Source file src/cmd/go/internal/work/buildid.go
1 // Copyright 2017 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 work 6 7 import ( 8 "bytes" 9 "fmt" 10 "os" 11 "os/exec" 12 "strings" 13 "sync" 14 15 "cmd/go/internal/base" 16 "cmd/go/internal/cache" 17 "cmd/go/internal/cfg" 18 "cmd/go/internal/fsys" 19 "cmd/go/internal/str" 20 "cmd/internal/buildid" 21 "cmd/internal/pathcache" 22 "cmd/internal/quoted" 23 "cmd/internal/telemetry/counter" 24 ) 25 26 // Build IDs 27 // 28 // Go packages and binaries are stamped with build IDs that record both 29 // the action ID, which is a hash of the inputs to the action that produced 30 // the packages or binary, and the content ID, which is a hash of the action 31 // output, namely the archive or binary itself. The hash is the same one 32 // used by the build artifact cache (see cmd/go/internal/cache), but 33 // truncated when stored in packages and binaries, as the full length is not 34 // needed and is a bit unwieldy. The precise form is 35 // 36 // actionID/[.../]contentID 37 // 38 // where the actionID and contentID are prepared by buildid.HashToString below. 39 // and are found by looking for the first or last slash. 40 // Usually the buildID is simply actionID/contentID, but see below for an 41 // exception. 42 // 43 // The build ID serves two primary purposes. 44 // 45 // 1. The action ID half allows installed packages and binaries to serve as 46 // one-element cache entries. If we intend to build math.a with a given 47 // set of inputs summarized in the action ID, and the installed math.a already 48 // has that action ID, we can reuse the installed math.a instead of rebuilding it. 49 // 50 // 2. The content ID half allows the easy preparation of action IDs for steps 51 // that consume a particular package or binary. The content hash of every 52 // input file for a given action must be included in the action ID hash. 53 // Storing the content ID in the build ID lets us read it from the file with 54 // minimal I/O, instead of reading and hashing the entire file. 55 // This is especially effective since packages and binaries are typically 56 // the largest inputs to an action. 57 // 58 // Separating action ID from content ID is important for reproducible builds. 59 // The compiler is compiled with itself. If an output were represented by its 60 // own action ID (instead of content ID) when computing the action ID of 61 // the next step in the build process, then the compiler could never have its 62 // own input action ID as its output action ID (short of a miraculous hash collision). 63 // Instead we use the content IDs to compute the next action ID, and because 64 // the content IDs converge, so too do the action IDs and therefore the 65 // build IDs and the overall compiler binary. See cmd/dist's cmdbootstrap 66 // for the actual convergence sequence. 67 // 68 // The “one-element cache” purpose is a bit more complex for installed 69 // binaries. For a binary, like cmd/gofmt, there are two steps: compile 70 // cmd/gofmt/*.go into main.a, and then link main.a into the gofmt binary. 71 // We do not install gofmt's main.a, only the gofmt binary. Being able to 72 // decide that the gofmt binary is up-to-date means computing the action ID 73 // for the final link of the gofmt binary and comparing it against the 74 // already-installed gofmt binary. But computing the action ID for the link 75 // means knowing the content ID of main.a, which we did not keep. 76 // To sidestep this problem, each binary actually stores an expanded build ID: 77 // 78 // actionID(binary)/actionID(main.a)/contentID(main.a)/contentID(binary) 79 // 80 // (Note that this can be viewed equivalently as: 81 // 82 // actionID(binary)/buildID(main.a)/contentID(binary) 83 // 84 // Storing the buildID(main.a) in the middle lets the computations that care 85 // about the prefix or suffix halves ignore the middle and preserves the 86 // original build ID as a contiguous string.) 87 // 88 // During the build, when it's time to build main.a, the gofmt binary has the 89 // information needed to decide whether the eventual link would produce 90 // the same binary: if the action ID for main.a's inputs matches and then 91 // the action ID for the link step matches when assuming the given main.a 92 // content ID, then the binary as a whole is up-to-date and need not be rebuilt. 