hashdebug.go

Documentation: cmd/compile/internal/base

     1  // Copyright 2022 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 base
     6  
     7  import (
     8  	"bytes"
     9  	"cmd/internal/obj"
    10  	"cmd/internal/src"
    11  	"fmt"
    12  	"internal/bisect"
    13  	"io"
    14  	"os"
    15  	"path/filepath"
    16  	"strconv"
    17  	"strings"
    18  	"sync"
    19  )
    20  
    21  type hashAndMask struct {
    22  	// a hash h matches if (h^hash)&mask == 0
    23  	hash uint64
    24  	mask uint64
    25  	name string // base name, or base name + "0", "1", etc.
    26  }
    27  
    28  type HashDebug struct {
    29  	mu   sync.Mutex // for logfile, posTmp, bytesTmp
    30  	name string     // base name of the flag/variable.
    31  	// what file (if any) receives the yes/no logging?
    32  	// default is os.Stdout
    33  	logfile          io.Writer
    34  	posTmp           []src.Pos
    35  	bytesTmp         bytes.Buffer
    36  	matches          []hashAndMask // A hash matches if one of these matches.
    37  	excludes         []hashAndMask // explicitly excluded hash suffixes
    38  	bisect           *bisect.Matcher
    39  	fileSuffixOnly   bool // for Pos hashes, remove the directory prefix.
    40  	inlineSuffixOnly bool // for Pos hashes, remove all but the most inline position.
    41  }
    42  
    43  // SetInlineSuffixOnly controls whether hashing and reporting use the entire
    44  // inline position, or just the most-inline suffix.  Compiler debugging tends
    45  // to want the whole inlining, debugging user problems (loopvarhash, e.g.)
    46  // typically does not need to see the entire inline tree, there is just one
    47  // copy of the source code.
    48  func (d *HashDebug) SetInlineSuffixOnly(b bool) *HashDebug {
    49  	d.inlineSuffixOnly = b
    50  	return d
    51  }
    52  
    53  // The default compiler-debugging HashDebug, for "-d=gossahash=..."
    54  var hashDebug *HashDebug
    55  
    56  var FmaHash *HashDebug         // for debugging fused-multiply-add floating point changes
    57  var LoopVarHash *HashDebug     // for debugging shared/private loop variable changes
    58  var PGOHash *HashDebug         // for debugging PGO optimization decisions
    59  var MergeLocalsHash *HashDebug // for debugging local stack slot merging changes
    60  
    61  // DebugHashMatchPkgFunc reports whether debug variable Gossahash
    62  //
    63  //  1. is empty (returns true; this is a special more-quickly implemented case of 4 below)
    64  //
    65  //  2. is "y" or "Y" (returns true)
    66  //
    67  //  3. is "n" or "N" (returns false)
    68  //
    69  //  4. does not explicitly exclude the sha1 hash of pkgAndName (see step 6)
    70  //
    71  //  5. is a suffix of the sha1 hash of pkgAndName (returns true)
    72  //
    73  //  6. OR
    74  //     if the (non-empty) value is in the regular language
    75  //     "(-[01]+/)+?([01]+(/[01]+)+?"
    76  //     (exclude..)(....include...)
    77  //     test the [01]+ exclude substrings, if any suffix-match, return false (4 above)
    78  //     test the [01]+ include substrings, if any suffix-match, return true
    79  //     The include substrings AFTER the first slash are numbered 0,1, etc and
    80  //     are named fmt.Sprintf("%s%d", varname, number)
    81  //     As an extra-special case for multiple failure search,
    82  //     an excludes-only string ending in a slash (terminated, not separated)
    83  //     implicitly specifies the include string "0/1", that is, match everything.
    84  //     (Exclude strings are used for automated search for multiple failures.)
    85  //     Clause 6 is not really intended for human use and only
    86  //     matters for failures that require multiple triggers.
    87  //
    88  // Otherwise it returns false.
    89  //
    90  // Unless Flags.Gossahash is empty, when DebugHashMatchPkgFunc returns true the message
    91  //
    92  //	"%s triggered %s\n", varname, pkgAndName
    93  //
    94  // is printed on the file named in environment variable GSHS_LOGFILE,
    95  // or standard out if that is empty.  "Varname" is either the name of
    96  // the variable or the name of the substring, depending on which matched.
