Source file src/runtime/print.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"runtime/internal/atomic"
     9  	"runtime/internal/sys"
    10  	"unsafe"
    11  )
    12  
    13  // The compiler knows that a print of a value of this type
    14  // should use printhex instead of printuint (decimal).
    15  type hex uint64
    16  
    17  func bytes(s string) (ret []byte) {
    18  	rp := (*slice)(unsafe.Pointer(&ret))
    19  	sp := stringStructOf(&s)
    20  	rp.array = sp.str
    21  	rp.len = sp.len
    22  	rp.cap = sp.len
    23  	return
    24  }
    25  
    26  var (
    27  	// printBacklog is a circular buffer of messages written with the builtin
    28  	// print* functions, for use in postmortem analysis of core dumps.
    29  	printBacklog      [512]byte
    30  	printBacklogIndex int
    31  )
    32  
    33  // recordForPanic maintains a circular buffer of messages written by the
    34  // runtime leading up to a process crash, allowing the messages to be
    35  // extracted from a core dump.
    36  //
    37  // The text written during a process crash (following "panic" or "fatal
    38  // error") is not saved, since the goroutine stacks will generally be readable
    39  // from the runtime datastructures in the core file.
    40  func recordForPanic(b []byte) {
    41  	printlock()
    42  
    43  	if atomic.Load(&panicking) == 0 {
    44  		// Not actively crashing: maintain circular buffer of print output.
    45  		for i := 0; i < len(b); {
    46  			n := copy(printBacklog[printBacklogIndex:], b[i:])
    47  			i += n
    48  			printBacklogIndex += n
    49  			printBacklogIndex %= len(printBacklog)
    50  		}
    51  	}
    52  
    53  	printunlock()
    54  }
    55  
    56  var debuglock mutex
    57  
    58  // The compiler emits calls to printlock and printunlock around
    59  // the multiple calls that implement a single Go print or println
    60  // statement. Some of the print helpers (printslice, for example)
    61  // call print recursively. There is also the problem of a crash
    62  // happening during the print routines and needing to acquire
    63  // the print lock to print information about the crash.
    64  // For both these reasons, let a thread acquire the printlock 'recursively'.
    65  
    66  func printlock() {
    67  	mp := getg().m
    68  	mp.locks++ // do not reschedule between printlock++ and lock(&debuglock).
    69  	mp.printlock++
    70  	if mp.printlock == 1 {
    71  		lock(&debuglock)
    72  	}
    73  	mp.locks-- // now we know debuglock is held and holding up mp.locks for us.
    74  }
    75  
    76  func printunlock() {
    77  	mp := getg().m
    78  	mp.printlock--
    79  	if mp.printlock == 0 {
    80  		unlock(&debuglock)
    81  	}
    82  }
    83  
    84  // write to goroutine-local buffer if diverting output,
    85  // or else standard error.
    86  func gwrite(b []byte) {
    87  	if len(b) == 0 {
    88  		return
    89  	}
    90  	recordForPanic(b)
    91  	gp := getg()
    92  	// Don't use the writebuf if gp.m is dying. We want anything
    93  	// written through gwrite to appear in the terminal rather
    94  	// than be written to in some buffer, if we're in a panicking state.
    95  	// Note that we can't just clear writebuf in the gp.m.dying case
    96  	// because a panic isn't allowed to have any write barriers.
    97  	if gp == nil || gp.writebuf == nil || gp.m.dying > 0 {
    98  		writeErr(b)
    99  		return
   100  	}
   101  
   102  	n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
   103  	gp.writebuf = gp.writebuf[:len(gp.writebuf)+n]
   104  }
   105  
   106  func printsp() {
   107  	printstring(" ")
   108  }
   109  
   110  func printnl() {
   111  	printstring("\n")
   112  }
   113  
   114  func printbool(v bool) {
   115  	if v {
   116  		printstring("true")
   117  	} else {
   118  		printstring("false")
   119  	}
   120  }
   121  
   122  func printfloat(v float64) {
   123  	switch {
   124  	case v != v:
   125  		printstring("NaN")
   126  		return
   127  	case v+v == v && v > 0:
   128  		printstring("+Inf")
   129  		return
   130  	case v+v == v && v < 0:
   131  		printstring("-Inf")
   132  		return
   133  	}
   134  
   135  	const n = 7 // digits printed
   136  	var buf [n + 7]byte
   137  	buf[0] = '+'
   138  	e := 0 // exp
   139  	if v == 0 {
   140  		if 1/v < 0 {
   141  			buf[0] = '-'
   142  		}
   143  	} else {
   144  		if v < 0 {
   145  			v = -v
   146  			buf[0] = '-'
   147  		}
   148  
   149  		// normalize
   150  		for v >= 10 {
   151  			e++
   152  			v /= 10
   153  		}
   154  		for v < 1 {
   155  			e--
   156  			v *= 10
   157  		}
   158  
   159  		// round
   160  		h := 5.0
   161  		for i := 0; i < n; i++ {
   162  			h /= 10
   163  		}
   164  		v += h
   165  		if v >= 10 {
   166  			e++
   167  			v /= 10
   168  		}
   169  	}
   170  
   171  	// format +d.dddd+edd
   172  	for i := 0; i < n; i++ {
   173  		s := int(v)
   174  		buf[i+2] = byte(s + '0')
   175  		v -= float64(s)
   176  		v *= 10
   177  	}
   178  	buf[1] = buf[2]
   179  	buf[2] = '.'