93 // 94 // This is all a bit complex and may be simplified once we can rely on the 95 // main cache, but at least at the start we will be using the content-based 96 // staleness determination without a cache beyond the usual installed 97 // package and binary locations. 98 99 const buildIDSeparator = "/" 100 101 // actionID returns the action ID half of a build ID. 102 func actionID(buildID string) string { 103 i := strings.Index(buildID, buildIDSeparator) 104 if i < 0 { 105 return buildID 106 } 107 return buildID[:i] 108 } 109 110 // contentID returns the content ID half of a build ID. 111 func contentID(buildID string) string { 112 return buildID[strings.LastIndex(buildID, buildIDSeparator)+1:] 113 } 114 115 // toolID returns the unique ID to use for the current copy of the 116 // named tool (asm, compile, cover, link). 117 // 118 // It is important that if the tool changes (for example a compiler bug is fixed 119 // and the compiler reinstalled), toolID returns a different string, so that old 120 // package archives look stale and are rebuilt (with the fixed compiler). 121 // This suggests using a content hash of the tool binary, as stored in the build ID. 122 // 123 // Unfortunately, we can't just open the tool binary, because the tool might be 124 // invoked via a wrapper program specified by -toolexec and we don't know 125 // what the wrapper program does. In particular, we want "-toolexec toolstash" 126 // to continue working: it does no good if "-toolexec toolstash" is executing a 127 // stashed copy of the compiler but the go command is acting as if it will run 128 // the standard copy of the compiler. The solution is to ask the tool binary to tell 129 // us its own build ID using the "-V=full" flag now supported by all tools. 130 // Then we know we're getting the build ID of the compiler that will actually run 131 // during the build. (How does the compiler binary know its own content hash? 132 // We store it there using updateBuildID after the standard link step.) 133 // 134 // A final twist is that we'd prefer to have reproducible builds for release toolchains. 135 // It should be possible to cross-compile for Windows from either Linux or Mac 136 // or Windows itself and produce the same binaries, bit for bit. If the tool ID, 137 // which influences the action ID half of the build ID, is based on the content ID, 138 // then the Linux compiler binary and Mac compiler binary will have different tool IDs 139 // and therefore produce executables with different action IDs. 140 // To avoid this problem, for releases we use the release version string instead 141 // of the compiler binary's content hash. This assumes that all compilers built 142 // on all different systems are semantically equivalent, which is of course only true 143 // modulo bugs. (Producing the exact same executables also requires that the different 144 // build setups agree on details like $GOROOT and file name paths, but at least the 145 // tool IDs do not make it impossible.) 146 func (b *Builder) toolID(name string) string { 147 return b.toolIDCache.Do(name, func() string { 148 path := base.Tool(name) 149 desc := "go tool " + name 150 151 // Special case: undocumented -vettool overrides usual vet, 152 // for testing vet or supplying an alternative analysis tool. 153 if name == "vet" && VetTool != "" { 154 path = VetTool 155 desc = VetTool 156 } 157 158 cmdline := str.StringList(cfg.BuildToolexec, path, "-V=full") 159 cmd := exec.Command(cmdline[0], cmdline[1:]...) 160 var stdout, stderr strings.Builder 161 cmd.Stdout = &stdout 162 cmd.Stderr = &stderr 163 if err := cmd.Run(); err != nil { 164 if stderr.Len() > 0 { 165 os.Stderr.WriteString(stderr.String()) 166 } 167 base.Fatalf("go: error obtaining buildID for %s: %v", desc, err) 168 } 169 170 line := stdout.String() 171 f := strings.Fields(line) 172 if len(f) < 3 || f[0] != name && path != VetTool || f[1] != "version" || f[2] == "devel" && !strings.HasPrefix(f[len(f)-1], "buildID=") { 173 base.Fatalf("go: parsing buildID from %s -V=full: unexpected output:\n\t%s", desc, line) 174 } 175 if f[2] == "devel" { 176 // On the development branch, use the content ID part of the build ID. 177 return contentID(f[len(f)-1]) 178 } 179 // For a release, the output is like: "compile version go1.9.1 X:framepointer". 