Source file src/runtime/symtab.go

     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  	"internal/abi"
     9  	"internal/goarch"
    10  	"internal/runtime/atomic"
    11  	"internal/runtime/sys"
    12  	"unsafe"
    13  )
    14  
    15  // Frames may be used to get function/file/line information for a
    16  // slice of PC values returned by [Callers].
    17  type Frames struct {
    18  	// callers is a slice of PCs that have not yet been expanded to frames.
    19  	callers []uintptr
    20  
    21  	// nextPC is a next PC to expand ahead of processing callers.
    22  	nextPC uintptr
    23  
    24  	// frames is a slice of Frames that have yet to be returned.
    25  	frames     []Frame
    26  	frameStore [2]Frame
    27  }
    28  
    29  // Frame is the information returned by [Frames] for each call frame.
    30  type Frame struct {
    31  	// PC is the program counter for the location in this frame.
    32  	// For a frame that calls another frame, this will be the
    33  	// program counter of a call instruction. Because of inlining,
    34  	// multiple frames may have the same PC value, but different
    35  	// symbolic information.
    36  	PC uintptr
    37  
    38  	// Func is the Func value of this call frame. This may be nil
    39  	// for non-Go code or fully inlined functions.
    40  	Func *Func
    41  
    42  	// Function is the package path-qualified function name of
    43  	// this call frame. If non-empty, this string uniquely
    44  	// identifies a single function in the program.
    45  	// This may be the empty string if not known.
    46  	// If Func is not nil then Function == Func.Name().
    47  	Function string
    48  
    49  	// File and Line are the file name and line number of the
    50  	// location in this frame. For non-leaf frames, this will be
    51  	// the location of a call. These may be the empty string and
    52  	// zero, respectively, if not known. The file name uses
    53  	// forward slashes, even on Windows.
    54  	File string
    55  	Line int
    56  
    57  	// startLine is the line number of the beginning of the function in
    58  	// this frame. Specifically, it is the line number of the func keyword
    59  	// for Go functions. Note that //line directives can change the
    60  	// filename and/or line number arbitrarily within a function, meaning
    61  	// that the Line - startLine offset is not always meaningful.
    62  	//
    63  	// This may be zero if not known.
    64  	startLine int
    65  
    66  	// Entry point program counter for the function; may be zero
    67  	// if not known. If Func is not nil then Entry ==
    68  	// Func.Entry().
    69  	Entry uintptr
    70  
    71  	// The runtime's internal view of the function. This field
    72  	// is set (funcInfo.valid() returns true) only for Go functions,
    73  	// not for C functions.
    74  	funcInfo funcInfo
    75  }
    76  
    77  // CallersFrames takes a slice of PC values returned by [Callers] and
    78  // prepares to return function/file/line information.
    79  // Do not change the slice until you are done with the [Frames].
    80  func CallersFrames(callers []uintptr) *Frames {
    81  	f := &Frames{callers: callers}
    82  	f.frames = f.frameStore[:0]
    83  	return f
    84  }
    85  
    86  // Next returns a [Frame] representing the next call frame in the slice
    87  // of PC values. If it has already returned all call frames, Next
    88  // returns a zero [Frame].
    89  //
    90  // The more result indicates whether the next call to Next will return
    91  // a valid [Frame]. It does not necessarily indicate whether this call
    92  // returned one.
    93  //
    94  // See the [Frames] example for idiomatic usage.
    95  func (ci *Frames) Next() (frame Frame, more bool) {
    96  	for len(ci.frames) < 2 {
    97  		// Find the next frame.
    98  		// We need to look for 2 frames so we know what
    99  		// to return for the "more" result.
   100  		if len(ci.callers) == 0 {
   101  			break
   102  		}
   103  		var pc uintptr
   104  		if ci.nextPC != 0 {
   105  			pc, ci.nextPC = ci.nextPC, 0
   106  		} else {
   107  			pc, ci.callers = ci.callers[0], ci.callers[1:]
   108  		}
   109  		funcInfo := findfunc(pc)
   110  		if !funcInfo.valid() {
   111  			if cgoSymbolizerAvailable() {
   112  				// Pre-expand cgo frames. We could do this
   113  				// incrementally, too, but there's no way to
   114  				// avoid allocation in this case anyway.
   115  				ci.frames = append(ci.frames, expandCgoFrames(pc)...)
   116  			}
   117  			continue
   118  		}
   119  		f := funcInfo._Func()
   120  		entry := f.Entry()
   121  		// We store the pc of the start of the instruction following
   122  		// the instruction in question (the call or the inline mark).
   123  		// This is done for historical reasons, and to make FuncForPC
   124  		// work correctly for entries in the result of runtime.Callers.
   125  		// Decrement to get back to the instruction we care about.
   126  		//
   127  		// It is not possible to get pc == entry from runtime.Callers,
   128  		// but if the caller does provide one, provide best-effort
   129  		// results by avoiding backing out of the function entirely.
   130  		if pc > entry {
   131  			pc--
   132  		}
   133  		// It's important that interpret pc non-strictly as cgoTraceback may
   134  		// have added bogus PCs with a valid funcInfo but invalid PCDATA.
   135  		u, uf := newInlineUnwinder(funcInfo, pc)
   136  		sf := u.srcFunc(uf)
   137  		if u.isInlined(uf) {
   138  			// Note: entry is not modified. It always refers to a real frame, not an inlined one.
   139  			// File/line from funcline1 below are already correct.
   140  			f = nil
   141  
   142  			// When CallersFrame is invoked using the PC list returned by Callers,
   143  			// the PC list includes virtual PCs corresponding to each outer frame
   144  			// around an innermost real inlined PC.
   145  			// We also want to support code passing in a PC list extracted from a
   146  			// stack trace, and there only the real PCs are printed, not the virtual ones.
   147  			// So check to see if the implied virtual PC for this PC (obtained from the
   148  			// unwinder itself) is the next PC in ci.callers. If not, insert it.
   149  			// The +1 here correspond to the pc-- above: the output of Callers
   150  			// and therefore the input to CallersFrames is return PCs from the stack;
   151  			// The pc-- backs up into the CALL instruction (not the first byte of the CALL
   152  			// instruction, but good enough to find it nonetheless).
   153  			// There are no cycles in implied virtual PCs (some number of frames were
   154  			// inlined, but that number is finite), so this unpacking cannot cause an infinite loop.
   155  			for unext := u.next(uf); unext.valid() && len(ci.callers) > 0 && ci.callers[0] != unext.pc+1; unext = u.next(unext) {
   156  				snext := u.srcFunc(unext)
   157  				if snext.funcID == abi.FuncIDWrapper && elideWrapperCalling(sf.funcID) {
   158  					// Skip, because tracebackPCs (inside runtime.Callers) would too.
