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 skipPC uintptr
    39  
    40  func tracebackinit() {
    41  	// Go variable initialization happens late during runtime startup.
    42  	// Instead of initializing the variables above in the declarations,
    43  	// schedinit calls this function so that the variables are
    44  	// initialized and available earlier in the startup sequence.
    45  	skipPC = funcPC(skipPleaseUseCallersFrames)
    46  }
    47  
    48  // Traceback over the deferred function calls.
    49  // Report them like calls that have been invoked but not started executing yet.
    50  func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
    51  	var frame stkframe
    52  	for d := gp._defer; d != nil; d = d.link {
    53  		fn := d.fn
    54  		if fn == nil {
    55  			// Defer of nil function. Args don't matter.
    56  			frame.pc = 0
    57  			frame.fn = funcInfo{}
    58  			frame.argp = 0
    59  			frame.arglen = 0
    60  			frame.argmap = nil
    61  		} else {
    62  			frame.pc = fn.fn
    63  			f := findfunc(frame.pc)
    64  			if !f.valid() {
    65  				print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
    66  				throw("unknown pc")
    67  			}
    68  			frame.fn = f
    69  			frame.argp = uintptr(deferArgs(d))
    70  			var ok bool
    71  			frame.arglen, frame.argmap, ok = getArgInfoFast(f, true)
    72  			if !ok {
    73  				frame.arglen, frame.argmap = getArgInfo(&frame, f, true, fn)
    74  			}
    75  		}
    76  		frame.continpc = frame.pc
    77  		if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
    78  			return
    79  		}
    80  	}
    81  }
    82  
    83  const sizeofSkipFunction = 256
    84  
    85  // This function is defined in asm.s to be sizeofSkipFunction bytes long.
    86  func skipPleaseUseCallersFrames()
    87  
    88  // Generic traceback. Handles runtime stack prints (pcbuf == nil),
    89  // the runtime.Callers function (pcbuf != nil), as well as the garbage
    90  // collector (callback != nil).  A little clunky to merge these, but avoids
    91  // duplicating the code and all its subtlety.
    92  //
    93  // The skip argument is only valid with pcbuf != nil and counts the number
    94  // of logical frames to skip rather than physical frames (with inlining, a
    95  // PC in pcbuf can represent multiple calls). If a PC is partially skipped
    96  // and max > 1, pcbuf[1] will be runtime.skipPleaseUseCallersFrames+N where
    97  // N indicates the number of logical frames to skip in pcbuf[0].
    98  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 {
    99  	if skip > 0 && callback != nil {
   100  		throw("gentraceback callback cannot be used with non-zero skip")
   101  	}
   102  
   103  	// Don't call this "g"; it's too easy get "g" and "gp" confused.
   104  	if ourg := getg(); ourg == gp && ourg == ourg.m.curg {
   105  		// The starting sp has been passed in as a uintptr, and the caller may
   106  		// have other uintptr-typed stack references as well.
   107  		// If during one of the calls that got us here or during one of the
   108  		// callbacks below the stack must be grown, all these uintptr references
   109  		// to the stack will not be updated, and gentraceback will continue
   110  		// to inspect the old stack memory, which may no longer be valid.
   111  		// Even if all the variables were updated correctly, it is not clear that
   112  		// we want to expose a traceback that begins on one stack and ends
   113  		// on another stack. That could confuse callers quite a bit.
   114  		// Instead, we require that gentraceback and any other function that
   115  		// accepts an sp for the current goroutine (typically obtained by
   116  		// calling getcallersp) must not run on that goroutine's stack but
   117  		// instead on the g0 stack.
   118  		throw("gentraceback cannot trace user goroutine on its own stack")
   119  	}
   120  	level, _, _ := gotraceback()
   121  
   122  	var ctxt *funcval // Context pointer for unstarted goroutines. See issue #25897.
   123  
   124  	if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.
   125  		if gp.syscallsp != 0 {
   126  			pc0 = gp.syscallpc
   127  			sp0 = gp.syscallsp
   128  			if usesLR {
   129  				lr0 = 0
   130  			}
   131  		} else {
   132  			pc0 = gp.sched.pc
   133  			sp0 = gp.sched.sp
   134  			if usesLR {
   135  				lr0 = gp.sched.lr
   136  			}
   137  			ctxt = (*funcval)(gp.sched.ctxt)
   138  		}
   139  	}
   140  
   141  	nprint := 0
   142  	var frame stkframe
   143  	frame.pc = pc0
   144  	frame.sp = sp0
   145  	if usesLR {
   146  		frame.lr = lr0
   147  	}
   148  	waspanic := false
   149  	cgoCtxt := gp.cgoCtxt
   150  	printing := pcbuf == nil && callback == nil
   151  
   152  	// If the PC is zero, it's likely a nil function call.
   153  	// Start in the caller's frame.
   154  	if frame.pc == 0 {
   155  		if usesLR {
   156  			frame.pc = *(*uintptr)(unsafe.Pointer(frame.sp))
   157  			frame.lr = 0
   158  		} else {
   159  			frame.pc = uintptr(*(*sys.Uintreg)(unsafe.Pointer(frame.sp)))
   160  			frame.sp += sys.RegSize
   161  		}
   162  	}
   163  
   164  	f := findfunc(frame.pc)
   165  	if !f.valid() {
   166  		if callback != nil || printing {
   167  			print("runtime: unknown pc ", hex(frame.pc), "\n")
   168  			tracebackHexdump(gp.stack, &frame, 0)
   169  		}
   170  		if callback != nil {
   171  			throw("unknown pc")
   172  		}
   173  		return 0
   174  	}
   175  	frame.fn = f
   176  
   177  	var cache pcvalueCache
   178  
   179  	lastFuncID := funcID_normal
   180  	n := 0
   181  	for n < max {
   182  		// Typically:
   183  		//	pc is the PC of the running function.
   184  		//	sp is the stack pointer at that program counter.
   185  		//	fp is the frame pointer (caller's stack pointer) at that program counter, or nil if unknown.
   186  		//	stk is the stack containing sp.
   187  		//	The caller's program counter is lr, unless lr is zero, in which case it is *(uintptr*)sp.
   188  		f = frame.fn
   189  		if f.pcsp == 0 {
   190  			// No frame information, must be external function, like race support.
   191  			// See golang.org/issue/13568.
   192  			break
   193  		}
   194  
   195  		// Found an actual function.
   196  		// Derive frame pointer and link register.
   197  		if frame.fp == 0 {
   198  			// Jump over system stack transitions. If we're on g0 and there's a user
   199  			// goroutine, try to jump. Otherwise this is a regular call.
   200  			if flags&_TraceJumpStack != 0 && gp == gp.m.g0 && gp.m.curg != nil {
   201  				switch f.funcID {
   202  				case funcID_morestack:
   203  					// morestack does not return normally -- newstack()
   204  					// gogo's to curg.sched. Match that.