180 // Use the whole line. 181 return strings.TrimSpace(line) 182 }) 183 } 184 185 // gccToolID returns the unique ID to use for a tool that is invoked 186 // by the GCC driver. This is used particularly for gccgo, but this can also 187 // be used for gcc, g++, gfortran, etc.; those tools all use the GCC 188 // driver under different names. The approach used here should also 189 // work for sufficiently new versions of clang. Unlike toolID, the 190 // name argument is the program to run. The language argument is the 191 // type of input file as passed to the GCC driver's -x option. 192 // 193 // For these tools we have no -V=full option to dump the build ID, 194 // but we can run the tool with -v -### to reliably get the compiler proper 195 // and hash that. That will work in the presence of -toolexec. 196 // 197 // In order to get reproducible builds for released compilers, we 198 // detect a released compiler by the absence of "experimental" in the 199 // --version output, and in that case we just use the version string. 200 // 201 // gccToolID also returns the underlying executable for the compiler. 202 // The caller assumes that stat of the exe can be used, combined with the id, 203 // to detect changes in the underlying compiler. The returned exe can be empty, 204 // which means to rely only on the id. 205 func (b *Builder) gccToolID(name, language string) (id, exe string, err error) { 206 //TODO: Use par.Cache instead of a mutex and a map. See Builder.toolID. 207 key := name + "." + language 208 b.id.Lock() 209 id = b.gccToolIDCache[key] 210 exe = b.gccToolIDCache[key+".exe"] 211 b.id.Unlock() 212 213 if id != "" { 214 return id, exe, nil 215 } 216 217 // Invoke the driver with -### to see the subcommands and the 218 // version strings. Use -x to set the language. Pretend to 219 // compile an empty file on standard input. 220 cmdline := str.StringList(cfg.BuildToolexec, name, "-###", "-x", language, "-c", "-") 221 cmd := exec.Command(cmdline[0], cmdline[1:]...) 222 // Force untranslated output so that we see the string "version". 223 cmd.Env = append(os.Environ(), "LC_ALL=C") 224 out, err := cmd.CombinedOutput() 225 if err != nil { 226 return "", "", fmt.Errorf("%s: %v; output: %q", name, err, out) 227 } 228 229 version := "" 230 lines := strings.Split(string(out), "\n") 231 for _, line := range lines { 232 fields := strings.Fields(line) 233 for i, field := range fields { 234 if strings.HasSuffix(field, ":") { 235 // Avoid parsing fields of lines like "Configured with: …", which may 236 // contain arbitrary substrings. 237 break 238 } 239 if field == "version" && i < len(fields)-1 { 240 // Check that the next field is plausibly a version number. 241 // We require only that it begins with an ASCII digit, 242 // since we don't know what version numbering schemes a given 243 // C compiler may use. (Clang and GCC mostly seem to follow the scheme X.Y.Z, 244 // but in https://go.dev/issue/64619 we saw "8.3 [DragonFly]", and who knows 245 // what other C compilers like "zig cc" might report?) 246 next := fields[i+1] 247 if len(next) > 0 && next[0] >= '0' && next[0] <= '9' { 248 version = line 249 break 250 } 251 } 252 } 253 if version != "" { 254 break 255 } 256 } 257 if version == "" { 258 return "", "", fmt.Errorf("%s: can not find version number in %q", name, out) 259 } 260 261 if !strings.Contains(version, "experimental") { 262 // This is a release. Use this line as the tool ID. 263 id = version 264 } else { 265 // This is a development version. The first line with 266 // a leading space is the compiler proper. 