Source file src/runtime/traceback.go

     1  // Copyright 2009 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/bytealg"
     9  	"runtime/internal/atomic"
    10  	"runtime/internal/sys"
    11  	"unsafe"
    12  )
    13  
    14  // The code in this file implements stack trace walking for all architectures.
    15  // The most important fact about a given architecture is whether it uses a link register.
    16  // On systems with link registers, the prologue for a non-leaf function stores the
    17  // incoming value of LR at the bottom of the newly allocated stack frame.
    18  // On systems without link registers (x86), the architecture pushes a return PC during
    19  // the call instruction, so the return PC ends up above the stack frame.
    20  // In this file, the return PC is always called LR, no matter how it was found.
    21  
    22  const usesLR = sys.MinFrameSize > 0
    23  
    24  // Traceback over the deferred function calls.
    25  // Report them like calls that have been invoked but not started executing yet.
    26  func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
    27  	var frame stkframe
    28  	for d := gp._defer; d != nil; d = d.link {
    29  		fn := d.fn
    30  		if fn == nil {
    31  			// Defer of nil function. Args don't matter.
    32  			frame.pc = 0
    33  			frame.fn = funcInfo{}
    34  			frame.argp = 0
    35  			frame.arglen = 0
    36  			frame.argmap = nil
    37  		} else {
    38  			frame.pc = fn.fn
    39  			f := findfunc(frame.pc)
    40  			if !f.valid() {
    41  				print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
    42  				throw("unknown pc")
    43  			}
    44  			frame.fn = f
    45  			frame.argp = uintptr(deferArgs(d))
    46  			var ok bool
    47  			frame.arglen, frame.argmap, ok = getArgInfoFast(f, true)
    48  			if !ok {
    49  				frame.arglen, frame.argmap = getArgInfo(&frame, f, true, fn)
    50  			}
    51  		}
    52  		frame.continpc = frame.pc
    53  		if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
    54  			return
    55  		}
    56  	}
    57  }
    58  
    59  // Generic traceback. Handles runtime stack prints (pcbuf == nil),
    60  // the runtime.Callers function (pcbuf != nil), as well as the garbage
    61  // collector (callback != nil).  A little clunky to merge these, but avoids
    62  // duplicating the code and all its subtlety.
    63  //
    64  // The skip argument is only valid with pcbuf != nil and counts the number
    65  // of logical frames to skip rather than physical frames (with inlining, a
    66  // PC in pcbuf can represent multiple calls).
    67  func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max int, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) int {
    68  	if skip > 0 && callback != nil {
    69  		throw("gentraceback callback cannot be used with non-zero skip")
    70  	}
    71  
    72  	// Don't call this "g"; it's too easy get "g" and "gp" confused.
    73  	if ourg := getg(); ourg == gp && ourg == ourg.m.curg {
    74  		// The starting sp has been passed in as a uintptr, and the caller may
    75  		// have other uintptr-typed stack references as well.
    76  		// If during one of the calls that got us here or during one of the
    77  		// callbacks below the stack must be grown, all these uintptr references
    78  		// to the stack will not be updated, and gentraceback will continue
    79  		// to inspect the old stack memory, which may no longer be valid.
    80  		// Even if all the variables were updated correctly, it is not clear that
    81  		// we want to expose a traceback that begins on one stack and ends
    82  		// on another stack. That could confuse callers quite a bit.
    83  		// Instead, we require that gentraceback and any other function that
    84  		// accepts an sp for the current goroutine (typically obtained by
    85  		// calling getcallersp) must not run on that goroutine's stack but
    86  		// instead on the g0 stack.
    87  		throw("gentraceback cannot trace user goroutine on its own stack")
    88  	}
    89  	level, _, _ := gotraceback()
    90  
    91  	var ctxt *funcval // Context pointer for unstarted goroutines. See issue #25897.
    92  
    93  	if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.
    94  		if gp.syscallsp != 0 {
    95  			pc0 = gp.syscallpc
    96  			sp0 = gp.syscallsp
    97  			if usesLR {
    98  				lr0 = 0
    99  			}
   100  		} else {
   101  			pc0 = gp.sched.pc
   102  			sp0 = gp.sched.sp
   103  			if usesLR {
   104  				lr0 = gp.sched.lr
   105  			}
   106  			ctxt = (*funcval)(gp.sched.ctxt)
   107  		}
   108  	}
   109  
   110  	nprint := 0
   111  	var frame stkframe
   112  	frame.pc = pc0
   113  	frame.sp = sp0
   114  	if usesLR {
   115  		frame.lr = lr0
   116  	}
   117  	waspanic := false
   118  	cgoCtxt := gp.cgoCtxt
   119  	printing := pcbuf == nil && callback == nil
   120  
   121  	// If the PC is zero, it's likely a nil function call.
   122  	// Start in the caller's frame.
   123  	if frame.pc == 0 {
   124  		if usesLR {
   125  			frame.pc = *(*uintptr)(unsafe.Pointer(frame.sp))
   126  			frame.lr = 0
   127  		} else {
   128  			frame.pc = uintptr(*(*uintptr)(unsafe.Pointer(frame.sp)))
   129  			frame.sp += sys.PtrSize
   130  		}
   131  	}
   132  
   133  	f := findfunc(frame.pc)
   134  	if !f.valid() {
   135  		if callback != nil || printing {
   136  			print("runtime: unknown pc ", hex(frame.pc), "\n")
   137  			tracebackHexdump(gp.stack, &frame, 0)
   138  		}
   139  		if callback != nil {
   140  			throw("unknown pc")
   141  		}
   142  		return 0
   143  	}
   144  	frame.fn = f
   145  
   146  	var cache pcvalueCache
   147  
   148  	lastFuncID := funcID_normal
   149  	n := 0
   150  	for n < max {
   151  		// Typically:
   152  		//	pc is the PC of the running function.
   153  		//	sp is the stack pointer at that program counter.
   154  		//	fp is the frame pointer (caller's stack pointer) at that program counter, or nil if unknown.
   155  		//	stk is the stack containing sp.
   156  		//	The caller's program counter is lr, unless lr is zero, in which case it is *(uintptr*)sp.
   157  		f = frame.fn
   158  		if f.pcsp == 0 {
   159  			// No frame information, must be external function, like race support.
   160  			// See golang.org/issue/13568.
   161  			break
   162  		}
   163  
   164  		// Compute function info flags.
   165  		flag := f.flag
   166  		if f.funcID == funcID_cgocallback {
   167  			// cgocallback does write SP to switch from the g0 to the curg stack,
   168  			// but it carefully arranges that during the transition BOTH stacks
   169  			// have cgocallback frame valid for unwinding through.
   170  			// So we don't need to exclude it with the other SP-writing functions.
   171  			flag &^= funcFlag_SPWRITE
   172  		}
   173  		if frame.pc == pc0 && frame.sp == sp0 && pc0 == gp.syscallpc && sp0 == gp.syscallsp {
   174  			// Some Syscall functions write to SP, but they do so only after
   175  			// saving the entry PC/SP using entersyscall.
   176  			// Since we are using the entry PC/SP, the later SP write doesn't matter.
   177  			flag &^= funcFlag_SPWRITE
   178  		}
   179  
   180  		// Found an actual function.
   181  		// Derive frame pointer and link register.
   182  		if frame.fp == 0 {
   183  			// Jump over system stack transitions. If we're on g0 and there's a user
   184  			// goroutine, try to jump. Otherwise this is a regular call.