    97  //
    98  // Typical use:
    99  //
   100  //  1. you make a change to the compiler, say, adding a new phase
   101  //
   102  //  2. it is broken in some mystifying way, for example, make.bash builds a broken
   103  //     compiler that almost works, but crashes compiling a test in run.bash.
   104  //
   105  //  3. add this guard to the code, which by default leaves it broken, but does not
   106  //     run the broken new code if Flags.Gossahash is non-empty and non-matching:
   107  //
   108  //     if !base.DebugHashMatch(ir.PkgFuncName(fn)) {
   109  //     return nil // early exit, do nothing
   110  //     }
   111  //
   112  //  4. rebuild w/o the bad code,
   113  //     GOCOMPILEDEBUG=gossahash=n ./all.bash
   114  //     to verify that you put the guard in the right place with the right sense of the test.
   115  //
   116  //  5. use github.com/dr2chase/gossahash to search for the error:
   117  //
   118  //     go install github.com/dr2chase/gossahash@latest
   119  //
   120  //     gossahash -- <the thing that fails>
   121  //
   122  //     for example: GOMAXPROCS=1 gossahash -- ./all.bash
   123  //
   124  //  6. gossahash should return a single function whose miscompilation
   125  //     causes the problem, and you can focus on that.
   126  func DebugHashMatchPkgFunc(pkg, fn string) bool {
   127  	return hashDebug.MatchPkgFunc(pkg, fn, nil)
   128  }
   129  
   130  func DebugHashMatchPos(pos src.XPos) bool {
   131  	return hashDebug.MatchPos(pos, nil)
   132  }
   133  
   134  // HasDebugHash returns true if Flags.Gossahash is non-empty, which
   135  // results in hashDebug being not-nil.  I.e., if !HasDebugHash(),
   136  // there is no need to create the string for hashing and testing.
   137  func HasDebugHash() bool {
   138  	return hashDebug != nil
   139  }
   140  
   141  // TODO: Delete when we switch to bisect-only.
   142  func toHashAndMask(s, varname string) hashAndMask {
   143  	l := len(s)
   144  	if l > 64 {
   145  		s = s[l-64:]
   146  		l = 64
   147  	}
   148  	m := ^(^uint64(0) << l)
   149  	h, err := strconv.ParseUint(s, 2, 64)
   150  	if err != nil {
   151  		Fatalf("Could not parse %s (=%s) as a binary number", varname, s)
   152  	}
   153  
   154  	return hashAndMask{name: varname, hash: h, mask: m}
   155  }
   156  
   157  // NewHashDebug returns a new hash-debug tester for the
   158  // environment variable ev.  If ev is not set, it returns
   159  // nil, allowing a lightweight check for normal-case behavior.
   160  func NewHashDebug(ev, s string, file io.Writer) *HashDebug {
   161  	if s == "" {
   162  		return nil
   163  	}
   164  
   165  	hd := &HashDebug{name: ev, logfile: file}
   166  	if !strings.Contains(s, "/") {
   167  		m, err := bisect.New(s)
   168  		if err != nil {
   169  			Fatalf("%s: %v", ev, err)
   170  		}
   171  		hd.bisect = m
   172  		return hd
   173  	}
   174  
   175  	// TODO: Delete remainder of function when we switch to bisect-only.
   176  	ss := strings.Split(s, "/")
   177  	// first remove any leading exclusions; these are preceded with "-"
   178  	i := 0
   179  	for len(ss) > 0 {
   180  		s := ss[0]
   181  		if len(s) == 0 || len(s) > 0 && s[0] != '-' {
   182  			break
   183  		}
   184  		ss = ss[1:]
   185  		hd.excludes = append(hd.excludes, toHashAndMask(s[1:], fmt.Sprintf("%s%d", "HASH_EXCLUDE", i)))
   186  		i++
   187  	}
   188  	// hash searches may use additional EVs with 0, 1, 2, ... suffixes.
   189  	i = 0
   190  	for _, s := range ss {
   191  		if s == "" {
   192  			if i != 0 || len(ss) > 1 && ss[1] != "" || len(ss) > 2 {
   193  				Fatalf("Empty hash match string for %s should be first (and only) one", ev)
   194  			}
   195  			// Special case of should match everything.