267 compiler := "" 268 for _, line := range lines { 269 if strings.HasPrefix(line, " ") && !strings.HasPrefix(line, " (in-process)") { 270 compiler = line 271 break 272 } 273 } 274 if compiler == "" { 275 return "", "", fmt.Errorf("%s: can not find compilation command in %q", name, out) 276 } 277 278 fields, _ := quoted.Split(compiler) 279 if len(fields) == 0 { 280 return "", "", fmt.Errorf("%s: compilation command confusion %q", name, out) 281 } 282 exe = fields[0] 283 if !strings.ContainsAny(exe, `/\`) { 284 if lp, err := pathcache.LookPath(exe); err == nil { 285 exe = lp 286 } 287 } 288 id, err = buildid.ReadFile(exe) 289 if err != nil { 290 return "", "", err 291 } 292 293 // If we can't find a build ID, use a hash. 294 if id == "" { 295 id = b.fileHash(exe) 296 } 297 } 298 299 b.id.Lock() 300 b.gccToolIDCache[key] = id 301 b.gccToolIDCache[key+".exe"] = exe 302 b.id.Unlock() 303 304 return id, exe, nil 305 } 306 307 // Check if assembler used by gccgo is GNU as. 308 func assemblerIsGas() bool { 309 cmd := exec.Command(BuildToolchain.compiler(), "-print-prog-name=as") 310 assembler, err := cmd.Output() 311 if err == nil { 312 cmd := exec.Command(strings.TrimSpace(string(assembler)), "--version") 313 out, err := cmd.Output() 314 return err == nil && strings.Contains(string(out), "GNU") 315 } else { 316 return false 317 } 318 } 319 320 // gccgoBuildIDFile creates an assembler file that records the 321 // action's build ID in an SHF_EXCLUDE section for ELF files or 322 // in a CSECT in XCOFF files. 323 func (b *Builder) gccgoBuildIDFile(a *Action) (string, error) { 324 sfile := a.Objdir + "_buildid.s" 325 326 var buf bytes.Buffer 327 if cfg.Goos == "aix" { 328 fmt.Fprintf(&buf, "\t.csect .go.buildid[XO]\n") 329 } else if (cfg.Goos != "solaris" && cfg.Goos != "illumos") || assemblerIsGas() { 330 fmt.Fprintf(&buf, "\t"+`.section .go.buildid,"e"`+"\n") 331 } else if cfg.Goarch == "sparc" || cfg.Goarch == "sparc64" { 332 fmt.Fprintf(&buf, "\t"+`.section ".go.buildid",#exclude`+"\n") 333 } else { // cfg.Goarch == "386" || cfg.Goarch == "amd64" 334 fmt.Fprintf(&buf, "\t"+`.section .go.buildid,#exclude`+"\n") 335 } 336 fmt.Fprintf(&buf, "\t.byte ") 337 for i := 0; i < len(a.buildID); i++ { 338 if i > 0 { 339 if i%8 == 0 { 340 fmt.Fprintf(&buf, "\n\t.byte ") 341 } else { 342 fmt.Fprintf(&buf, ",") 343 } 344 } 345 fmt.Fprintf(&buf, "%#02x", a.buildID[i]) 346 } 347 fmt.Fprintf(&buf, "\n") 348 if cfg.Goos != "solaris" && cfg.Goos != "illumos" && cfg.Goos != "aix" { 349 secType := "@progbits" 350 if cfg.Goarch == "arm" { 351 secType = "%progbits" 352 } 353 fmt.Fprintf(&buf, "\t"+`.section .note.GNU-stack,"",%s`+"\n", secType) 354 fmt.Fprintf(&buf, "\t"+`.section .note.GNU-split-stack,"",%s`+"\n", secType) 355 } 356 357 if err := b.Shell(a).writeFile(sfile, buf.Bytes()); err != nil { 358 return "", err 359 } 360 361 return sfile, nil 362 } 363 364 // buildID returns the build ID found in the given file. 365 // If no build ID is found, buildID returns the content hash of the file. 366 func (b *Builder) buildID(file string) string { 367 b.id.Lock() 368 id := b.buildIDCache[file] 369 b.id.Unlock() 370 371 if id != "" { 372 return id 373 } 374 375 id, err := buildid.ReadFile(file) 376 if err != nil { 377 id = b.fileHash(file) 378 } 379 380 b.id.Lock() 381 b.buildIDCache[file] = id 382 b.id.Unlock() 383 384 return id 385 } 386 387 // fileHash returns the content hash of the named file. 388 func (b *Builder) fileHash(file string) string { 389 sum, err := cache.FileHash(fsys.Actual(file)) 390 if err != nil { 391 return "" 392 } 393 return buildid.HashToString(sum) 394 } 395 396 var ( 397 counterCacheHit = counter.New("go/buildcache/hit") 398 counterCacheMiss = counter.New("go/buildcache/miss") 399 400 stdlibRecompiled = counter.New("go/buildcache/stdlib-recompiled") 401 stdlibRecompiledIncOnce = sync.OnceFunc(stdlibRecompiled.Inc) 402 ) 403 404 // useCache tries to satisfy the action a, which has action ID actionHash, 405 // by using a cached result from an earlier build. 406 // If useCache decides that the cache can be used, it sets a.buildID 407 // and a.built for use by parent actions and then returns true. 408 // Otherwise it sets a.buildID to a temporary build ID for use in the build 409 // and returns false. When useCache returns false the expectation is that 410 // the caller will build the target and then call updateBuildID to finish the 411 // build ID computation. 