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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package base
import (
"cmd/internal/notsha256"
"fmt"
"io"
"os"
"strconv"
"strings"
"sync"
)
type writeSyncer interface {
io.Writer
Sync() error
}
type hashAndMask struct {
// a hash h matches if (h^hash)&mask == 0
hash uint64
mask uint64
name string // base name, or base name + "0", "1", etc.
}
type HashDebug struct {
mu sync.Mutex
name string // base name of the flag/variable.
// what file (if any) receives the yes/no logging?
// default is os.Stdout
logfile writeSyncer
matches []hashAndMask // A hash matches if one of these matches.
yes, no bool
}
// The default compiler-debugging HashDebug, for "-d=gossahash=..."
var hashDebug *HashDebug
// DebugHashMatch reports whether debug variable Gossahash
//
// 1. is empty (returns true; this is a special more-quickly implemented case of 4 below)
//
// 2. is "y" or "Y" (returns true)
//
// 3. is "n" or "N" (returns false)
//
// 4. is a suffix of the sha1 hash of pkgAndName (returns true)
//
// 5. OR
// if the value is in the regular language "[01]+(;[01]+)+"
// test the [01]+ substrings after in order returning true
// for the first one that suffix-matches. The substrings AFTER
// the first semicolon are numbered 0,1, etc and are named
// fmt.Sprintf("%s%d", varname, number)
// Clause 5 is not really intended for human use and only
// matters for failures that require multiple triggers.
//
// Otherwise it returns false.
//
// Unless Flags.Gossahash is empty, when DebugHashMatch returns true the message
//
// "%s triggered %s\n", varname, pkgAndName
//
// is printed on the file named in environment variable GSHS_LOGFILE,
// or standard out if that is empty. "Varname" is either the name of
// the variable or the name of the substring, depending on which matched.
//
// Typical use:
//
// 1. you make a change to the compiler, say, adding a new phase
//
// 2. it is broken in some mystifying way, for example, make.bash builds a broken
// compiler that almost works, but crashes compiling a test in run.bash.
//
// 3. add this guard to the code, which by default leaves it broken, but does not
// run the broken new code if Flags.Gossahash is non-empty and non-matching:
//
// if !base.DebugHashMatch(ir.PkgFuncName(fn)) {
// return nil // early exit, do nothing
// }
//
// 4. rebuild w/o the bad code,
// GOCOMPILEDEBUG=gossahash=n ./all.bash
// to verify that you put the guard in the right place with the right sense of the test.
//
// 5. use github.com/dr2chase/gossahash to search for the error:
//
// go install github.com/dr2chase/gossahash@latest
//
// gossahash -- <the thing that fails>
//
// for example: GOMAXPROCS=1 gossahash -- ./all.bash
//
// 6. gossahash should return a single function whose miscompilation
// causes the problem, and you can focus on that.
func DebugHashMatch(pkgAndName string) bool {
return hashDebug.DebugHashMatch(pkgAndName)
}
// HasDebugHash returns true if Flags.Gossahash is non-empty, which
// results in hashDebug being not-nil. I.e., if !HasDebugHash(),
// there is no need to create the string for hashing and testing.
func HasDebugHash() bool {
return hashDebug != nil
}
func toHashAndMask(s, varname string) hashAndMask {
l := len(s)
if l > 64 {
s = s[l-64:]
l = 64
}
m := ^(^uint64(0) << l)
h, err := strconv.ParseUint(s, 2, 64)
if err != nil {
Fatalf("Could not parse %s (=%s) as a binary number", varname, s)
}
return hashAndMask{name: varname, hash: h, mask: m}
}
// NewHashDebug returns a new hash-debug tester for the
// environment variable ev. If ev is not set, it returns
// nil, allowing a lightweight check for normal-case behavior.