   196  			hd.matches = append(hd.matches, toHashAndMask("0", fmt.Sprintf("%s0", ev)))
   197  			hd.matches = append(hd.matches, toHashAndMask("1", fmt.Sprintf("%s1", ev)))
   198  			break
   199  		}
   200  		if i == 0 {
   201  			hd.matches = append(hd.matches, toHashAndMask(s, ev))
   202  		} else {
   203  			hd.matches = append(hd.matches, toHashAndMask(s, fmt.Sprintf("%s%d", ev, i-1)))
   204  		}
   205  		i++
   206  	}
   207  	return hd
   208  }
   209  
   210  // TODO: Delete when we switch to bisect-only.
   211  func (d *HashDebug) excluded(hash uint64) bool {
   212  	for _, m := range d.excludes {
   213  		if (m.hash^hash)&m.mask == 0 {
   214  			return true
   215  		}
   216  	}
   217  	return false
   218  }
   219  
   220  // TODO: Delete when we switch to bisect-only.
   221  func hashString(hash uint64) string {
   222  	hstr := ""
   223  	if hash == 0 {
   224  		hstr = "0"
   225  	} else {
   226  		for ; hash != 0; hash = hash >> 1 {
   227  			hstr = string('0'+byte(hash&1)) + hstr
   228  		}
   229  	}
   230  	if len(hstr) > 24 {
   231  		hstr = hstr[len(hstr)-24:]
   232  	}
   233  	return hstr
   234  }
   235  
   236  // TODO: Delete when we switch to bisect-only.
   237  func (d *HashDebug) match(hash uint64) *hashAndMask {
   238  	for i, m := range d.matches {
   239  		if (m.hash^hash)&m.mask == 0 {
   240  			return &d.matches[i]
   241  		}
   242  	}
   243  	return nil
   244  }
   245  
   246  // MatchPkgFunc returns true if either the variable used to create d is
   247  // unset, or if its value is y, or if it is a suffix of the base-two
   248  // representation of the hash of pkg and fn.  If the variable is not nil,
   249  // then a true result is accompanied by stylized output to d.logfile, which
   250  // is used for automated bug search.
   251  func (d *HashDebug) MatchPkgFunc(pkg, fn string, note func() string) bool {
   252  	if d == nil {
   253  		return true
   254  	}
   255  	// Written this way to make inlining likely.
   256  	return d.matchPkgFunc(pkg, fn, note)
   257  }
   258  
   259  func (d *HashDebug) matchPkgFunc(pkg, fn string, note func() string) bool {
   260  	hash := bisect.Hash(pkg, fn)
   261  	return d.matchAndLog(hash, func() string { return pkg + "." + fn }, note)
   262  }
   263  
   264  // MatchPos is similar to MatchPkgFunc, but for hash computation
   265  // it uses the source position including all inlining information instead of
   266  // package name and path.
   267  // Note that the default answer for no environment variable (d == nil)
   268  // is "yes", do the thing.
   269  func (d *HashDebug) MatchPos(pos src.XPos, desc func() string) bool {
   270  	if d == nil {
   271  		return true
   272  	}
   273  	// Written this way to make inlining likely.
   274  	return d.matchPos(Ctxt, pos, desc)
   275  }
   276  
   277  func (d *HashDebug) matchPos(ctxt *obj.Link, pos src.XPos, note func() string) bool {
   278  	return d.matchPosWithInfo(ctxt, pos, nil, note)
   279  }
   280  
   281  func (d *HashDebug) matchPosWithInfo(ctxt *obj.Link, pos src.XPos, info any, note func() string) bool {
   282  	hash := d.hashPos(ctxt, pos)
   283  	if info != nil {
   284  		hash = bisect.Hash(hash, info)
   285  	}
   286  	return d.matchAndLog(hash,
   287  		func() string {
   288  			r := d.fmtPos(ctxt, pos)
   289  			if info != nil {
   290  				r += fmt.Sprintf(" (%v)", info)
   291  			}
   292  			return r
   293  		},
   294  		note)
   295  }
   296  
   297  // MatchPosWithInfo is similar to MatchPos, but with additional information
   298  // that is included for hash computation, so it can distinguish multiple
   299  // matches on the same source location.
   300  // Note that the default answer for no environment variable (d == nil)
   301  // is "yes", do the thing.
   302  func (d *HashDebug) MatchPosWithInfo(pos src.XPos, info any, desc func() string) bool {
   303  	if d == nil {
   304  		return true
   305  	}
   306  	// Written this way to make inlining likely.
   307  	return d.matchPosWithInfo(Ctxt, pos, info, desc)
   308  }
   309  
   310  // matchAndLog is the core matcher. It reports whether the hash matches the pattern.