412 // When useCache returns false, it may have initiated buffering of output 413 // during a's work. The caller should defer b.flushOutput(a), to make sure 414 // that flushOutput is eventually called regardless of whether the action 415 // succeeds. The flushOutput call must happen after updateBuildID. 416 func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string, printOutput bool) (ok bool) { 417 // The second half of the build ID here is a placeholder for the content hash. 418 // It's important that the overall buildID be unlikely verging on impossible 419 // to appear in the output by chance, but that should be taken care of by 420 // the actionID half; if it also appeared in the input that would be like an 421 // engineered 120-bit partial SHA256 collision. 422 a.actionID = actionHash 423 actionID := buildid.HashToString(actionHash) 424 if a.json != nil { 425 a.json.ActionID = actionID 426 } 427 contentID := actionID // temporary placeholder, likely unique 428 a.buildID = actionID + buildIDSeparator + contentID 429 430 // Executable binaries also record the main build ID in the middle. 431 // See "Build IDs" comment above. 432 if a.Mode == "link" { 433 mainpkg := a.Deps[0] 434 a.buildID = actionID + buildIDSeparator + mainpkg.buildID + buildIDSeparator + contentID 435 } 436 437 // If user requested -a, we force a rebuild, so don't use the cache. 438 if cfg.BuildA { 439 if p := a.Package; p != nil && !p.Stale { 440 p.Stale = true 441 p.StaleReason = "build -a flag in use" 442 } 443 // Begin saving output for later writing to cache. 444 a.output = []byte{} 445 return false 446 } 447 448 defer func() { 449 // Increment counters for cache hits and misses based on the return value 450 // of this function. Don't increment counters if we return early because of 451 // cfg.BuildA above because we don't even look at the cache in that case. 452 if ok { 453 counterCacheHit.Inc() 454 } else { 455 if a.Package != nil && a.Package.Standard { 456 stdlibRecompiledIncOnce() 457 } 458 counterCacheMiss.Inc() 459 } 460 }() 461 462 c := cache.Default() 463 464 if target != "" { 465 buildID, _ := buildid.ReadFile(target) 466 if strings.HasPrefix(buildID, actionID+buildIDSeparator) { 467 a.buildID = buildID 468 if a.json != nil { 469 a.json.BuildID = a.buildID 470 } 471 a.built = target 472 // Poison a.Target to catch uses later in the build. 473 a.Target = "DO NOT USE - " + a.Mode 474 return true 475 } 476 // Special case for building a main package: if the only thing we 477 // want the package for is to link a binary, and the binary is 478 // already up-to-date, then to avoid a rebuild, report the package 479 // as up-to-date as well. See "Build IDs" comment above. 480 // TODO(rsc): Rewrite this code to use a TryCache func on the link action. 481 if !b.NeedExport && a.Mode == "build" && len(a.triggers) == 1 && a.triggers[0].Mode == "link" { 482 if id := strings.Split(buildID, buildIDSeparator); len(id) == 4 && id[1] == actionID { 483 // Temporarily assume a.buildID is the package build ID 484 // stored in the installed binary, and see if that makes 485 // the upcoming link action ID a match. If so, report that 486 // we built the package, safe in the knowledge that the 487 // link step will not ask us for the actual package file. 488 // Note that (*Builder).LinkAction arranged that all of 489 // a.triggers[0]'s dependencies other than a are also 490 // dependencies of a, so that we can be sure that, 491 // other than a.buildID, b.linkActionID is only accessing 492 // build IDs of completed actions. 493 oldBuildID := a.buildID 494 a.buildID = id[1] + buildIDSeparator + id[2] 495 linkID := buildid.HashToString(b.linkActionID(a.triggers[0])) 496 if id[0] == linkID { 497 // Best effort attempt to display output from the compile and link steps. 498 // If it doesn't work, it doesn't work: reusing the cached binary is more 499 // important than reprinting diagnostic information. 500 if printOutput { 501 showStdout(b, c, a, "stdout") // compile output 502 showStdout(b, c, a, "link-stdout") // link output 503 } 504 505 // Poison a.Target to catch uses later in the build. 