   180  
   181  	buf[n+2] = 'e'
   182  	buf[n+3] = '+'
   183  	if e < 0 {
   184  		e = -e
   185  		buf[n+3] = '-'
   186  	}
   187  
   188  	buf[n+4] = byte(e/100) + '0'
   189  	buf[n+5] = byte(e/10)%10 + '0'
   190  	buf[n+6] = byte(e%10) + '0'
   191  	gwrite(buf[:])
   192  }
   193  
   194  func printcomplex(c complex128) {
   195  	print("(", real(c), imag(c), "i)")
   196  }
   197  
   198  func printuint(v uint64) {
   199  	var buf [100]byte
   200  	i := len(buf)
   201  	for i--; i > 0; i-- {
   202  		buf[i] = byte(v%10 + '0')
   203  		if v < 10 {
   204  			break
   205  		}
   206  		v /= 10
   207  	}
   208  	gwrite(buf[i:])
   209  }
   210  
   211  func printint(v int64) {
   212  	if v < 0 {
   213  		printstring("-")
   214  		v = -v
   215  	}
   216  	printuint(uint64(v))
   217  }
   218  
   219  var minhexdigits = 0 // protected by printlock
   220  
   221  func printhex(v uint64) {
   222  	const dig = "0123456789abcdef"
   223  	var buf [100]byte
   224  	i := len(buf)
   225  	for i--; i > 0; i-- {
   226  		buf[i] = dig[v%16]
   227  		if v < 16 && len(buf)-i >= minhexdigits {
   228  			break
   229  		}
   230  		v /= 16
   231  	}
   232  	i--
   233  	buf[i] = 'x'
   234  	i--
   235  	buf[i] = '0'
   236  	gwrite(buf[i:])
   237  }
   238  
   239  func printpointer(p unsafe.Pointer) {
   240  	printhex(uint64(uintptr(p)))
   241  }
   242  func printuintptr(p uintptr) {
   243  	printhex(uint64(p))
   244  }
   245  
   246  func printstring(s string) {
   247  	gwrite(bytes(s))
   248  }
   249  
   250  func printslice(s []byte) {
   251  	sp := (*slice)(unsafe.Pointer(&s))
   252  	print("[", len(s), "/", cap(s), "]")
   253  	printpointer(sp.array)
   254  }
   255  
   256  func printeface(e eface) {
   257  	print("(", e._type, ",", e.data, ")")
   258  }
   259  
   260  func printiface(i iface) {
   261  	print("(", i.tab, ",", i.data, ")")
   262  }
   263  
   264  // hexdumpWords prints a word-oriented hex dump of [p, end).
   265  //
   266  // If mark != nil, it will be called with each printed word's address
   267  // and should return a character mark to appear just before that
   268  // word's value. It can return 0 to indicate no mark.
   269  func hexdumpWords(p, end uintptr, mark func(uintptr) byte) {
   270  	printlock()
   271  	var markbuf [1]byte
   272  	markbuf[0] = ' '
   273  	minhexdigits = int(unsafe.Sizeof(uintptr(0)) * 2)
   274  	for i := uintptr(0); p+i < end; i += sys.PtrSize {
   275  		if i%16 == 0 {
   276  			if i != 0 {
   277  				println()
   278  			}
   279  			print(hex(p+i), ": ")
   280  		}
   281  
   282  		if mark != nil {
   283  			markbuf[0] = mark(p + i)
   284  			if markbuf[0] == 0 {
   285  				markbuf[0] = ' '
   286  			}
   287  		}
   288  		gwrite(markbuf[:])
   289  		val := *(*uintptr)(unsafe.Pointer(p + i))
   290  		print(hex(val))
   291  		print(" ")
   292  
   293  		// Can we symbolize val?
   294  		fn := findfunc(val)
   295  		if fn.valid() {
   296  			print("<", funcname(fn), "+", hex(val-fn.entry), "> ")
   297  		}
   298  	}
   299  	minhexdigits = 0
   300  	println()
   301  	printunlock()
   302  }
   303  

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