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Source file src/runtime/traceback.go

Documentation: runtime

     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  	"runtime/internal/atomic"
     9  	"runtime/internal/sys"
    10  	"unsafe"
    11  )
    12  
    13  // The code in this file implements stack trace walking for all architectures.
    14  // The most important fact about a given architecture is whether it uses a link register.
    15  // On systems with link registers, the prologue for a non-leaf function stores the
    16  // incoming value of LR at the bottom of the newly allocated stack frame.
    17  // On systems without link registers, the architecture pushes a return PC during
    18  // the call instruction, so the return PC ends up above the stack frame.
    19  // In this file, the return PC is always called LR, no matter how it was found.
    20  //
    21  // To date, the opposite of a link register architecture is an x86 architecture.
    22  // This code may need to change if some other kind of non-link-register
    23  // architecture comes along.
    24  //
    25  // The other important fact is the size of a pointer: on 32-bit systems the LR
    26  // takes up only 4 bytes on the stack, while on 64-bit systems it takes up 8 bytes.
    27  // Typically this is ptrSize.
    28  //
    29  // As an exception, amd64p32 has ptrSize == 4 but the CALL instruction still
    30  // stores an 8-byte return PC onto the stack. To accommodate this, we use regSize
    31  // as the size of the architecture-pushed return PC.
    32  //
    33  // usesLR is defined below in terms of minFrameSize, which is defined in
    34  // arch_$GOARCH.go. ptrSize and regSize are defined in stubs.go.
    35  
    36  const usesLR = sys.MinFrameSize > 0
    37  
    38  var (
    39  	// initialized in tracebackinit
    40  	goexitPC             uintptr
    41  	jmpdeferPC           uintptr
    42  	mcallPC              uintptr
    43  	morestackPC          uintptr
    44  	mstartPC             uintptr
    45  	rt0_goPC             uintptr
    46  	asmcgocallPC         uintptr
    47  	sigpanicPC           uintptr
    48  	runfinqPC            uintptr
    49  	bgsweepPC            uintptr
    50  	forcegchelperPC      uintptr
    51  	timerprocPC          uintptr
    52  	gcBgMarkWorkerPC     uintptr
    53  	systemstack_switchPC uintptr
    54  	systemstackPC        uintptr
    55  	cgocallback_gofuncPC uintptr
    56  	skipPC               uintptr
    57  
    58  	gogoPC uintptr
    59  
    60  	externalthreadhandlerp uintptr // initialized elsewhere
    61  )
    62  
    63  func tracebackinit() {
    64  	// Go variable initialization happens late during runtime startup.
    65  	// Instead of initializing the variables above in the declarations,
    66  	// schedinit calls this function so that the variables are
    67  	// initialized and available earlier in the startup sequence.
    68  	goexitPC = funcPC(goexit)
    69  	jmpdeferPC = funcPC(jmpdefer)
    70  	mcallPC = funcPC(mcall)
    71  	morestackPC = funcPC(morestack)
    72  	mstartPC = funcPC(mstart)
    73  	rt0_goPC = funcPC(rt0_go)
    74  	asmcgocallPC = funcPC(asmcgocall)
    75  	sigpanicPC = funcPC(sigpanic)
    76  	runfinqPC = funcPC(runfinq)
    77  	bgsweepPC = funcPC(bgsweep)
    78  	forcegchelperPC = funcPC(forcegchelper)
    79  	timerprocPC = funcPC(timerproc)
    80  	gcBgMarkWorkerPC = funcPC(gcBgMarkWorker)
    81  	systemstack_switchPC = funcPC(systemstack_switch)
    82  	systemstackPC = funcPC(systemstack)
    83  	cgocallback_gofuncPC = funcPC(cgocallback_gofunc)
    84  	skipPC = funcPC(skipPleaseUseCallersFrames)
    85  
    86  	// used by sigprof handler
    87  	gogoPC = funcPC(gogo)
    88  }
    89  
    90  // Traceback over the deferred function calls.
    91  // Report them like calls that have been invoked but not started executing yet.
    92  func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
    93  	var frame stkframe
    94  	for d := gp._defer; d != nil; d = d.link {
    95  		fn := d.fn
    96  		if fn == nil {
    97  			// Defer of nil function. Args don't matter.
    98  			frame.pc = 0
    99  			frame.fn = funcInfo{}
   100  			frame.argp = 0
   101  			frame.arglen = 0
   102  			frame.argmap = nil
   103  		} else {
   104  			frame.pc = fn.fn
   105  			f := findfunc(frame.pc)
   106  			if !f.valid() {
   107  				print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
   108  				throw("unknown pc")
   109  			}
   110  			frame.fn = f
   111  			frame.argp = uintptr(deferArgs(d))
   112  			frame.arglen, frame.argmap = getArgInfo(&frame, f, true, fn)
   113  		}
   114  		frame.continpc = frame.pc
   115  		if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
   116  			return
   117  		}
   118  	}
   119  }
   120  
   121  const sizeofSkipFunction = 256
   122  
   123  // This function is defined in asm.s to be sizeofSkipFunction bytes long.
   124  func skipPleaseUseCallersFrames()
   125  
   126  // Generic traceback. Handles runtime stack prints (pcbuf == nil),
   127  // the runtime.Callers function (pcbuf != nil), as well as the garbage
   128  // collector (callback != nil).  A little clunky to merge these, but avoids
   129  // duplicating the code and all its subtlety.
   130  //
   131  // The skip argument is only valid with pcbuf != nil and counts the number
   132  // of logical frames to skip rather than physical frames (with inlining, a
   133  // PC in pcbuf can represent multiple calls). If a PC is partially skipped
   134  // and max > 1, pcbuf[1] will be runtime.skipPleaseUseCallersFrames+N where
   135  // N indicates the number of logical frames to skip in pcbuf[0].
   136  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 {
   137  	if skip > 0 && callback != nil {
   138  		throw("gentraceback callback cannot be used with non-zero skip")
   139  	}
   140  	if goexitPC == 0 {
   141  		throw("gentraceback before goexitPC initialization")
   142  	}
   143  	g := getg()
   144  	if g == gp && g == g.m.curg {
   145  		// The starting sp has been passed in as a uintptr, and the caller may
   146  		// have other uintptr-typed stack references as well.
   147  		// If during one of the calls that got us here or during one of the
   148  		// callbacks below the stack must be grown, all these uintptr references
   149  		// to the stack will not be updated, and gentraceback will continue
   150  		// to inspect the old stack memory, which may no longer be valid.