   159  					continue
   160  				}
   161  				ci.nextPC = unext.pc + 1
   162  				break
   163  			}
   164  		}
   165  		ci.frames = append(ci.frames, Frame{
   166  			PC:        pc,
   167  			Func:      f,
   168  			Function:  funcNameForPrint(sf.name()),
   169  			Entry:     entry,
   170  			startLine: int(sf.startLine),
   171  			funcInfo:  funcInfo,
   172  			// Note: File,Line set below
   173  		})
   174  	}
   175  
   176  	// Pop one frame from the frame list. Keep the rest.
   177  	// Avoid allocation in the common case, which is 1 or 2 frames.
   178  	switch len(ci.frames) {
   179  	case 0: // In the rare case when there are no frames at all, we return Frame{}.
   180  		return
   181  	case 1:
   182  		frame = ci.frames[0]
   183  		ci.frames = ci.frameStore[:0]
   184  	case 2:
   185  		frame = ci.frames[0]
   186  		ci.frameStore[0] = ci.frames[1]
   187  		ci.frames = ci.frameStore[:1]
   188  	default:
   189  		frame = ci.frames[0]
   190  		ci.frames = ci.frames[1:]
   191  	}
   192  	more = len(ci.frames) > 0
   193  	if frame.funcInfo.valid() {
   194  		// Compute file/line just before we need to return it,
   195  		// as it can be expensive. This avoids computing file/line
   196  		// for the Frame we find but don't return. See issue 32093.
   197  		file, line := funcline1(frame.funcInfo, frame.PC, false)
   198  		frame.File, frame.Line = file, int(line)
   199  	}
   200  	return
   201  }
   202  
   203  // runtime_FrameStartLine returns the start line of the function in a Frame.
   204  //
   205  // runtime_FrameStartLine should be an internal detail,
   206  // but widely used packages access it using linkname.
   207  // Notable members of the hall of shame include:
   208  //   - github.com/grafana/pyroscope-go/godeltaprof
   209  //
   210  // Do not remove or change the type signature.
   211  // See go.dev/issue/67401.
   212  //
   213  //go:linkname runtime_FrameStartLine runtime/pprof.runtime_FrameStartLine
   214  func runtime_FrameStartLine(f *Frame) int {
   215  	return f.startLine
   216  }
   217  
   218  // runtime_FrameSymbolName returns the full symbol name of the function in a Frame.
   219  // For generic functions this differs from f.Function in that this doesn't replace
   220  // the shape name to "...".
   221  //
   222  // runtime_FrameSymbolName should be an internal detail,
   223  // but widely used packages access it using linkname.
   224  // Notable members of the hall of shame include:
   225  //   - github.com/grafana/pyroscope-go/godeltaprof
   226  //
   227  // Do not remove or change the type signature.
   228  // See go.dev/issue/67401.
   229  //
   230  //go:linkname runtime_FrameSymbolName runtime/pprof.runtime_FrameSymbolName
   231  func runtime_FrameSymbolName(f *Frame) string {
   232  	if !f.funcInfo.valid() {
   233  		return f.Function
   234  	}
   235  	u, uf := newInlineUnwinder(f.funcInfo, f.PC)
   236  	sf := u.srcFunc(uf)
   237  	return sf.name()
   238  }
   239  
   240  // runtime_expandFinalInlineFrame expands the final pc in stk to include all
   241  // "callers" if pc is inline.
   242  //
   243  // runtime_expandFinalInlineFrame should be an internal detail,
   244  // but widely used packages access it using linkname.
   245  // Notable members of the hall of shame include:
   246  //   - github.com/grafana/pyroscope-go/godeltaprof
   247  //   - github.com/pyroscope-io/godeltaprof
   248  //
   249  // Do not remove or change the type signature.
   250  // See go.dev/issue/67401.
   251  //
   252  //go:linkname runtime_expandFinalInlineFrame runtime/pprof.runtime_expandFinalInlineFrame
   253  func runtime_expandFinalInlineFrame(stk []uintptr) []uintptr {
   254  	// TODO: It would be more efficient to report only physical PCs to pprof and
   255  	// just expand the whole stack.
   256  	if len(stk) == 0 {
   257  		return stk
   258  	}
   259  	pc := stk[len(stk)-1]
   260  	tracepc := pc - 1
   261  
   262  	f := findfunc(tracepc)
   263  	if !f.valid() {
   264  		// Not a Go function.
   265  		return stk
   266  	}
   267  
   268  	u, uf := newInlineUnwinder(f, tracepc)
   269  	if !u.isInlined(uf) {
   270  		// Nothing inline at tracepc.
   271  		return stk
   272  	}
   273  
   274  	// Treat the previous func as normal. We haven't actually checked, but
   275  	// since this pc was included in the stack, we know it shouldn't be
   276  	// elided.
   277  	calleeID := abi.FuncIDNormal
   278  
   279  	// Remove pc from stk; we'll re-add it below.
   280  	stk = stk[:len(stk)-1]
   281  
   282  	for ; uf.valid(); uf = u.next(uf) {
   283  		funcID := u.srcFunc(uf).funcID
   284  		if funcID == abi.FuncIDWrapper && elideWrapperCalling(calleeID) {
   285  			// ignore wrappers
   286  		} else {
   287  			stk = append(stk, uf.pc+1)
   288  		}
   289  		calleeID = funcID
   290  	}
   291  
   292  	return stk
   293  }
   294  
   295  // expandCgoFrames expands frame information for pc, known to be
   296  // a non-Go function, using the cgoSymbolizer hook. expandCgoFrames
   297  // returns nil if pc could not be expanded.
   298  //
   299  // Preconditions: cgoSymbolizerAvailable returns true.
   300  func expandCgoFrames(pc uintptr) []Frame {
   301  	arg := cgoSymbolizerArg{pc: pc}
   302  	callCgoSymbolizer(&arg)
   303  
   304  	if arg.file == nil && arg.funcName == nil {
   305  		// No useful information from symbolizer.
   306  		return nil
   307  	}
   308  
   309  	var frames []Frame
   310  	for {
   311  		frames = append(frames, Frame{
   312  			PC:       pc,
   313  			Func:     nil,
   314  			Function: gostring(arg.funcName),
   315  			File:     gostring(arg.file),
   316  			Line:     int(arg.lineno),
   317  			Entry:    arg.entry,
   318  			// funcInfo is zero, which implies !funcInfo.valid().
   319  			// That ensures that we use the File/Line info given here.
   320  		})
   321  		if arg.more == 0 {
   322  			break
   323  		}
   324  		callCgoSymbolizer(&arg)
   325  	}
   326  
   327  	// No more frames for this PC. Tell the symbolizer we are done.
   328  	// We don't try to maintain a single cgoSymbolizerArg for the
   329  	// whole use of Frames, because there would be no good way to tell
   330  	// the symbolizer when we are done.
   331  	arg.pc = 0
   332  	callCgoSymbolizer(&arg)
   333  
   334  	return frames
   335  }
   336  
   337  // NOTE: Func does not expose the actual unexported fields, because we return *Func
   338  // values to users, and we want to keep them from being able to overwrite the data
   339  // with (say) *f = Func{}.
