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  	"internal/strconv"
     9  	"unsafe"
    10  )
    11  
    12  // The compiler knows that a print of a value of this type
    13  // should use printhex instead of printuint (decimal).
    14  type hex uint64
    15  
    16  // The compiler knows that a print of a value of this type should use
    17  // printquoted instead of printstring.
    18  type quoted string
    19  
    20  func bytes(s string) (ret []byte) {
    21  	rp := (*slice)(unsafe.Pointer(&ret))
    22  	sp := stringStructOf(&s)
    23  	rp.array = sp.str
    24  	rp.len = sp.len
    25  	rp.cap = sp.len
    26  	return
    27  }
    28  
    29  var (
    30  	// printBacklog is a circular buffer of messages written with the builtin
    31  	// print* functions, for use in postmortem analysis of core dumps.
    32  	printBacklog      [512]byte
    33  	printBacklogIndex int
    34  )
    35  
    36  // recordForPanic maintains a circular buffer of messages written by the
    37  // runtime leading up to a process crash, allowing the messages to be
    38  // extracted from a core dump.
    39  //
    40  // The text written during a process crash (following "panic" or "fatal
    41  // error") is not saved, since the goroutine stacks will generally be readable
    42  // from the runtime data structures in the core file.
    43  func recordForPanic(b []byte) {
    44  	printlock()
    45  
    46  	if panicking.Load() == 0 {
    47  		// Not actively crashing: maintain circular buffer of print output.
    48  		for i := 0; i < len(b); {
    49  			n := copy(printBacklog[printBacklogIndex:], b[i:])
    50  			i += n
    51  			printBacklogIndex += n
    52  			printBacklogIndex %= len(printBacklog)
    53  		}
    54  	}
    55  
    56  	printunlock()
    57  }
    58  
    59  var debuglock mutex
    60  
    61  // The compiler emits calls to printlock and printunlock around
    62  // the multiple calls that implement a single Go print or println
    63  // statement. Some of the print helpers (printslice, for example)
    64  // call print recursively. There is also the problem of a crash
    65  // happening during the print routines and needing to acquire
    66  // the print lock to print information about the crash.
    67  // For both these reasons, let a thread acquire the printlock 'recursively'.
    68  
    69  func printlock() {
    70  	mp := getg().m
    71  	mp.locks++ // do not reschedule between printlock++ and lock(&debuglock).
    72  	mp.printlock++
    73  	if mp.printlock == 1 {
    74  		lock(&debuglock)
    75  	}
    76  	mp.locks-- // now we know debuglock is held and holding up mp.locks for us.
    77  }
    78  
    79  func printunlock() {
    80  	mp := getg().m
    81  	mp.printlock--
    82  	if mp.printlock == 0 {
    83  		unlock(&debuglock)
    84  	}
    85  }
    86  
    87  // write to goroutine-local buffer if diverting output,
    88  // or else standard error.
    89  func gwrite(b []byte) {
    90  	if len(b) == 0 {
    91  		return
    92  	}
    93  	recordForPanic(b)
    94  	gp := getg()
    95  	// Don't use the writebuf if gp.m is dying. We want anything
    96  	// written through gwrite to appear in the terminal rather
    97  	// than be written to in some buffer, if we're in a panicking state.
    98  	// Note that we can't just clear writebuf in the gp.m.dying case
    99  	// because a panic isn't allowed to have any write barriers.
   100  	if gp == nil || gp.writebuf == nil || gp.m.dying > 0 {
   101  		writeErr(b)
   102  		return
   103  	}
   104  
   105  	n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
   106  	gp.writebuf = gp.writebuf[:len(gp.writebuf)+n]
   107  }
   108  
   109  func printsp() {
   110  	printstring(" ")
   111  }
   112  
   113  func printnl() {
   114  	printstring("\n")
   115  }
   116  
   117  func printbool(v bool) {
   118  	if v {
   119  		printstring("true")
   120  	} else {
   121  		printstring("false")
   122  	}
   123  }
   124  
   125  func printfloat64(v float64) {
   126  	var buf [20]byte
   127  	gwrite(strconv.AppendFloat(buf[:0], v, 'g', -1, 64))
   128  }
   129  
   130  func printfloat32(v float32) {
   131  	var buf [20]byte
   132  	gwrite(strconv.AppendFloat(buf[:0], float64(v), 'g', -1, 32))
   133  }
   134  
   135  func printcomplex128(c complex128) {
   136  	var buf [44]byte
   137  	gwrite(strconv.AppendComplex(buf[:0], c, 'g', -1, 128))
   138  }
   139  
   140  func printcomplex64(c complex64) {
   141  	var buf [44]byte
   142  	gwrite(strconv.AppendComplex(buf[:0], complex128(c), 'g', -1, 64))
   143  }
   144  
   145  func printuint(v uint64) {
   146  	// Note: Avoiding strconv.AppendUint so that it's clearer
   147  	// that there are no allocations in this routine.
