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 "io/ioutil" 11 "os" 12 "os/exec" 13 "strings" 14 15 "cmd/go/internal/base" 16 "cmd/go/internal/cache" 17 "cmd/go/internal/cfg" 18 "cmd/go/internal/load" 19 "cmd/go/internal/str" 20 "cmd/internal/buildid" 21 ) 22 23 // Build IDs 24 // 25 // Go packages and binaries are stamped with build IDs that record both 26 // the action ID, which is a hash of the inputs to the action that produced 27 // the packages or binary, and the content ID, which is a hash of the action 28 // output, namely the archive or binary itself. The hash is the same one 29 // used by the build artifact cache (see cmd/go/internal/cache), but 30 // truncated when stored in packages and binaries, as the full length is not 31 // needed and is a bit unwieldy. The precise form is 32 // 33 // actionID/[.../]contentID 34 // 35 // where the actionID and contentID are prepared by hashToString below. 36 // and are found by looking for the first or last slash. 37 // Usually the buildID is simply actionID/contentID, but see below for an 38 // exception. 39 // 40 // The build ID serves two primary purposes. 41 // 42 // 1. The action ID half allows installed packages and binaries to serve as 43 // one-element cache entries. If we intend to build math.a with a given 44 // set of inputs summarized in the action ID, and the installed math.a already 45 // has that action ID, we can reuse the installed math.a instead of rebuilding it. 46 // 47 // 2. The content ID half allows the easy preparation of action IDs for steps 48 // that consume a particular package or binary. The content hash of every 49 // input file for a given action must be included in the action ID hash. 50 // Storing the content ID in the build ID lets us read it from the file with 51 // minimal I/O, instead of reading and hashing the entire file. 52 // This is especially effective since packages and binaries are typically 53 // the largest inputs to an action. 54 // 55 // Separating action ID from content ID is important for reproducible builds. 56 // The compiler is compiled with itself. If an output were represented by its 57 // own action ID (instead of content ID) when computing the action ID of 58 // the next step in the build process, then the compiler could never have its 59 // own input action ID as its output action ID (short of a miraculous hash collision). 60 // Instead we use the content IDs to compute the next action ID, and because 61 // the content IDs converge, so too do the action IDs and therefore the 62 // build IDs and the overall compiler binary. See cmd/dist's cmdbootstrap 63 // for the actual convergence sequence. 64 // 65 // The “one-element cache” purpose is a bit more complex for installed 66 // binaries. For a binary, like cmd/gofmt, there are two steps: compile 67 // cmd/gofmt/*.go into main.a, and then link main.a into the gofmt binary. 68 // We do not install gofmt's main.a, only the gofmt binary. Being able to 69 // decide that the gofmt binary is up-to-date means computing the action ID 70 // for the final link of the gofmt binary and comparing it against the 71 // already-installed gofmt binary. But computing the action ID for the link 72 // means knowing the content ID of main.a, which we did not keep. 73 // To sidestep this problem, each binary actually stores an expanded build ID: 74 // 75 // actionID(binary)/actionID(main.a)/contentID(main.a)/contentID(binary) 76 // 77 // (Note that this can be viewed equivalently as: 78 // 79 // actionID(binary)/buildID(main.a)/contentID(binary) 80 // 81 // Storing the buildID(main.a) in the middle lets the computations that care 82 // about the prefix or suffix halves ignore the middle and preserves the 83 // original build ID as a contiguous string.) 84 // 85 // During the build, when it's time to build main.a, the gofmt binary has the 86 // information needed to decide whether the eventual link would produce 87 // the same binary: if the action ID for main.a's inputs matches and then 88 // the action ID for the link step matches when assuming the given main.a 89 // content ID, then the binary as a whole is up-to-date and need not be rebuilt. 90 // 91 // This is all a bit complex and may be simplified once we can rely on the 92 // main cache, but at least at the start we will be using the content-based 93 // staleness determination without a cache beyond the usual installed 94 // package and binary locations. 