   340  // All code operating on a *Func must call raw() to get the *_func
   341  // or funcInfo() to get the funcInfo instead.
   342  
   343  // A Func represents a Go function in the running binary.
   344  type Func struct {
   345  	opaque struct{} // unexported field to disallow conversions
   346  }
   347  
   348  func (f *Func) raw() *_func {
   349  	return (*_func)(unsafe.Pointer(f))
   350  }
   351  
   352  func (f *Func) funcInfo() funcInfo {
   353  	return f.raw().funcInfo()
   354  }
   355  
   356  func (f *_func) funcInfo() funcInfo {
   357  	// Find the module containing fn. fn is located in the pclntable.
   358  	// The unsafe.Pointer to uintptr conversions and arithmetic
   359  	// are safe because we are working with module addresses.
   360  	ptr := uintptr(unsafe.Pointer(f))
   361  	var mod *moduledata
   362  	for datap := &firstmoduledata; datap != nil; datap = datap.next {
   363  		if len(datap.pclntable) == 0 {
   364  			continue
   365  		}
   366  		base := uintptr(unsafe.Pointer(&datap.pclntable[0]))
   367  		if base <= ptr && ptr < base+uintptr(len(datap.pclntable)) {
   368  			mod = datap
   369  			break
   370  		}
   371  	}
   372  	return funcInfo{f, mod}
   373  }
   374  
   375  // pcHeader holds data used by the pclntab lookups.
   376  type pcHeader struct {
   377  	magic      uint32 // 0xFFFFFFF1
   378  	pad1, pad2 uint8  // 0,0
   379  	minLC      uint8  // min instruction size
   380  	ptrSize    uint8  // size of a ptr in bytes
   381  	nfunc      int    // number of functions in the module
   382  	nfiles     uint   // number of entries in the file tab
   383  
   384  	// The next field used to be textStart. This is no longer stored
   385  	// as it requires a relocation. Code should use the moduledata text
   386  	// field instead. This unused field can be removed in coordination
   387  	// with Delve.
   388  	_ uintptr
   389  
   390  	funcnameOffset uintptr // offset to the funcnametab variable from pcHeader
   391  	cuOffset       uintptr // offset to the cutab variable from pcHeader
   392  	filetabOffset  uintptr // offset to the filetab variable from pcHeader
   393  	pctabOffset    uintptr // offset to the pctab variable from pcHeader
   394  	pclnOffset     uintptr // offset to the pclntab variable from pcHeader
   395  }
   396  
   397  // moduledata records information about the layout of the executable
   398  // image. It is written by the linker. Any changes here must be
   399  // matched changes to the code in cmd/link/internal/ld/symtab.go:symtab.
   400  // moduledata is stored in statically allocated non-pointer memory;
   401  // none of the pointers here are visible to the garbage collector.
   402  type moduledata struct {
   403  	sys.NotInHeap // Only in static data
   404  
   405  	pcHeader     *pcHeader
   406  	funcnametab  []byte
   407  	cutab        []uint32
   408  	filetab      []byte
   409  	pctab        []byte
   410  	pclntable    []byte
   411  	ftab         []functab
   412  	findfunctab  uintptr
   413  	minpc, maxpc uintptr
   414  
   415  	text, etext           uintptr
   416  	noptrdata, enoptrdata uintptr
   417  	data, edata           uintptr
   418  	bss, ebss             uintptr
   419  	noptrbss, enoptrbss   uintptr
   420  	covctrs, ecovctrs     uintptr
   421  	end, gcdata, gcbss    uintptr
   422  	types, etypes         uintptr
   423  	rodata                uintptr
   424  	gofunc                uintptr // go.func.*
   425  
   426  	textsectmap []textsect
   427  	typelinks   []int32 // offsets from types
   428  	itablinks   []*itab
   429  
   430  	ptab []ptabEntry
   431  
   432  	pluginpath string
   433  	pkghashes  []modulehash
   434  
   435  	// This slice records the initializing tasks that need to be
   436  	// done to start up the program. It is built by the linker.
   437  	inittasks []*initTask
   438  
   439  	modulename   string
   440  	modulehashes []modulehash
   441  
   442  	hasmain uint8 // 1 if module contains the main function, 0 otherwise
   443  	bad     bool  // module failed to load and should be ignored
   444  
   445  	gcdatamask, gcbssmask bitvector
   446  
   447  	typemap map[typeOff]*_type // offset to *_rtype in previous module
   448  
   449  	next *moduledata
   450  }
   451  
   452  // A modulehash is used to compare the ABI of a new module or a
   453  // package in a new module with the loaded program.
   454  //
   455  // For each shared library a module links against, the linker creates an entry in the
   456  // moduledata.modulehashes slice containing the name of the module, the abi hash seen
   457  // at link time and a pointer to the runtime abi hash. These are checked in
   458  // moduledataverify1 below.
   459  //
   460  // For each loaded plugin, the pkghashes slice has a modulehash of the
   461  // newly loaded package that can be used to check the plugin's version of
   462  // a package against any previously loaded version of the package.
   463  // This is done in plugin.lastmoduleinit.
   464  type modulehash struct {
   465  	modulename   string
   466  	linktimehash string
   467  	runtimehash  *string
   468  }
   469  
   470  // pinnedTypemaps are the map[typeOff]*_type from the moduledata objects.
   471  //
   472  // These typemap objects are allocated at run time on the heap, but the
   473  // only direct reference to them is in the moduledata, created by the
   474  // linker and marked SNOPTRDATA so it is ignored by the GC.
   475  //
   476  // To make sure the map isn't collected, we keep a second reference here.
   477  var pinnedTypemaps []map[typeOff]*_type
   478  
   479  // aixStaticDataBase (used only on AIX) holds the unrelocated address
   480  // of the data section, set by the linker.
   481  //
   482  // On AIX, an R_ADDR relocation from an RODATA symbol to a DATA symbol
   483  // does not work, as the dynamic loader can change the address of the
   484  // data section, and it is not possible to apply a dynamic relocation
   485  // to RODATA. In order to get the correct address, we need to apply
   486  // the delta between unrelocated and relocated data section addresses.
   487  // aixStaticDataBase is the unrelocated address, and moduledata.data is
   488  // the relocated one.
   489  var aixStaticDataBase uintptr // linker symbol
   490  
   491  var firstmoduledata moduledata // linker symbol
   492  
   493  // lastmoduledatap should be an internal detail,
   494  // but widely used packages access it using linkname.
   495  // Notable members of the hall of shame include:
   496  //   - github.com/bytedance/sonic
   497  //
   498  // Do not remove or change the type signature.
   499  // See go.dev/issues/67401.
   500  // See go.dev/issues/71672.
   501  //
   502  //go:linkname lastmoduledatap
   503  var lastmoduledatap *moduledata // linker symbol
   504  
   505  var modulesSlice *[]*moduledata // see activeModules
   506  
   507  // activeModules returns a slice of active modules.