   205  					// This keeps morestack() from showing up in the backtrace,
   206  					// but that makes some sense since it'll never be returned
   207  					// to.
   208  					frame.pc = gp.m.curg.sched.pc
   209  					frame.fn = findfunc(frame.pc)
   210  					f = frame.fn
   211  					frame.sp = gp.m.curg.sched.sp
   212  					cgoCtxt = gp.m.curg.cgoCtxt
   213  				case funcID_systemstack:
   214  					// systemstack returns normally, so just follow the
   215  					// stack transition.
   216  					frame.sp = gp.m.curg.sched.sp
   217  					cgoCtxt = gp.m.curg.cgoCtxt
   218  				}
   219  			}
   220  			frame.fp = frame.sp + uintptr(funcspdelta(f, frame.pc, &cache))
   221  			if !usesLR {
   222  				// On x86, call instruction pushes return PC before entering new function.
   223  				frame.fp += sys.RegSize
   224  			}
   225  		}
   226  		var flr funcInfo
   227  		if topofstack(f, gp.m != nil && gp == gp.m.g0) {
   228  			frame.lr = 0
   229  			flr = funcInfo{}
   230  		} else if usesLR && f.funcID == funcID_jmpdefer {
   231  			// jmpdefer modifies SP/LR/PC non-atomically.
   232  			// If a profiling interrupt arrives during jmpdefer,
   233  			// the stack unwind may see a mismatched register set
   234  			// and get confused. Stop if we see PC within jmpdefer
   235  			// to avoid that confusion.
   236  			// See golang.org/issue/8153.
   237  			if callback != nil {
   238  				throw("traceback_arm: found jmpdefer when tracing with callback")
   239  			}
   240  			frame.lr = 0
   241  		} else {
   242  			var lrPtr uintptr
   243  			if usesLR {
   244  				if n == 0 && frame.sp < frame.fp || frame.lr == 0 {
   245  					lrPtr = frame.sp
   246  					frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
   247  				}
   248  			} else {
   249  				if frame.lr == 0 {
   250  					lrPtr = frame.fp - sys.RegSize
   251  					frame.lr = uintptr(*(*sys.Uintreg)(unsafe.Pointer(lrPtr)))
   252  				}
   253  			}
   254  			flr = findfunc(frame.lr)
   255  			if !flr.valid() {
   256  				// This happens if you get a profiling interrupt at just the wrong time.
   257  				// In that context it is okay to stop early.
   258  				// But if callback is set, we're doing a garbage collection and must
   259  				// get everything, so crash loudly.
   260  				doPrint := printing
   261  				if doPrint && gp.m.incgo && f.funcID == funcID_sigpanic {
   262  					// We can inject sigpanic
   263  					// calls directly into C code,
   264  					// in which case we'll see a C
   265  					// return PC. Don't complain.
   266  					doPrint = false
   267  				}
   268  				if callback != nil || doPrint {
   269  					print("runtime: unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
   270  					tracebackHexdump(gp.stack, &frame, lrPtr)
   271  				}
   272  				if callback != nil {
   273  					throw("unknown caller pc")
   274  				}
   275  			}
   276  		}
   277  
   278  		frame.varp = frame.fp
   279  		if !usesLR {
   280  			// On x86, call instruction pushes return PC before entering new function.
   281  			frame.varp -= sys.RegSize
   282  		}
   283  
   284  		// If framepointer_enabled and there's a frame, then
   285  		// there's a saved bp here.
   286  		if frame.varp > frame.sp && (framepointer_enabled && GOARCH == "amd64" || GOARCH == "arm64") {
   287  			frame.varp -= sys.RegSize
   288  		}
   289  
   290  		// Derive size of arguments.
   291  		// Most functions have a fixed-size argument block,
   292  		// so we can use metadata about the function f.
   293  		// Not all, though: there are some variadic functions
   294  		// in package runtime and reflect, and for those we use call-specific
   295  		// metadata recorded by f's caller.
   296  		if callback != nil || printing {
   297  			frame.argp = frame.fp + sys.MinFrameSize
   298  			var ok bool
   299  			frame.arglen, frame.argmap, ok = getArgInfoFast(f, callback != nil)
   300  			if !ok {
   301  				frame.arglen, frame.argmap = getArgInfo(&frame, f, callback != nil, ctxt)
   302  			}
   303  		}
   304  		ctxt = nil // ctxt is only needed to get arg maps for the topmost frame
   305  
   306  		// Determine frame's 'continuation PC', where it can continue.
   307  		// Normally this is the return address on the stack, but if sigpanic
   308  		// is immediately below this function on the stack, then the frame
   309  		// stopped executing due to a trap, and frame.pc is probably not
   310  		// a safe point for looking up liveness information. In this panicking case,
   311  		// the function either doesn't return at all (if it has no defers or if the
   312  		// defers do not recover) or it returns from one of the calls to
   313  		// deferproc a second time (if the corresponding deferred func recovers).
   314  		// In the latter case, use a deferreturn call site as the continuation pc.
   315  		frame.continpc = frame.pc
   316  		if waspanic {
   317  			if frame.fn.deferreturn != 0 {
   318  				frame.continpc = frame.fn.entry + uintptr(frame.fn.deferreturn) + 1
   319  				// Note: this may perhaps keep return variables alive longer than
   320  				// strictly necessary, as we are using "function has a defer statement"
   321  				// as a proxy for "function actually deferred something". It seems
   322  				// to be a minor drawback. (We used to actually look through the
   323  				// gp._defer for a defer corresponding to this function, but that
   324  				// is hard to do with defer records on the stack during a stack copy.)
   325  				// Note: the +1 is to offset the -1 that
   326  				// stack.go:getStackMap does to back up a return
   327  				// address make sure the pc is in the CALL instruction.
   328  			} else {
   329  				frame.continpc = 0
   330  			}
   331  		}
   332  
   333  		if callback != nil {
   334  			if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
   335  				return n
   336  			}
   337  		}
   338  
   339  		if pcbuf != nil {
   340  			pc := frame.pc
   341  			// backup to CALL instruction to read inlining info (same logic as below)
   342  			tracepc := pc
   343  			if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
   344  				tracepc--
   345  			}
   346  
   347  			// If there is inlining info, record the inner frames.
   348  			if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   349  				inltree := (*[1 << 20]inlinedCall)(inldata)
   350  				for {
   351  					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, &cache)
   352  					if ix < 0 {
   353  						break
   354  					}
   355  					if inltree[ix].funcID == funcID_wrapper && elideWrapperCalling(lastFuncID) {
   356  						// ignore wrappers
   357  					} else if skip > 0 {
   358  						skip--
   359  					} else if n < max {
   360  						(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   361  						n++
   362  					}
   363  					lastFuncID = inltree[ix].funcID
   364  					// Back up to an instruction in the "caller".
