symtab.go

Documentation: runtime

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"runtime/internal/atomic"
     9  	"runtime/internal/sys"
    10  	"unsafe"
    11  )
    12  
    13  // Frames may be used to get function/file/line information for a
    14  // slice of PC values returned by Callers.
    15  type Frames struct {
    16  	// callers is a slice of PCs that have not yet been expanded to frames.
    17  	callers []uintptr
    18  
    19  	// frames is a slice of Frames that have yet to be returned.
    20  	frames     []Frame
    21  	frameStore [2]Frame
    22  }
    23  
    24  // Frame is the information returned by Frames for each call frame.
    25  type Frame struct {
    26  	// PC is the program counter for the location in this frame.
    27  	// For a frame that calls another frame, this will be the
    28  	// program counter of a call instruction. Because of inlining,
    29  	// multiple frames may have the same PC value, but different
    30  	// symbolic information.
    31  	PC uintptr
    32  
    33  	// Func is the Func value of this call frame. This may be nil
    34  	// for non-Go code or fully inlined functions.
    35  	Func *Func
    36  
    37  	// Function is the package path-qualified function name of
    38  	// this call frame. If non-empty, this string uniquely
    39  	// identifies a single function in the program.
    40  	// This may be the empty string if not known.
    41  	// If Func is not nil then Function == Func.Name().
    42  	Function string
    43  
    44  	// File and Line are the file name and line number of the
    45  	// location in this frame. For non-leaf frames, this will be
    46  	// the location of a call. These may be the empty string and
    47  	// zero, respectively, if not known.
    48  	File string
    49  	Line int
    50  
    51  	// Entry point program counter for the function; may be zero
    52  	// if not known. If Func is not nil then Entry ==
    53  	// Func.Entry().
    54  	Entry uintptr
    55  }
    56  
    57  // CallersFrames takes a slice of PC values returned by Callers and
    58  // prepares to return function/file/line information.
    59  // Do not change the slice until you are done with the Frames.
    60  func CallersFrames(callers []uintptr) *Frames {
    61  	f := &Frames{callers: callers}
    62  	f.frames = f.frameStore[:0]
    63  	return f
    64  }
    65  
    66  // Next returns frame information for the next caller.
    67  // If more is false, there are no more callers (the Frame value is valid).
    68  func (ci *Frames) Next() (frame Frame, more bool) {
    69  	for len(ci.frames) < 2 {
    70  		// Find the next frame.
    71  		// We need to look for 2 frames so we know what
    72  		// to return for the "more" result.
    73  		if len(ci.callers) == 0 {
    74  			break
    75  		}
    76  		pc := ci.callers[0]
    77  		ci.callers = ci.callers[1:]
    78  		funcInfo := findfunc(pc)
    79  		if !funcInfo.valid() {
    80  			if cgoSymbolizer != nil {
    81  				// Pre-expand cgo frames. We could do this
    82  				// incrementally, too, but there's no way to
    83  				// avoid allocation in this case anyway.
    84  				ci.frames = append(ci.frames, expandCgoFrames(pc)...)
    85  			}
    86  			continue
    87  		}
    88  		f := funcInfo._Func()
    89  		entry := f.Entry()
    90  		if pc > entry {
    91  			// We store the pc of the start of the instruction following
    92  			// the instruction in question (the call or the inline mark).
    93  			// This is done for historical reasons, and to make FuncForPC
    94  			// work correctly for entries in the result of runtime.Callers.
    95  			pc--
    96  		}
    97  		name := funcname(funcInfo)
    98  		file, line := funcline1(funcInfo, pc, false)
    99  		if inldata := funcdata(funcInfo, _FUNCDATA_InlTree); inldata != nil {
   100  			inltree := (*[1 << 20]inlinedCall)(inldata)
   101  			ix := pcdatavalue(funcInfo, _PCDATA_InlTreeIndex, pc, nil)
   102  			if ix >= 0 {
   103  				// Note: entry is not modified. It always refers to a real frame, not an inlined one.
   104  				f = nil
   105  				name = funcnameFromNameoff(funcInfo, inltree[ix].func_)
   106  				// File/line is already correct.
   107  				// TODO: remove file/line from InlinedCall?
   108  			}
   109  		}
   110  		ci.frames = append(ci.frames, Frame{
   111  			PC:       pc,
   112  			Func:     f,
   113  			Function: name,
   114  			File:     file,
   115  			Line:     int(line),
   116  			Entry:    entry,
   117  		})
   118  	}
   119  
   120  	// Pop one frame from the frame list. Keep the rest.