   185  			if flags&_TraceJumpStack != 0 && gp == gp.m.g0 && gp.m.curg != nil {
   186  				switch f.funcID {
   187  				case funcID_morestack:
   188  					// morestack does not return normally -- newstack()
   189  					// gogo's to curg.sched. Match that.
   190  					// This keeps morestack() from showing up in the backtrace,
   191  					// but that makes some sense since it'll never be returned
   192  					// to.
   193  					frame.pc = gp.m.curg.sched.pc
   194  					frame.fn = findfunc(frame.pc)
   195  					f = frame.fn
   196  					flag = f.flag
   197  					frame.sp = gp.m.curg.sched.sp
   198  					cgoCtxt = gp.m.curg.cgoCtxt
   199  				case funcID_systemstack:
   200  					// systemstack returns normally, so just follow the
   201  					// stack transition.
   202  					frame.sp = gp.m.curg.sched.sp
   203  					cgoCtxt = gp.m.curg.cgoCtxt
   204  					flag &^= funcFlag_SPWRITE
   205  				}
   206  			}
   207  			frame.fp = frame.sp + uintptr(funcspdelta(f, frame.pc, &cache))
   208  			if !usesLR {
   209  				// On x86, call instruction pushes return PC before entering new function.
   210  				frame.fp += sys.PtrSize
   211  			}
   212  		}
   213  		var flr funcInfo
   214  		if flag&funcFlag_TOPFRAME != 0 {
   215  			// This function marks the top of the stack. Stop the traceback.
   216  			frame.lr = 0
   217  			flr = funcInfo{}
   218  		} else if flag&funcFlag_SPWRITE != 0 && (callback == nil || n > 0) {
   219  			// The function we are in does a write to SP that we don't know
   220  			// how to encode in the spdelta table. Examples include context
   221  			// switch routines like runtime.gogo but also any code that switches
   222  			// to the g0 stack to run host C code. Since we can't reliably unwind
   223  			// the SP (we might not even be on the stack we think we are),
   224  			// we stop the traceback here.
   225  			// This only applies for profiling signals (callback == nil).
   226  			//
   227  			// For a GC stack traversal (callback != nil), we should only see
   228  			// a function when it has voluntarily preempted itself on entry
   229  			// during the stack growth check. In that case, the function has
   230  			// not yet had a chance to do any writes to SP and is safe to unwind.
   231  			// isAsyncSafePoint does not allow assembly functions to be async preempted,
   232  			// and preemptPark double-checks that SPWRITE functions are not async preempted.
   233  			// So for GC stack traversal we leave things alone (this if body does not execute for n == 0)
   234  			// at the bottom frame of the stack. But farther up the stack we'd better not
   235  			// find any.
   236  			if callback != nil {
   237  				println("traceback: unexpected SPWRITE function", funcname(f))
   238  				throw("traceback")
   239  			}
   240  			frame.lr = 0
   241  			flr = funcInfo{}
   242  		} else {
   243  			var lrPtr uintptr
   244  			if usesLR {
   245  				if n == 0 && frame.sp < frame.fp || frame.lr == 0 {
   246  					lrPtr = frame.sp
   247  					frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
   248  				}
   249  			} else {
   250  				if frame.lr == 0 {
   251  					lrPtr = frame.fp - sys.PtrSize
   252  					frame.lr = uintptr(*(*uintptr)(unsafe.Pointer(lrPtr)))
   253  				}
   254  			}
   255  			flr = findfunc(frame.lr)
   256  			if !flr.valid() {
   257  				// This happens if you get a profiling interrupt at just the wrong time.
   258  				// In that context it is okay to stop early.
   259  				// But if callback is set, we're doing a garbage collection and must
   260  				// get everything, so crash loudly.
   261  				doPrint := printing
   262  				if doPrint && gp.m.incgo && f.funcID == funcID_sigpanic {
   263  					// We can inject sigpanic
   264  					// calls directly into C code,
   265  					// in which case we'll see a C
   266  					// return PC. Don't complain.
   267  					doPrint = false
   268  				}
   269  				if callback != nil || doPrint {
   270  					print("runtime: unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
   271  					tracebackHexdump(gp.stack, &frame, lrPtr)
   272  				}
   273  				if callback != nil {
   274  					throw("unknown caller pc")
   275  				}
   276  			}
   277  		}
   278  
   279  		frame.varp = frame.fp
   280  		if !usesLR {
   281  			// On x86, call instruction pushes return PC before entering new function.
   282  			frame.varp -= sys.PtrSize
   283  		}
   284  
   285  		// For architectures with frame pointers, if there's
   286  		// a frame, then there's a saved frame pointer here.
   287  		//
   288  		// NOTE: This code is not as general as it looks.
   289  		// On x86, the ABI is to save the frame pointer word at the
   290  		// top of the stack frame, so we have to back down over it.
   291  		// On arm64, the frame pointer should be at the bottom of
   292  		// the stack (with R29 (aka FP) = RSP), in which case we would
   293  		// not want to do the subtraction here. But we started out without
   294  		// any frame pointer, and when we wanted to add it, we didn't
   295  		// want to break all the assembly doing direct writes to 8(RSP)
   296  		// to set the first parameter to a called function.
   297  		// So we decided to write the FP link *below* the stack pointer
   298  		// (with R29 = RSP - 8 in Go functions).
   299  		// This is technically ABI-compatible but not standard.
   300  		// And it happens to end up mimicking the x86 layout.
   301  		// Other architectures may make different decisions.
   302  		if frame.varp > frame.sp && framepointer_enabled {
   303  			frame.varp -= sys.PtrSize
   304  		}
   305  
   306  		// Derive size of arguments.
   307  		// Most functions have a fixed-size argument block,
   308  		// so we can use metadata about the function f.
   309  		// Not all, though: there are some variadic functions
   310  		// in package runtime and reflect, and for those we use call-specific
   311  		// metadata recorded by f's caller.
   312  		if callback != nil || printing {
   313  			frame.argp = frame.fp + sys.MinFrameSize
   314  			var ok bool
   315  			frame.arglen, frame.argmap, ok = getArgInfoFast(f, callback != nil)
   316  			if !ok {
   317  				frame.arglen, frame.argmap = getArgInfo(&frame, f, callback != nil, ctxt)
   318  			}
   319  		}
   320  		ctxt = nil // ctxt is only needed to get arg maps for the topmost frame
   321  
   322  		// Determine frame's 'continuation PC', where it can continue.
   323  		// Normally this is the return address on the stack, but if sigpanic
   324  		// is immediately below this function on the stack, then the frame
   325  		// stopped executing due to a trap, and frame.pc is probably not
   326  		// a safe point for looking up liveness information. In this panicking case,
   327  		// the function either doesn't return at all (if it has no defers or if the
   328  		// defers do not recover) or it returns from one of the calls to
   329  		// deferproc a second time (if the corresponding deferred func recovers).
   330  		// In the latter case, use a deferreturn call site as the continuation pc.
   331  		frame.continpc = frame.pc
   332  		if waspanic {
   333  			if frame.fn.deferreturn != 0 {
   334  				frame.continpc = frame.fn.entry + uintptr(frame.fn.deferreturn) + 1
   335  				// Note: this may perhaps keep return variables alive longer than
   336  				// strictly necessary, as we are using "function has a defer statement"
   337  				// as a proxy for "function actually deferred something". It seems
   338  				// to be a minor drawback. (We used to actually look through the
   339  				// gp._defer for a defer corresponding to this function, but that
   340  				// is hard to do with defer records on the stack during a stack copy.)