   365  					tracepc = frame.fn.entry + uintptr(inltree[ix].parentPc)
   366  					pc = tracepc + 1
   367  				}
   368  			}
   369  			// Record the main frame.
   370  			if f.funcID == funcID_wrapper && elideWrapperCalling(lastFuncID) {
   371  				// Ignore wrapper functions (except when they trigger panics).
   372  			} else if skip > 0 {
   373  				skip--
   374  			} else if n < max {
   375  				(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   376  				n++
   377  			}
   378  			lastFuncID = f.funcID
   379  			n-- // offset n++ below
   380  		}
   381  
   382  		if printing {
   383  			// assume skip=0 for printing.
   384  			//
   385  			// Never elide wrappers if we haven't printed
   386  			// any frames. And don't elide wrappers that
   387  			// called panic rather than the wrapped
   388  			// function. Otherwise, leave them out.
   389  
   390  			// backup to CALL instruction to read inlining info (same logic as below)
   391  			tracepc := frame.pc
   392  			if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
   393  				tracepc--
   394  			}
   395  			// If there is inlining info, print the inner frames.
   396  			if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   397  				inltree := (*[1 << 20]inlinedCall)(inldata)
   398  				for {
   399  					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, nil)
   400  					if ix < 0 {
   401  						break
   402  					}
   403  					if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp, nprint == 0, inltree[ix].funcID, lastFuncID) {
   404  						name := funcnameFromNameoff(f, inltree[ix].func_)
   405  						file, line := funcline(f, tracepc)
   406  						print(name, "(...)\n")
   407  						print("\t", file, ":", line, "\n")
   408  						nprint++
   409  					}
   410  					lastFuncID = inltree[ix].funcID
   411  					// Back up to an instruction in the "caller".
   412  					tracepc = frame.fn.entry + uintptr(inltree[ix].parentPc)
   413  				}
   414  			}
   415  			if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp, nprint == 0, f.funcID, lastFuncID) {
   416  				// Print during crash.
   417  				//	main(0x1, 0x2, 0x3)
   418  				//		/home/rsc/go/src/runtime/x.go:23 +0xf
   419  				//
   420  				name := funcname(f)
   421  				file, line := funcline(f, tracepc)
   422  				if name == "runtime.gopanic" {
   423  					name = "panic"
   424  				}
   425  				print(name, "(")
   426  				argp := (*[100]uintptr)(unsafe.Pointer(frame.argp))
   427  				for i := uintptr(0); i < frame.arglen/sys.PtrSize; i++ {
   428  					if i >= 10 {
   429  						print(", ...")
   430  						break
   431  					}
   432  					if i != 0 {
   433  						print(", ")
   434  					}
   435  					print(hex(argp[i]))
   436  				}
   437  				print(")\n")
   438  				print("\t", file, ":", line)
   439  				if frame.pc > f.entry {
   440  					print(" +", hex(frame.pc-f.entry))
   441  				}
   442  				if gp.m != nil && gp.m.throwing > 0 && gp == gp.m.curg || level >= 2 {
   443  					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp), " pc=", hex(frame.pc))
   444  				}
   445  				print("\n")
   446  				nprint++
   447  			}
   448  			lastFuncID = f.funcID
   449  		}
   450  		n++
   451  
   452  		if f.funcID == funcID_cgocallback_gofunc && len(cgoCtxt) > 0 {
   453  			ctxt := cgoCtxt[len(cgoCtxt)-1]
   454  			cgoCtxt = cgoCtxt[:len(cgoCtxt)-1]
   455  
   456  			// skip only applies to Go frames.
   457  			// callback != nil only used when we only care
   458  			// about Go frames.
   459  			if skip == 0 && callback == nil {
   460  				n = tracebackCgoContext(pcbuf, printing, ctxt, n, max)
   461  			}
   462  		}
   463  
   464  		waspanic = f.funcID == funcID_sigpanic
   465  
   466  		// Do not unwind past the bottom of the stack.
   467  		if !flr.valid() {
   468  			break
   469  		}
   470  
   471  		// Unwind to next frame.
   472  		frame.fn = flr
   473  		frame.pc = frame.lr
   474  		frame.lr = 0
   475  		frame.sp = frame.fp
   476  		frame.fp = 0
   477  		frame.argmap = nil
   478  
   479  		// On link register architectures, sighandler saves the LR on stack
   480  		// before faking a call to sigpanic.
   481  		if usesLR && waspanic {
   482  			x := *(*uintptr)(unsafe.Pointer(frame.sp))
   483  			frame.sp += sys.MinFrameSize
   484  			if GOARCH == "arm64" {
   485  				// arm64 needs 16-byte aligned SP, always
   486  				frame.sp += sys.PtrSize
   487  			}
   488  			f = findfunc(frame.pc)
   489  			frame.fn = f
   490  			if !f.valid() {
   491  				frame.pc = x
   492  			} else if funcspdelta(f, frame.pc, &cache) == 0 {
   493  				frame.lr = x
   494  			}
   495  		}
   496  	}
   497  
   498  	if printing {
   499  		n = nprint
   500  	}
   501  
   502  	// Note that panic != nil is okay here: there can be leftover panics,
   503  	// because the defers on the panic stack do not nest in frame order as
   504  	// they do on the defer stack. If you have:
   505  	//
   506  	//	frame 1 defers d1
   507  	//	frame 2 defers d2
   508  	//	frame 3 defers d3
   509  	//	frame 4 panics
   510  	//	frame 4's panic starts running defers
   511  	//	frame 5, running d3, defers d4
   512  	//	frame 5 panics
   513  	//	frame 5's panic starts running defers
   514  	//	frame 6, running d4, garbage collects
   515  	//	frame 6, running d2, garbage collects
   516  	//
   517  	// During the execution of d4, the panic stack is d4 -> d3, which
   518  	// is nested properly, and we'll treat frame 3 as resumable, because we
   519  	// can find d3. (And in fact frame 3 is resumable. If d4 recovers
   520  	// and frame 5 continues running, d3, d3 can recover and we'll
   521  	// resume execution in (returning from) frame 3.)
   522  	//
   523  	// During the execution of d2, however, the panic stack is d2 -> d3,
   524  	// which is inverted. The scan will match d2 to frame 2 but having
   525  	// d2 on the stack until then means it will not match d3 to frame 3.
   526  	// This is okay: if we're running d2, then all the defers after d2 have
   527  	// completed and their corresponding frames are dead. Not finding d3
   528  	// for frame 3 means we'll set frame 3's continpc == 0, which is correct
   529  	// (frame 3 is dead). At the end of the walk the panic stack can thus
   530  	// contain defers (d3 in this case) for dead frames. The inversion here
   531  	// always indicates a dead frame, and the effect of the inversion on the
   532  	// scan is to hide those dead frames, so the scan is still okay:
   533  	// what's left on the panic stack are exactly (and only) the dead frames.
