.symOff {
+			continue
+		}
+		for ; ; symIndex++ {
+			hash := info.chain[symIndex-info.symOff]
+			if hash|1 == k.gnuHash|1 {
+				// Found a hash match.
+				if apply(symIndex, k) {
+					break
+				}
+			}
+			if hash&1 != 0 {
+				// End of chain.
+				break
+			}
+		}
+	}
+}
+
+func vdsoauxv(tag, val uintptr) {
+	switch tag {
+	case _AT_SYSINFO_EHDR:
+		if val == 0 {
+			// Something went wrong
+			return
+		}
+		var info vdsoInfo
+		// TODO(rsc): I don't understand why the compiler thinks info escapes
+		// when passed to the three functions below.
+		info1 := (*vdsoInfo)(noescape(unsafe.Pointer(&info)))
+		vdsoInitFromSysinfoEhdr(info1, (*elfEhdr)(unsafe.Pointer(val)))
+		vdsoParseSymbols(info1, vdsoFindVersion(info1, &vdsoLinuxVersion))
+	}
+}
+
+// vdsoMarker reports whether PC is on the VDSO page.
+//
+//go:nosplit
+func inVDSOPage(pc uintptr) bool {
+	for _, k := range vdsoSymbolKeys {
+		if *k.ptr != 0 {
+			page := *k.ptr &^ (physPageSize - 1)
+			return pc >= page && pc < page+physPageSize
+		}
+	}
+	return false
+}