   341  				// Note: the +1 is to offset the -1 that
   342  				// stack.go:getStackMap does to back up a return
   343  				// address make sure the pc is in the CALL instruction.
   344  			} else {
   345  				frame.continpc = 0
   346  			}
   347  		}
   348  
   349  		if callback != nil {
   350  			if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
   351  				return n
   352  			}
   353  		}
   354  
   355  		if pcbuf != nil {
   356  			pc := frame.pc
   357  			// backup to CALL instruction to read inlining info (same logic as below)
   358  			tracepc := pc
   359  			// Normally, pc is a return address. In that case, we want to look up
   360  			// file/line information using pc-1, because that is the pc of the
   361  			// call instruction (more precisely, the last byte of the call instruction).
   362  			// Callers expect the pc buffer to contain return addresses and do the
   363  			// same -1 themselves, so we keep pc unchanged.
   364  			// When the pc is from a signal (e.g. profiler or segv) then we want
   365  			// to look up file/line information using pc, and we store pc+1 in the
   366  			// pc buffer so callers can unconditionally subtract 1 before looking up.
   367  			// See issue 34123.
   368  			// The pc can be at function entry when the frame is initialized without
   369  			// actually running code, like runtime.mstart.
   370  			if (n == 0 && flags&_TraceTrap != 0) || waspanic || pc == f.entry {
   371  				pc++
   372  			} else {
   373  				tracepc--
   374  			}
   375  
   376  			// If there is inlining info, record the inner frames.
   377  			if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   378  				inltree := (*[1 << 20]inlinedCall)(inldata)
   379  				for {
   380  					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, &cache)
   381  					if ix < 0 {
   382  						break
   383  					}
   384  					if inltree[ix].funcID == funcID_wrapper && elideWrapperCalling(lastFuncID) {
   385  						// ignore wrappers
   386  					} else if skip > 0 {
   387  						skip--
   388  					} else if n < max {
   389  						(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   390  						n++
   391  					}
   392  					lastFuncID = inltree[ix].funcID
   393  					// Back up to an instruction in the "caller".
   394  					tracepc = frame.fn.entry + uintptr(inltree[ix].parentPc)
   395  					pc = tracepc + 1
   396  				}
   397  			}
   398  			// Record the main frame.
   399  			if f.funcID == funcID_wrapper && elideWrapperCalling(lastFuncID) {
   400  				// Ignore wrapper functions (except when they trigger panics).
   401  			} else if skip > 0 {
   402  				skip--
   403  			} else if n < max {
   404  				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   405  				n++
   406  			}
   407  			lastFuncID = f.funcID
   408  			n-- // offset n++ below
   409  		}
   410  
   411  		if printing {
   412  			// assume skip=0 for printing.
   413  			//
   414  			// Never elide wrappers if we haven't printed
   415  			// any frames. And don't elide wrappers that
   416  			// called panic rather than the wrapped
   417  			// function. Otherwise, leave them out.
   418  
   419  			// backup to CALL instruction to read inlining info (same logic as below)
   420  			tracepc := frame.pc
   421  			if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
   422  				tracepc--
   423  			}
   424  			// If there is inlining info, print the inner frames.
   425  			if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   426  				inltree := (*[1 << 20]inlinedCall)(inldata)
   427  				var inlFunc _func
   428  				inlFuncInfo := funcInfo{&inlFunc, f.datap}
   429  				for {
   430  					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, nil)
   431  					if ix < 0 {
   432  						break
   433  					}
   434  
   435  					// Create a fake _func for the
   436  					// inlined function.
   437  					inlFunc.nameoff = inltree[ix].func_
   438  					inlFunc.funcID = inltree[ix].funcID
   439  
   440  					if (flags&_TraceRuntimeFrames) != 0 || showframe(inlFuncInfo, gp, nprint == 0, inlFuncInfo.funcID, lastFuncID) {
   441  						name := funcname(inlFuncInfo)
   442  						file, line := funcline(f, tracepc)
   443  						print(name, "(...)\n")
   444  						print("\t", file, ":", line, "\n")
   445  						nprint++
   446  					}
   447  					lastFuncID = inltree[ix].funcID
   448  					// Back up to an instruction in the "caller".
   449  					tracepc = frame.fn.entry + uintptr(inltree[ix].parentPc)
   450  				}
   451  			}
   452  			if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp, nprint == 0, f.funcID, lastFuncID) {
   453  				// Print during crash.
   454  				//	main(0x1, 0x2, 0x3)
   455  				//		/home/rsc/go/src/runtime/x.go:23 +0xf
   456  				//
   457  				name := funcname(f)
   458  				file, line := funcline(f, tracepc)
   459  				if name == "runtime.gopanic" {
   460  					name = "panic"
   461  				}
   462  				print(name, "(")
   463  				argp := unsafe.Pointer(frame.argp)
   464  				printArgs(f, argp)
   465  				print(")\n")
   466  				print("\t", file, ":", line)
   467  				if frame.pc > f.entry {
   468  					print(" +", hex(frame.pc-f.entry))
   469  				}
   470  				if gp.m != nil && gp.m.throwing > 0 && gp == gp.m.curg || level >= 2 {
   471  					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp), " pc=", hex(frame.pc))
   472  				}
   473  				print("\n")
   474  				nprint++
   475  			}
   476  			lastFuncID = f.funcID
   477  		}
   478  		n++
   479  
   480  		if f.funcID == funcID_cgocallback && len(cgoCtxt) > 0 {
   481  			ctxt := cgoCtxt[len(cgoCtxt)-1]
   482  			cgoCtxt = cgoCtxt[:len(cgoCtxt)-1]
   483  
   484  			// skip only applies to Go frames.
   485  			// callback != nil only used when we only care
   486  			// about Go frames.
   487  			if skip == 0 && callback == nil {
   488  				n = tracebackCgoContext(pcbuf, printing, ctxt, n, max)
   489  			}
   490  		}
   491  
   492  		waspanic = f.funcID == funcID_sigpanic
   493  		injectedCall := waspanic || f.funcID == funcID_asyncPreempt
   494  
   495  		// Do not unwind past the bottom of the stack.
   496  		if !flr.valid() {
   497  			break
   498  		}
   499  
   500  		// Unwind to next frame.
   501  		frame.fn = flr
   502  		frame.pc = frame.lr
   503  		frame.lr = 0
   504  		frame.sp = frame.fp
   505  		frame.fp = 0
   506  		frame.argmap = nil
   507  
   508  		// On link register architectures, sighandler saves the LR on stack
   509  		// before faking a call.
   510  		if usesLR && injectedCall {
   511  			x := *(*uintptr)(unsafe.Pointer(frame.sp))
   512  			frame.sp += alignUp(sys.MinFrameSize, sys.StackAlign)
   513  			f = findfunc(frame.pc)
   514  			frame.fn = f
   515  			if !f.valid() {
   516  				frame.pc = x
   517  			} else if funcspdelta(f, frame.pc, &cache) == 0 {
   518  				frame.lr = x
   519  			}
   520  		}
   521  	}
   522  
   523  	if printing {
   524  		n = nprint
   525  	}
   526  
   527  	// Note that panic != nil is okay here: there can be leftover panics,
   528  	// because the defers on the panic stack do not nest in frame order as
   529  	// they do on the defer stack. If you have:
   530  	//
   531  	//	frame 1 defers d1
   532  	//	frame 2 defers d2
   533  	//	frame 3 defers d3
   534  	//	frame 4 panics
   535  	//	frame 4's panic starts running defers
   536  	//	frame 5, running d3, defers d4
   537  	//	frame 5 panics
   538  	//	frame 5's panic starts running defers
   539  	//	frame 6, running d4, garbage collects
   540  	//	frame 6, running d2, garbage collects
   541  	//
   542  	// During the execution of d4, the panic stack is d4 -> d3, which
   543  	// is nested properly, and we'll treat frame 3 as resumable, because we
   544  	// can find d3. (And in fact frame 3 is resumable. If d4 recovers
   545  	// and frame 5 continues running, d3, d3 can recover and we'll
   546  	// resume execution in (returning from) frame 3.)