   534  	//
   535  	// We require callback != nil here because only when callback != nil
   536  	// do we know that gentraceback is being called in a "must be correct"
   537  	// context as opposed to a "best effort" context. The tracebacks with
   538  	// callbacks only happen when everything is stopped nicely.
   539  	// At other times, such as when gathering a stack for a profiling signal
   540  	// or when printing a traceback during a crash, everything may not be
   541  	// stopped nicely, and the stack walk may not be able to complete.
   542  	if callback != nil && n < max && frame.sp != gp.stktopsp {
   543  		print("runtime: g", gp.goid, ": frame.sp=", hex(frame.sp), " top=", hex(gp.stktopsp), "\n")
   544  		print("\tstack=[", hex(gp.stack.lo), "-", hex(gp.stack.hi), "] n=", n, " max=", max, "\n")
   545  		throw("traceback did not unwind completely")
   546  	}
   547  
   548  	return n
   549  }
   550  
   551  // reflectMethodValue is a partial duplicate of reflect.makeFuncImpl
   552  // and reflect.methodValue.
   553  type reflectMethodValue struct {
   554  	fn     uintptr
   555  	stack  *bitvector // ptrmap for both args and results
   556  	argLen uintptr    // just args
   557  }
   558  
   559  // getArgInfoFast returns the argument frame information for a call to f.
   560  // It is short and inlineable. However, it does not handle all functions.
   561  // If ok reports false, you must call getArgInfo instead.
   562  // TODO(josharian): once we do mid-stack inlining,
   563  // call getArgInfo directly from getArgInfoFast and stop returning an ok bool.
   564  func getArgInfoFast(f funcInfo, needArgMap bool) (arglen uintptr, argmap *bitvector, ok bool) {
   565  	return uintptr(f.args), nil, !(needArgMap && f.args == _ArgsSizeUnknown)
   566  }
   567  
   568  // getArgInfo returns the argument frame information for a call to f
   569  // with call frame frame.
   570  //
   571  // This is used for both actual calls with active stack frames and for
   572  // deferred calls or goroutines that are not yet executing. If this is an actual
   573  // call, ctxt must be nil (getArgInfo will retrieve what it needs from
   574  // the active stack frame). If this is a deferred call or unstarted goroutine,
   575  // ctxt must be the function object that was deferred or go'd.
   576  func getArgInfo(frame *stkframe, f funcInfo, needArgMap bool, ctxt *funcval) (arglen uintptr, argmap *bitvector) {
   577  	arglen = uintptr(f.args)
   578  	if needArgMap && f.args == _ArgsSizeUnknown {
   579  		// Extract argument bitmaps for reflect stubs from the calls they made to reflect.
   580  		switch funcname(f) {
   581  		case "reflect.makeFuncStub", "reflect.methodValueCall":
   582  			// These take a *reflect.methodValue as their
   583  			// context register.
   584  			var mv *reflectMethodValue
   585  			var retValid bool
   586  			if ctxt != nil {
   587  				// This is not an actual call, but a
   588  				// deferred call or an unstarted goroutine.
   589  				// The function value is itself the *reflect.methodValue.
   590  				mv = (*reflectMethodValue)(unsafe.Pointer(ctxt))
   591  			} else {
   592  				// This is a real call that took the
   593  				// *reflect.methodValue as its context
   594  				// register and immediately saved it
   595  				// to 0(SP). Get the methodValue from
   596  				// 0(SP).
   597  				arg0 := frame.sp + sys.MinFrameSize
   598  				mv = *(**reflectMethodValue)(unsafe.Pointer(arg0))
   599  				// Figure out whether the return values are valid.
   600  				// Reflect will update this value after it copies
   601  				// in the return values.
   602  				retValid = *(*bool)(unsafe.Pointer(arg0 + 3*sys.PtrSize))
   603  			}
   604  			if mv.fn != f.entry {
   605  				print("runtime: confused by ", funcname(f), "\n")
   606  				throw("reflect mismatch")
   607  			}
   608  			bv := mv.stack
   609  			arglen = uintptr(bv.n * sys.PtrSize)
   610  			if !retValid {
   611  				arglen = uintptr(mv.argLen) &^ (sys.PtrSize - 1)
   612  			}
   613  			argmap = bv
   614  		}
   615  	}
   616  	return
   617  }
   618  
   619  // tracebackCgoContext handles tracing back a cgo context value, from
   620  // the context argument to setCgoTraceback, for the gentraceback
   621  // function. It returns the new value of n.
   622  func tracebackCgoContext(pcbuf *uintptr, printing bool, ctxt uintptr, n, max int) int {
   623  	var cgoPCs [32]uintptr
   624  	cgoContextPCs(ctxt, cgoPCs[:])
   625  	var arg cgoSymbolizerArg
   626  	anySymbolized := false
   627  	for _, pc := range cgoPCs {
   628  		if pc == 0 || n >= max {
   629  			break
   630  		}
   631  		if pcbuf != nil {
   632  			(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = pc
   633  		}
   634  		if printing {
   635  			if cgoSymbolizer == nil {
   636  				print("non-Go function at pc=", hex(pc), "\n")
   637  			} else {
   638  				c := printOneCgoTraceback(pc, max-n, &arg)
   639  				n += c - 1 // +1 a few lines down
   640  				anySymbolized = true
   641  			}
   642  		}
   643  		n++
   644  	}
   645  	if anySymbolized {
   646  		arg.pc = 0
   647  		callCgoSymbolizer(&arg)
   648  	}
   649  	return n
   650  }
   651  
   652  func printcreatedby(gp *g) {
   653  	// Show what created goroutine, except main goroutine (goid 1).
   654  	pc := gp.gopc
   655  	f := findfunc(pc)
   656  	if f.valid() && showframe(f, gp, false, funcID_normal, funcID_normal) && gp.goid != 1 {
   657  		printcreatedby1(f, pc)
   658  	}
   659  }
   660  
   661  func printcreatedby1(f funcInfo, pc uintptr) {
   662  	print("created by ", funcname(f), "\n")
   663  	tracepc := pc // back up to CALL instruction for funcline.
   664  	if pc > f.entry {
   665  		tracepc -= sys.PCQuantum
   666  	}
   667  	file, line := funcline(f, tracepc)
   668  	print("\t", file, ":", line)
   669  	if pc > f.entry {
   670  		print(" +", hex(pc-f.entry))
   671  	}
   672  	print("\n")
   673  }
   674  
   675  func traceback(pc, sp, lr uintptr, gp *g) {
   676  	traceback1(pc, sp, lr, gp, 0)
   677  }
   678  
   679  // tracebacktrap is like traceback but expects that the PC and SP were obtained
   680  // from a trap, not from gp->sched or gp->syscallpc/gp->syscallsp or getcallerpc/getcallersp.
