// Copyright 2014 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.
package runtime
import "unsafe"
// NOTE: Func does not expose the actual unexported fields, because we return *Func
// values to users, and we want to keep them from being able to overwrite the data
// with (say) *f = Func{}.
// All code operating on a *Func must call raw to get the *_func instead.
// A Func represents a Go function in the running binary.
type Func struct {
opaque struct{} // unexported field to disallow conversions
}
func (f *Func) raw() *_func {
return (*_func)(unsafe.Pointer(f))
}
// funcdata.h
const (
_PCDATA_StackMapIndex = 0
_FUNCDATA_ArgsPointerMaps = 0
_FUNCDATA_LocalsPointerMaps = 1
_FUNCDATA_DeadValueMaps = 2
_ArgsSizeUnknown = -0x80000000
)
// moduledata records information about the layout of the executable
// image. It is written by the linker. Any changes here must be
// matched changes to the code in cmd/internal/ld/symtab.go:symtab.
// moduledata is stored in read-only memory; none of the pointers here
// are visible to the garbage collector.
type moduledata struct {
pclntable []byte
ftab []functab
filetab []uint32
findfunctab uintptr
minpc, maxpc uintptr
text, etext uintptr
noptrdata, enoptrdata uintptr
data, edata uintptr
bss, ebss uintptr
noptrbss, enoptrbss uintptr
end, gcdata, gcbss uintptr
typelinks []*_type
modulename string
modulehashes []modulehash
gcdatamask, gcbssmask bitvector
next *moduledata
}
// For each shared library a module links against, the linker creates an entry in the
// moduledata.modulehashes slice containing the name of the module, the abi hash seen
// at link time and a pointer to the runtime abi hash. These are checked in
// moduledataverify1 below.
type modulehash struct {
modulename string
linktimehash string
runtimehash *string
}
var firstmoduledata moduledata // linker symbol
var lastmoduledatap *moduledata // linker symbol
type functab struct {
entry uintptr
funcoff uintptr
}
const minfunc = 16 // minimum function size
const pcbucketsize = 256 * minfunc // size of bucket in the pc->func lookup table
// findfunctab is an array of these structures.
// Each bucket represents 4096 bytes of the text segment.
// Each subbucket represents 256 bytes of the text segment.
// To find a function given a pc, locate the bucket and subbucket for
// that pc. Add together the idx and subbucket value to obtain a
// function index. Then scan the functab array starting at that
// index to find the target function.
// This table uses 20 bytes for every 4096 bytes of code, or ~0.5% overhead.
type findfuncbucket struct {
idx uint32
subbuckets [16]byte
}
func moduledataverify() {
for datap := &firstmoduledata; datap != nil; datap = datap.next {
moduledataverify1(datap)
}
}
const debugPcln = false
func moduledataverify1(datap *moduledata) {
// See golang.org/s/go12symtab for header: 0xfffffffb,
// two zero bytes, a byte giving the PC quantum,
// and a byte giving the pointer width in bytes.
pcln := *(**[8]byte)(unsafe.Pointer(&datap.pclntable))
pcln32 := *(**[2]uint32)(unsafe.Pointer(&datap.pclntable))
if pcln32[0] != 0xfffffffb || pcln[4] != 0 || pcln[5] != 0 || pcln[6] != _PCQuantum || pcln[7] != ptrSize {
println("runtime: function symbol table header:", hex(pcln32[0]), hex(pcln[4]), hex(pcln[5]), hex(pcln[6]), hex(pcln[7]))
throw("invalid function symbol table\n")
}
// ftab is lookup table for function by program counter.
nftab := len(datap.ftab) - 1
for i := 0; i < nftab; i++ {
// NOTE: ftab[nftab].entry is legal; it is the address beyond the final function.
if datap.ftab[i].entry > datap.ftab[i+1].entry {
f1 := (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i].funcoff]))
f2 := (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i+1].funcoff]))
f2name := "end"
if i+1 < nftab {
f2name = funcname(f2)
}
println("function symbol table not sorted by program counter:", hex(datap.ftab[i].entry), funcname(f1), ">", hex(datap.ftab[i+1].entry), f2name)
for j := 0; j <= i; j++ {
print("\t", hex(datap.ftab[j].entry), " ", funcname((*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[j].funcoff]))), "\n")
}
throw("invalid runtime symbol table")
}
if debugPcln || nftab-i < 5 {
// Check a PC near but not at the very end.