   547  	//
   548  	// During the execution of d2, however, the panic stack is d2 -> d3,
   549  	// which is inverted. The scan will match d2 to frame 2 but having
   550  	// d2 on the stack until then means it will not match d3 to frame 3.
   551  	// This is okay: if we're running d2, then all the defers after d2 have
   552  	// completed and their corresponding frames are dead. Not finding d3
   553  	// for frame 3 means we'll set frame 3's continpc == 0, which is correct
   554  	// (frame 3 is dead). At the end of the walk the panic stack can thus
   555  	// contain defers (d3 in this case) for dead frames. The inversion here
   556  	// always indicates a dead frame, and the effect of the inversion on the
   557  	// scan is to hide those dead frames, so the scan is still okay:
   558  	// what's left on the panic stack are exactly (and only) the dead frames.
   559  	//
   560  	// We require callback != nil here because only when callback != nil
   561  	// do we know that gentraceback is being called in a "must be correct"
   562  	// context as opposed to a "best effort" context. The tracebacks with
   563  	// callbacks only happen when everything is stopped nicely.
   564  	// At other times, such as when gathering a stack for a profiling signal
   565  	// or when printing a traceback during a crash, everything may not be
   566  	// stopped nicely, and the stack walk may not be able to complete.
   567  	if callback != nil && n < max && frame.sp != gp.stktopsp {
   568  		print("runtime: g", gp.goid, ": frame.sp=", hex(frame.sp), " top=", hex(gp.stktopsp), "\n")
   569  		print("\tstack=[", hex(gp.stack.lo), "-", hex(gp.stack.hi), "] n=", n, " max=", max, "\n")
   570  		throw("traceback did not unwind completely")
   571  	}
   572  
   573  	return n
   574  }
   575  
   576  // printArgs prints function arguments in traceback.
   577  func printArgs(f funcInfo, argp unsafe.Pointer) {
   578  	// The "instruction" of argument printing is encoded in _FUNCDATA_ArgInfo.
   579  	// See cmd/compile/internal/ssagen.emitArgInfo for the description of the
   580  	// encoding.
   581  	// These constants need to be in sync with the compiler.
   582  	const (
   583  		_endSeq         = 0xff
   584  		_startAgg       = 0xfe
   585  		_endAgg         = 0xfd
   586  		_dotdotdot      = 0xfc
   587  		_offsetTooLarge = 0xfb
   588  	)
   589  
   590  	const (
   591  		limit    = 10                       // print no more than 10 args/components
   592  		maxDepth = 5                        // no more than 5 layers of nesting
   593  		maxLen   = (maxDepth*3+2)*limit + 1 // max length of _FUNCDATA_ArgInfo (see the compiler side for reasoning)
   594  	)
   595  
   596  	p := (*[maxLen]uint8)(funcdata(f, _FUNCDATA_ArgInfo))
   597  	if p == nil {
   598  		return
   599  	}
   600  
   601  	print1 := func(off, sz uint8) {
   602  		x := readUnaligned64(add(argp, uintptr(off)))
   603  		// mask out irrelavant bits
   604  		if sz < 8 {
   605  			shift := 64 - sz*8
   606  			if sys.BigEndian {
   607  				x = x >> shift
   608  			} else {
   609  				x = x << shift >> shift
   610  			}
   611  		}
   612  		print(hex(x))
   613  	}
   614  
   615  	start := true
   616  	printcomma := func() {
   617  		if !start {
   618  			print(", ")
   619  		}
   620  	}
   621  	pi := 0
   622  printloop:
   623  	for {
   624  		o := p[pi]
   625  		pi++
   626  		switch o {
   627  		case _endSeq:
   628  			break printloop
   629  		case _startAgg:
   630  			printcomma()
   631  			print("{")
   632  			start = true
   633  			continue
   634  		case _endAgg:
   635  			print("}")
   636  		case _dotdotdot:
   637  			printcomma()
   638  			print("...")
   639  		case _offsetTooLarge:
   640  			printcomma()
   641  			print("_")
   642  		default:
   643  			printcomma()
   644  			sz := p[pi]
   645  			pi++
   646  			print1(o, sz)
   647  		}
   648  		start = false
   649  	}
   650  }
   651  
   652  // reflectMethodValue is a partial duplicate of reflect.makeFuncImpl
   653  // and reflect.methodValue.
   654  type reflectMethodValue struct {
   655  	fn     uintptr
   656  	stack  *bitvector // ptrmap for both args and results
   657  	argLen uintptr    // just args
   658  }
   659  
   660  // getArgInfoFast returns the argument frame information for a call to f.
   661  // It is short and inlineable. However, it does not handle all functions.
   662  // If ok reports false, you must call getArgInfo instead.
   663  // TODO(josharian): once we do mid-stack inlining,
   664  // call getArgInfo directly from getArgInfoFast and stop returning an ok bool.
   665  func getArgInfoFast(f funcInfo, needArgMap bool) (arglen uintptr, argmap *bitvector, ok bool) {
   666  	return uintptr(f.args), nil, !(needArgMap && f.args == _ArgsSizeUnknown)
   667  }
   668  
   669  // getArgInfo returns the argument frame information for a call to f
   670  // with call frame frame.
   671  //
   672  // This is used for both actual calls with active stack frames and for
   673  // deferred calls or goroutines that are not yet executing. If this is an actual
   674  // call, ctxt must be nil (getArgInfo will retrieve what it needs from
   675  // the active stack frame). If this is a deferred call or unstarted goroutine,
   676  // ctxt must be the function object that was deferred or go'd.
   677  func getArgInfo(frame *stkframe, f funcInfo, needArgMap bool, ctxt *funcval) (arglen uintptr, argmap *bitvector) {
   678  	arglen = uintptr(f.args)
   679  	if needArgMap && f.args == _ArgsSizeUnknown {
   680  		// Extract argument bitmaps for reflect stubs from the calls they made to reflect.
   681  		switch funcname(f) {
   682  		case "reflect.makeFuncStub", "reflect.methodValueCall":
   683  			// These take a *reflect.methodValue as their
   684  			// context register.
   685  			var mv *reflectMethodValue
   686  			var retValid bool
   687  			if ctxt != nil {
   688  				// This is not an actual call, but a
   689  				// deferred call or an unstarted goroutine.
   690  				// The function value is itself the *reflect.methodValue.
   691  				mv = (*reflectMethodValue)(unsafe.Pointer(ctxt))
   692  			} else {
   693  				// This is a real call that took the
   694  				// *reflect.methodValue as its context
   695  				// register and immediately saved it
   696  				// to 0(SP). Get the methodValue from
   697  				// 0(SP).
   698  				arg0 := frame.sp + sys.MinFrameSize
   699  				mv = *(**reflectMethodValue)(unsafe.Pointer(arg0))
   700  				// Figure out whether the return values are valid.