   681  // Because they are from a trap instead of from a saved pair,
   682  // the initial PC must not be rewound to the previous instruction.
   683  // (All the saved pairs record a PC that is a return address, so we
   684  // rewind it into the CALL instruction.)
   685  // If gp.m.libcall{g,pc,sp} information is available, it uses that information in preference to
   686  // the pc/sp/lr passed in.
   687  func tracebacktrap(pc, sp, lr uintptr, gp *g) {
   688  	if gp.m.libcallsp != 0 {
   689  		// We're in C code somewhere, traceback from the saved position.
   690  		traceback1(gp.m.libcallpc, gp.m.libcallsp, 0, gp.m.libcallg.ptr(), 0)
   691  		return
   692  	}
   693  	traceback1(pc, sp, lr, gp, _TraceTrap)
   694  }
   695  
   696  func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
   697  	// If the goroutine is in cgo, and we have a cgo traceback, print that.
   698  	if iscgo && gp.m != nil && gp.m.ncgo > 0 && gp.syscallsp != 0 && gp.m.cgoCallers != nil && gp.m.cgoCallers[0] != 0 {
   699  		// Lock cgoCallers so that a signal handler won't
   700  		// change it, copy the array, reset it, unlock it.
   701  		// We are locked to the thread and are not running
   702  		// concurrently with a signal handler.
   703  		// We just have to stop a signal handler from interrupting
   704  		// in the middle of our copy.
   705  		atomic.Store(&gp.m.cgoCallersUse, 1)
   706  		cgoCallers := *gp.m.cgoCallers
   707  		gp.m.cgoCallers[0] = 0
   708  		atomic.Store(&gp.m.cgoCallersUse, 0)
   709  
   710  		printCgoTraceback(&cgoCallers)
   711  	}
   712  
   713  	var n int
   714  	if readgstatus(gp)&^_Gscan == _Gsyscall {
   715  		// Override registers if blocked in system call.
   716  		pc = gp.syscallpc
   717  		sp = gp.syscallsp
   718  		flags &^= _TraceTrap
   719  	}
   720  	// Print traceback. By default, omits runtime frames.
   721  	// If that means we print nothing at all, repeat forcing all frames printed.
   722  	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
   723  	if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
   724  		n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags|_TraceRuntimeFrames)
   725  	}
   726  	if n == _TracebackMaxFrames {
   727  		print("...additional frames elided...\n")
   728  	}
   729  	printcreatedby(gp)
   730  
   731  	if gp.ancestors == nil {
   732  		return
   733  	}
   734  	for _, ancestor := range *gp.ancestors {
   735  		printAncestorTraceback(ancestor)
   736  	}
   737  }
   738  
   739  // printAncestorTraceback prints the traceback of the given ancestor.
   740  // TODO: Unify this with gentraceback and CallersFrames.
   741  func printAncestorTraceback(ancestor ancestorInfo) {
   742  	print("[originating from goroutine ", ancestor.goid, "]:\n")
   743  	for fidx, pc := range ancestor.pcs {
   744  		f := findfunc(pc) // f previously validated
   745  		if showfuncinfo(f, fidx == 0, funcID_normal, funcID_normal) {
   746  			printAncestorTracebackFuncInfo(f, pc)
   747  		}
   748  	}
   749  	if len(ancestor.pcs) == _TracebackMaxFrames {
   750  		print("...additional frames elided...\n")
   751  	}
   752  	// Show what created goroutine, except main goroutine (goid 1).
   753  	f := findfunc(ancestor.gopc)
   754  	if f.valid() && showfuncinfo(f, false, funcID_normal, funcID_normal) && ancestor.goid != 1 {
   755  		printcreatedby1(f, ancestor.gopc)
   756  	}
   757  }
   758  
   759  // printAncestorTraceback prints the given function info at a given pc
   760  // within an ancestor traceback. The precision of this info is reduced
   761  // due to only have access to the pcs at the time of the caller
   762  // goroutine being created.
   763  func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) {
   764  	name := funcname(f)
   765  	if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
   766  		inltree := (*[1 << 20]inlinedCall)(inldata)
   767  		ix := pcdatavalue(f, _PCDATA_InlTreeIndex, pc, nil)
   768  		if ix >= 0 {
   769  			name = funcnameFromNameoff(f, inltree[ix].func_)
   770  		}
   771  	}
   772  	file, line := funcline(f, pc)
   773  	if name == "runtime.gopanic" {
   774  		name = "panic"
   775  	}
   776  	print(name, "(...)\n")
   777  	print("\t", file, ":", line)
   778  	if pc > f.entry {
   779  		print(" +", hex(pc-f.entry))
   780  	}
   781  	print("\n")
   782  }
   783  
   784  func callers(skip int, pcbuf []uintptr) int {
   785  	sp := getcallersp()
   786  	pc := getcallerpc()
   787  	gp := getg()
   788  	var n int
   789  	systemstack(func() {
   790  		n = gentraceback(pc, sp, 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
   791  	})
   792  	return n
   793  }
   794  
   795  func gcallers(gp *g, skip int, pcbuf []uintptr) int {
   796  	return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
   797  }
   798  
   799  // showframe reports whether the frame with the given characteristics should
   800  // be printed during a traceback.
   801  func showframe(f funcInfo, gp *g, firstFrame bool, funcID, childID funcID) bool {
   802  	g := getg()
   803  	if g.m.throwing > 0 && gp != nil && (gp == g.m.curg || gp == g.m.caughtsig.ptr()) {
   804  		return true
   805  	}
   806  	return showfuncinfo(f, firstFrame, funcID, childID)
   807  }
   808  
   809  // showfuncinfo reports whether a function with the given characteristics should
   810  // be printed during a traceback.
   811  func showfuncinfo(f funcInfo, firstFrame bool, funcID, childID funcID) bool {
   812  	level, _, _ := gotraceback()
   813  	if level > 1 {
   814  		// Show all frames.
   815  		return true
   816  	}
   817  
   818  	if !f.valid() {
   819  		return false
   820  	}
   821  
   822  	if funcID == funcID_wrapper && elideWrapperCalling(childID) {
   823  		return false
   824  	}
   825  
   826  	name := funcname(f)
   827  
   828  	// Special case: always show runtime.gopanic frame
   829  	// in the middle of a stack trace, so that we can
   830  	// see the boundary between ordinary code and
   831  	// panic-induced deferred code.
   832  	// See golang.org/issue/5832.