   151  		// Even if all the variables were updated correctly, it is not clear that
   152  		// we want to expose a traceback that begins on one stack and ends
   153  		// on another stack. That could confuse callers quite a bit.
   154  		// Instead, we require that gentraceback and any other function that
   155  		// accepts an sp for the current goroutine (typically obtained by
   156  		// calling getcallersp) must not run on that goroutine's stack but
   157  		// instead on the g0 stack.
   158  		throw("gentraceback cannot trace user goroutine on its own stack")
   159  	}
   160  	level, _, _ := gotraceback()
   161  
   162  	if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.
   163  		if gp.syscallsp != 0 {
   164  			pc0 = gp.syscallpc
   165  			sp0 = gp.syscallsp
   166  			if usesLR {
   167  				lr0 = 0
   168  			}
   169  		} else {
   170  			pc0 = gp.sched.pc
   171  			sp0 = gp.sched.sp
   172  			if usesLR {
   173  				lr0 = gp.sched.lr
   174  			}
   175  		}
   176  	}
   177  
   178  	nprint := 0
   179  	var frame stkframe
   180  	frame.pc = pc0
   181  	frame.sp = sp0
   182  	if usesLR {
   183  		frame.lr = lr0
   184  	}
   185  	waspanic := false
   186  	cgoCtxt := gp.cgoCtxt
   187  	printing := pcbuf == nil && callback == nil
   188  	_defer := gp._defer
   189  	elideWrapper := false
   190  
   191  	for _defer != nil && _defer.sp == _NoArgs {
   192  		_defer = _defer.link
   193  	}
   194  
   195  	// If the PC is zero, it's likely a nil function call.
   196  	// Start in the caller's frame.
   197  	if frame.pc == 0 {
   198  		if usesLR {
   199  			frame.pc = *(*uintptr)(unsafe.Pointer(frame.sp))
   200  			frame.lr = 0
   201  		} else {
   202  			frame.pc = uintptr(*(*sys.Uintreg)(unsafe.Pointer(frame.sp)))
   203  			frame.sp += sys.RegSize
   204  		}
   205  	}
   206  
   207  	f := findfunc(frame.pc)
   208  	if !f.valid() {
   209  		if callback != nil || printing {
   210  			print("runtime: unknown pc ", hex(frame.pc), "\n")
   211  			tracebackHexdump(gp.stack, &frame, 0)
   212  		}
   213  		if callback != nil {
   214  			throw("unknown pc")
   215  		}
   216  		return 0
   217  	}
   218  	frame.fn = f
   219  
   220  	var cache pcvalueCache
   221  
   222  	n := 0
   223  	for n < max {
   224  		// Typically:
   225  		//	pc is the PC of the running function.
   226  		//	sp is the stack pointer at that program counter.
   227  		//	fp is the frame pointer (caller's stack pointer) at that program counter, or nil if unknown.
   228  		//	stk is the stack containing sp.
   229  		//	The caller's program counter is lr, unless lr is zero, in which case it is *(uintptr*)sp.
   230  		f = frame.fn
   231  		if f.pcsp == 0 {
   232  			// No frame information, must be external function, like race support.
   233  			// See golang.org/issue/13568.
   234  			break
   235  		}
   236  
   237  		// Found an actual function.
   238  		// Derive frame pointer and link register.
   239  		if frame.fp == 0 {
   240  			// We want to jump over the systemstack switch. If we're running on the
   241  			// g0, this systemstack is at the top of the stack.
   242  			// if we're not on g0 or there's a no curg, then this is a regular call.
   243  			sp := frame.sp
   244  			if flags&_TraceJumpStack != 0 && f.entry == systemstackPC && gp == g.m.g0 && gp.m.curg != nil {
   245  				sp = gp.m.curg.sched.sp
   246  				frame.sp = sp
   247  				cgoCtxt = gp.m.curg.cgoCtxt
   248  			}
   249  			frame.fp = sp + uintptr(funcspdelta(f, frame.pc, &cache))
   250  			if !usesLR {
   251  				// On x86, call instruction pushes return PC before entering new function.
   252  				frame.fp += sys.RegSize
   253  			}
   254  		}
   255  		var flr funcInfo
   256  		if topofstack(f, gp.m != nil && gp == gp.m.g0) {
   257  			frame.lr = 0
   258  			flr = funcInfo{}
   259  		} else if usesLR && f.entry == jmpdeferPC {
   260  			// jmpdefer modifies SP/LR/PC non-atomically.
   261  			// If a profiling interrupt arrives during jmpdefer,
   262  			// the stack unwind may see a mismatched register set
   263  			// and get confused. Stop if we see PC within jmpdefer
   264  			// to avoid that confusion.
   265  			// See golang.org/issue/8153.
   266  			if callback != nil {
   267  				throw("traceback_arm: found jmpdefer when tracing with callback")
   268  			}
   269  			frame.lr = 0
   270  		} else {
   271  			var lrPtr uintptr
   272  			if usesLR {
   273  				if n == 0 && frame.sp < frame.fp || frame.lr == 0 {
   274  					lrPtr = frame.sp
   275  					frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
   276  				}
   277  			} else {
   278  				if frame.lr == 0 {
   279  					lrPtr = frame.fp - sys.RegSize
   280  					frame.lr = uintptr(*(*sys.Uintreg)(unsafe.Pointer(lrPtr)))
   281  				}
   282  			}
   283  			flr = findfunc(frame.lr)
   284  			if !flr.valid() {
   285  				// This happens if you get a profiling interrupt at just the wrong time.
   286  				// In that context it is okay to stop early.
   287  				// But if callback is set, we're doing a garbage collection and must
   288  				// get everything, so crash loudly.
   289  				doPrint := printing
   290  				if doPrint && gp.m.incgo {
   291  					// We can inject sigpanic
   292  					// calls directly into C code,
   293  					// in which case we'll see a C
   294  					// return PC. Don't complain.
   295  					doPrint = false
   296  				}
   297  				if callback != nil || doPrint {
   298  					print("runtime: unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
   299  					tracebackHexdump(gp.stack, &frame, lrPtr)
   300  				}
   301  				if callback != nil {
   302  					throw("unknown caller pc")
   303  				}
   304  			}
   305  		}
   306  
   307  		frame.varp = frame.fp
   308  		if !usesLR {
   309  			// On x86, call instruction pushes return PC before entering new function.