   701  				// Reflect will update this value after it copies
   702  				// in the return values.
   703  				retValid = *(*bool)(unsafe.Pointer(arg0 + 4*sys.PtrSize))
   704  			}
   705  			if mv.fn != f.entry {
   706  				print("runtime: confused by ", funcname(f), "\n")
   707  				throw("reflect mismatch")
   708  			}
   709  			bv := mv.stack
   710  			arglen = uintptr(bv.n * sys.PtrSize)
   711  			if !retValid {
   712  				arglen = uintptr(mv.argLen) &^ (sys.PtrSize - 1)
   713  			}
   714  			argmap = bv
   715  		}
   716  	}
   717  	return
   718  }
   719  
   720  // tracebackCgoContext handles tracing back a cgo context value, from
   721  // the context argument to setCgoTraceback, for the gentraceback
   722  // function. It returns the new value of n.
   723  func tracebackCgoContext(pcbuf *uintptr, printing bool, ctxt uintptr, n, max int) int {
   724  	var cgoPCs [32]uintptr
   725  	cgoContextPCs(ctxt, cgoPCs[:])
   726  	var arg cgoSymbolizerArg
   727  	anySymbolized := false
   728  	for _, pc := range cgoPCs {
   729  		if pc == 0 || n >= max {
   730  			break
   731  		}
   732  		if pcbuf != nil {
   733  			(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   734  		}
   735  		if printing {
   736  			if cgoSymbolizer == nil {
   737  				print("non-Go function at pc=", hex(pc), "\n")
   738  			} else {
   739  				c := printOneCgoTraceback(pc, max-n, &arg)
   740  				n += c - 1 // +1 a few lines down
   741  				anySymbolized = true
   742  			}
   743  		}
   744  		n++
   745  	}
   746  	if anySymbolized {
   747  		arg.pc = 0
   748  		callCgoSymbolizer(&arg)
   749  	}
   750  	return n
   751  }
   752  
   753  func printcreatedby(gp *g) {
   754  	// Show what created goroutine, except main goroutine (goid 1).
   755  	pc := gp.gopc
   756  	f := findfunc(pc)
   757  	if f.valid() && showframe(f, gp, false, funcID_normal, funcID_normal) && gp.goid != 1 {
   758  		printcreatedby1(f, pc)
   759  	}
   760  }
   761  
   762  func printcreatedby1(f funcInfo, pc uintptr) {
   763  	print("created by ", funcname(f), "\n")
   764  	tracepc := pc // back up to CALL instruction for funcline.
   765  	if pc > f.entry {
   766  		tracepc -= sys.PCQuantum
   767  	}
   768  	file, line := funcline(f, tracepc)
   769  	print("\t", file, ":", line)
   770  	if pc > f.entry {
   771  		print(" +", hex(pc-f.entry))
   772  	}
   773  	print("\n")
   774  }
   775  
   776  func traceback(pc, sp, lr uintptr, gp *g) {
   777  	traceback1(pc, sp, lr, gp, 0)
   778  }
   779  
   780  // tracebacktrap is like traceback but expects that the PC and SP were obtained
   781  // from a trap, not from gp->sched or gp->syscallpc/gp->syscallsp or getcallerpc/getcallersp.
   782  // Because they are from a trap instead of from a saved pair,
   783  // the initial PC must not be rewound to the previous instruction.
   784  // (All the saved pairs record a PC that is a return address, so we
   785  // rewind it into the CALL instruction.)
   786  // If gp.m.libcall{g,pc,sp} information is available, it uses that information in preference to
   787  // the pc/sp/lr passed in.
   788  func tracebacktrap(pc, sp, lr uintptr, gp *g) {
   789  	if gp.m.libcallsp != 0 {
   790  		// We're in C code somewhere, traceback from the saved position.
   791  		traceback1(gp.m.libcallpc, gp.m.libcallsp, 0, gp.m.libcallg.ptr(), 0)
   792  		return
   793  	}
   794  	traceback1(pc, sp, lr, gp, _TraceTrap)
   795  }
   796  
   797  func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
   798  	// If the goroutine is in cgo, and we have a cgo traceback, print that.
   799  	if iscgo && gp.m != nil && gp.m.ncgo > 0 && gp.syscallsp != 0 && gp.m.cgoCallers != nil && gp.m.cgoCallers[0] != 0 {
   800  		// Lock cgoCallers so that a signal handler won't
   801  		// change it, copy the array, reset it, unlock it.
   802  		// We are locked to the thread and are not running
   803  		// concurrently with a signal handler.
   804  		// We just have to stop a signal handler from interrupting
   805  		// in the middle of our copy.
   806  		atomic.Store(&gp.m.cgoCallersUse, 1)
   807  		cgoCallers := *gp.m.cgoCallers
   808  		gp.m.cgoCallers[0] = 0
   809  		atomic.Store(&gp.m.cgoCallersUse, 0)
   810  
   811  		printCgoTraceback(&cgoCallers)
   812  	}
   813  
   814  	var n int
   815  	if readgstatus(gp)&^_Gscan == _Gsyscall {
   816  		// Override registers if blocked in system call.
   817  		pc = gp.syscallpc
   818  		sp = gp.syscallsp
   819  		flags &^= _TraceTrap
   820  	}
   821  	// Print traceback. By default, omits runtime frames.
   822  	// If that means we print nothing at all, repeat forcing all frames printed.
   823  	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
   824  	if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
   825  		n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags|_TraceRuntimeFrames)
   826  	}
   827  	if n == _TracebackMaxFrames {
   828  		print("...additional frames elided...\n")
   829  	}
   830  	printcreatedby(gp)
   831  
   832  	if gp.ancestors == nil {
   833  		return
   834  	}
   835  	for _, ancestor := range *gp.ancestors {
   836  		printAncestorTraceback(ancestor)
   837  	}
   838  }
   839  
   840  // printAncestorTraceback prints the traceback of the given ancestor.
   841  // TODO: Unify this with gentraceback and CallersFrames.
   842  func printAncestorTraceback(ancestor ancestorInfo) {
   843  	print("[originating from goroutine ", ancestor.goid, "]:\n")
   844  	for fidx, pc := range ancestor.pcs {
   845  		f := findfunc(pc) // f previously validated
   846  		if showfuncinfo(f, fidx == 0, funcID_normal, funcID_normal) {
   847  			printAncestorTracebackFuncInfo(f, pc)
   848  		}
   849  	}
   850  	if len(ancestor.pcs) == _TracebackMaxFrames {
   851  		print("...additional frames elided...\n")
   852  	}
   853  	// Show what created goroutine, except main goroutine (goid 1).
   854  	f := findfunc(ancestor.gopc)
   855  	if f.valid() && showfuncinfo(f, false, funcID_normal, funcID_normal) && ancestor.goid != 1 {
   856  		printcreatedby1(f, ancestor.gopc)
   857  	}
   858  }
   859  
   860  // printAncestorTraceback prints the given function info at a given pc
   861  // within an ancestor traceback. The precision of this info is reduced
   862  // due to only have access to the pcs at the time of the caller
   863  // goroutine being created.