func NewHashDebug(ev, s string, file writeSyncer) *HashDebug {
if s == "" {
return nil
}
hd := &HashDebug{name: ev, logfile: file}
switch s[0] {
case 'y', 'Y':
hd.yes = true
return hd
case 'n', 'N':
hd.no = true
return hd
}
ss := strings.Split(s, ";")
hd.matches = append(hd.matches, toHashAndMask(ss[0], ev))
// hash searches may use additional EVs with 0, 1, 2, ... suffixes.
for i := 1; i < len(ss); i++ {
evi := fmt.Sprintf("%s%d", ev, i-1) // convention is extras begin indexing at zero
hd.matches = append(hd.matches, toHashAndMask(ss[i], evi))
}
return hd
}
func hashOf(pkgAndName string, param uint64) uint64 {
hbytes := notsha256.Sum256([]byte(pkgAndName))
hash := uint64(hbytes[7])<<56 + uint64(hbytes[6])<<48 +
uint64(hbytes[5])<<40 + uint64(hbytes[4])<<32 +
uint64(hbytes[3])<<24 + uint64(hbytes[2])<<16 +
uint64(hbytes[1])<<8 + uint64(hbytes[0])
if param != 0 {
// Because param is probably a line number, probably near zero,
// hash it up a little bit, but even so only the lower-order bits
// likely matter because search focuses on those.
p0 := param + uint64(hbytes[9]) + uint64(hbytes[10])<<8 +
uint64(hbytes[11])<<16 + uint64(hbytes[12])<<24
p1 := param + uint64(hbytes[13]) + uint64(hbytes[14])<<8 +
uint64(hbytes[15])<<16 + uint64(hbytes[16])<<24
param += p0 * p1
param ^= param>>17 ^ param<<47
}
return hash ^ param
}
// DebugHashMatch returns true if either the variable used to create d is
// unset, or if its value is y, or if it is a suffix of the base-two
// representation of the hash of pkgAndName. If the variable is not nil,
// then a true result is accompanied by stylized output to d.logfile, which
// is used for automated bug search.
func (d *HashDebug) DebugHashMatch(pkgAndName string) bool {
return d.DebugHashMatchParam(pkgAndName, 0)
}
// DebugHashMatchParam returns true if either the variable used to create d is
// unset, or if its value is y, or if it is a suffix of the base-two
// representation of the hash of pkgAndName and param. If the variable is not
// nil, then a true result is accompanied by stylized output to d.logfile,
// which is used for automated bug search.
func (d *HashDebug) DebugHashMatchParam(pkgAndName string, param uint64) bool {
if d == nil {
return true
}
if d.no {
return false
}
if d.yes {
d.logDebugHashMatch(d.name, pkgAndName, "y", param)
return true
}
hash := hashOf(pkgAndName, param)
for _, m := range d.matches {
if (m.hash^hash)&m.mask == 0 {
hstr := ""
if hash == 0 {
hstr = "0"
} else {
for ; hash != 0; hash = hash >> 1 {
hstr = string('0'+byte(hash&1)) + hstr
}
}
d.logDebugHashMatch(m.name, pkgAndName, hstr, param)
return true
}
}
return false
}
func (d *HashDebug) logDebugHashMatch(varname, name, hstr string, param uint64) {
d.mu.Lock()
defer d.mu.Unlock()
file := d.logfile
if file == nil {
if tmpfile := os.Getenv("GSHS_LOGFILE"); tmpfile != "" {
var err error
file, err = os.OpenFile(tmpfile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
if err != nil {
Fatalf("could not open hash-testing logfile %s", tmpfile)
return
}
}
if file == nil {
file = os.Stdout
}
d.logfile = file
}
if len(hstr) > 24 {
hstr = hstr[len(hstr)-24:]
}
// External tools depend on this string
if param == 0 {
fmt.Fprintf(file, "%s triggered %s %s\n", varname, name, hstr)
} else {
fmt.Fprintf(file, "%s triggered %s:%d %s\n", varname, name, param, hstr)
}
file.Sync()
}
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