   833  	if name == "runtime.gopanic" && !firstFrame {
   834  		return true
   835  	}
   836  
   837  	return contains(name, ".") && (!hasPrefix(name, "runtime.") || isExportedRuntime(name))
   838  }
   839  
   840  // isExportedRuntime reports whether name is an exported runtime function.
   841  // It is only for runtime functions, so ASCII A-Z is fine.
   842  func isExportedRuntime(name string) bool {
   843  	const n = len("runtime.")
   844  	return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
   845  }
   846  
   847  // elideWrapperCalling reports whether a wrapper function that called
   848  // function id should be elided from stack traces.
   849  func elideWrapperCalling(id funcID) bool {
   850  	// If the wrapper called a panic function instead of the
   851  	// wrapped function, we want to include it in stacks.
   852  	return !(id == funcID_gopanic || id == funcID_sigpanic || id == funcID_panicwrap)
   853  }
   854  
   855  var gStatusStrings = [...]string{
   856  	_Gidle:      "idle",
   857  	_Grunnable:  "runnable",
   858  	_Grunning:   "running",
   859  	_Gsyscall:   "syscall",
   860  	_Gwaiting:   "waiting",
   861  	_Gdead:      "dead",
   862  	_Gcopystack: "copystack",
   863  }
   864  
   865  func goroutineheader(gp *g) {
   866  	gpstatus := readgstatus(gp)
   867  
   868  	isScan := gpstatus&_Gscan != 0
   869  	gpstatus &^= _Gscan // drop the scan bit
   870  
   871  	// Basic string status
   872  	var status string
   873  	if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
   874  		status = gStatusStrings[gpstatus]
   875  	} else {
   876  		status = "???"
   877  	}
   878  
   879  	// Override.
   880  	if gpstatus == _Gwaiting && gp.waitreason != waitReasonZero {
   881  		status = gp.waitreason.String()
   882  	}
   883  
   884  	// approx time the G is blocked, in minutes
   885  	var waitfor int64
   886  	if (gpstatus == _Gwaiting || gpstatus == _Gsyscall) && gp.waitsince != 0 {
   887  		waitfor = (nanotime() - gp.waitsince) / 60e9
   888  	}
   889  	print("goroutine ", gp.goid, " [", status)
   890  	if isScan {
   891  		print(" (scan)")
   892  	}
   893  	if waitfor >= 1 {
   894  		print(", ", waitfor, " minutes")
   895  	}
   896  	if gp.lockedm != 0 {
   897  		print(", locked to thread")
   898  	}
   899  	print("]:\n")
   900  }
   901  
   902  func tracebackothers(me *g) {
   903  	level, _, _ := gotraceback()
   904  
   905  	// Show the current goroutine first, if we haven't already.
   906  	g := getg()
   907  	gp := g.m.curg
   908  	if gp != nil && gp != me {
   909  		print("\n")
   910  		goroutineheader(gp)
   911  		traceback(^uintptr(0), ^uintptr(0), 0, gp)
   912  	}
   913  
   914  	lock(&allglock)
   915  	for _, gp := range allgs {
   916  		if gp == me || gp == g.m.curg || readgstatus(gp) == _Gdead || isSystemGoroutine(gp, false) && level < 2 {
   917  			continue
   918  		}
   919  		print("\n")
   920  		goroutineheader(gp)
   921  		// Note: gp.m == g.m occurs when tracebackothers is
   922  		// called from a signal handler initiated during a
   923  		// systemstack call. The original G is still in the
   924  		// running state, and we want to print its stack.
   925  		if gp.m != g.m && readgstatus(gp)&^_Gscan == _Grunning {
   926  			print("\tgoroutine running on other thread; stack unavailable\n")
   927  			printcreatedby(gp)
   928  		} else {
   929  			traceback(^uintptr(0), ^uintptr(0), 0, gp)
   930  		}
   931  	}
   932  	unlock(&allglock)
   933  }
   934  
   935  // tracebackHexdump hexdumps part of stk around frame.sp and frame.fp
   936  // for debugging purposes. If the address bad is included in the
   937  // hexdumped range, it will mark it as well.
   938  func tracebackHexdump(stk stack, frame *stkframe, bad uintptr) {
   939  	const expand = 32 * sys.PtrSize
   940  	const maxExpand = 256 * sys.PtrSize
   941  	// Start around frame.sp.
   942  	lo, hi := frame.sp, frame.sp
   943  	// Expand to include frame.fp.
   944  	if frame.fp != 0 && frame.fp < lo {
   945  		lo = frame.fp
   946  	}
   947  	if frame.fp != 0 && frame.fp > hi {
   948  		hi = frame.fp
   949  	}
   950  	// Expand a bit more.
   951  	lo, hi = lo-expand, hi+expand
   952  	// But don't go too far from frame.sp.
   953  	if lo < frame.sp-maxExpand {
   954  		lo = frame.sp - maxExpand
   955  	}
   956  	if hi > frame.sp+maxExpand {
   957  		hi = frame.sp + maxExpand
   958  	}
   959  	// And don't go outside the stack bounds.
   960  	if lo < stk.lo {
   961  		lo = stk.lo
   962  	}
   963  	if hi > stk.hi {
   964  		hi = stk.hi
   965  	}
   966  
   967  	// Print the hex dump.
   968  	print("stack: frame={sp:", hex(frame.sp), ", fp:", hex(frame.fp), "} stack=[", hex(stk.lo), ",", hex(stk.hi), ")\n")
   969  	hexdumpWords(lo, hi, func(p uintptr) byte {
   970  		switch p {
   971  		case frame.fp:
   972  			return '>'
   973  		case frame.sp:
   974  			return '<'
   975  		case bad:
   976  			return '!'
   977  		}
   978  		return 0
   979  	})
   980  }
   981  
   982  // Does f mark the top of a goroutine stack?
   983  func topofstack(f funcInfo, g0 bool) bool {
   984  	return f.funcID == funcID_goexit ||
   985  		f.funcID == funcID_mstart ||
   986  		f.funcID == funcID_mcall ||
   987  		f.funcID == funcID_morestack ||
   988  		f.funcID == funcID_rt0_go ||
   989  		f.funcID == funcID_externalthreadhandler ||
   990  		// asmcgocall is TOS on the system stack because it
   991  		// switches to the system stack, but in this case we
   992  		// can come back to the regular stack and still want
   993  		// to be able to unwind through the call that appeared
   994  		// on the regular stack.
   995  		(g0 && f.funcID == funcID_asmcgocall)
   996  }
   997  
   998  // isSystemGoroutine reports whether the goroutine g must be omitted
   999  // in stack dumps and deadlock detector. This is any goroutine that
  1000  // starts at a runtime.* entry point, except for runtime.main and
  1001  // sometimes runtime.runfinq.