   310  			frame.varp -= sys.RegSize
   311  		}
   312  
   313  		// If framepointer_enabled and there's a frame, then
   314  		// there's a saved bp here.
   315  		if framepointer_enabled && GOARCH == "amd64" && frame.varp > frame.sp {
   316  			frame.varp -= sys.RegSize
   317  		}
   318  
   319  		// Derive size of arguments.
   320  		// Most functions have a fixed-size argument block,
   321  		// so we can use metadata about the function f.
   322  		// Not all, though: there are some variadic functions
   323  		// in package runtime and reflect, and for those we use call-specific
   324  		// metadata recorded by f's caller.
   325  		if callback != nil || printing {
   326  			frame.argp = frame.fp + sys.MinFrameSize
   327  			frame.arglen, frame.argmap = getArgInfo(&frame, f, callback != nil, nil)
   328  		}
   329  
   330  		// Determine frame's 'continuation PC', where it can continue.
   331  		// Normally this is the return address on the stack, but if sigpanic
   332  		// is immediately below this function on the stack, then the frame
   333  		// stopped executing due to a trap, and frame.pc is probably not
   334  		// a safe point for looking up liveness information. In this panicking case,
   335  		// the function either doesn't return at all (if it has no defers or if the
   336  		// defers do not recover) or it returns from one of the calls to
   337  		// deferproc a second time (if the corresponding deferred func recovers).
   338  		// It suffices to assume that the most recent deferproc is the one that
   339  		// returns; everything live at earlier deferprocs is still live at that one.
   340  		frame.continpc = frame.pc
   341  		if waspanic {
   342  			if _defer != nil && _defer.sp == frame.sp {
   343  				frame.continpc = _defer.pc
   344  			} else {
   345  				frame.continpc = 0
   346  			}
   347  		}
   348  
   349  		// Unwind our local defer stack past this frame.
   350  		for _defer != nil && (_defer.sp == frame.sp || _defer.sp == _NoArgs) {
   351  			_defer = _defer.link
   352  		}
   353  
   354  		if callback != nil {
   355  			if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
   356  				return n
   357  			}
   358  		}
   359  
   360  		if pcbuf != nil {
   361  			if skip == 0 {
   362  				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
   363  			} else {
   364  				// backup to CALL instruction to read inlining info (same logic as below)
   365  				tracepc := frame.pc
   366  				if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
   367  					tracepc--
   368  				}
   369  				inldata := funcdata(f, _FUNCDATA_InlTree)
   370  
   371  				// no inlining info, skip the physical frame
   372  				if inldata == nil {
   373  					skip--
   374  					goto skipped
   375  				}
   376  
   377  				ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, &cache)
   378  				inltree := (*[1 << 20]inlinedCall)(inldata)
   379  				// skip the logical (inlined) frames
   380  				logicalSkipped := 0
   381  				for ix >= 0 && skip > 0 {
   382  					skip--
   383  					logicalSkipped++
   384  					ix = inltree[ix].parent
   385  				}
   386  
   387  				// skip the physical frame if there's more to skip
   388  				if skip > 0 {
   389  					skip--
   390  					goto skipped
   391  				}
   392  
   393  				// now we have a partially skipped frame
   394  				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
   395  
   396  				// if there's room, pcbuf[1] is a skip PC that encodes the number of skipped frames in pcbuf[0]
   397  				if n+1 < max {
   398  					n++
   399  					skipPC := funcPC(skipPleaseUseCallersFrames) + uintptr(logicalSkipped)
   400  					(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = skipPC
   401  				}
   402  			}
   403  		}
   404  
   405  		if printing {
   406  			// assume skip=0 for printing.
   407  			//
   408  			// Never elide wrappers if we haven't printed
   409  			// any frames. And don't elide wrappers that
   410  			// called panic rather than the wrapped
   411  			// function. Otherwise, leave them out.
   412  			name := funcname(f)
   413  			nextElideWrapper := elideWrapperCalling(name)
   414  			if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp, nprint == 0, elideWrapper && nprint != 0) {
   415  				// Print during crash.
   416  				//	main(0x1, 0x2, 0x3)
   417  				//		/home/rsc/go/src/runtime/x.go:23 +0xf
   418  				//
   419  				tracepc := frame.pc // back up to CALL instruction for funcline.
   420  				if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
   421  					tracepc--
   422  				}
   423  				file, line := funcline(f, tracepc)
   424  				inldata := funcdata(f, _FUNCDATA_InlTree)
   425  				if inldata != nil {
   426  					inltree := (*[1 << 20]inlinedCall)(inldata)
   427  					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, nil)
   428  					for ix != -1 {
   429  						name := funcnameFromNameoff(f, inltree[ix].func_)
   430  						print(name, "(...)\n")
   431  						print("\t", file, ":", line, "\n")
   432  
   433  						file = funcfile(f, inltree[ix].file)
   434  						line = inltree[ix].line
   435  						ix = inltree[ix].parent
   436  					}
   437  				}
   438  				if name == "runtime.gopanic" {
   439  					name = "panic"
   440  				}
   441  				print(name, "(")
   442  				argp := (*[100]uintptr)(unsafe.Pointer(frame.argp))
   443  				for i := uintptr(0); i < frame.arglen/sys.PtrSize; i++ {
   444  					if i >= 10 {
   445  						print(", ...")
   446  						break
   447  					}
   448  					if i != 0 {
   449  						print(", ")
   450  					}
   451  					print(hex(argp[i]))
   452  				}
   453  				print(")\n")
   454  				print("\t", file, ":", line)
   455  				if frame.pc > f.entry {
   456  					print(" +", hex(frame.pc-f.entry))
   457  				}
   458  				if g.m.throwing > 0 && gp == g.m.curg || level >= 2 {
   459  					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp), " pc=", hex(frame.pc))
   460  				}
   461  				print("\n")
   462  				nprint++
   463  			}
   464  			elideWrapper = nextElideWrapper
   465  		}
   466  		n++
   467  
   468  	skipped:
   469  		if f.entry == cgocallback_gofuncPC && len(cgoCtxt) > 0 {
   470  			ctxt := cgoCtxt[len(cgoCtxt)-1]
   471  			cgoCtxt = cgoCtxt[:len(cgoCtxt)-1]
   472  
   473  			// skip only applies to Go frames.
   474  			// callback != nil only used when we only care
   475  			// about Go frames.