   148  	// cmd/link/internal/ld.TestAbstractOriginSanity
   149  	// sees the append and doesn't realize it doesn't allocate.
   150  	var buf [20]byte
   151  	i := strconv.RuntimeFormatBase10(buf[:], v)
   152  	gwrite(buf[i:])
   153  }
   154  
   155  func printint(v int64) {
   156  	// Note: Avoiding strconv.AppendUint so that it's clearer
   157  	// that there are no allocations in this routine.
   158  	// cmd/link/internal/ld.TestAbstractOriginSanity
   159  	// sees the append and doesn't realize it doesn't allocate.
   160  	neg := v < 0
   161  	u := uint64(v)
   162  	if neg {
   163  		u = -u
   164  	}
   165  	var buf [20]byte
   166  	i := strconv.RuntimeFormatBase10(buf[:], u)
   167  	if neg {
   168  		i--
   169  		buf[i] = '-'
   170  	}
   171  	gwrite(buf[i:])
   172  }
   173  
   174  var minhexdigits = 0 // protected by printlock
   175  
   176  func printhexopts(include0x bool, mindigits int, v uint64) {
   177  	const dig = "0123456789abcdef"
   178  	var buf [100]byte
   179  	i := len(buf)
   180  	for i--; i > 0; i-- {
   181  		buf[i] = dig[v%16]
   182  		if v < 16 && len(buf)-i >= mindigits {
   183  			break
   184  		}
   185  		v /= 16
   186  	}
   187  	if include0x {
   188  		i--
   189  		buf[i] = 'x'
   190  		i--
   191  		buf[i] = '0'
   192  	}
   193  	gwrite(buf[i:])
   194  }
   195  
   196  func printhex(v uint64) {
   197  	printhexopts(true, minhexdigits, v)
   198  }
   199  
   200  func printquoted(s string) {
   201  	printlock()
   202  	gwrite([]byte(`"`))
   203  	for _, r := range s {
   204  		switch r {
   205  		case '\n':
   206  			gwrite([]byte(`\n`))
   207  			continue
   208  		case '\r':
   209  			gwrite([]byte(`\r`))
   210  			continue
   211  		case '\t':
   212  			gwrite([]byte(`\t`))
   213  			print()
   214  			continue
   215  		case '\\', '"':
   216  			gwrite([]byte{byte('\\'), byte(r)})
   217  			continue
   218  		}
   219  		// For now, only allow basic printable ascii through unescaped
   220  		if r >= ' ' && r <= '~' {
   221  			gwrite([]byte{byte(r)})
   222  		} else if r < 127 {
   223  			gwrite(bytes(`\x`))
   224  			printhexopts(false, 2, uint64(r))
   225  		} else if r < 0x1_0000 {
   226  			gwrite(bytes(`\u`))
   227  			printhexopts(false, 4, uint64(r))
   228  		} else {
   229  			gwrite(bytes(`\U`))
   230  			printhexopts(false, 8, uint64(r))
   231  		}
   232  	}
   233  	gwrite([]byte{byte('"')})
   234  	printunlock()
   235  }
   236  
   237  func printpointer(p unsafe.Pointer) {
   238  	printhex(uint64(uintptr(p)))
   239  }
   240  func printuintptr(p uintptr) {
   241  	printhex(uint64(p))
   242  }
   243  
   244  func printstring(s string) {
   245  	gwrite(bytes(s))
   246  }
   247  
   248  func printslice(s []byte) {
   249  	sp := (*slice)(unsafe.Pointer(&s))
   250  	print("[", len(s), "/", cap(s), "]")
   251  	printpointer(sp.array)
   252  }
   253  
   254  func printeface(e eface) {
   255  	print("(", e._type, ",", e.data, ")")
   256  }
   257  
   258  func printiface(i iface) {
   259  	print("(", i.tab, ",", i.data, ")")
   260  }
   261
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