  1002  //
  1003  // If fixed is true, any goroutine that can vary between user and
  1004  // system (that is, the finalizer goroutine) is considered a user
  1005  // goroutine.
  1006  func isSystemGoroutine(gp *g, fixed bool) bool {
  1007  	// Keep this in sync with cmd/trace/trace.go:isSystemGoroutine.
  1008  	f := findfunc(gp.startpc)
  1009  	if !f.valid() {
  1010  		return false
  1011  	}
  1012  	if f.funcID == funcID_runtime_main {
  1013  		return false
  1014  	}
  1015  	if f.funcID == funcID_runfinq {
  1016  		// We include the finalizer goroutine if it's calling
  1017  		// back into user code.
  1018  		if fixed {
  1019  			// This goroutine can vary. In fixed mode,
  1020  			// always consider it a user goroutine.
  1021  			return false
  1022  		}
  1023  		return !fingRunning
  1024  	}
  1025  	return hasPrefix(funcname(f), "runtime.")
  1026  }
  1027  
  1028  // SetCgoTraceback records three C functions to use to gather
  1029  // traceback information from C code and to convert that traceback
  1030  // information into symbolic information. These are used when printing
  1031  // stack traces for a program that uses cgo.
  1032  //
  1033  // The traceback and context functions may be called from a signal
  1034  // handler, and must therefore use only async-signal safe functions.
  1035  // The symbolizer function may be called while the program is
  1036  // crashing, and so must be cautious about using memory.  None of the
  1037  // functions may call back into Go.
  1038  //
  1039  // The context function will be called with a single argument, a
  1040  // pointer to a struct:
  1041  //
  1042  //	struct {
  1043  //		Context uintptr
  1044  //	}
  1045  //
  1046  // In C syntax, this struct will be
  1047  //
  1048  //	struct {
  1049  //		uintptr_t Context;
  1050  //	};
  1051  //
  1052  // If the Context field is 0, the context function is being called to
  1053  // record the current traceback context. It should record in the
  1054  // Context field whatever information is needed about the current
  1055  // point of execution to later produce a stack trace, probably the
  1056  // stack pointer and PC. In this case the context function will be
  1057  // called from C code.
  1058  //
  1059  // If the Context field is not 0, then it is a value returned by a
  1060  // previous call to the context function. This case is called when the
  1061  // context is no longer needed; that is, when the Go code is returning
  1062  // to its C code caller. This permits the context function to release
  1063  // any associated resources.
  1064  //
  1065  // While it would be correct for the context function to record a
  1066  // complete a stack trace whenever it is called, and simply copy that
  1067  // out in the traceback function, in a typical program the context
  1068  // function will be called many times without ever recording a
  1069  // traceback for that context. Recording a complete stack trace in a
  1070  // call to the context function is likely to be inefficient.
  1071  //
  1072  // The traceback function will be called with a single argument, a
  1073  // pointer to a struct:
  1074  //
  1075  //	struct {
  1076  //		Context    uintptr
  1077  //		SigContext uintptr
  1078  //		Buf        *uintptr
  1079  //		Max        uintptr
  1080  //	}
  1081  //
  1082  // In C syntax, this struct will be
  1083  //
  1084  //	struct {
  1085  //		uintptr_t  Context;
  1086  //		uintptr_t  SigContext;
  1087  //		uintptr_t* Buf;
  1088  //		uintptr_t  Max;
  1089  //	};
  1090  //
  1091  // The Context field will be zero to gather a traceback from the
  1092  // current program execution point. In this case, the traceback
  1093  // function will be called from C code.
  1094  //
  1095  // Otherwise Context will be a value previously returned by a call to
  1096  // the context function. The traceback function should gather a stack
  1097  // trace from that saved point in the program execution. The traceback
  1098  // function may be called from an execution thread other than the one
  1099  // that recorded the context, but only when the context is known to be
  1100  // valid and unchanging. The traceback function may also be called
  1101  // deeper in the call stack on the same thread that recorded the
  1102  // context. The traceback function may be called multiple times with
  1103  // the same Context value; it will usually be appropriate to cache the
  1104  // result, if possible, the first time this is called for a specific
  1105  // context value.
  1106  //
  1107  // If the traceback function is called from a signal handler on a Unix
  1108  // system, SigContext will be the signal context argument passed to
  1109  // the signal handler (a C ucontext_t* cast to uintptr_t). This may be
  1110  // used to start tracing at the point where the signal occurred. If
  1111  // the traceback function is not called from a signal handler,
  1112  // SigContext will be zero.
  1113  //
  1114  // Buf is where the traceback information should be stored. It should
  1115  // be PC values, such that Buf[0] is the PC of the caller, Buf[1] is
  1116  // the PC of that function's caller, and so on.  Max is the maximum
  1117  // number of entries to store.  The function should store a zero to
  1118  // indicate the top of the stack, or that the caller is on a different
  1119  // stack, presumably a Go stack.
  1120  //
  1121  // Unlike runtime.Callers, the PC values returned should, when passed
  1122  // to the symbolizer function, return the file/line of the call
  1123  // instruction.  No additional subtraction is required or appropriate.
  1124  //
  1125  // On all platforms, the traceback function is invoked when a call from
  1126  // Go to C to Go requests a stack trace. On linux/amd64, linux/ppc64le,
  1127  // and freebsd/amd64, the traceback function is also invoked when a
  1128  // signal is received by a thread that is executing a cgo call. The
  1129  // traceback function should not make assumptions about when it is
  1130  // called, as future versions of Go may make additional calls.
  1131  //
  1132  // The symbolizer function will be called with a single argument, a
  1133  // pointer to a struct:
  1134  //
  1135  //	struct {
  1136  //		PC      uintptr // program counter to fetch information for
  1137  //		File    *byte   // file name (NUL terminated)
  1138  //		Lineno  uintptr // line number
  1139  //		Func    *byte   // function name (NUL terminated)
  1140  //		Entry   uintptr // function entry point
  1141  //		More    uintptr // set non-zero if more info for this PC
  1142  //		Data    uintptr // unused by runtime, available for function
  1143  //	}
  1144  //
  1145  // In C syntax, this struct will be
  1146  //
  1147  //	struct {
  1148  //		uintptr_t PC;
  1149  //		char*     File;
  1150  //		uintptr_t Lineno;
  1151  //		char*     Func;
  1152  //		uintptr_t Entry;
  1153  //		uintptr_t More;
  1154  //		uintptr_t Data;
  1155  //	};
  1156  //
  1157  // The PC field will be a value returned by a call to the traceback
  1158  // function.