506 a.Target = "DO NOT USE - main build pseudo-cache Target" 507 a.built = "DO NOT USE - main build pseudo-cache built" 508 if a.json != nil { 509 a.json.BuildID = a.buildID 510 } 511 return true 512 } 513 // Otherwise restore old build ID for main build. 514 a.buildID = oldBuildID 515 } 516 } 517 } 518 519 // TODO(matloob): If we end up caching all executables, the test executable will 520 // already be cached so building it won't do any work. But for now we won't 521 // cache all executables and instead only want to cache some: 522 // we only cache executables produced for 'go run' (and soon, for 'go tool'). 523 // 524 // Special case for linking a test binary: if the only thing we 525 // want the binary for is to run the test, and the test result is cached, 526 // then to avoid the link step, report the link as up-to-date. 527 // We avoid the nested build ID problem in the previous special case 528 // by recording the test results in the cache under the action ID half. 529 if len(a.triggers) == 1 && a.triggers[0].TryCache != nil && a.triggers[0].TryCache(b, a.triggers[0]) { 530 // Best effort attempt to display output from the compile and link steps. 531 // If it doesn't work, it doesn't work: reusing the test result is more 532 // important than reprinting diagnostic information. 533 if printOutput { 534 showStdout(b, c, a.Deps[0], "stdout") // compile output 535 showStdout(b, c, a.Deps[0], "link-stdout") // link output 536 } 537 538 // Poison a.Target to catch uses later in the build. 539 a.Target = "DO NOT USE - pseudo-cache Target" 540 a.built = "DO NOT USE - pseudo-cache built" 541 return true 542 } 543 544 // Check to see if the action output is cached. 545 if file, _, err := cache.GetFile(c, actionHash); err == nil { 546 if a.Mode == "preprocess PGO profile" { 547 // Preprocessed PGO profiles don't embed a build ID, so 548 // skip the build ID lookup. 549 // TODO(prattmic): better would be to add a build ID to the format. 550 a.built = file 551 a.Target = "DO NOT USE - using cache" 552 return true 553 } 554 if buildID, err := buildid.ReadFile(file); err == nil { 555 if printOutput { 556 switch a.Mode { 557 case "link": 558 // The link output is stored using the build action's action ID. 559 // See corresponding code storing the link output in updateBuildID. 560 for _, a1 := range a.Deps { 561 showStdout(b, c, a1, "link-stdout") // link output 562 } 563 default: 564 showStdout(b, c, a, "stdout") // compile output 565 } 566 } 567 a.built = file 568 a.Target = "DO NOT USE - using cache" 569 a.buildID = buildID 570 if a.json != nil { 571 a.json.BuildID = a.buildID 572 } 573 if p := a.Package; p != nil && target != "" { 574 p.Stale = true 575 // Clearer than explaining that something else is stale. 576 p.StaleReason = "not installed but available in build cache" 577 } 578 return true 579 } 580 } 581 582 // If we've reached this point, we can't use the cache for the action. 583 if p := a.Package; p != nil && !p.Stale { 584 p.Stale = true 585 p.StaleReason = "build ID mismatch" 586 if b.IsCmdList { 587 // Since we may end up printing StaleReason, include more detail. 588 for _, p1 := range p.Internal.Imports { 589 if p1.Stale && p1.StaleReason != "" { 590 if strings.HasPrefix(p1.StaleReason, "stale dependency: ") { 591 p.StaleReason = p1.StaleReason 592 break 593 } 594 if strings.HasPrefix(p.StaleReason, "build ID mismatch") { 595 p.StaleReason = "stale dependency: " + p1.ImportPath 596 } 597 } 598 } 599 } 600 } 601 602 // Begin saving output for later writing to cache. 603 a.output = []byte{} 604 return false 605 } 606 607 func showStdout(b *Builder, c cache.Cache, a *Action, key string) error { 608 actionID := a.actionID 609 610 stdout, stdoutEntry, err := cache.GetBytes(c, cache.Subkey(actionID, key)) 611 if err != nil { 612 return err 613 } 614 615 if len(stdout) > 0 { 616 sh := b.Shell(a) 617 if cfg.BuildX || cfg.BuildN { 618 sh.ShowCmd("", "%s # internal", joinUnambiguously(str.StringList("cat", c.OutputFile(stdoutEntry.OutputID)))) 619 } 620 if !cfg.BuildN { 621 sh.Printf("%s", stdout) 622 } 623 } 624 return nil 625 } 626 627 // flushOutput flushes the output being queued in a. 628 func (b *Builder) flushOutput(a *Action) { 629 b.Shell(a).Printf("%s", a.output) 630 a.output = nil 631 } 632 633 // updateBuildID updates the build ID in the target written by action a. 634 // It requires that useCache was called for action a and returned false, 635 // and that the build was then carried out and given the temporary 636 // a.buildID to record as the build ID in the resulting package or binary. 