   864  func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) {
   865  	name := funcname(f)
   866  	if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   867  		inltree := (*[1 << 20]inlinedCall)(inldata)
   868  		ix := pcdatavalue(f, _PCDATA_InlTreeIndex, pc, nil)
   869  		if ix >= 0 {
   870  			name = funcnameFromNameoff(f, inltree[ix].func_)
   871  		}
   872  	}
   873  	file, line := funcline(f, pc)
   874  	if name == "runtime.gopanic" {
   875  		name = "panic"
   876  	}
   877  	print(name, "(...)\n")
   878  	print("\t", file, ":", line)
   879  	if pc > f.entry {
   880  		print(" +", hex(pc-f.entry))
   881  	}
   882  	print("\n")
   883  }
   884  
   885  func callers(skip int, pcbuf []uintptr) int {
   886  	sp := getcallersp()
   887  	pc := getcallerpc()
   888  	gp := getg()
   889  	var n int
   890  	systemstack(func() {
   891  		n = gentraceback(pc, sp, 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
   892  	})
   893  	return n
   894  }
   895  
   896  func gcallers(gp *g, skip int, pcbuf []uintptr) int {
   897  	return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
   898  }
   899  
   900  // showframe reports whether the frame with the given characteristics should
   901  // be printed during a traceback.
   902  func showframe(f funcInfo, gp *g, firstFrame bool, funcID, childID funcID) bool {
   903  	g := getg()
   904  	if g.m.throwing > 0 && gp != nil && (gp == g.m.curg || gp == g.m.caughtsig.ptr()) {
   905  		return true
   906  	}
   907  	return showfuncinfo(f, firstFrame, funcID, childID)
   908  }
   909  
   910  // showfuncinfo reports whether a function with the given characteristics should
   911  // be printed during a traceback.
   912  func showfuncinfo(f funcInfo, firstFrame bool, funcID, childID funcID) bool {
   913  	// Note that f may be a synthesized funcInfo for an inlined
   914  	// function, in which case only nameoff and funcID are set.
   915  
   916  	level, _, _ := gotraceback()
   917  	if level > 1 {
   918  		// Show all frames.
   919  		return true
   920  	}
   921  
   922  	if !f.valid() {
   923  		return false
   924  	}
   925  
   926  	if funcID == funcID_wrapper && elideWrapperCalling(childID) {
   927  		return false
   928  	}
   929  
   930  	name := funcname(f)
   931  
   932  	// Special case: always show runtime.gopanic frame
   933  	// in the middle of a stack trace, so that we can
   934  	// see the boundary between ordinary code and
   935  	// panic-induced deferred code.
   936  	// See golang.org/issue/5832.
   937  	if name == "runtime.gopanic" && !firstFrame {
   938  		return true
   939  	}
   940  
   941  	return bytealg.IndexByteString(name, '.') >= 0 && (!hasPrefix(name, "runtime.") || isExportedRuntime(name))
   942  }
   943  
   944  // isExportedRuntime reports whether name is an exported runtime function.
   945  // It is only for runtime functions, so ASCII A-Z is fine.
   946  func isExportedRuntime(name string) bool {
   947  	const n = len("runtime.")
   948  	return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
   949  }
   950  
   951  // elideWrapperCalling reports whether a wrapper function that called
   952  // function id should be elided from stack traces.
   953  func elideWrapperCalling(id funcID) bool {
   954  	// If the wrapper called a panic function instead of the
   955  	// wrapped function, we want to include it in stacks.
   956  	return !(id == funcID_gopanic || id == funcID_sigpanic || id == funcID_panicwrap)
   957  }
   958  
   959  var gStatusStrings = [...]string{
   960  	_Gidle:      "idle",
   961  	_Grunnable:  "runnable",
   962  	_Grunning:   "running",
   963  	_Gsyscall:   "syscall",
   964  	_Gwaiting:   "waiting",
   965  	_Gdead:      "dead",
   966  	_Gcopystack: "copystack",
   967  	_Gpreempted: "preempted",
   968  }
   969  
   970  func goroutineheader(gp *g) {
   971  	gpstatus := readgstatus(gp)
   972  
   973  	isScan := gpstatus&_Gscan != 0
   974  	gpstatus &^= _Gscan // drop the scan bit
   975  
   976  	// Basic string status
   977  	var status string
   978  	if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
   979  		status = gStatusStrings[gpstatus]
   980  	} else {
   981  		status = "???"
   982  	}
   983  
   984  	// Override.
   985  	if gpstatus == _Gwaiting && gp.waitreason != waitReasonZero {
   986  		status = gp.waitreason.String()
   987  	}
   988  
   989  	// approx time the G is blocked, in minutes
   990  	var waitfor int64
   991  	if (gpstatus == _Gwaiting || gpstatus == _Gsyscall) && gp.waitsince != 0 {
   992  		waitfor = (nanotime() - gp.waitsince) / 60e9
   993  	}
   994  	print("goroutine ", gp.goid, " [", status)
   995  	if isScan {
   996  		print(" (scan)")
   997  	}
   998  	if waitfor >= 1 {
   999  		print(", ", waitfor, " minutes")
  1000  	}
  1001  	if gp.lockedm != 0 {
  1002  		print(", locked to thread")
  1003  	}
  1004  	print("]:\n")
  1005  }
  1006  
  1007  func tracebackothers(me *g) {
  1008  	level, _, _ := gotraceback()
  1009  
  1010  	// Show the current goroutine first, if we haven't already.
  1011  	curgp := getg().m.curg
  1012  	if curgp != nil && curgp != me {
  1013  		print("\n")
  1014  		goroutineheader(curgp)
  1015  		traceback(^uintptr(0), ^uintptr(0), 0, curgp)
  1016  	}
  1017  
  1018  	// We can't call locking forEachG here because this may be during fatal
  1019  	// throw/panic, where locking could be out-of-order or a direct
  1020  	// deadlock.
  1021  	//
  1022  	// Instead, use forEachGRace, which requires no locking. We don't lock
  1023  	// against concurrent creation of new Gs, but even with allglock we may
  1024  	// miss Gs created after this loop.
  1025  	forEachGRace(func(gp *g) {
  1026  		if gp == me || gp == curgp || readgstatus(gp) == _Gdead || isSystemGoroutine(gp, false) && level < 2 {
  1027  			return
  1028  		}
  1029  		print("\n")
  1030  		goroutineheader(gp)
  1031  		// Note: gp.m == g.m occurs when tracebackothers is
  1032  		// called from a signal handler initiated during a
  1033  		// systemstack call. The original G is still in the
  1034  		// running state, and we want to print its stack.
  1035  		if gp.m != getg().m && readgstatus(gp)&^_Gscan == _Grunning {
  1036  			print("\tgoroutine running on other thread; stack unavailable\n")
  1037  			printcreatedby(gp)
  1038  		} else {
  1039  			traceback(^uintptr(0), ^uintptr(0), 0, gp)
  1040  		}
  1041  	})
  1042  }
  1043  
  1044  // tracebackHexdump hexdumps part of stk around frame.sp and frame.fp
  1045  // for debugging purposes. If the address bad is included in the
  1046  // hexdumped range, it will mark it as well.
  1047  func tracebackHexdump(stk stack, frame *stkframe, bad uintptr) {
  1048  	const expand = 32 * sys.PtrSize
  1049  	const maxExpand = 256 * sys.PtrSize
  1050  	// Start around frame.sp.
  1051  	lo, hi := frame.sp, frame.sp
  1052  	// Expand to include frame.fp.
  1053  	if frame.fp != 0 && frame.fp < lo {
  1054  		lo = frame.fp
  1055  	}
  1056  	if frame.fp != 0 && frame.fp > hi {
  1057  		hi = frame.fp
  1058  	}
  1059  	// Expand a bit more.
  1060  	lo, hi = lo-expand, hi+expand
  1061  	// But don't go too far from frame.sp.