   121  	// Avoid allocation in the common case, which is 1 or 2 frames.
   122  	switch len(ci.frames) {
   123  	case 0: // In the rare case when there are no frames at all, we return Frame{}.
   124  	case 1:
   125  		frame = ci.frames[0]
   126  		ci.frames = ci.frameStore[:0]
   127  	case 2:
   128  		frame = ci.frames[0]
   129  		ci.frameStore[0] = ci.frames[1]
   130  		ci.frames = ci.frameStore[:1]
   131  	default:
   132  		frame = ci.frames[0]
   133  		ci.frames = ci.frames[1:]
   134  	}
   135  	more = len(ci.frames) > 0
   136  	return
   137  }
   138  
   139  // expandCgoFrames expands frame information for pc, known to be
   140  // a non-Go function, using the cgoSymbolizer hook. expandCgoFrames
   141  // returns nil if pc could not be expanded.
   142  func expandCgoFrames(pc uintptr) []Frame {
   143  	arg := cgoSymbolizerArg{pc: pc}
   144  	callCgoSymbolizer(&arg)
   145  
   146  	if arg.file == nil && arg.funcName == nil {
   147  		// No useful information from symbolizer.
   148  		return nil
   149  	}
   150  
   151  	var frames []Frame
   152  	for {
   153  		frames = append(frames, Frame{
   154  			PC:       pc,
   155  			Func:     nil,
   156  			Function: gostring(arg.funcName),
   157  			File:     gostring(arg.file),
   158  			Line:     int(arg.lineno),
   159  			Entry:    arg.entry,
   160  		})
   161  		if arg.more == 0 {
   162  			break
   163  		}
   164  		callCgoSymbolizer(&arg)
   165  	}
   166  
   167  	// No more frames for this PC. Tell the symbolizer we are done.
   168  	// We don't try to maintain a single cgoSymbolizerArg for the
   169  	// whole use of Frames, because there would be no good way to tell
   170  	// the symbolizer when we are done.
   171  	arg.pc = 0
   172  	callCgoSymbolizer(&arg)
   173  
   174  	return frames
   175  }
   176  
   177  // NOTE: Func does not expose the actual unexported fields, because we return *Func
   178  // values to users, and we want to keep them from being able to overwrite the data
   179  // with (say) *f = Func{}.
   180  // All code operating on a *Func must call raw() to get the *_func
   181  // or funcInfo() to get the funcInfo instead.
   182  
   183  // A Func represents a Go function in the running binary.
   184  type Func struct {
   185  	opaque struct{} // unexported field to disallow conversions
   186  }
   187  
   188  func (f *Func) raw() *_func {
   189  	return (*_func)(unsafe.Pointer(f))
   190  }
   191  
   192  func (f *Func) funcInfo() funcInfo {
   193  	fn := f.raw()
   194  	return funcInfo{fn, findmoduledatap(fn.entry)}
   195  }
   196  
   197  // PCDATA and FUNCDATA table indexes.
   198  //
   199  // See funcdata.h and ../cmd/internal/objabi/funcdata.go.
   200  const (
   201  	_PCDATA_StackMapIndex       = 0
   202  	_PCDATA_InlTreeIndex        = 1
   203  	_PCDATA_RegMapIndex         = 2
   204  	_FUNCDATA_ArgsPointerMaps   = 0
   205  	_FUNCDATA_LocalsPointerMaps = 1
   206  	_FUNCDATA_InlTree           = 2
   207  	_FUNCDATA_RegPointerMaps    = 3
   208  	_FUNCDATA_StackObjects      = 4
   209  	_ArgsSizeUnknown            = -0x80000000
   210  )
   211  
   212  // A FuncID identifies particular functions that need to be treated
   213  // specially by the runtime.
   214  // Note that in some situations involving plugins, there may be multiple
   215  // copies of a particular special runtime function.
   216  // Note: this list must match the list in cmd/internal/objabi/funcid.go.