// The very end might be just padding that is not covered by the tables.
// No architecture rounds function entries to more than 16 bytes,
// but if one came along we'd need to subtract more here.
// But don't use the next PC if it corresponds to a foreign object chunk
// (no pcln table, f2.pcln == 0). That chunk might have an alignment
// more than 16 bytes.
f := (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i].funcoff]))
end := f.entry
if i+1 < nftab {
f2 := (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i+1].funcoff]))
if f2.pcln != 0 {
end = f2.entry - 16
if end < f.entry {
end = f.entry
}
}
}
pcvalue(f, f.pcfile, end, true)
pcvalue(f, f.pcln, end, true)
pcvalue(f, f.pcsp, end, true)
}
}
if datap.minpc != datap.ftab[0].entry ||
datap.maxpc != datap.ftab[nftab].entry {
throw("minpc or maxpc invalid")
}
for _, modulehash := range datap.modulehashes {
if modulehash.linktimehash != *modulehash.runtimehash {
println("abi mismatch detected between", datap.modulename, "and", modulehash.modulename)
throw("abi mismatch")
}
}
}
// FuncForPC returns a *Func describing the function that contains the
// given program counter address, or else nil.
func FuncForPC(pc uintptr) *Func {
return (*Func)(unsafe.Pointer(findfunc(pc)))
}
// Name returns the name of the function.
func (f *Func) Name() string {
return funcname(f.raw())
}
// Entry returns the entry address of the function.
func (f *Func) Entry() uintptr {
return f.raw().entry
}
// FileLine returns the file name and line number of the
// source code corresponding to the program counter pc.
// The result will not be accurate if pc is not a program
// counter within f.
func (f *Func) FileLine(pc uintptr) (file string, line int) {
// Pass strict=false here, because anyone can call this function,
// and they might just be wrong about targetpc belonging to f.
file, line32 := funcline1(f.raw(), pc, false)
return file, int(line32)
}
func findmoduledatap(pc uintptr) *moduledata {
for datap := &firstmoduledata; datap != nil; datap = datap.next {
if datap.minpc <= pc && pc <= datap.maxpc {
return datap
}
}
return nil
}
func findfunc(pc uintptr) *_func {
datap := findmoduledatap(pc)
if datap == nil {
return nil
}
const nsub = uintptr(len(findfuncbucket{}.subbuckets))
x := pc - datap.minpc
b := x / pcbucketsize
i := x % pcbucketsize / (pcbucketsize / nsub)
ffb := (*findfuncbucket)(add(unsafe.Pointer(datap.findfunctab), b*unsafe.Sizeof(findfuncbucket{})))
idx := ffb.idx + uint32(ffb.subbuckets[i])
if pc < datap.ftab[idx].entry {
throw("findfunc: bad findfunctab entry")
}
// linear search to find func with pc >= entry.
for datap.ftab[idx+1].entry <= pc {
idx++
}
return (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[idx].funcoff]))
}
func pcvalue(f *_func, off int32, targetpc uintptr, strict bool) int32 {
if off == 0 {
return -1
}
datap := findmoduledatap(f.entry) // inefficient
if datap == nil {
if strict && panicking == 0 {
print("runtime: no module data for ", hex(f.entry), "\n")
throw("no module data")
}
return -1
}
p := datap.pclntable[off:]
pc := f.entry
val := int32(-1)
for {
var ok bool
p, ok = step(p, &pc, &val, pc == f.entry)
if !ok {
break
}
if targetpc < pc {
return val
}
}
// If there was a table, it should have covered all program counters.