   508  //
   509  // A module is active once its gcdatamask and gcbssmask have been
   510  // assembled and it is usable by the GC.
   511  //
   512  // This is nosplit/nowritebarrier because it is called by the
   513  // cgo pointer checking code.
   514  //
   515  //go:nosplit
   516  //go:nowritebarrier
   517  func activeModules() []*moduledata {
   518  	p := (*[]*moduledata)(atomic.Loadp(unsafe.Pointer(&modulesSlice)))
   519  	if p == nil {
   520  		return nil
   521  	}
   522  	return *p
   523  }
   524  
   525  // modulesinit creates the active modules slice out of all loaded modules.
   526  //
   527  // When a module is first loaded by the dynamic linker, an .init_array
   528  // function (written by cmd/link) is invoked to call addmoduledata,
   529  // appending to the module to the linked list that starts with
   530  // firstmoduledata.
   531  //
   532  // There are two times this can happen in the lifecycle of a Go
   533  // program. First, if compiled with -linkshared, a number of modules
   534  // built with -buildmode=shared can be loaded at program initialization.
   535  // Second, a Go program can load a module while running that was built
   536  // with -buildmode=plugin.
   537  //
   538  // After loading, this function is called which initializes the
   539  // moduledata so it is usable by the GC and creates a new activeModules
   540  // list.
   541  //
   542  // Only one goroutine may call modulesinit at a time.
   543  func modulesinit() {
   544  	modules := new([]*moduledata)
   545  	for md := &firstmoduledata; md != nil; md = md.next {
   546  		if md.bad {
   547  			continue
   548  		}
   549  		*modules = append(*modules, md)
   550  		if md.gcdatamask == (bitvector{}) {
   551  			scanDataSize := md.edata - md.data
   552  			md.gcdatamask = progToPointerMask((*byte)(unsafe.Pointer(md.gcdata)), scanDataSize)
   553  			scanBSSSize := md.ebss - md.bss
   554  			md.gcbssmask = progToPointerMask((*byte)(unsafe.Pointer(md.gcbss)), scanBSSSize)
   555  			gcController.addGlobals(int64(scanDataSize + scanBSSSize))
   556  		}
   557  	}
   558  
   559  	// Modules appear in the moduledata linked list in the order they are
   560  	// loaded by the dynamic loader, with one exception: the
   561  	// firstmoduledata itself the module that contains the runtime. This
   562  	// is not always the first module (when using -buildmode=shared, it
   563  	// is typically libstd.so, the second module). The order matters for
   564  	// typelinksinit, so we swap the first module with whatever module
   565  	// contains the main function.
   566  	//
   567  	// See Issue #18729.
   568  	for i, md := range *modules {
   569  		if md.hasmain != 0 {
   570  			(*modules)[0] = md
   571  			(*modules)[i] = &firstmoduledata
   572  			break
   573  		}
   574  	}
   575  
   576  	atomicstorep(unsafe.Pointer(&modulesSlice), unsafe.Pointer(modules))
   577  }
   578  
   579  type functab struct {
   580  	entryoff uint32 // relative to runtime.text
   581  	funcoff  uint32
   582  }
   583  
   584  // Mapping information for secondary text sections
   585  
   586  type textsect struct {
   587  	vaddr    uintptr // prelinked section vaddr
   588  	end      uintptr // vaddr + section length
   589  	baseaddr uintptr // relocated section address
   590  }
   591  
   592  // findfuncbucket is an array of these structures.
   593  // Each bucket represents 4096 bytes of the text segment.
   594  // Each subbucket represents 256 bytes of the text segment.
   595  // To find a function given a pc, locate the bucket and subbucket for
   596  // that pc. Add together the idx and subbucket value to obtain a
   597  // function index. Then scan the functab array starting at that
   598  // index to find the target function.
   599  // This table uses 20 bytes for every 4096 bytes of code, or ~0.5% overhead.
   600  type findfuncbucket struct {
   601  	idx        uint32
   602  	subbuckets [16]byte
   603  }
   604  
   605  func moduledataverify() {
   606  	for datap := &firstmoduledata; datap != nil; datap = datap.next {
   607  		moduledataverify1(datap)
   608  	}
   609  }
   610  
   611  const debugPcln = false
   612  
   613  // moduledataverify1 should be an internal detail,
   614  // but widely used packages access it using linkname.
   615  // Notable members of the hall of shame include:
   616  //   - github.com/bytedance/sonic
   617  //
   618  // Do not remove or change the type signature.
   619  // See go.dev/issues/67401.
   620  // See go.dev/issues/71672.
   621  //
   622  //go:linkname moduledataverify1
   623  func moduledataverify1(datap *moduledata) {
   624  	// Check that the pclntab's format is valid.
   625  	hdr := datap.pcHeader
   626  	if hdr.magic != 0xfffffff1 || hdr.pad1 != 0 || hdr.pad2 != 0 ||
   627  		hdr.minLC != sys.PCQuantum || hdr.ptrSize != goarch.PtrSize {
   628  		println("runtime: pcHeader: magic=", hex(hdr.magic), "pad1=", hdr.pad1, "pad2=", hdr.pad2,
   629  			"minLC=", hdr.minLC, "ptrSize=", hdr.ptrSize, "pluginpath=", datap.pluginpath)
   630  		throw("invalid function symbol table")
   631  	}
   632  
   633  	// ftab is lookup table for function by program counter.
   634  	nftab := len(datap.ftab) - 1
   635  	for i := 0; i < nftab; i++ {
   636  		// NOTE: ftab[nftab].entry is legal; it is the address beyond the final function.
   637  		if datap.ftab[i].entryoff > datap.ftab[i+1].entryoff {
   638  			f1 := funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i].funcoff])), datap}
   639  			f2 := funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i+1].funcoff])), datap}
   640  			f2name := "end"
   641  			if i+1 < nftab {
   642  				f2name = funcname(f2)
   643  			}
   644  			println("function symbol table not sorted by PC offset:", hex(datap.ftab[i].entryoff), funcname(f1), ">", hex(datap.ftab[i+1].entryoff), f2name, ", plugin:", datap.pluginpath)
   645  			for j := 0; j <= i; j++ {
   646  				println("\t", hex(datap.ftab[j].entryoff), funcname(funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[j].funcoff])), datap}))
   647  			}
   648  			if GOOS == "aix" && isarchive {
   649  				println("-Wl,-bnoobjreorder is mandatory on aix/ppc64 with c-archive")
   650  			}
   651  			throw("invalid runtime symbol table")
   652  		}
   653  	}
   654  
   655  	min := datap.textAddr(datap.ftab[0].entryoff)
   656  	max := datap.textAddr(datap.ftab[nftab].entryoff)
   657  	minpc := datap.minpc
   658  	maxpc := datap.maxpc
   659  	if GOARCH == "wasm" {
   660  		// On Wasm, the func table contains the function index, whereas
   661  		// the "PC" is function index << 16 + block index.