  1062  	if lo < frame.sp-maxExpand {
  1063  		lo = frame.sp - maxExpand
  1064  	}
  1065  	if hi > frame.sp+maxExpand {
  1066  		hi = frame.sp + maxExpand
  1067  	}
  1068  	// And don't go outside the stack bounds.
  1069  	if lo < stk.lo {
  1070  		lo = stk.lo
  1071  	}
  1072  	if hi > stk.hi {
  1073  		hi = stk.hi
  1074  	}
  1075  
  1076  	// Print the hex dump.
  1077  	print("stack: frame={sp:", hex(frame.sp), ", fp:", hex(frame.fp), "} stack=[", hex(stk.lo), ",", hex(stk.hi), ")\n")
  1078  	hexdumpWords(lo, hi, func(p uintptr) byte {
  1079  		switch p {
  1080  		case frame.fp:
  1081  			return '>'
  1082  		case frame.sp:
  1083  			return '<'
  1084  		case bad:
  1085  			return '!'
  1086  		}
  1087  		return 0
  1088  	})
  1089  }
  1090  
  1091  // isSystemGoroutine reports whether the goroutine g must be omitted
  1092  // in stack dumps and deadlock detector. This is any goroutine that
  1093  // starts at a runtime.* entry point, except for runtime.main,
  1094  // runtime.handleAsyncEvent (wasm only) and sometimes runtime.runfinq.
  1095  //
  1096  // If fixed is true, any goroutine that can vary between user and
  1097  // system (that is, the finalizer goroutine) is considered a user
  1098  // goroutine.
  1099  func isSystemGoroutine(gp *g, fixed bool) bool {
  1100  	// Keep this in sync with cmd/trace/trace.go:isSystemGoroutine.
  1101  	f := findfunc(gp.startpc)
  1102  	if !f.valid() {
  1103  		return false
  1104  	}
  1105  	if f.funcID == funcID_runtime_main || f.funcID == funcID_handleAsyncEvent {
  1106  		return false
  1107  	}
  1108  	if f.funcID == funcID_runfinq {
  1109  		// We include the finalizer goroutine if it's calling
  1110  		// back into user code.
  1111  		if fixed {
  1112  			// This goroutine can vary. In fixed mode,
  1113  			// always consider it a user goroutine.
  1114  			return false
  1115  		}
  1116  		return !fingRunning
  1117  	}
  1118  	return hasPrefix(funcname(f), "runtime.")
  1119  }
  1120  
  1121  // SetCgoTraceback records three C functions to use to gather
  1122  // traceback information from C code and to convert that traceback
  1123  // information into symbolic information. These are used when printing
  1124  // stack traces for a program that uses cgo.
  1125  //
  1126  // The traceback and context functions may be called from a signal
  1127  // handler, and must therefore use only async-signal safe functions.
  1128  // The symbolizer function may be called while the program is
  1129  // crashing, and so must be cautious about using memory.  None of the
  1130  // functions may call back into Go.
  1131  //
  1132  // The context function will be called with a single argument, a
  1133  // pointer to a struct:
  1134  //
  1135  //	struct {
  1136  //		Context uintptr
  1137  //	}
  1138  //
  1139  // In C syntax, this struct will be
  1140  //
  1141  //	struct {
  1142  //		uintptr_t Context;
  1143  //	};
  1144  //
  1145  // If the Context field is 0, the context function is being called to
  1146  // record the current traceback context. It should record in the
  1147  // Context field whatever information is needed about the current
  1148  // point of execution to later produce a stack trace, probably the
  1149  // stack pointer and PC. In this case the context function will be
  1150  // called from C code.
  1151  //
  1152  // If the Context field is not 0, then it is a value returned by a
  1153  // previous call to the context function. This case is called when the
  1154  // context is no longer needed; that is, when the Go code is returning
  1155  // to its C code caller. This permits the context function to release
  1156  // any associated resources.
  1157  //
  1158  // While it would be correct for the context function to record a
  1159  // complete a stack trace whenever it is called, and simply copy that
  1160  // out in the traceback function, in a typical program the context
  1161  // function will be called many times without ever recording a
  1162  // traceback for that context. Recording a complete stack trace in a
  1163  // call to the context function is likely to be inefficient.
  1164  //
  1165  // The traceback function will be called with a single argument, a
  1166  // pointer to a struct:
  1167  //
  1168  //	struct {
  1169  //		Context    uintptr
  1170  //		SigContext uintptr
  1171  //		Buf        *uintptr
  1172  //		Max        uintptr
  1173  //	}
  1174  //
  1175  // In C syntax, this struct will be
  1176  //
  1177  //	struct {
  1178  //		uintptr_t  Context;
  1179  //		uintptr_t  SigContext;
  1180  //		uintptr_t* Buf;
  1181  //		uintptr_t  Max;
  1182  //	};
  1183  //
  1184  // The Context field will be zero to gather a traceback from the
  1185  // current program execution point. In this case, the traceback
  1186  // function will be called from C code.
  1187  //
  1188  // Otherwise Context will be a value previously returned by a call to
  1189  // the context function. The traceback function should gather a stack
  1190  // trace from that saved point in the program execution. The traceback
  1191  // function may be called from an execution thread other than the one
  1192  // that recorded the context, but only when the context is known to be
  1193  // valid and unchanging. The traceback function may also be called
  1194  // deeper in the call stack on the same thread that recorded the
  1195  // context. The traceback function may be called multiple times with
  1196  // the same Context value; it will usually be appropriate to cache the
  1197  // result, if possible, the first time this is called for a specific
  1198  // context value.
  1199  //
  1200  // If the traceback function is called from a signal handler on a Unix
  1201  // system, SigContext will be the signal context argument passed to
  1202  // the signal handler (a C ucontext_t* cast to uintptr_t). This may be
  1203  // used to start tracing at the point where the signal occurred. If
  1204  // the traceback function is not called from a signal handler,
  1205  // SigContext will be zero.
  1206  //
  1207  // Buf is where the traceback information should be stored. It should
  1208  // be PC values, such that Buf[0] is the PC of the caller, Buf[1] is
  1209  // the PC of that function's caller, and so on.  Max is the maximum
  1210  // number of entries to store.  The function should store a zero to
  1211  // indicate the top of the stack, or that the caller is on a different
  1212  // stack, presumably a Go stack.
  1213  //
  1214  // Unlike runtime.Callers, the PC values returned should, when passed
  1215  // to the symbolizer function, return the file/line of the call
  1216  // instruction.  No additional subtraction is required or appropriate.
  1217  //
  1218  // On all platforms, the traceback function is invoked when a call from
  1219  // Go to C to Go requests a stack trace. On linux/amd64, linux/ppc64le,
  1220  // and freebsd/amd64, the traceback function is also invoked when a
  1221  // signal is received by a thread that is executing a cgo call. The
  1222  // traceback function should not make assumptions about when it is
  1223  // called, as future versions of Go may make additional calls.
  1224  //
  1225  // The symbolizer function will be called with a single argument, a
  1226  // pointer to a struct:
  1227  //
  1228  //	struct {
  1229  //		PC      uintptr // program counter to fetch information for
  1230  //		File    *byte   // file name (NUL terminated)
  1231  //		Lineno  uintptr // line number
  1232  //		Func    *byte   // function name (NUL terminated)
  1233  //		Entry   uintptr // function entry point
  1234  //		More    uintptr // set non-zero if more info for this PC
  1235  //		Data    uintptr // unused by runtime, available for function
  1236  //	}
  1237  //
  1238  // In C syntax, this struct will be
  1239  //
  1240  //	struct {
  1241  //		uintptr_t PC;
  1242  //		char*     File;
  1243  //		uintptr_t Lineno;
  1244  //		char*     Func;
  1245  //		uintptr_t Entry;
  1246  //		uintptr_t More;
  1247  //		uintptr_t Data;
  1248  //	};
  1249  //
  1250  // The PC field will be a value returned by a call to the traceback
  1251  // function.