   217  type funcID uint8
   218  
   219  const (
   220  	funcID_normal funcID = iota // not a special function
   221  	funcID_runtime_main
   222  	funcID_goexit
   223  	funcID_jmpdefer
   224  	funcID_mcall
   225  	funcID_morestack
   226  	funcID_mstart
   227  	funcID_rt0_go
   228  	funcID_asmcgocall
   229  	funcID_sigpanic
   230  	funcID_runfinq
   231  	funcID_gcBgMarkWorker
   232  	funcID_systemstack_switch
   233  	funcID_systemstack
   234  	funcID_cgocallback_gofunc
   235  	funcID_gogo
   236  	funcID_externalthreadhandler
   237  	funcID_debugCallV1
   238  	funcID_gopanic
   239  	funcID_panicwrap
   240  	funcID_wrapper // any autogenerated code (hash/eq algorithms, method wrappers, etc.)
   241  )
   242  
   243  // moduledata records information about the layout of the executable
   244  // image. It is written by the linker. Any changes here must be
   245  // matched changes to the code in cmd/internal/ld/symtab.go:symtab.
   246  // moduledata is stored in statically allocated non-pointer memory;
   247  // none of the pointers here are visible to the garbage collector.
   248  type moduledata struct {
   249  	pclntable    []byte
   250  	ftab         []functab
   251  	filetab      []uint32
   252  	findfunctab  uintptr
   253  	minpc, maxpc uintptr
   254  
   255  	text, etext           uintptr
   256  	noptrdata, enoptrdata uintptr
   257  	data, edata           uintptr
   258  	bss, ebss             uintptr
   259  	noptrbss, enoptrbss   uintptr
   260  	end, gcdata, gcbss    uintptr
   261  	types, etypes         uintptr
   262  
   263  	textsectmap []textsect
   264  	typelinks   []int32 // offsets from types
   265  	itablinks   []*itab
   266  
   267  	ptab []ptabEntry
   268  
   269  	pluginpath string
   270  	pkghashes  []modulehash
   271  
   272  	modulename   string
   273  	modulehashes []modulehash
   274  
   275  	hasmain uint8 // 1 if module contains the main function, 0 otherwise
   276  
   277  	gcdatamask, gcbssmask bitvector
   278  
   279  	typemap map[typeOff]*_type // offset to *_rtype in previous module
   280  
   281  	bad bool // module failed to load and should be ignored
   282  
   283  	next *moduledata
   284  }
   285  
   286  // A modulehash is used to compare the ABI of a new module or a
   287  // package in a new module with the loaded program.
   288  //
   289  // For each shared library a module links against, the linker creates an entry in the
   290  // moduledata.modulehashes slice containing the name of the module, the abi hash seen
   291  // at link time and a pointer to the runtime abi hash. These are checked in
   292  // moduledataverify1 below.
   293  //
   294  // For each loaded plugin, the pkghashes slice has a modulehash of the
   295  // newly loaded package that can be used to check the plugin's version of
   296  // a package against any previously loaded version of the package.
   297  // This is done in plugin.lastmoduleinit.
   298  type modulehash struct {
   299  	modulename   string
   300  	linktimehash string
   301  	runtimehash  *string
   302  }
   303  
   304  // pinnedTypemaps are the map[typeOff]*_type from the moduledata objects.
   305  //
   306  // These typemap objects are allocated at run time on the heap, but the
   307  // only direct reference to them is in the moduledata, created by the
   308  // linker and marked SNOPTRDATA so it is ignored by the GC.
   309  //
   310  // To make sure the map isn't collected, we keep a second reference here.
   311  var pinnedTypemaps []map[typeOff]*_type
   312  
   313  var firstmoduledata moduledata  // linker symbol
   314  var lastmoduledatap *moduledata // linker symbol
   315  var modulesSlice *[]*moduledata // see activeModules
   316  
   317  // activeModules returns a slice of active modules.
   318  //
   319  // A module is active once its gcdatamask and gcbssmask have been
   320  // assembled and it is usable by the GC.
   321  //
   322  // This is nosplit/nowritebarrier because it is called by the
   323  // cgo pointer checking code.
   324  //go:nosplit
   325  //go:nowritebarrier
   326  func activeModules() []*moduledata {
   327  	p := (*[]*moduledata)(atomic.Loadp(unsafe.Pointer(&modulesSlice)))
   328  	if p == nil {
   329  		return nil
   330  	}
   331  	return *p
   332  }
   333  
   334  // modulesinit creates the active modules slice out of all loaded modules.
   335  //
   336  // When a module is first loaded by the dynamic linker, an .init_array
   337  // function (written by cmd/link) is invoked to call addmoduledata,
   338  // appending to the module to the linked list that starts with
   339  // firstmoduledata.