   662  		maxpc = alignUp(maxpc, 1<<16) // round up for end PC
   663  	}
   664  	if minpc != min || maxpc != max {
   665  		println("minpc=", hex(minpc), "min=", hex(min), "maxpc=", hex(maxpc), "max=", hex(max))
   666  		throw("minpc or maxpc invalid")
   667  	}
   668  
   669  	for _, modulehash := range datap.modulehashes {
   670  		if modulehash.linktimehash != *modulehash.runtimehash {
   671  			println("abi mismatch detected between", datap.modulename, "and", modulehash.modulename)
   672  			throw("abi mismatch")
   673  		}
   674  	}
   675  }
   676  
   677  // textAddr returns md.text + off, with special handling for multiple text sections.
   678  // off is a (virtual) offset computed at internal linking time,
   679  // before the external linker adjusts the sections' base addresses.
   680  //
   681  // The text, or instruction stream is generated as one large buffer.
   682  // The off (offset) for a function is its offset within this buffer.
   683  // If the total text size gets too large, there can be issues on platforms like ppc64
   684  // if the target of calls are too far for the call instruction.
   685  // To resolve the large text issue, the text is split into multiple text sections
   686  // to allow the linker to generate long calls when necessary.
   687  // When this happens, the vaddr for each text section is set to its offset within the text.
   688  // Each function's offset is compared against the section vaddrs and ends to determine the containing section.
   689  // Then the section relative offset is added to the section's
   690  // relocated baseaddr to compute the function address.
   691  //
   692  // It is nosplit because it is part of the findfunc implementation.
   693  //
   694  //go:nosplit
   695  func (md *moduledata) textAddr(off32 uint32) uintptr {
   696  	off := uintptr(off32)
   697  	res := md.text + off
   698  	if len(md.textsectmap) > 1 {
   699  		for i, sect := range md.textsectmap {
   700  			// For the last section, include the end address (etext), as it is included in the functab.
   701  			if off >= sect.vaddr && off < sect.end || (i == len(md.textsectmap)-1 && off == sect.end) {
   702  				res = sect.baseaddr + off - sect.vaddr
   703  				break
   704  			}
   705  		}
   706  		if res > md.etext && GOARCH != "wasm" { // on wasm, functions do not live in the same address space as the linear memory
   707  			println("runtime: textAddr", hex(res), "out of range", hex(md.text), "-", hex(md.etext))
   708  			throw("runtime: text offset out of range")
   709  		}
   710  	}
   711  	if GOARCH == "wasm" {
   712  		// On Wasm, a text offset (e.g. in the method table) is function index, whereas
   713  		// the "PC" is function index << 16 + block index.
   714  		res <<= 16
   715  	}
   716  	return res
   717  }
   718  
   719  // textOff is the opposite of textAddr. It converts a PC to a (virtual) offset
   720  // to md.text, and returns if the PC is in any Go text section.
   721  //
   722  // It is nosplit because it is part of the findfunc implementation.
   723  //
   724  //go:nosplit
   725  func (md *moduledata) textOff(pc uintptr) (uint32, bool) {
   726  	off := pc - md.text
   727  	if GOARCH == "wasm" {
   728  		// On Wasm, the func table contains the function index, whereas
   729  		// the "PC" is function index << 16 + block index.
   730  		off >>= 16
   731  	}
   732  	res := uint32(off)
   733  	if len(md.textsectmap) > 1 {
   734  		if GOARCH == "wasm" {
   735  			fatal("unexpected multiple text sections on Wasm")
   736  		}
   737  		for i, sect := range md.textsectmap {
   738  			if sect.baseaddr > pc {
   739  				// pc is not in any section.
   740  				return 0, false
   741  			}
   742  			end := sect.baseaddr + (sect.end - sect.vaddr)
   743  			// For the last section, include the end address (etext), as it is included in the functab.
   744  			if i == len(md.textsectmap)-1 {
   745  				end++
   746  			}
   747  			if pc < end {
   748  				res = uint32(pc - sect.baseaddr + sect.vaddr)
   749  				break
   750  			}
   751  		}
   752  	}
   753  	return res, true
   754  }
   755  
   756  // funcName returns the string at nameOff in the function name table.
   757  func (md *moduledata) funcName(nameOff int32) string {
   758  	if nameOff == 0 {
   759  		return ""
   760  	}
   761  	return gostringnocopy(&md.funcnametab[nameOff])
   762  }
   763  
   764  // Despite being an exported symbol,
   765  // FuncForPC is linknamed by widely used packages.
   766  // Notable members of the hall of shame include:
   767  //   - gitee.com/quant1x/gox
   768  //
   769  // Do not remove or change the type signature.
   770  // See go.dev/issue/67401.
   771  //
   772  // Note that this comment is not part of the doc comment.
   773  //
   774  //go:linkname FuncForPC
   775  
   776  // FuncForPC returns a *[Func] describing the function that contains the
   777  // given program counter address, or else nil.
   778  //
   779  // If pc represents multiple functions because of inlining, it returns
   780  // the *Func describing the innermost function, but with an entry of
   781  // the outermost function.
   782  func FuncForPC(pc uintptr) *Func {
   783  	f := findfunc(pc)
   784  	if !f.valid() {
   785  		return nil
   786  	}
   787  	// This must interpret PC non-strictly so bad PCs (those between functions) don't crash the runtime.
   788  	// We just report the preceding function in that situation. See issue 29735.
   789  	// TODO: Perhaps we should report no function at all in that case.
   790  	// The runtime currently doesn't have function end info, alas.
   791  	u, uf := newInlineUnwinder(f, pc)
   792  	if !u.isInlined(uf) {
   793  		return f._Func()
   794  	}
   795  	sf := u.srcFunc(uf)
   796  	file, line := u.fileLine(uf)
   797  	fi := &funcinl{
   798  		ones:      ^uint32(0),
   799  		entry:     f.entry(), // entry of the real (the outermost) function.
   800  		name:      sf.name(),
   801  		file:      file,
   802  		line:      int32(line),
   803  		startLine: sf.startLine,
   804  	}
   805  	return (*Func)(unsafe.Pointer(fi))
   806  }
   807  
   808  // Name returns the name of the function.
   809  func (f *Func) Name() string {
   810  	if f == nil {
   811  		return ""
   812  	}
   813  	fn := f.raw()
   814  	if fn.isInlined() { // inlined version
   815  		fi := (*funcinl)(unsafe.Pointer(fn))
   816  		return funcNameForPrint(fi.name)
   817  	}
   818  	return funcNameForPrint(funcname(f.funcInfo()))
   819  }
   820  
   821  // Entry returns the entry address of the function.
   822  func (f *Func) Entry() uintptr {
   823  	fn := f.raw()
   824  	if fn.isInlined() { // inlined version
   825  		fi := (*funcinl)(unsafe.Pointer(fn))
   826  		return fi.entry
   827  	}
   828  	return fn.funcInfo().entry()
   829  }
   830  
   831  // FileLine returns the file name and line number of the
   832  // source code corresponding to the program counter pc.