   476  			if skip == 0 && callback == nil {
   477  				n = tracebackCgoContext(pcbuf, printing, ctxt, n, max)
   478  			}
   479  		}
   480  
   481  		waspanic = f.entry == sigpanicPC
   482  
   483  		// Do not unwind past the bottom of the stack.
   484  		if !flr.valid() {
   485  			break
   486  		}
   487  
   488  		// Unwind to next frame.
   489  		frame.fn = flr
   490  		frame.pc = frame.lr
   491  		frame.lr = 0
   492  		frame.sp = frame.fp
   493  		frame.fp = 0
   494  		frame.argmap = nil
   495  
   496  		// On link register architectures, sighandler saves the LR on stack
   497  		// before faking a call to sigpanic.
   498  		if usesLR && waspanic {
   499  			x := *(*uintptr)(unsafe.Pointer(frame.sp))
   500  			frame.sp += sys.MinFrameSize
   501  			if GOARCH == "arm64" {
   502  				// arm64 needs 16-byte aligned SP, always
   503  				frame.sp += sys.PtrSize
   504  			}
   505  			f = findfunc(frame.pc)
   506  			frame.fn = f
   507  			if !f.valid() {
   508  				frame.pc = x
   509  			} else if funcspdelta(f, frame.pc, &cache) == 0 {
   510  				frame.lr = x
   511  			}
   512  		}
   513  	}
   514  
   515  	if printing {
   516  		n = nprint
   517  	}
   518  
   519  	// If callback != nil, we're being called to gather stack information during
   520  	// garbage collection or stack growth. In that context, require that we used
   521  	// up the entire defer stack. If not, then there is a bug somewhere and the
   522  	// garbage collection or stack growth may not have seen the correct picture
   523  	// of the stack. Crash now instead of silently executing the garbage collection
   524  	// or stack copy incorrectly and setting up for a mysterious crash later.
   525  	//
   526  	// Note that panic != nil is okay here: there can be leftover panics,
   527  	// because the defers on the panic stack do not nest in frame order as
   528  	// they do on the defer stack. If you have:
   529  	//
   530  	//	frame 1 defers d1
   531  	//	frame 2 defers d2
   532  	//	frame 3 defers d3
   533  	//	frame 4 panics
   534  	//	frame 4's panic starts running defers
   535  	//	frame 5, running d3, defers d4
   536  	//	frame 5 panics
   537  	//	frame 5's panic starts running defers
   538  	//	frame 6, running d4, garbage collects
   539  	//	frame 6, running d2, garbage collects
   540  	//
   541  	// During the execution of d4, the panic stack is d4 -> d3, which
   542  	// is nested properly, and we'll treat frame 3 as resumable, because we
   543  	// can find d3. (And in fact frame 3 is resumable. If d4 recovers
   544  	// and frame 5 continues running, d3, d3 can recover and we'll
   545  	// resume execution in (returning from) frame 3.)
   546  	//
   547  	// During the execution of d2, however, the panic stack is d2 -> d3,
   548  	// which is inverted. The scan will match d2 to frame 2 but having
   549  	// d2 on the stack until then means it will not match d3 to frame 3.
   550  	// This is okay: if we're running d2, then all the defers after d2 have
   551  	// completed and their corresponding frames are dead. Not finding d3
   552  	// for frame 3 means we'll set frame 3's continpc == 0, which is correct
   553  	// (frame 3 is dead). At the end of the walk the panic stack can thus
   554  	// contain defers (d3 in this case) for dead frames. The inversion here
   555  	// always indicates a dead frame, and the effect of the inversion on the
   556  	// scan is to hide those dead frames, so the scan is still okay:
   557  	// what's left on the panic stack are exactly (and only) the dead frames.
   558  	//
   559  	// We require callback != nil here because only when callback != nil
   560  	// do we know that gentraceback is being called in a "must be correct"
   561  	// context as opposed to a "best effort" context. The tracebacks with
   562  	// callbacks only happen when everything is stopped nicely.
   563  	// At other times, such as when gathering a stack for a profiling signal
   564  	// or when printing a traceback during a crash, everything may not be
   565  	// stopped nicely, and the stack walk may not be able to complete.
   566  	// It's okay in those situations not to use up the entire defer stack:
   567  	// incomplete information then is still better than nothing.
   568  	if callback != nil && n < max && _defer != nil {
   569  		if _defer != nil {
   570  			print("runtime: g", gp.goid, ": leftover defer sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
   571  		}
   572  		for _defer = gp._defer; _defer != nil; _defer = _defer.link {
   573  			print("\tdefer ", _defer, " sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
   574  		}
   575  		throw("traceback has leftover defers")
   576  	}
   577  
   578  	if callback != nil && n < max && frame.sp != gp.stktopsp {
   579  		print("runtime: g", gp.goid, ": frame.sp=", hex(frame.sp), " top=", hex(gp.stktopsp), "\n")
   580  		print("\tstack=[", hex(gp.stack.lo), "-", hex(gp.stack.hi), "] n=", n, " max=", max, "\n")
   581  		throw("traceback did not unwind completely")
   582  	}
   583  
   584  	return n
   585  }
   586  
   587  // reflectMethodValue is a partial duplicate of reflect.makeFuncImpl
   588  // and reflect.methodValue.
   589  type reflectMethodValue struct {
   590  	fn    uintptr
   591  	stack *bitvector // args bitmap
   592  }
   593  
   594  // getArgInfo returns the argument frame information for a call to f
   595  // with call frame frame.
   596  //
   597  // This is used for both actual calls with active stack frames and for
   598  // deferred calls that are not yet executing. If this is an actual
   599  // call, ctxt must be nil (getArgInfo will retrieve what it needs from
   600  // the active stack frame). If this is a deferred call, ctxt must be
   601  // the function object that was deferred.
   602  func getArgInfo(frame *stkframe, f funcInfo, needArgMap bool, ctxt *funcval) (arglen uintptr, argmap *bitvector) {
   603  	arglen = uintptr(f.args)
   604  	if needArgMap && f.args == _ArgsSizeUnknown {
   605  		// Extract argument bitmaps for reflect stubs from the calls they made to reflect.
   606  		switch funcname(f) {
   607  		case "reflect.makeFuncStub", "reflect.methodValueCall":
   608  			// These take a *reflect.methodValue as their
   609  			// context register.
   610  			var mv *reflectMethodValue
   611  			if ctxt != nil {
   612  				// This is not an actual call, but a
   613  				// deferred call. The function value
   614  				// is itself the *reflect.methodValue.