637 // updateBuildID computes the final content ID and updates the build IDs 638 // in the binary. 639 // 640 // Keep in sync with src/cmd/buildid/buildid.go 641 func (b *Builder) updateBuildID(a *Action, target string) error { 642 sh := b.Shell(a) 643 644 if cfg.BuildX || cfg.BuildN { 645 sh.ShowCmd("", "%s # internal", joinUnambiguously(str.StringList(base.Tool("buildid"), "-w", target))) 646 if cfg.BuildN { 647 return nil 648 } 649 } 650 651 c := cache.Default() 652 653 // Cache output from compile/link, even if we don't do the rest. 654 switch a.Mode { 655 case "build": 656 cache.PutBytes(c, cache.Subkey(a.actionID, "stdout"), a.output) 657 case "link": 658 // Even though we don't cache the binary, cache the linker text output. 659 // We might notice that an installed binary is up-to-date but still 660 // want to pretend to have run the linker. 661 // Store it under the main package's action ID 662 // to make it easier to find when that's all we have. 663 for _, a1 := range a.Deps { 664 if p1 := a1.Package; p1 != nil && p1.Name == "main" { 665 cache.PutBytes(c, cache.Subkey(a1.actionID, "link-stdout"), a.output) 666 break 667 } 668 } 669 } 670 671 // Find occurrences of old ID and compute new content-based ID. 672 r, err := os.Open(target) 673 if err != nil { 674 return err 675 } 676 matches, hash, err := buildid.FindAndHash(r, a.buildID, 0) 677 r.Close() 678 if err != nil { 679 return err 680 } 681 newID := a.buildID[:strings.LastIndex(a.buildID, buildIDSeparator)] + buildIDSeparator + buildid.HashToString(hash) 682 if len(newID) != len(a.buildID) { 683 return fmt.Errorf("internal error: build ID length mismatch %q vs %q", a.buildID, newID) 684 } 685 686 // Replace with new content-based ID. 687 a.buildID = newID 688 if a.json != nil { 689 a.json.BuildID = a.buildID 690 } 691 if len(matches) == 0 { 692 // Assume the user specified -buildid= to override what we were going to choose. 693 return nil 694 } 695 696 // Replace the build id in the file with the content-based ID. 697 w, err := os.OpenFile(target, os.O_RDWR, 0) 698 if err != nil { 699 return err 700 } 701 err = buildid.Rewrite(w, matches, newID) 702 if err != nil { 703 w.Close() 704 return err 705 } 706 if err := w.Close(); err != nil { 707 return err 708 } 709 710 // Cache package builds, and cache executable builds if 711 // executable caching was requested. Executables are not 712 // cached by default because they are not reused 713 // nearly as often as individual packages, and they're 714 // much larger, so the cache-footprint-to-utility ratio 715 // of executables is much lower for executables. 716 if a.Mode == "build" { 717 r, err := os.Open(target) 718 if err == nil { 719 if a.output == nil { 720 panic("internal error: a.output not set") 721 } 722 outputID, _, err := c.Put(a.actionID, r) 723 r.Close() 724 if err == nil && cfg.BuildX { 725 sh.ShowCmd("", "%s # internal", joinUnambiguously(str.StringList("cp", target, c.OutputFile(outputID)))) 726 } 727 if b.NeedExport { 728 if err != nil { 729 return err 730 } 731 a.Package.Export = c.OutputFile(outputID) 732 a.Package.BuildID = a.buildID 733 } 734 } 735 } 736 if c, ok := c.(*cache.DiskCache); a.Mode == "link" && a.CacheExecutable && ok { 737 r, err := os.Open(target) 738 if err == nil { 739 if a.output == nil { 740 panic("internal error: a.output not set") 741 } 742 name := a.Package.Internal.ExeName 743 if name == "" { 744 name = a.Package.DefaultExecName() 745 } 746 outputID, _, err := c.PutExecutable(a.actionID, name+cfg.ExeSuffix, r) 747 r.Close() 748 if err == nil && cfg.BuildX { 749 sh.ShowCmd("", "%s # internal", joinUnambiguously(str.StringList("cp", target, c.OutputFile(outputID)))) 750 } 751 } 752 } 753 754 return nil 755 } 756