   340  //
   341  // There are two times this can happen in the lifecycle of a Go
   342  // program. First, if compiled with -linkshared, a number of modules
   343  // built with -buildmode=shared can be loaded at program initialization.
   344  // Second, a Go program can load a module while running that was built
   345  // with -buildmode=plugin.
   346  //
   347  // After loading, this function is called which initializes the
   348  // moduledata so it is usable by the GC and creates a new activeModules
   349  // list.
   350  //
   351  // Only one goroutine may call modulesinit at a time.
   352  func modulesinit() {
   353  	modules := new([]*moduledata)
   354  	for md := &firstmoduledata; md != nil; md = md.next {
   355  		if md.bad {
   356  			continue
   357  		}
   358  		*modules = append(*modules, md)
   359  		if md.gcdatamask == (bitvector{}) {
   360  			md.gcdatamask = progToPointerMask((*byte)(unsafe.Pointer(md.gcdata)), md.edata-md.data)
   361  			md.gcbssmask = progToPointerMask((*byte)(unsafe.Pointer(md.gcbss)), md.ebss-md.bss)
   362  		}
   363  	}
   364  
   365  	// Modules appear in the moduledata linked list in the order they are
   366  	// loaded by the dynamic loader, with one exception: the
   367  	// firstmoduledata itself the module that contains the runtime. This
   368  	// is not always the first module (when using -buildmode=shared, it
   369  	// is typically libstd.so, the second module). The order matters for
   370  	// typelinksinit, so we swap the first module with whatever module
   371  	// contains the main function.
   372  	//
   373  	// See Issue #18729.
   374  	for i, md := range *modules {
   375  		if md.hasmain != 0 {
   376  			(*modules)[0] = md
   377  			(*modules)[i] = &firstmoduledata
   378  			break
   379  		}
   380  	}
   381  
   382  	atomicstorep(unsafe.Pointer(&modulesSlice), unsafe.Pointer(modules))
   383  }
   384  
   385  type functab struct {
   386  	entry   uintptr
   387  	funcoff uintptr
   388  }
   389  
   390  // Mapping information for secondary text sections
   391  
   392  type textsect struct {
   393  	vaddr    uintptr // prelinked section vaddr
   394  	length   uintptr // section length
   395  	baseaddr uintptr // relocated section address
   396  }
   397  
   398  const minfunc = 16                 // minimum function size
   399  const pcbucketsize = 256 * minfunc // size of bucket in the pc->func lookup table
   400  
   401  // findfunctab is an array of these structures.
   402  // Each bucket represents 4096 bytes of the text segment.
   403  // Each subbucket represents 256 bytes of the text segment.
   404  // To find a function given a pc, locate the bucket and subbucket for
   405  // that pc. Add together the idx and subbucket value to obtain a
   406  // function index. Then scan the functab array starting at that
   407  // index to find the target function.
   408  // This table uses 20 bytes for every 4096 bytes of code, or ~0.5% overhead.
   409  type findfuncbucket struct {
   410  	idx        uint32
   411  	subbuckets [16]byte
   412  }
   413  
   414  func moduledataverify() {
   415  	for datap := &firstmoduledata; datap != nil; datap = datap.next {
   416  		moduledataverify1(datap)
   417  	}
   418  }
   419  
   420  const debugPcln = false
   421  
   422  func moduledataverify1(datap *moduledata) {
   423  	// See golang.org/s/go12symtab for header: 0xfffffffb,
   424  	// two zero bytes, a byte giving the PC quantum,
   425  	// and a byte giving the pointer width in bytes.
   426  	pcln := *(**[8]byte)(unsafe.Pointer(&datap.pclntable))
   427  	pcln32 := *(**[2]uint32)(unsafe.Pointer(&datap.pclntable))
   428  	if pcln32[0] != 0xfffffffb || pcln[4] != 0 || pcln[5] != 0 || pcln[6] != sys.PCQuantum || pcln[7] != sys.PtrSize {
   429  		println("runtime: function symbol table header:", hex(pcln32[0]), hex(pcln[4]), hex(pcln[5]), hex(pcln[6]), hex(pcln[7]))
   430  		throw("invalid function symbol table\n")
   431  	}
   432  
   433  	// ftab is lookup table for function by program counter.