   833  // The result will not be accurate if pc is not a program
   834  // counter within f.
   835  func (f *Func) FileLine(pc uintptr) (file string, line int) {
   836  	fn := f.raw()
   837  	if fn.isInlined() { // inlined version
   838  		fi := (*funcinl)(unsafe.Pointer(fn))
   839  		return fi.file, int(fi.line)
   840  	}
   841  	// Pass strict=false here, because anyone can call this function,
   842  	// and they might just be wrong about targetpc belonging to f.
   843  	file, line32 := funcline1(f.funcInfo(), pc, false)
   844  	return file, int(line32)
   845  }
   846  
   847  // startLine returns the starting line number of the function. i.e., the line
   848  // number of the func keyword.
   849  func (f *Func) startLine() int32 {
   850  	fn := f.raw()
   851  	if fn.isInlined() { // inlined version
   852  		fi := (*funcinl)(unsafe.Pointer(fn))
   853  		return fi.startLine
   854  	}
   855  	return fn.funcInfo().startLine
   856  }
   857  
   858  // findmoduledatap looks up the moduledata for a PC.
   859  //
   860  // It is nosplit because it's part of the isgoexception
   861  // implementation.
   862  //
   863  //go:nosplit
   864  func findmoduledatap(pc uintptr) *moduledata {
   865  	for datap := &firstmoduledata; datap != nil; datap = datap.next {
   866  		if datap.minpc <= pc && pc < datap.maxpc {
   867  			return datap
   868  		}
   869  	}
   870  	return nil
   871  }
   872  
   873  type funcInfo struct {
   874  	*_func
   875  	datap *moduledata
   876  }
   877  
   878  func (f funcInfo) valid() bool {
   879  	return f._func != nil
   880  }
   881  
   882  func (f funcInfo) _Func() *Func {
   883  	return (*Func)(unsafe.Pointer(f._func))
   884  }
   885  
   886  // isInlined reports whether f should be re-interpreted as a *funcinl.
   887  func (f *_func) isInlined() bool {
   888  	return f.entryOff == ^uint32(0) // see comment for funcinl.ones
   889  }
   890  
   891  // entry returns the entry PC for f.
   892  //
   893  // entry should be an internal detail,
   894  // but widely used packages access it using linkname.
   895  // Notable members of the hall of shame include:
   896  //   - github.com/phuslu/log
   897  //
   898  // Do not remove or change the type signature.
   899  // See go.dev/issue/67401.
   900  func (f funcInfo) entry() uintptr {
   901  	return f.datap.textAddr(f.entryOff)
   902  }
   903  
   904  //go:linkname badFuncInfoEntry runtime.funcInfo.entry
   905  func badFuncInfoEntry(funcInfo) uintptr
   906  
   907  // findfunc looks up function metadata for a PC.
   908  //
   909  // It is nosplit because it's part of the isgoexception
   910  // implementation.
   911  //
   912  // findfunc should be an internal detail,
   913  // but widely used packages access it using linkname.
   914  // Notable members of the hall of shame include:
   915  //   - github.com/phuslu/log
   916  //
   917  // Do not remove or change the type signature.
   918  // See go.dev/issue/67401.
   919  //
   920  //go:nosplit
   921  //go:linkname findfunc
   922  func findfunc(pc uintptr) funcInfo {
   923  	datap := findmoduledatap(pc)
   924  	if datap == nil {
   925  		return funcInfo{}
   926  	}
   927  	const nsub = uintptr(len(findfuncbucket{}.subbuckets))
   928  
   929  	pcOff, ok := datap.textOff(pc)
   930  	if !ok {
   931  		return funcInfo{}
   932  	}
   933  
   934  	x := uintptr(pcOff) + datap.text - datap.minpc // TODO: are datap.text and datap.minpc always equal?
   935  	if GOARCH == "wasm" {
   936  		// On Wasm, pcOff is the function index, whereas
   937  		// the "PC" is function index << 16 + block index.
   938  		x = uintptr(pcOff)<<16 + datap.text - datap.minpc
   939  	}
   940  	b := x / abi.FuncTabBucketSize
   941  	i := x % abi.FuncTabBucketSize / (abi.FuncTabBucketSize / nsub)
   942  
   943  	ffb := (*findfuncbucket)(add(unsafe.Pointer(datap.findfunctab), b*unsafe.Sizeof(findfuncbucket{})))
   944  	idx := ffb.idx + uint32(ffb.subbuckets[i])
   945  
   946  	// Find the ftab entry.
   947  	for datap.ftab[idx+1].entryoff <= pcOff {
   948  		idx++
   949  	}
   950  
   951  	funcoff := datap.ftab[idx].funcoff
   952  	return funcInfo{(*_func)(unsafe.Pointer(&datap.pclntable[funcoff])), datap}
   953  }
   954  
   955  // A srcFunc represents a logical function in the source code. This may
   956  // correspond to an actual symbol in the binary text, or it may correspond to a
   957  // source function that has been inlined.
   958  type srcFunc struct {
   959  	datap     *moduledata
   960  	nameOff   int32
   961  	startLine int32
   962  	funcID    abi.FuncID
   963  }
   964  
   965  func (f funcInfo) srcFunc() srcFunc {
   966  	if !f.valid() {
   967  		return srcFunc{}
   968  	}
   969  	return srcFunc{f.datap, f.nameOff, f.startLine, f.funcID}
   970  }
   971  
   972  // name should be an internal detail,
   973  // but widely used packages access it using linkname.
   974  // Notable members of the hall of shame include:
   975  //   - github.com/phuslu/log
   976  //
   977  // Do not remove or change the type signature.
   978  // See go.dev/issue/67401.
   979  func (s srcFunc) name() string {
   980  	if s.datap == nil {
   981  		return ""
   982  	}
   983  	return s.datap.funcName(s.nameOff)
   984  }
   985  
   986  //go:linkname badSrcFuncName runtime.srcFunc.name
   987  func badSrcFuncName(srcFunc) string
   988  
   989  type pcvalueCache struct {
   990  	entries [2][8]pcvalueCacheEnt
   991  	inUse   int
   992  }
   993  
   994  type pcvalueCacheEnt struct {
   995  	// targetpc and off together are the key of this cache entry.
   996  	targetpc uintptr
   997  	off      uint32
   998  
   999  	val   int32   // The value of this entry.
  1000  	valPC uintptr // The PC at which val starts
  1001  }
  1002  
  1003  // pcvalueCacheKey returns the outermost index in a pcvalueCache to use for targetpc.
  1004  // It must be very cheap to calculate.
  1005  // For now, align to goarch.PtrSize and reduce mod the number of entries.
  1006  // In practice, this appears to be fairly randomly and evenly distributed.
  1007  func pcvalueCacheKey(targetpc uintptr) uintptr {
  1008  	return (targetpc / goarch.PtrSize) % uintptr(len(pcvalueCache{}.entries))
  1009  }
  1010  
  1011  // Returns the PCData value, and the PC where this value starts.