// If not, something is wrong.
if panicking != 0 || !strict {
return -1
}
print("runtime: invalid pc-encoded table f=", funcname(f), " pc=", hex(pc), " targetpc=", hex(targetpc), " tab=", p, "\n")
p = datap.pclntable[off:]
pc = f.entry
val = -1
for {
var ok bool
p, ok = step(p, &pc, &val, pc == f.entry)
if !ok {
break
}
print("\tvalue=", val, " until pc=", hex(pc), "\n")
}
throw("invalid runtime symbol table")
return -1
}
func cfuncname(f *_func) *byte {
if f == nil || f.nameoff == 0 {
return nil
}
datap := findmoduledatap(f.entry) // inefficient
if datap == nil {
return nil
}
return (*byte)(unsafe.Pointer(&datap.pclntable[f.nameoff]))
}
func funcname(f *_func) string {
return gostringnocopy(cfuncname(f))
}
func funcline1(f *_func, targetpc uintptr, strict bool) (file string, line int32) {
datap := findmoduledatap(f.entry) // inefficient
if datap == nil {
return "?", 0
}
fileno := int(pcvalue(f, f.pcfile, targetpc, strict))
line = pcvalue(f, f.pcln, targetpc, strict)
if fileno == -1 || line == -1 || fileno >= len(datap.filetab) {
// print("looking for ", hex(targetpc), " in ", funcname(f), " got file=", fileno, " line=", lineno, "\n")
return "?", 0
}
file = gostringnocopy(&datap.pclntable[datap.filetab[fileno]])
return
}
func funcline(f *_func, targetpc uintptr) (file string, line int32) {
return funcline1(f, targetpc, true)
}
func funcspdelta(f *_func, targetpc uintptr) int32 {
x := pcvalue(f, f.pcsp, targetpc, true)
if x&(ptrSize-1) != 0 {
print("invalid spdelta ", funcname(f), " ", hex(f.entry), " ", hex(targetpc), " ", hex(f.pcsp), " ", x, "\n")
}
return x
}
func pcdatavalue(f *_func, table int32, targetpc uintptr) int32 {
if table < 0 || table >= f.npcdata {
return -1
}
off := *(*int32)(add(unsafe.Pointer(&f.nfuncdata), unsafe.Sizeof(f.nfuncdata)+uintptr(table)*4))
return pcvalue(f, off, targetpc, true)
}
func funcdata(f *_func, i int32) unsafe.Pointer {
if i < 0 || i >= f.nfuncdata {
return nil
}
p := add(unsafe.Pointer(&f.nfuncdata), unsafe.Sizeof(f.nfuncdata)+uintptr(f.npcdata)*4)
if ptrSize == 8 && uintptr(p)&4 != 0 {
if uintptr(unsafe.Pointer(f))&4 != 0 {
println("runtime: misaligned func", f)
}
p = add(p, 4)
}
return *(*unsafe.Pointer)(add(p, uintptr(i)*ptrSize))
}
// step advances to the next pc, value pair in the encoded table.
func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool) {
p, uvdelta := readvarint(p)
if uvdelta == 0 && !first {
return nil, false
}
if uvdelta&1 != 0 {
uvdelta = ^(uvdelta >> 1)
} else {
uvdelta >>= 1
}
vdelta := int32(uvdelta)
p, pcdelta := readvarint(p)
*pc += uintptr(pcdelta * _PCQuantum)
*val += vdelta
return p, true
}
// readvarint reads a varint from p.
func readvarint(p []byte) (newp []byte, val uint32) {
var v, shift uint32
for {
b := p[0]
p = p[1:]
v |= (uint32(b) & 0x7F) << shift
if b&0x80 == 0 {
break
}
shift += 7
}
return p, v
}
type stackmap struct {
n int32 // number of bitmaps
nbit int32 // number of bits in each bitmap
bytedata [1]byte // bitmaps, each starting on a 32-bit boundary
}
//go:nowritebarrier
func stackmapdata(stkmap *stackmap, n int32) bitvector {
if n < 0 || n >= stkmap.n {
throw("stackmapdata: index out of range")
}
return bitvector{stkmap.nbit, (*byte)(add(unsafe.Pointer(&stkmap.bytedata), uintptr(n*((stkmap.nbit+31)/32*4))))}
}