   615  				mv = (*reflectMethodValue)(unsafe.Pointer(ctxt))
   616  			} else {
   617  				// This is a real call that took the
   618  				// *reflect.methodValue as its context
   619  				// register and immediately saved it
   620  				// to 0(SP). Get the methodValue from
   621  				// 0(SP).
   622  				arg0 := frame.sp + sys.MinFrameSize
   623  				mv = *(**reflectMethodValue)(unsafe.Pointer(arg0))
   624  			}
   625  			if mv.fn != f.entry {
   626  				print("runtime: confused by ", funcname(f), "\n")
   627  				throw("reflect mismatch")
   628  			}
   629  			bv := mv.stack
   630  			arglen = uintptr(bv.n * sys.PtrSize)
   631  			argmap = bv
   632  		}
   633  	}
   634  	return
   635  }
   636  
   637  // tracebackCgoContext handles tracing back a cgo context value, from
   638  // the context argument to setCgoTraceback, for the gentraceback
   639  // function. It returns the new value of n.
   640  func tracebackCgoContext(pcbuf *uintptr, printing bool, ctxt uintptr, n, max int) int {
   641  	var cgoPCs [32]uintptr
   642  	cgoContextPCs(ctxt, cgoPCs[:])
   643  	var arg cgoSymbolizerArg
   644  	anySymbolized := false
   645  	for _, pc := range cgoPCs {
   646  		if pc == 0 || n >= max {
   647  			break
   648  		}
   649  		if pcbuf != nil {
   650  			(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   651  		}
   652  		if printing {
   653  			if cgoSymbolizer == nil {
   654  				print("non-Go function at pc=", hex(pc), "\n")
   655  			} else {
   656  				c := printOneCgoTraceback(pc, max-n, &arg)
   657  				n += c - 1 // +1 a few lines down
   658  				anySymbolized = true
   659  			}
   660  		}
   661  		n++
   662  	}
   663  	if anySymbolized {
   664  		arg.pc = 0
   665  		callCgoSymbolizer(&arg)
   666  	}
   667  	return n
   668  }
   669  
   670  func printcreatedby(gp *g) {
   671  	// Show what created goroutine, except main goroutine (goid 1).
   672  	pc := gp.gopc
   673  	f := findfunc(pc)
   674  	if f.valid() && showframe(f, gp, false, false) && gp.goid != 1 {
   675  		print("created by ", funcname(f), "\n")
   676  		tracepc := pc // back up to CALL instruction for funcline.
   677  		if pc > f.entry {
   678  			tracepc -= sys.PCQuantum
   679  		}
   680  		file, line := funcline(f, tracepc)
   681  		print("\t", file, ":", line)
   682  		if pc > f.entry {
   683  			print(" +", hex(pc-f.entry))
   684  		}
   685  		print("\n")
   686  	}
   687  }
   688  
   689  func traceback(pc, sp, lr uintptr, gp *g) {
   690  	traceback1(pc, sp, lr, gp, 0)
   691  }
   692  
   693  // tracebacktrap is like traceback but expects that the PC and SP were obtained
   694  // from a trap, not from gp->sched or gp->syscallpc/gp->syscallsp or getcallerpc/getcallersp.
   695  // Because they are from a trap instead of from a saved pair,
   696  // the initial PC must not be rewound to the previous instruction.
   697  // (All the saved pairs record a PC that is a return address, so we
   698  // rewind it into the CALL instruction.)
   699  func tracebacktrap(pc, sp, lr uintptr, gp *g) {
   700  	traceback1(pc, sp, lr, gp, _TraceTrap)
   701  }
   702  
   703  func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
   704  	// If the goroutine is in cgo, and we have a cgo traceback, print that.
   705  	if iscgo && gp.m != nil && gp.m.ncgo > 0 && gp.syscallsp != 0 && gp.m.cgoCallers != nil && gp.m.cgoCallers[0] != 0 {
   706  		// Lock cgoCallers so that a signal handler won't
   707  		// change it, copy the array, reset it, unlock it.
   708  		// We are locked to the thread and are not running
   709  		// concurrently with a signal handler.
   710  		// We just have to stop a signal handler from interrupting
   711  		// in the middle of our copy.
   712  		atomic.Store(&gp.m.cgoCallersUse, 1)
   713  		cgoCallers := *gp.m.cgoCallers
   714  		gp.m.cgoCallers[0] = 0
   715  		atomic.Store(&gp.m.cgoCallersUse, 0)
   716  
   717  		printCgoTraceback(&cgoCallers)
   718  	}
   719  
   720  	var n int
   721  	if readgstatus(gp)&^_Gscan == _Gsyscall {
   722  		// Override registers if blocked in system call.
   723  		pc = gp.syscallpc
   724  		sp = gp.syscallsp
   725  		flags &^= _TraceTrap
   726  	}
   727  	// Print traceback. By default, omits runtime frames.
   728  	// If that means we print nothing at all, repeat forcing all frames printed.
   729  	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
   730  	if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
   731  		n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags|_TraceRuntimeFrames)
   732  	}
   733  	if n == _TracebackMaxFrames {
   734  		print("...additional frames elided...\n")
   735  	}
   736  	printcreatedby(gp)
   737  }
   738  
   739  func callers(skip int, pcbuf []uintptr) int {
   740  	sp := getcallersp(unsafe.Pointer(&skip))
   741  	pc := getcallerpc()
   742  	gp := getg()
   743  	var n int
   744  	systemstack(func() {
   745  		n = gentraceback(pc, sp, 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
   746  	})
   747  	return n
   748  }
   749  
   750  func gcallers(gp *g, skip int, pcbuf []uintptr) int {
   751  	return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
   752  }
   753  
   754  func showframe(f funcInfo, gp *g, firstFrame, elideWrapper bool) bool {
   755  	g := getg()
   756  	if g.m.throwing > 0 && gp != nil && (gp == g.m.curg || gp == g.m.caughtsig.ptr()) {
   757  		return true
   758  	}
   759  	level, _, _ := gotraceback()
   760  	if level > 1 {
   761  		// Show all frames.
   762  		return true
   763  	}
   764  
   765  	if !f.valid() {
   766  		return false
   767  	}
   768  
   769  	if elideWrapper {
   770  		file, _ := funcline(f, f.entry)
   771  		if file == "<autogenerated>" {
   772  			return false
   773  		}
   774  	}
   775  
   776  	name := funcname(f)
   777  
   778  	// Special case: always show runtime.gopanic frame
   779  	// in the middle of a stack trace, so that we can
   780  	// see the boundary between ordinary code and
   781  	// panic-induced deferred code.