  1159  //
  1160  // The first time the function is called for a particular traceback,
  1161  // all the fields except PC will be 0. The function should fill in the
  1162  // other fields if possible, setting them to 0/nil if the information
  1163  // is not available. The Data field may be used to store any useful
  1164  // information across calls. The More field should be set to non-zero
  1165  // if there is more information for this PC, zero otherwise. If More
  1166  // is set non-zero, the function will be called again with the same
  1167  // PC, and may return different information (this is intended for use
  1168  // with inlined functions). If More is zero, the function will be
  1169  // called with the next PC value in the traceback. When the traceback
  1170  // is complete, the function will be called once more with PC set to
  1171  // zero; this may be used to free any information. Each call will
  1172  // leave the fields of the struct set to the same values they had upon
  1173  // return, except for the PC field when the More field is zero. The
  1174  // function must not keep a copy of the struct pointer between calls.
  1175  //
  1176  // When calling SetCgoTraceback, the version argument is the version
  1177  // number of the structs that the functions expect to receive.
  1178  // Currently this must be zero.
  1179  //
  1180  // The symbolizer function may be nil, in which case the results of
  1181  // the traceback function will be displayed as numbers. If the
  1182  // traceback function is nil, the symbolizer function will never be
  1183  // called. The context function may be nil, in which case the
  1184  // traceback function will only be called with the context field set
  1185  // to zero.  If the context function is nil, then calls from Go to C
  1186  // to Go will not show a traceback for the C portion of the call stack.
  1187  //
  1188  // SetCgoTraceback should be called only once, ideally from an init function.
  1189  func SetCgoTraceback(version int, traceback, context, symbolizer unsafe.Pointer) {
  1190  	if version != 0 {
  1191  		panic("unsupported version")
  1192  	}
  1193  
  1194  	if cgoTraceback != nil && cgoTraceback != traceback ||
  1195  		cgoContext != nil && cgoContext != context ||
  1196  		cgoSymbolizer != nil && cgoSymbolizer != symbolizer {
  1197  		panic("call SetCgoTraceback only once")
  1198  	}
  1199  
  1200  	cgoTraceback = traceback
  1201  	cgoContext = context
  1202  	cgoSymbolizer = symbolizer
  1203  
  1204  	// The context function is called when a C function calls a Go
  1205  	// function. As such it is only called by C code in runtime/cgo.
  1206  	if _cgo_set_context_function != nil {
  1207  		cgocall(_cgo_set_context_function, context)
  1208  	}
  1209  }
  1210  
  1211  var cgoTraceback unsafe.Pointer
  1212  var cgoContext unsafe.Pointer
  1213  var cgoSymbolizer unsafe.Pointer
  1214  
  1215  // cgoTracebackArg is the type passed to cgoTraceback.
  1216  type cgoTracebackArg struct {
  1217  	context    uintptr
  1218  	sigContext uintptr
  1219  	buf        *uintptr
  1220  	max        uintptr
  1221  }
  1222  
  1223  // cgoContextArg is the type passed to the context function.
  1224  type cgoContextArg struct {
  1225  	context uintptr
  1226  }
  1227  
  1228  // cgoSymbolizerArg is the type passed to cgoSymbolizer.
  1229  type cgoSymbolizerArg struct {
  1230  	pc       uintptr
  1231  	file     *byte
  1232  	lineno   uintptr
  1233  	funcName *byte
  1234  	entry    uintptr
  1235  	more     uintptr
  1236  	data     uintptr
  1237  }
  1238  
  1239  // cgoTraceback prints a traceback of callers.
  1240  func printCgoTraceback(callers *cgoCallers) {
  1241  	if cgoSymbolizer == nil {
  1242  		for _, c := range callers {
  1243  			if c == 0 {
  1244  				break
  1245  			}
  1246  			print("non-Go function at pc=", hex(c), "\n")
  1247  		}
  1248  		return
  1249  	}
  1250  
  1251  	var arg cgoSymbolizerArg
  1252  	for _, c := range callers {
  1253  		if c == 0 {
  1254  			break
  1255  		}
  1256  		printOneCgoTraceback(c, 0x7fffffff, &arg)
  1257  	}
  1258  	arg.pc = 0
  1259  	callCgoSymbolizer(&arg)
  1260  }
  1261  
  1262  // printOneCgoTraceback prints the traceback of a single cgo caller.
  1263  // This can print more than one line because of inlining.
  1264  // Returns the number of frames printed.
  1265  func printOneCgoTraceback(pc uintptr, max int, arg *cgoSymbolizerArg) int {
  1266  	c := 0
  1267  	arg.pc = pc
  1268  	for c <= max {
  1269  		callCgoSymbolizer(arg)
  1270  		if arg.funcName != nil {
  1271  			// Note that we don't print any argument
  1272  			// information here, not even parentheses.
  1273  			// The symbolizer must add that if appropriate.
  1274  			println(gostringnocopy(arg.funcName))
  1275  		} else {
  1276  			println("non-Go function")
  1277  		}
  1278  		print("\t")
  1279  		if arg.file != nil {
  1280  			print(gostringnocopy(arg.file), ":", arg.lineno, " ")
  1281  		}
  1282  		print("pc=", hex(pc), "\n")
  1283  		c++
  1284  		if arg.more == 0 {
  1285  			break
  1286  		}
  1287  	}
  1288  	return c
  1289  }
  1290  
  1291  // callCgoSymbolizer calls the cgoSymbolizer function.
  1292  func callCgoSymbolizer(arg *cgoSymbolizerArg) {
  1293  	call := cgocall
  1294  	if panicking > 0 || getg().m.curg != getg() {
  1295  		// We do not want to call into the scheduler when panicking
  1296  		// or when on the system stack.
  1297  		call = asmcgocall
  1298  	}
  1299  	if msanenabled {
  1300  		msanwrite(unsafe.Pointer(arg), unsafe.Sizeof(cgoSymbolizerArg{}))
  1301  	}
  1302  	call(cgoSymbolizer, noescape(unsafe.Pointer(arg)))
  1303  }
  1304  
  1305  // cgoContextPCs gets the PC values from a cgo traceback.
  1306  func cgoContextPCs(ctxt uintptr, buf []uintptr) {
  1307  	if cgoTraceback == nil {
  1308  		return
  1309  	}
  1310  	call := cgocall
  1311  	if panicking > 0 || getg().m.curg != getg() {
  1312  		// We do not want to call into the scheduler when panicking
  1313  		// or when on the system stack.
  1314  		call = asmcgocall
  1315  	}
  1316  	arg := cgoTracebackArg{
  1317  		context: ctxt,
  1318  		buf:     (*uintptr)(noescape(unsafe.Pointer(&buf[0]))),
  1319  		max:     uintptr(len(buf)),
  1320  	}
  1321  	if msanenabled {
  1322  		msanwrite(unsafe.Pointer(&arg), unsafe.Sizeof(arg))
  1323  	}
  1324  	call(cgoTraceback, noescape(unsafe.Pointer(&arg)))
  1325  }
  1326  

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