   434  	nftab := len(datap.ftab) - 1
   435  	for i := 0; i < nftab; i++ {
   436  		// NOTE: ftab[nftab].entry is legal; it is the address beyond the final function.
   437  		if datap.ftab[i].entry > datap.ftab[i+1].entry {
   438  			f1 := funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i].funcoff])), datap}
   439  			f2 := funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i+1].funcoff])), datap}
   440  			f2name := "end"
   441  			if i+1 < nftab {
   442  				f2name = funcname(f2)
   443  			}
   444  			println("function symbol table not sorted by program counter:", hex(datap.ftab[i].entry), funcname(f1), ">", hex(datap.ftab[i+1].entry), f2name)
   445  			for j := 0; j <= i; j++ {
   446  				print("\t", hex(datap.ftab[j].entry), " ", funcname(funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[j].funcoff])), datap}), "\n")
   447  			}
   448  			throw("invalid runtime symbol table")
   449  		}
   450  	}
   451  
   452  	if datap.minpc != datap.ftab[0].entry ||
   453  		datap.maxpc != datap.ftab[nftab].entry {
   454  		throw("minpc or maxpc invalid")
   455  	}
   456  
   457  	for _, modulehash := range datap.modulehashes {
   458  		if modulehash.linktimehash != *modulehash.runtimehash {
   459  			println("abi mismatch detected between", datap.modulename, "and", modulehash.modulename)
   460  			throw("abi mismatch")
   461  		}
   462  	}
   463  }
   464  
   465  // FuncForPC returns a *Func describing the function that contains the
   466  // given program counter address, or else nil.
   467  //
   468  // If pc represents multiple functions because of inlining, it returns
   469  // the a *Func describing the innermost function, but with an entry
   470  // of the outermost function.
   471  func FuncForPC(pc uintptr) *Func {
   472  	f := findfunc(pc)
   473  	if !f.valid() {
   474  		return nil
   475  	}
   476  	if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   477  		// Note: strict=false so bad PCs (those between functions) don't crash the runtime.
   478  		// We just report the preceeding function in that situation. See issue 29735.
   479  		// TODO: Perhaps we should report no function at all in that case.
   480  		// The runtime currently doesn't have function end info, alas.
   481  		if ix := pcdatavalue1(f, _PCDATA_InlTreeIndex, pc, nil, false); ix >= 0 {
   482  			inltree := (*[1 << 20]inlinedCall)(inldata)
   483  			name := funcnameFromNameoff(f, inltree[ix].func_)
   484  			file, line := funcline(f, pc)
   485  			fi := &funcinl{
   486  				entry: f.entry, // entry of the real (the outermost) function.
   487  				name:  name,
   488  				file:  file,
   489  				line:  int(line),
   490  			}
   491  			return (*Func)(unsafe.Pointer(fi))
   492  		}
   493  	}
   494  	return f._Func()
   495  }
   496  
   497  // Name returns the name of the function.
   498  func (f *Func) Name() string {
   499  	if f == nil {
   500  		return ""
   501  	}
   502  	fn := f.raw()
   503  	if fn.entry == 0 { // inlined version
   504  		fi := (*funcinl)(unsafe.Pointer(fn))
   505  		return fi.name
   506  	}
   507  	return funcname(f.funcInfo())
   508  }
   509  
   510  // Entry returns the entry address of the function.
   511  func (f *Func) Entry() uintptr {
   512  	fn := f.raw()
   513  	if fn.entry == 0 { // inlined version
   514  		fi := (*funcinl)(unsafe.Pointer(fn))
   515  		return fi.entry
   516  	}
   517  	return fn.entry
   518  }
   519  
   520  // FileLine returns the file name and line number of the
   521  // source code corresponding to the program counter pc.
   522  // The result will not be accurate if pc is not a program
   523  // counter within f.
   524  func (f *Func) FileLine(pc uintptr) (file string, line int) {
   525  	fn := f.raw()
   526  	if fn.entry == 0 { // inlined version
   527  		fi := (*funcinl)(unsafe.Pointer(fn))
   528  		return fi.file, fi.line
   529  	}
   530  	// Pass strict=false here, because anyone can call this function,
   531  	// and they might just be wrong about targetpc belonging to f.