  1012  func pcvalue(f funcInfo, off uint32, targetpc uintptr, strict bool) (int32, uintptr) {
  1013  	// If true, when we get a cache hit, still look up the data and make sure it
  1014  	// matches the cached contents.
  1015  	const debugCheckCache = false
  1016  
  1017  	// If true, skip checking the cache entirely.
  1018  	const skipCache = false
  1019  
  1020  	if off == 0 {
  1021  		return -1, 0
  1022  	}
  1023  
  1024  	// Check the cache. This speeds up walks of deep stacks, which
  1025  	// tend to have the same recursive functions over and over,
  1026  	// or repetitive stacks between goroutines.
  1027  	var checkVal int32
  1028  	var checkPC uintptr
  1029  	ck := pcvalueCacheKey(targetpc)
  1030  	if !skipCache {
  1031  		mp := acquirem()
  1032  		cache := &mp.pcvalueCache
  1033  		// The cache can be used by the signal handler on this M. Avoid
  1034  		// re-entrant use of the cache. The signal handler can also write inUse,
  1035  		// but will always restore its value, so we can use a regular increment
  1036  		// even if we get signaled in the middle of it.
  1037  		cache.inUse++
  1038  		if cache.inUse == 1 {
  1039  			for i := range cache.entries[ck] {
  1040  				// We check off first because we're more
  1041  				// likely to have multiple entries with
  1042  				// different offsets for the same targetpc
  1043  				// than the other way around, so we'll usually
  1044  				// fail in the first clause.
  1045  				ent := &cache.entries[ck][i]
  1046  				if ent.off == off && ent.targetpc == targetpc {
  1047  					val, pc := ent.val, ent.valPC
  1048  					if debugCheckCache {
  1049  						checkVal, checkPC = ent.val, ent.valPC
  1050  						break
  1051  					} else {
  1052  						cache.inUse--
  1053  						releasem(mp)
  1054  						return val, pc
  1055  					}
  1056  				}
  1057  			}
  1058  		} else if debugCheckCache && (cache.inUse < 1 || cache.inUse > 2) {
  1059  			// Catch accounting errors or deeply reentrant use. In principle
  1060  			// "inUse" should never exceed 2.
  1061  			throw("cache.inUse out of range")
  1062  		}
  1063  		cache.inUse--
  1064  		releasem(mp)
  1065  	}
  1066  
  1067  	if !f.valid() {
  1068  		if strict && panicking.Load() == 0 {
  1069  			println("runtime: no module data for", hex(f.entry()))
  1070  			throw("no module data")
  1071  		}
  1072  		return -1, 0
  1073  	}
  1074  	datap := f.datap
  1075  	p := datap.pctab[off:]
  1076  	pc := f.entry()
  1077  	prevpc := pc
  1078  	val := int32(-1)
  1079  	for {
  1080  		var ok bool
  1081  		p, ok = step(p, &pc, &val, pc == f.entry())
  1082  		if !ok {
  1083  			break
  1084  		}
  1085  		if targetpc < pc {
  1086  			// Replace a random entry in the cache. Random
  1087  			// replacement prevents a performance cliff if
  1088  			// a recursive stack's cycle is slightly
  1089  			// larger than the cache.
  1090  			// Put the new element at the beginning,
  1091  			// since it is the most likely to be newly used.
  1092  			if debugCheckCache && checkPC != 0 {
  1093  				if checkVal != val || checkPC != prevpc {
  1094  					print("runtime: table value ", val, "@", prevpc, " != cache value ", checkVal, "@", checkPC, " at PC ", targetpc, " off ", off, "\n")
  1095  					throw("bad pcvalue cache")
  1096  				}
  1097  			} else {
  1098  				mp := acquirem()
  1099  				cache := &mp.pcvalueCache
  1100  				cache.inUse++
  1101  				if cache.inUse == 1 {
  1102  					e := &cache.entries[ck]
  1103  					ci := cheaprandn(uint32(len(cache.entries[ck])))
  1104  					e[ci] = e[0]
  1105  					e[0] = pcvalueCacheEnt{
  1106  						targetpc: targetpc,
  1107  						off:      off,
  1108  						val:      val,
  1109  						valPC:    prevpc,
  1110  					}
  1111  				}
  1112  				cache.inUse--
  1113  				releasem(mp)
  1114  			}
  1115  
  1116  			return val, prevpc
  1117  		}
  1118  		prevpc = pc
  1119  	}
  1120  
  1121  	// If there was a table, it should have covered all program counters.
  1122  	// If not, something is wrong.
  1123  	if panicking.Load() != 0 || !strict {
  1124  		return -1, 0
  1125  	}
  1126  
  1127  	print("runtime: invalid pc-encoded table f=", funcname(f), " pc=", hex(pc), " targetpc=", hex(targetpc), " tab=", p, "\n")
  1128  
  1129  	p = datap.pctab[off:]
  1130  	pc = f.entry()
  1131  	val = -1
  1132  	for {
  1133  		var ok bool
  1134  		p, ok = step(p, &pc, &val, pc == f.entry())
  1135  		if !ok {
  1136  			break
  1137  		}
  1138  		print("\tvalue=", val, " until pc=", hex(pc), "\n")
  1139  	}
  1140  
  1141  	throw("invalid runtime symbol table")
  1142  	return -1, 0
  1143  }
  1144  
  1145  func funcname(f funcInfo) string {
  1146  	if !f.valid() {
  1147  		return ""
  1148  	}
  1149  	return f.datap.funcName(f.nameOff)
  1150  }
  1151  
  1152  func funcpkgpath(f funcInfo) string {
  1153  	name := funcNameForPrint(funcname(f))
  1154  	i := len(name) - 1
  1155  	for ; i > 0; i-- {
  1156  		if name[i] == '/' {
  1157  			break
  1158  		}
  1159  	}
  1160  	for ; i < len(name); i++ {
  1161  		if name[i] == '.' {
  1162  			break
  1163  		}
  1164  	}
  1165  	return name[:i]
  1166  }
  1167  
  1168  func funcfile(f funcInfo, fileno int32) string {
  1169  	datap := f.datap
  1170  	if !f.valid() {
  1171  		return "?"
  1172  	}
  1173  	// Make sure the cu index and file offset are valid
  1174  	if fileoff := datap.cutab[f.cuOffset+uint32(fileno)]; fileoff != ^uint32(0) {
  1175  		return gostringnocopy(&datap.filetab[fileoff])
  1176  	}
  1177  	// pcln section is corrupt.
  1178  	return "?"
  1179  }
  1180  
  1181  // funcline1 should be an internal detail,
  1182  // but widely used packages access it using linkname.
  1183  // Notable members of the hall of shame include:
  1184  //   - github.com/phuslu/log
  1185  //
  1186  // Do not remove or change the type signature.
  1187  // See go.dev/issue/67401.