   311  // If a report needs to be printed, match prints that report to the log file.
   312  // The text func must be non-nil and should return a user-readable
   313  // representation of what was hashed. The note func may be nil; if non-nil,
   314  // it should return additional information to display to the user when this
   315  // change is selected.
   316  func (d *HashDebug) matchAndLog(hash uint64, text, note func() string) bool {
   317  	if d.bisect != nil {
   318  		enabled := d.bisect.ShouldEnable(hash)
   319  		if d.bisect.ShouldPrint(hash) {
   320  			disabled := ""
   321  			if !enabled {
   322  				disabled = " [DISABLED]"
   323  			}
   324  			var t string
   325  			if !d.bisect.MarkerOnly() {
   326  				t = text()
   327  				if note != nil {
   328  					if n := note(); n != "" {
   329  						t += ": " + n + disabled
   330  						disabled = ""
   331  					}
   332  				}
   333  			}
   334  			d.log(d.name, hash, strings.TrimSpace(t+disabled))
   335  		}
   336  		return enabled
   337  	}
   338  
   339  	// TODO: Delete rest of function body when we switch to bisect-only.
   340  	if d.excluded(hash) {
   341  		return false
   342  	}
   343  	if m := d.match(hash); m != nil {
   344  		d.log(m.name, hash, text())
   345  		return true
   346  	}
   347  	return false
   348  }
   349  
   350  // short returns the form of file name to use for d.
   351  // The default is the full path, but fileSuffixOnly selects
   352  // just the final path element.
   353  func (d *HashDebug) short(name string) string {
   354  	if d.fileSuffixOnly {
   355  		return filepath.Base(name)
   356  	}
   357  	return name
   358  }
   359  
   360  // hashPos returns a hash of the position pos, including its entire inline stack.
   361  // If d.inlineSuffixOnly is true, hashPos only considers the innermost (leaf) position on the inline stack.
   362  func (d *HashDebug) hashPos(ctxt *obj.Link, pos src.XPos) uint64 {
   363  	if d.inlineSuffixOnly {
   364  		p := ctxt.InnermostPos(pos)
   365  		return bisect.Hash(d.short(p.Filename()), p.Line(), p.Col())
   366  	}
   367  	h := bisect.Hash()
   368  	ctxt.AllPos(pos, func(p src.Pos) {
   369  		h = bisect.Hash(h, d.short(p.Filename()), p.Line(), p.Col())
   370  	})
   371  	return h
   372  }
   373  
   374  // fmtPos returns a textual formatting of the position pos, including its entire inline stack.
   375  // If d.inlineSuffixOnly is true, fmtPos only considers the innermost (leaf) position on the inline stack.
   376  func (d *HashDebug) fmtPos(ctxt *obj.Link, pos src.XPos) string {
   377  	format := func(p src.Pos) string {
   378  		return fmt.Sprintf("%s:%d:%d", d.short(p.Filename()), p.Line(), p.Col())
   379  	}
   380  	if d.inlineSuffixOnly {
   381  		return format(ctxt.InnermostPos(pos))
   382  	}
   383  	var stk []string
   384  	ctxt.AllPos(pos, func(p src.Pos) {
   385  		stk = append(stk, format(p))
   386  	})
   387  	return strings.Join(stk, "; ")
   388  }
   389  
   390  // log prints a match with the given hash and textual formatting.
   391  // TODO: Delete varname parameter when we switch to bisect-only.
   392  func (d *HashDebug) log(varname string, hash uint64, text string) {
   393  	d.mu.Lock()
   394  	defer d.mu.Unlock()
   395  
   396  	file := d.logfile
   397  	if file == nil {
   398  		if tmpfile := os.Getenv("GSHS_LOGFILE"); tmpfile != "" {
   399  			var err error
   400  			file, err = os.OpenFile(tmpfile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
   401  			if err != nil {
   402  				Fatalf("could not open hash-testing logfile %s", tmpfile)
   403  				return
   404  			}
   405  		}
   406  		if file == nil {
   407  			file = os.Stdout
   408  		}
   409  		d.logfile = file
   410  	}
   411  
   412  	// Bisect output.
   413  	fmt.Fprintf(file, "%s %s\n", text, bisect.Marker(hash))
   414  
   415  	// Gossahash output.
   416  	// TODO: Delete rest of function when we switch to bisect-only.
   417  	fmt.Fprintf(file, "%s triggered %s %s\n", varname, text, hashString(hash))
   418  }
   419
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