   532  	file, line32 := funcline1(f.funcInfo(), pc, false)
   533  	return file, int(line32)
   534  }
   535  
   536  func findmoduledatap(pc uintptr) *moduledata {
   537  	for datap := &firstmoduledata; datap != nil; datap = datap.next {
   538  		if datap.minpc <= pc && pc < datap.maxpc {
   539  			return datap
   540  		}
   541  	}
   542  	return nil
   543  }
   544  
   545  type funcInfo struct {
   546  	*_func
   547  	datap *moduledata
   548  }
   549  
   550  func (f funcInfo) valid() bool {
   551  	return f._func != nil
   552  }
   553  
   554  func (f funcInfo) _Func() *Func {
   555  	return (*Func)(unsafe.Pointer(f._func))
   556  }
   557  
   558  func findfunc(pc uintptr) funcInfo {
   559  	datap := findmoduledatap(pc)
   560  	if datap == nil {
   561  		return funcInfo{}
   562  	}
   563  	const nsub = uintptr(len(findfuncbucket{}.subbuckets))
   564  
   565  	x := pc - datap.minpc
   566  	b := x / pcbucketsize
   567  	i := x % pcbucketsize / (pcbucketsize / nsub)
   568  
   569  	ffb := (*findfuncbucket)(add(unsafe.Pointer(datap.findfunctab), b*unsafe.Sizeof(findfuncbucket{})))
   570  	idx := ffb.idx + uint32(ffb.subbuckets[i])
   571  
   572  	// If the idx is beyond the end of the ftab, set it to the end of the table and search backward.
   573  	// This situation can occur if multiple text sections are generated to handle large text sections
   574  	// and the linker has inserted jump tables between them.
   575  
   576  	if idx >= uint32(len(datap.ftab)) {
   577  		idx = uint32(len(datap.ftab) - 1)
   578  	}
   579  	if pc < datap.ftab[idx].entry {
   580  		// With multiple text sections, the idx might reference a function address that
   581  		// is higher than the pc being searched, so search backward until the matching address is found.
   582  
   583  		for datap.ftab[idx].entry > pc && idx > 0 {
   584  			idx--
   585  		}
   586  		if idx == 0 {
   587  			throw("findfunc: bad findfunctab entry idx")
   588  		}
   589  	} else {
   590  		// linear search to find func with pc >= entry.
   591  		for datap.ftab[idx+1].entry <= pc {
   592  			idx++
   593  		}
   594  	}
   595  	return funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[idx].funcoff])), datap}
   596  }
   597  
   598  type pcvalueCache struct {
   599  	entries [2][8]pcvalueCacheEnt
   600  }
   601  
   602  type pcvalueCacheEnt struct {
   603  	// targetpc and off together are the key of this cache entry.
   604  	targetpc uintptr
   605  	off      int32
   606  	// val is the value of this cached pcvalue entry.
   607  	val int32
   608  }
   609  
   610  // pcvalueCacheKey returns the outermost index in a pcvalueCache to use for targetpc.
   611  // It must be very cheap to calculate.
   612  // For now, align to sys.PtrSize and reduce mod the number of entries.
   613  // In practice, this appears to be fairly randomly and evenly distributed.
   614  func pcvalueCacheKey(targetpc uintptr) uintptr {
   615  	return (targetpc / sys.PtrSize) % uintptr(len(pcvalueCache{}.entries))
   616  }
   617  
   618  func pcvalue(f funcInfo, off int32, targetpc uintptr, cache *pcvalueCache, strict bool) int32 {
   619  	if off == 0 {
   620  		return -1
   621  	}
   622  
   623  	// Check the cache. This speeds up walks of deep stacks, which
   624  	// tend to have the same recursive functions over and over.
   625  	//
   626  	// This cache is small enough that full associativity is
   627  	// cheaper than doing the hashing for a less associative
   628  	// cache.
   629  	if cache != nil {
   630  		x := pcvalueCacheKey(targetpc)
   631  		for i := range cache.entries[x] {
   632  			// We check off first because we're more
   633  			// likely to have multiple entries with
   634  			// different offsets for the same targetpc
   635  			// than the other way around, so we'll usually
   636  			// fail in the first clause.