   782  	// See golang.org/issue/5832.
   783  	if name == "runtime.gopanic" && !firstFrame {
   784  		return true
   785  	}
   786  
   787  	return contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name))
   788  }
   789  
   790  // isExportedRuntime reports whether name is an exported runtime function.
   791  // It is only for runtime functions, so ASCII A-Z is fine.
   792  func isExportedRuntime(name string) bool {
   793  	const n = len("runtime.")
   794  	return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
   795  }
   796  
   797  // elideWrapperCalling returns whether a wrapper function that called
   798  // function "name" should be elided from stack traces.
   799  func elideWrapperCalling(name string) bool {
   800  	// If the wrapper called a panic function instead of the
   801  	// wrapped function, we want to include it in stacks.
   802  	return !(name == "runtime.gopanic" || name == "runtime.sigpanic" || name == "runtime.panicwrap")
   803  }
   804  
   805  var gStatusStrings = [...]string{
   806  	_Gidle:      "idle",
   807  	_Grunnable:  "runnable",
   808  	_Grunning:   "running",
   809  	_Gsyscall:   "syscall",
   810  	_Gwaiting:   "waiting",
   811  	_Gdead:      "dead",
   812  	_Gcopystack: "copystack",
   813  }
   814  
   815  func goroutineheader(gp *g) {
   816  	gpstatus := readgstatus(gp)
   817  
   818  	isScan := gpstatus&_Gscan != 0
   819  	gpstatus &^= _Gscan // drop the scan bit
   820  
   821  	// Basic string status
   822  	var status string
   823  	if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
   824  		status = gStatusStrings[gpstatus]
   825  	} else {
   826  		status = "???"
   827  	}
   828  
   829  	// Override.
   830  	if gpstatus == _Gwaiting && gp.waitreason != "" {
   831  		status = gp.waitreason
   832  	}
   833  
   834  	// approx time the G is blocked, in minutes
   835  	var waitfor int64
   836  	if (gpstatus == _Gwaiting || gpstatus == _Gsyscall) && gp.waitsince != 0 {
   837  		waitfor = (nanotime() - gp.waitsince) / 60e9
   838  	}
   839  	print("goroutine ", gp.goid, " [", status)
   840  	if isScan {
   841  		print(" (scan)")
   842  	}
   843  	if waitfor >= 1 {
   844  		print(", ", waitfor, " minutes")
   845  	}
   846  	if gp.lockedm != 0 {
   847  		print(", locked to thread")
   848  	}
   849  	print("]:\n")
   850  }
   851  
   852  func tracebackothers(me *g) {
   853  	level, _, _ := gotraceback()
   854  
   855  	// Show the current goroutine first, if we haven't already.
   856  	g := getg()
   857  	gp := g.m.curg
   858  	if gp != nil && gp != me {
   859  		print("\n")
   860  		goroutineheader(gp)
   861  		traceback(^uintptr(0), ^uintptr(0), 0, gp)
   862  	}
   863  
   864  	lock(&allglock)
   865  	for _, gp := range allgs {
   866  		if gp == me || gp == g.m.curg || readgstatus(gp) == _Gdead || isSystemGoroutine(gp) && level < 2 {
   867  			continue
   868  		}
   869  		print("\n")
   870  		goroutineheader(gp)
   871  		// Note: gp.m == g.m occurs when tracebackothers is
   872  		// called from a signal handler initiated during a
   873  		// systemstack call. The original G is still in the
   874  		// running state, and we want to print its stack.
   875  		if gp.m != g.m && readgstatus(gp)&^_Gscan == _Grunning {
   876  			print("\tgoroutine running on other thread; stack unavailable\n")
   877  			printcreatedby(gp)
   878  		} else {
   879  			traceback(^uintptr(0), ^uintptr(0), 0, gp)
   880  		}
   881  	}
   882  	unlock(&allglock)
   883  }
   884  
   885  // tracebackHexdump hexdumps part of stk around frame.sp and frame.fp
   886  // for debugging purposes. If the address bad is included in the
   887  // hexdumped range, it will mark it as well.
   888  func tracebackHexdump(stk stack, frame *stkframe, bad uintptr) {
   889  	const expand = 32 * sys.PtrSize
   890  	const maxExpand = 256 * sys.PtrSize
   891  	// Start around frame.sp.
   892  	lo, hi := frame.sp, frame.sp
   893  	// Expand to include frame.fp.
   894  	if frame.fp != 0 && frame.fp < lo {
   895  		lo = frame.fp
   896  	}
   897  	if frame.fp != 0 && frame.fp > hi {
   898  		hi = frame.fp
   899  	}
   900  	// Expand a bit more.
   901  	lo, hi = lo-expand, hi+expand
   902  	// But don't go too far from frame.sp.
   903  	if lo < frame.sp-maxExpand {
   904  		lo = frame.sp - maxExpand
   905  	}
   906  	if hi > frame.sp+maxExpand {
   907  		hi = frame.sp + maxExpand
   908  	}
   909  	// And don't go outside the stack bounds.
   910  	if lo < stk.lo {
   911  		lo = stk.lo
   912  	}
   913  	if hi > stk.hi {
   914  		hi = stk.hi
   915  	}
   916  
   917  	// Print the hex dump.
   918  	print("stack: frame={sp:", hex(frame.sp), ", fp:", hex(frame.fp), "} stack=[", hex(stk.lo), ",", hex(stk.hi), ")\n")
   919  	hexdumpWords(lo, hi, func(p uintptr) byte {
   920  		switch p {
   921  		case frame.fp:
   922  			return '>'
   923  		case frame.sp:
   924  			return '<'
   925  		case bad:
   926  			return '!'
   927  		}
   928  		return 0
   929  	})
   930  }
   931  
   932  // Does f mark the top of a goroutine stack?
   933  func topofstack(f funcInfo, g0 bool) bool {
   934  	pc := f.entry
   935  	return pc == goexitPC ||
   936  		pc == mstartPC ||
   937  		pc == mcallPC ||
   938  		pc == morestackPC ||
   939  		pc == rt0_goPC ||
   940  		externalthreadhandlerp != 0 && pc == externalthreadhandlerp ||
   941  		// asmcgocall is TOS on the system stack because it
   942  		// switches to the system stack, but in this case we
   943  		// can come back to the regular stack and still want
   944  		// to be able to unwind through the call that appeared
   945  		// on the regular stack.