  1252  //
  1253  // The first time the function is called for a particular traceback,
  1254  // all the fields except PC will be 0. The function should fill in the
  1255  // other fields if possible, setting them to 0/nil if the information
  1256  // is not available. The Data field may be used to store any useful
  1257  // information across calls. The More field should be set to non-zero
  1258  // if there is more information for this PC, zero otherwise. If More
  1259  // is set non-zero, the function will be called again with the same
  1260  // PC, and may return different information (this is intended for use
  1261  // with inlined functions). If More is zero, the function will be
  1262  // called with the next PC value in the traceback. When the traceback
  1263  // is complete, the function will be called once more with PC set to
  1264  // zero; this may be used to free any information. Each call will
  1265  // leave the fields of the struct set to the same values they had upon
  1266  // return, except for the PC field when the More field is zero. The
  1267  // function must not keep a copy of the struct pointer between calls.
  1268  //
  1269  // When calling SetCgoTraceback, the version argument is the version
  1270  // number of the structs that the functions expect to receive.
  1271  // Currently this must be zero.
  1272  //
  1273  // The symbolizer function may be nil, in which case the results of
  1274  // the traceback function will be displayed as numbers. If the
  1275  // traceback function is nil, the symbolizer function will never be
  1276  // called. The context function may be nil, in which case the
  1277  // traceback function will only be called with the context field set
  1278  // to zero.  If the context function is nil, then calls from Go to C
  1279  // to Go will not show a traceback for the C portion of the call stack.
  1280  //
  1281  // SetCgoTraceback should be called only once, ideally from an init function.
  1282  func SetCgoTraceback(version int, traceback, context, symbolizer unsafe.Pointer) {
  1283  	if version != 0 {
  1284  		panic("unsupported version")
  1285  	}
  1286  
  1287  	if cgoTraceback != nil && cgoTraceback != traceback ||
  1288  		cgoContext != nil && cgoContext != context ||
  1289  		cgoSymbolizer != nil && cgoSymbolizer != symbolizer {
  1290  		panic("call SetCgoTraceback only once")
  1291  	}
  1292  
  1293  	cgoTraceback = traceback
  1294  	cgoContext = context
  1295  	cgoSymbolizer = symbolizer
  1296  
  1297  	// The context function is called when a C function calls a Go
  1298  	// function. As such it is only called by C code in runtime/cgo.
  1299  	if _cgo_set_context_function != nil {
  1300  		cgocall(_cgo_set_context_function, context)
  1301  	}
  1302  }
  1303  
  1304  var cgoTraceback unsafe.Pointer
  1305  var cgoContext unsafe.Pointer
  1306  var cgoSymbolizer unsafe.Pointer
  1307  
  1308  // cgoTracebackArg is the type passed to cgoTraceback.
  1309  type cgoTracebackArg struct {
  1310  	context    uintptr
  1311  	sigContext uintptr
  1312  	buf        *uintptr
  1313  	max        uintptr
  1314  }
  1315  
  1316  // cgoContextArg is the type passed to the context function.
  1317  type cgoContextArg struct {
  1318  	context uintptr
  1319  }
  1320  
  1321  // cgoSymbolizerArg is the type passed to cgoSymbolizer.
  1322  type cgoSymbolizerArg struct {
  1323  	pc       uintptr
  1324  	file     *byte
  1325  	lineno   uintptr
  1326  	funcName *byte
  1327  	entry    uintptr
  1328  	more     uintptr
  1329  	data     uintptr
  1330  }
  1331  
  1332  // cgoTraceback prints a traceback of callers.
  1333  func printCgoTraceback(callers *cgoCallers) {
  1334  	if cgoSymbolizer == nil {
  1335  		for _, c := range callers {
  1336  			if c == 0 {
  1337  				break
  1338  			}
  1339  			print("non-Go function at pc=", hex(c), "\n")
  1340  		}
  1341  		return
  1342  	}
  1343  
  1344  	var arg cgoSymbolizerArg
  1345  	for _, c := range callers {
  1346  		if c == 0 {
  1347  			break
  1348  		}
  1349  		printOneCgoTraceback(c, 0x7fffffff, &arg)
  1350  	}
  1351  	arg.pc = 0
  1352  	callCgoSymbolizer(&arg)
  1353  }
  1354  
  1355  // printOneCgoTraceback prints the traceback of a single cgo caller.
  1356  // This can print more than one line because of inlining.
  1357  // Returns the number of frames printed.
  1358  func printOneCgoTraceback(pc uintptr, max int, arg *cgoSymbolizerArg) int {
  1359  	c := 0
  1360  	arg.pc = pc
  1361  	for c <= max {
  1362  		callCgoSymbolizer(arg)
  1363  		if arg.funcName != nil {
  1364  			// Note that we don't print any argument
  1365  			// information here, not even parentheses.
  1366  			// The symbolizer must add that if appropriate.
  1367  			println(gostringnocopy(arg.funcName))
  1368  		} else {
  1369  			println("non-Go function")
  1370  		}
  1371  		print("\t")
  1372  		if arg.file != nil {
  1373  			print(gostringnocopy(arg.file), ":", arg.lineno, " ")
  1374  		}
  1375  		print("pc=", hex(pc), "\n")
  1376  		c++
  1377  		if arg.more == 0 {
  1378  			break
  1379  		}
  1380  	}
  1381  	return c
  1382  }
  1383  
  1384  // callCgoSymbolizer calls the cgoSymbolizer function.
  1385  func callCgoSymbolizer(arg *cgoSymbolizerArg) {
  1386  	call := cgocall
  1387  	if panicking > 0 || getg().m.curg != getg() {
  1388  		// We do not want to call into the scheduler when panicking
  1389  		// or when on the system stack.
  1390  		call = asmcgocall
  1391  	}
  1392  	if msanenabled {
  1393  		msanwrite(unsafe.Pointer(arg), unsafe.Sizeof(cgoSymbolizerArg{}))
  1394  	}
  1395  	call(cgoSymbolizer, noescape(unsafe.Pointer(arg)))
  1396  }
  1397  
  1398  // cgoContextPCs gets the PC values from a cgo traceback.
  1399  func cgoContextPCs(ctxt uintptr, buf []uintptr) {
  1400  	if cgoTraceback == nil {
  1401  		return
  1402  	}
  1403  	call := cgocall
  1404  	if panicking > 0 || getg().m.curg != getg() {
  1405  		// We do not want to call into the scheduler when panicking
  1406  		// or when on the system stack.
  1407  		call = asmcgocall
  1408  	}
  1409  	arg := cgoTracebackArg{
  1410  		context: ctxt,
  1411  		buf:     (*uintptr)(noescape(unsafe.Pointer(&buf[0]))),
  1412  		max:     uintptr(len(buf)),
  1413  	}
  1414  	if msanenabled {
  1415  		msanwrite(unsafe.Pointer(&arg), unsafe.Sizeof(arg))
  1416  	}
  1417  	call(cgoTraceback, noescape(unsafe.Pointer(&arg)))
  1418  }
  1419  

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