   637  			ent := &cache.entries[x][i]
   638  			if ent.off == off && ent.targetpc == targetpc {
   639  				return ent.val
   640  			}
   641  		}
   642  	}
   643  
   644  	if !f.valid() {
   645  		if strict && panicking == 0 {
   646  			print("runtime: no module data for ", hex(f.entry), "\n")
   647  			throw("no module data")
   648  		}
   649  		return -1
   650  	}
   651  	datap := f.datap
   652  	p := datap.pclntable[off:]
   653  	pc := f.entry
   654  	val := int32(-1)
   655  	for {
   656  		var ok bool
   657  		p, ok = step(p, &pc, &val, pc == f.entry)
   658  		if !ok {
   659  			break
   660  		}
   661  		if targetpc < pc {
   662  			// Replace a random entry in the cache. Random
   663  			// replacement prevents a performance cliff if
   664  			// a recursive stack's cycle is slightly
   665  			// larger than the cache.
   666  			// Put the new element at the beginning,
   667  			// since it is the most likely to be newly used.
   668  			if cache != nil {
   669  				x := pcvalueCacheKey(targetpc)
   670  				e := &cache.entries[x]
   671  				ci := fastrand() % uint32(len(cache.entries[x]))
   672  				e[ci] = e[0]
   673  				e[0] = pcvalueCacheEnt{
   674  					targetpc: targetpc,
   675  					off:      off,
   676  					val:      val,
   677  				}
   678  			}
   679  
   680  			return val
   681  		}
   682  	}
   683  
   684  	// If there was a table, it should have covered all program counters.
   685  	// If not, something is wrong.
   686  	if panicking != 0 || !strict {
   687  		return -1
   688  	}
   689  
   690  	print("runtime: invalid pc-encoded table f=", funcname(f), " pc=", hex(pc), " targetpc=", hex(targetpc), " tab=", p, "\n")
   691  
   692  	p = datap.pclntable[off:]
   693  	pc = f.entry
   694  	val = -1
   695  	for {
   696  		var ok bool
   697  		p, ok = step(p, &pc, &val, pc == f.entry)
   698  		if !ok {
   699  			break
   700  		}
   701  		print("\tvalue=", val, " until pc=", hex(pc), "\n")
   702  	}
   703  
   704  	throw("invalid runtime symbol table")
   705  	return -1
   706  }
   707  
   708  func cfuncname(f funcInfo) *byte {
   709  	if !f.valid() || f.nameoff == 0 {
   710  		return nil
   711  	}
   712  	return &f.datap.pclntable[f.nameoff]
   713  }
   714  
   715  func funcname(f funcInfo) string {
   716  	return gostringnocopy(cfuncname(f))
   717  }
   718  
   719  func funcnameFromNameoff(f funcInfo, nameoff int32) string {
   720  	datap := f.datap
   721  	if !f.valid() {
   722  		return ""
   723  	}
   724  	cstr := &datap.pclntable[nameoff]
   725  	return gostringnocopy(cstr)
   726  }
   727  
   728  func funcfile(f funcInfo, fileno int32) string {
   729  	datap := f.datap
   730  	if !f.valid() {
   731  		return "?"
   732  	}
   733  	return gostringnocopy(&datap.pclntable[datap.filetab[fileno]])
   734  }
   735  
   736  func funcline1(f funcInfo, targetpc uintptr, strict bool) (file string, line int32) {
   737  	datap := f.datap
   738  	if !f.valid() {
   739  		return "?", 0
   740  	}
   741  	fileno := int(pcvalue(f, f.pcfile, targetpc, nil, strict))
   742  	line = pcvalue(f, f.pcln, targetpc, nil, strict)
   743  	if fileno == -1 || line == -1 || fileno >= len(datap.filetab) {
   744  		// print("looking for ", hex(targetpc), " in ", funcname(f), " got file=", fileno, " line=", lineno, "\n")
   745  		return "?", 0
   746  	}
   747  	file = gostringnocopy(&datap.pclntable[datap.filetab[fileno]])
   748  	return
   749  }
   750  
   751  func funcline(f funcInfo, targetpc uintptr) (file string, line int32) {
   752  	return funcline1(f, targetpc, true)
   753  }
   754  
   755  func funcspdelta(f funcInfo, targetpc uintptr, cache *pcvalueCache) int32 {
   756  	x := pcvalue(f, f.pcsp, targetpc, cache, true)
   757  	if x&(sys.PtrSize-1) != 0 {
   758  		print("invalid spdelta ", funcname(f), " ", hex(f.entry), " ", hex(targetpc), " ", hex(f.pcsp), " ", x, "\n")