   946  		(g0 && pc == asmcgocallPC)
   947  }
   948  
   949  // isSystemGoroutine reports whether the goroutine g must be omitted in
   950  // stack dumps and deadlock detector.
   951  func isSystemGoroutine(gp *g) bool {
   952  	pc := gp.startpc
   953  	return pc == runfinqPC && !fingRunning ||
   954  		pc == bgsweepPC ||
   955  		pc == forcegchelperPC ||
   956  		pc == timerprocPC ||
   957  		pc == gcBgMarkWorkerPC
   958  }
   959  
   960  // SetCgoTraceback records three C functions to use to gather
   961  // traceback information from C code and to convert that traceback
   962  // information into symbolic information. These are used when printing
   963  // stack traces for a program that uses cgo.
   964  //
   965  // The traceback and context functions may be called from a signal
   966  // handler, and must therefore use only async-signal safe functions.
   967  // The symbolizer function may be called while the program is
   968  // crashing, and so must be cautious about using memory.  None of the
   969  // functions may call back into Go.
   970  //
   971  // The context function will be called with a single argument, a
   972  // pointer to a struct:
   973  //
   974  //	struct {
   975  //		Context uintptr
   976  //	}
   977  //
   978  // In C syntax, this struct will be
   979  //
   980  //	struct {
   981  //		uintptr_t Context;
   982  //	};
   983  //
   984  // If the Context field is 0, the context function is being called to
   985  // record the current traceback context. It should record in the
   986  // Context field whatever information is needed about the current
   987  // point of execution to later produce a stack trace, probably the
   988  // stack pointer and PC. In this case the context function will be
   989  // called from C code.
   990  //
   991  // If the Context field is not 0, then it is a value returned by a
   992  // previous call to the context function. This case is called when the
   993  // context is no longer needed; that is, when the Go code is returning
   994  // to its C code caller. This permits the context function to release
   995  // any associated resources.
   996  //
   997  // While it would be correct for the context function to record a
   998  // complete a stack trace whenever it is called, and simply copy that
   999  // out in the traceback function, in a typical program the context
  1000  // function will be called many times without ever recording a
  1001  // traceback for that context. Recording a complete stack trace in a
  1002  // call to the context function is likely to be inefficient.
  1003  //
  1004  // The traceback function will be called with a single argument, a
  1005  // pointer to a struct:
  1006  //
  1007  //	struct {
  1008  //		Context    uintptr
  1009  //		SigContext uintptr
  1010  //		Buf        *uintptr
  1011  //		Max        uintptr
  1012  //	}
  1013  //
  1014  // In C syntax, this struct will be
  1015  //
  1016  //	struct {
  1017  //		uintptr_t  Context;
  1018  //		uintptr_t  SigContext;
  1019  //		uintptr_t* Buf;
  1020  //		uintptr_t  Max;
  1021  //	};
  1022  //
  1023  // The Context field will be zero to gather a traceback from the
  1024  // current program execution point. In this case, the traceback
  1025  // function will be called from C code.
  1026  //
  1027  // Otherwise Context will be a value previously returned by a call to
  1028  // the context function. The traceback function should gather a stack
  1029  // trace from that saved point in the program execution. The traceback
  1030  // function may be called from an execution thread other than the one
  1031  // that recorded the context, but only when the context is known to be
  1032  // valid and unchanging. The traceback function may also be called
  1033  // deeper in the call stack on the same thread that recorded the
  1034  // context. The traceback function may be called multiple times with
  1035  // the same Context value; it will usually be appropriate to cache the
  1036  // result, if possible, the first time this is called for a specific
  1037  // context value.
  1038  //
  1039  // If the traceback function is called from a signal handler on a Unix
  1040  // system, SigContext will be the signal context argument passed to
  1041  // the signal handler (a C ucontext_t* cast to uintptr_t). This may be
  1042  // used to start tracing at the point where the signal occurred. If
  1043  // the traceback function is not called from a signal handler,
  1044  // SigContext will be zero.
  1045  //
  1046  // Buf is where the traceback information should be stored. It should
  1047  // be PC values, such that Buf[0] is the PC of the caller, Buf[1] is
  1048  // the PC of that function's caller, and so on.  Max is the maximum
  1049  // number of entries to store.  The function should store a zero to
  1050  // indicate the top of the stack, or that the caller is on a different
  1051  // stack, presumably a Go stack.
  1052  //
  1053  // Unlike runtime.Callers, the PC values returned should, when passed
  1054  // to the symbolizer function, return the file/line of the call
  1055  // instruction.  No additional subtraction is required or appropriate.
  1056  //
  1057  // The symbolizer function will be called with a single argument, a
  1058  // pointer to a struct:
  1059  //
  1060  //	struct {
  1061  //		PC      uintptr // program counter to fetch information for
  1062  //		File    *byte   // file name (NUL terminated)
  1063  //		Lineno  uintptr // line number
  1064  //		Func    *byte   // function name (NUL terminated)
  1065  //		Entry   uintptr // function entry point
  1066  //		More    uintptr // set non-zero if more info for this PC
  1067  //		Data    uintptr // unused by runtime, available for function
  1068  //	}
  1069  //
  1070  // In C syntax, this struct will be
  1071  //
  1072  //	struct {
  1073  //		uintptr_t PC;
  1074  //		char*     File;
  1075  //		uintptr_t Lineno;
  1076  //		char*     Func;
  1077  //		uintptr_t Entry;
  1078  //		uintptr_t More;
  1079  //		uintptr_t Data;
  1080  //	};
  1081  //
  1082  // The PC field will be a value returned by a call to the traceback
  1083  // function.
  1084  //
  1085  // The first time the function is called for a particular traceback,
  1086  // all the fields except PC will be 0. The function should fill in the
  1087  // other fields if possible, setting them to 0/nil if the information
  1088  // is not available. The Data field may be used to store any useful
  1089  // information across calls. The More field should be set to non-zero
  1090  // if there is more information for this PC, zero otherwise. If More
  1091  // is set non-zero, the function will be called again with the same
  1092  // PC, and may return different information (this is intended for use
  1093  // with inlined functions). If More is zero, the function will be
  1094  // called with the next PC value in the traceback. When the traceback
  1095  // is complete, the function will be called once more with PC set to
  1096  // zero; this may be used to free any information. Each call will
  1097  // leave the fields of the struct set to the same values they had upon
  1098  // return, except for the PC field when the More field is zero. The
  1099  // function must not keep a copy of the struct pointer between calls.