  1188  //
  1189  //go:linkname funcline1
  1190  func funcline1(f funcInfo, targetpc uintptr, strict bool) (file string, line int32) {
  1191  	datap := f.datap
  1192  	if !f.valid() {
  1193  		return "?", 0
  1194  	}
  1195  	fileno, _ := pcvalue(f, f.pcfile, targetpc, strict)
  1196  	line, _ = pcvalue(f, f.pcln, targetpc, strict)
  1197  	if fileno == -1 || line == -1 || int(fileno) >= len(datap.filetab) {
  1198  		// print("looking for ", hex(targetpc), " in ", funcname(f), " got file=", fileno, " line=", lineno, "\n")
  1199  		return "?", 0
  1200  	}
  1201  	file = funcfile(f, fileno)
  1202  	return
  1203  }
  1204  
  1205  func funcline(f funcInfo, targetpc uintptr) (file string, line int32) {
  1206  	return funcline1(f, targetpc, true)
  1207  }
  1208  
  1209  func funcspdelta(f funcInfo, targetpc uintptr) int32 {
  1210  	x, _ := pcvalue(f, f.pcsp, targetpc, true)
  1211  	if debugPcln && x&(goarch.PtrSize-1) != 0 {
  1212  		print("invalid spdelta ", funcname(f), " ", hex(f.entry()), " ", hex(targetpc), " ", hex(f.pcsp), " ", x, "\n")
  1213  		throw("bad spdelta")
  1214  	}
  1215  	return x
  1216  }
  1217  
  1218  // funcMaxSPDelta returns the maximum spdelta at any point in f.
  1219  func funcMaxSPDelta(f funcInfo) int32 {
  1220  	datap := f.datap
  1221  	p := datap.pctab[f.pcsp:]
  1222  	pc := f.entry()
  1223  	val := int32(-1)
  1224  	most := int32(0)
  1225  	for {
  1226  		var ok bool
  1227  		p, ok = step(p, &pc, &val, pc == f.entry())
  1228  		if !ok {
  1229  			return most
  1230  		}
  1231  		most = max(most, val)
  1232  	}
  1233  }
  1234  
  1235  func pcdatastart(f funcInfo, table uint32) uint32 {
  1236  	return *(*uint32)(add(unsafe.Pointer(&f.nfuncdata), unsafe.Sizeof(f.nfuncdata)+uintptr(table)*4))
  1237  }
  1238  
  1239  func pcdatavalue(f funcInfo, table uint32, targetpc uintptr) int32 {
  1240  	if table >= f.npcdata {
  1241  		return -1
  1242  	}
  1243  	r, _ := pcvalue(f, pcdatastart(f, table), targetpc, true)
  1244  	return r
  1245  }
  1246  
  1247  func pcdatavalue1(f funcInfo, table uint32, targetpc uintptr, strict bool) int32 {
  1248  	if table >= f.npcdata {
  1249  		return -1
  1250  	}
  1251  	r, _ := pcvalue(f, pcdatastart(f, table), targetpc, strict)
  1252  	return r
  1253  }
  1254  
  1255  // Like pcdatavalue, but also return the start PC of this PCData value.
  1256  func pcdatavalue2(f funcInfo, table uint32, targetpc uintptr) (int32, uintptr) {
  1257  	if table >= f.npcdata {
  1258  		return -1, 0
  1259  	}
  1260  	return pcvalue(f, pcdatastart(f, table), targetpc, true)
  1261  }
  1262  
  1263  // funcdata returns a pointer to the ith funcdata for f.
  1264  // funcdata should be kept in sync with cmd/link:writeFuncs.
  1265  func funcdata(f funcInfo, i uint8) unsafe.Pointer {
  1266  	if i < 0 || i >= f.nfuncdata {
  1267  		return nil
  1268  	}
  1269  	base := f.datap.gofunc // load gofunc address early so that we calculate during cache misses
  1270  	p := uintptr(unsafe.Pointer(&f.nfuncdata)) + unsafe.Sizeof(f.nfuncdata) + uintptr(f.npcdata)*4 + uintptr(i)*4
  1271  	off := *(*uint32)(unsafe.Pointer(p))
  1272  	// Return off == ^uint32(0) ? 0 : f.datap.gofunc + uintptr(off), but without branches.
  1273  	// The compiler calculates mask on most architectures using conditional assignment.
  1274  	var mask uintptr
  1275  	if off == ^uint32(0) {
  1276  		mask = 1
  1277  	}
  1278  	mask--
  1279  	raw := base + uintptr(off)
  1280  	return unsafe.Pointer(raw & mask)
  1281  }
  1282  
  1283  // step advances to the next pc, value pair in the encoded table.
  1284  func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool) {
  1285  	// For both uvdelta and pcdelta, the common case (~70%)
  1286  	// is that they are a single byte. If so, avoid calling readvarint.
  1287  	uvdelta := uint32(p[0])
  1288  	if uvdelta == 0 && !first {
  1289  		return nil, false
  1290  	}
  1291  	n := uint32(1)
  1292  	if uvdelta&0x80 != 0 {
  1293  		n, uvdelta = readvarint(p)
  1294  	}
  1295  	*val += int32(-(uvdelta & 1) ^ (uvdelta >> 1))
  1296  	p = p[n:]
  1297  
  1298  	pcdelta := uint32(p[0])
  1299  	n = 1
  1300  	if pcdelta&0x80 != 0 {
  1301  		n, pcdelta = readvarint(p)
  1302  	}
  1303  	p = p[n:]
  1304  	*pc += uintptr(pcdelta * sys.PCQuantum)
  1305  	return p, true
  1306  }
  1307  
  1308  // readvarint reads a varint from p.
  1309  func readvarint(p []byte) (read uint32, val uint32) {
  1310  	var v, shift, n uint32
  1311  	for {
  1312  		b := p[n]
  1313  		n++
  1314  		v |= uint32(b&0x7F) << (shift & 31)
  1315  		if b&0x80 == 0 {
  1316  			break
  1317  		}
  1318  		shift += 7
  1319  	}
  1320  	return n, v
  1321  }
  1322  
  1323  type stackmap struct {
  1324  	n        int32   // number of bitmaps
  1325  	nbit     int32   // number of bits in each bitmap
  1326  	bytedata [1]byte // bitmaps, each starting on a byte boundary
  1327  }
  1328  
  1329  //go:nowritebarrier
  1330  func stackmapdata(stkmap *stackmap, n int32) bitvector {
  1331  	// Check this invariant only when stackDebug is on at all.
  1332  	// The invariant is already checked by many of stackmapdata's callers,
  1333  	// and disabling it by default allows stackmapdata to be inlined.
  1334  	if stackDebug > 0 && (n < 0 || n >= stkmap.n) {
  1335  		throw("stackmapdata: index out of range")
  1336  	}
  1337  	return bitvector{stkmap.nbit, addb(&stkmap.bytedata[0], uintptr(n*((stkmap.nbit+7)>>3)))}
  1338  }
  1339  

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