   759  	}
   760  	return x
   761  }
   762  
   763  func pcdatastart(f funcInfo, table int32) int32 {
   764  	return *(*int32)(add(unsafe.Pointer(&f.nfuncdata), unsafe.Sizeof(f.nfuncdata)+uintptr(table)*4))
   765  }
   766  
   767  func pcdatavalue(f funcInfo, table int32, targetpc uintptr, cache *pcvalueCache) int32 {
   768  	if table < 0 || table >= f.npcdata {
   769  		return -1
   770  	}
   771  	return pcvalue(f, pcdatastart(f, table), targetpc, cache, true)
   772  }
   773  
   774  func pcdatavalue1(f funcInfo, table int32, targetpc uintptr, cache *pcvalueCache, strict bool) int32 {
   775  	if table < 0 || table >= f.npcdata {
   776  		return -1
   777  	}
   778  	return pcvalue(f, pcdatastart(f, table), targetpc, cache, strict)
   779  }
   780  
   781  func funcdata(f funcInfo, i uint8) unsafe.Pointer {
   782  	if i < 0 || i >= f.nfuncdata {
   783  		return nil
   784  	}
   785  	p := add(unsafe.Pointer(&f.nfuncdata), unsafe.Sizeof(f.nfuncdata)+uintptr(f.npcdata)*4)
   786  	if sys.PtrSize == 8 && uintptr(p)&4 != 0 {
   787  		if uintptr(unsafe.Pointer(f._func))&4 != 0 {
   788  			println("runtime: misaligned func", f._func)
   789  		}
   790  		p = add(p, 4)
   791  	}
   792  	return *(*unsafe.Pointer)(add(p, uintptr(i)*sys.PtrSize))
   793  }
   794  
   795  // step advances to the next pc, value pair in the encoded table.
   796  func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool) {
   797  	// For both uvdelta and pcdelta, the common case (~70%)
   798  	// is that they are a single byte. If so, avoid calling readvarint.
   799  	uvdelta := uint32(p[0])
   800  	if uvdelta == 0 && !first {
   801  		return nil, false
   802  	}
   803  	n := uint32(1)
   804  	if uvdelta&0x80 != 0 {
   805  		n, uvdelta = readvarint(p)
   806  	}
   807  	*val += int32(-(uvdelta & 1) ^ (uvdelta >> 1))
   808  	p = p[n:]
   809  
   810  	pcdelta := uint32(p[0])
   811  	n = 1
   812  	if pcdelta&0x80 != 0 {
   813  		n, pcdelta = readvarint(p)
   814  	}
   815  	p = p[n:]
   816  	*pc += uintptr(pcdelta * sys.PCQuantum)
   817  	return p, true
   818  }
   819  
   820  // readvarint reads a varint from p.
   821  func readvarint(p []byte) (read uint32, val uint32) {
   822  	var v, shift, n uint32
   823  	for {
   824  		b := p[n]
   825  		n++
   826  		v |= uint32(b&0x7F) << (shift & 31)
   827  		if b&0x80 == 0 {
   828  			break
   829  		}
   830  		shift += 7
   831  	}
   832  	return n, v
   833  }
   834  
   835  type stackmap struct {
   836  	n        int32   // number of bitmaps
   837  	nbit     int32   // number of bits in each bitmap
   838  	bytedata [1]byte // bitmaps, each starting on a byte boundary
   839  }
   840  
   841  //go:nowritebarrier
   842  func stackmapdata(stkmap *stackmap, n int32) bitvector {
   843  	// Check this invariant only when stackDebug is on at all.
   844  	// The invariant is already checked by many of stackmapdata's callers,
   845  	// and disabling it by default allows stackmapdata to be inlined.
   846  	if stackDebug > 0 && (n < 0 || n >= stkmap.n) {
   847  		throw("stackmapdata: index out of range")
   848  	}
   849  	return bitvector{stkmap.nbit, addb(&stkmap.bytedata[0], uintptr(n*((stkmap.nbit+7)>>3)))}
   850  }
   851  
   852  // inlinedCall is the encoding of entries in the FUNCDATA_InlTree table.
   853  type inlinedCall struct {
   854  	parent   int16  // index of parent in the inltree, or < 0
   855  	funcID   funcID // type of the called function
   856  	_        byte
   857  	file     int32 // fileno index into filetab
   858  	line     int32 // line number of the call site
   859  	func_    int32 // offset into pclntab for name of called function
   860  	parentPc int32 // position of an instruction whose source position is the call site (offset from entry)
   861  }
   862
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