  1100  //
  1101  // When calling SetCgoTraceback, the version argument is the version
  1102  // number of the structs that the functions expect to receive.
  1103  // Currently this must be zero.
  1104  //
  1105  // The symbolizer function may be nil, in which case the results of
  1106  // the traceback function will be displayed as numbers. If the
  1107  // traceback function is nil, the symbolizer function will never be
  1108  // called. The context function may be nil, in which case the
  1109  // traceback function will only be called with the context field set
  1110  // to zero.  If the context function is nil, then calls from Go to C
  1111  // to Go will not show a traceback for the C portion of the call stack.
  1112  //
  1113  // SetCgoTraceback should be called only once, ideally from an init function.
  1114  func SetCgoTraceback(version int, traceback, context, symbolizer unsafe.Pointer) {
  1115  	if version != 0 {
  1116  		panic("unsupported version")
  1117  	}
  1118  
  1119  	if cgoTraceback != nil && cgoTraceback != traceback ||
  1120  		cgoContext != nil && cgoContext != context ||
  1121  		cgoSymbolizer != nil && cgoSymbolizer != symbolizer {
  1122  		panic("call SetCgoTraceback only once")
  1123  	}
  1124  
  1125  	cgoTraceback = traceback
  1126  	cgoContext = context
  1127  	cgoSymbolizer = symbolizer
  1128  
  1129  	// The context function is called when a C function calls a Go
  1130  	// function. As such it is only called by C code in runtime/cgo.
  1131  	if _cgo_set_context_function != nil {
  1132  		cgocall(_cgo_set_context_function, context)
  1133  	}
  1134  }
  1135  
  1136  var cgoTraceback unsafe.Pointer
  1137  var cgoContext unsafe.Pointer
  1138  var cgoSymbolizer unsafe.Pointer
  1139  
  1140  // cgoTracebackArg is the type passed to cgoTraceback.
  1141  type cgoTracebackArg struct {
  1142  	context    uintptr
  1143  	sigContext uintptr
  1144  	buf        *uintptr
  1145  	max        uintptr
  1146  }
  1147  
  1148  // cgoContextArg is the type passed to the context function.
  1149  type cgoContextArg struct {
  1150  	context uintptr
  1151  }
  1152  
  1153  // cgoSymbolizerArg is the type passed to cgoSymbolizer.
  1154  type cgoSymbolizerArg struct {
  1155  	pc       uintptr
  1156  	file     *byte
  1157  	lineno   uintptr
  1158  	funcName *byte
  1159  	entry    uintptr
  1160  	more     uintptr
  1161  	data     uintptr
  1162  }
  1163  
  1164  // cgoTraceback prints a traceback of callers.
  1165  func printCgoTraceback(callers *cgoCallers) {
  1166  	if cgoSymbolizer == nil {
  1167  		for _, c := range callers {
  1168  			if c == 0 {
  1169  				break
  1170  			}
  1171  			print("non-Go function at pc=", hex(c), "\n")
  1172  		}
  1173  		return
  1174  	}
  1175  
  1176  	var arg cgoSymbolizerArg
  1177  	for _, c := range callers {
  1178  		if c == 0 {
  1179  			break
  1180  		}
  1181  		printOneCgoTraceback(c, 0x7fffffff, &arg)
  1182  	}
  1183  	arg.pc = 0
  1184  	callCgoSymbolizer(&arg)
  1185  }
  1186  
  1187  // printOneCgoTraceback prints the traceback of a single cgo caller.
  1188  // This can print more than one line because of inlining.
  1189  // Returns the number of frames printed.
  1190  func printOneCgoTraceback(pc uintptr, max int, arg *cgoSymbolizerArg) int {
  1191  	c := 0
  1192  	arg.pc = pc
  1193  	for {
  1194  		if c > max {
  1195  			break
  1196  		}
  1197  		callCgoSymbolizer(arg)
  1198  		if arg.funcName != nil {
  1199  			// Note that we don't print any argument
  1200  			// information here, not even parentheses.
  1201  			// The symbolizer must add that if appropriate.
  1202  			println(gostringnocopy(arg.funcName))
  1203  		} else {
  1204  			println("non-Go function")
  1205  		}
  1206  		print("\t")
  1207  		if arg.file != nil {
  1208  			print(gostringnocopy(arg.file), ":", arg.lineno, " ")
  1209  		}
  1210  		print("pc=", hex(pc), "\n")
  1211  		c++
  1212  		if arg.more == 0 {
  1213  			break
  1214  		}
  1215  	}
  1216  	return c
  1217  }
  1218  
  1219  // callCgoSymbolizer calls the cgoSymbolizer function.
  1220  func callCgoSymbolizer(arg *cgoSymbolizerArg) {
  1221  	call := cgocall
  1222  	if panicking > 0 || getg().m.curg != getg() {
  1223  		// We do not want to call into the scheduler when panicking
  1224  		// or when on the system stack.
  1225  		call = asmcgocall
  1226  	}
  1227  	if msanenabled {
  1228  		msanwrite(unsafe.Pointer(arg), unsafe.Sizeof(cgoSymbolizerArg{}))
  1229  	}
  1230  	call(cgoSymbolizer, noescape(unsafe.Pointer(arg)))
  1231  }
  1232  
  1233  // cgoContextPCs gets the PC values from a cgo traceback.
  1234  func cgoContextPCs(ctxt uintptr, buf []uintptr) {
  1235  	if cgoTraceback == nil {
  1236  		return
  1237  	}
  1238  	call := cgocall
  1239  	if panicking > 0 || getg().m.curg != getg() {
  1240  		// We do not want to call into the scheduler when panicking
  1241  		// or when on the system stack.
  1242  		call = asmcgocall
  1243  	}
  1244  	arg := cgoTracebackArg{
  1245  		context: ctxt,
  1246  		buf:     (*uintptr)(noescape(unsafe.Pointer(&buf[0]))),
  1247  		max:     uintptr(len(buf)),
  1248  	}
  1249  	if msanenabled {
  1250  		msanwrite(unsafe.Pointer(&arg), unsafe.Sizeof(arg))
  1251  	}
  1252  	call(cgoTraceback, noescape(unsafe.Pointer(&arg)))
  1253  }
  1254  

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