95 96 const buildIDSeparator = "/" 97 98 // actionID returns the action ID half of a build ID. 99 func actionID(buildID string) string { 100 i := strings.Index(buildID, buildIDSeparator) 101 if i < 0 { 102 return buildID 103 } 104 return buildID[:i] 105 } 106 107 // contentID returns the content ID half of a build ID. 108 func contentID(buildID string) string { 109 return buildID[strings.LastIndex(buildID, buildIDSeparator)+1:] 110 } 111 112 // hashToString converts the hash h to a string to be recorded 113 // in package archives and binaries as part of the build ID. 114 // We use the first 96 bits of the hash and encode it in base64, 115 // resulting in a 16-byte string. Because this is only used for 116 // detecting the need to rebuild installed files (not for lookups 117 // in the object file cache), 96 bits are sufficient to drive the 118 // probability of a false "do not need to rebuild" decision to effectively zero. 119 // We embed two different hashes in archives and four in binaries, 120 // so cutting to 16 bytes is a significant savings when build IDs are displayed. 121 // (16*4+3 = 67 bytes compared to 64*4+3 = 259 bytes for the 122 // more straightforward option of printing the entire h in hex). 123 func hashToString(h [cache.HashSize]byte) string { 124 const b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_" 125 const chunks = 5 126 var dst [chunks * 4]byte 127 for i := 0; i < chunks; i++ { 128 v := uint32(h[3*i])<<16 | uint32(h[3*i+1])<<8 | uint32(h[3*i+2]) 129 dst[4*i+0] = b64[(v>>18)&0x3F] 130 dst[4*i+1] = b64[(v>>12)&0x3F] 131 dst[4*i+2] = b64[(v>>6)&0x3F] 132 dst[4*i+3] = b64[v&0x3F] 133 } 134 return string(dst[:]) 135 } 136 137 // toolID returns the unique ID to use for the current copy of the 138 // named tool (asm, compile, cover, link). 139 // 140 // It is important that if the tool changes (for example a compiler bug is fixed 141 // and the compiler reinstalled), toolID returns a different string, so that old 142 // package archives look stale and are rebuilt (with the fixed compiler). 143 // This suggests using a content hash of the tool binary, as stored in the build ID. 144 // 145 // Unfortunately, we can't just open the tool binary, because the tool might be 146 // invoked via a wrapper program specified by -toolexec and we don't know 147 // what the wrapper program does. In particular, we want "-toolexec toolstash" 148 // to continue working: it does no good if "-toolexec toolstash" is executing a 149 // stashed copy of the compiler but the go command is acting as if it will run 150 // the standard copy of the compiler. The solution is to ask the tool binary to tell 151 // us its own build ID using the "-V=full" flag now supported by all tools. 152 // Then we know we're getting the build ID of the compiler that will actually run 153 // during the build. (How does the compiler binary know its own content hash? 154 // We store it there using updateBuildID after the standard link step.) 155 // 156 // A final twist is that we'd prefer to have reproducible builds for release toolchains. 157 // It should be possible to cross-compile for Windows from either Linux or Mac 158 // or Windows itself and produce the same binaries, bit for bit. If the tool ID, 159 // which influences the action ID half of the build ID, is based on the content ID, 160 // then the Linux compiler binary and Mac compiler binary will have different tool IDs 161 // and therefore produce executables with different action IDs. 162 // To avoid this problem, for releases we use the release version string instead 163 // of the compiler binary's content hash. This assumes that all compilers built 164 // on all different systems are semantically equivalent, which is of course only true 165 // modulo bugs. (Producing the exact same executables also requires that the different 166 // build setups agree on details like $GOROOT and file name paths, but at least the 167 // tool IDs do not make it impossible.) 168 func (b *Builder) toolID(name string) string { 169 b.id.Lock() 170 id := b.toolIDCache[name] 171 b.id.Unlock() 172 173 if id != "" { 174 return id 175 } 176 177 path := base.Tool(name) 178 desc := "go tool " + name 179 180 // Special case: undocumented -vettool overrides usual vet, 181 // for testing vet or supplying an alternative analysis tool. 182 if name == "vet" && VetTool != "" { 183 path = VetTool 184 desc = VetTool 185 } 186 187 cmdline := str.StringList(cfg.BuildToolexec, path, "-V=full") 188 cmd := exec.Command(cmdline[0], cmdline[1:]...) 189 cmd.Env = base.EnvForDir(cmd.Dir, os.Environ()) 190 var stdout, stderr bytes.Buffer 191 cmd.Stdout = &stdout 192 cmd.Stderr = &stderr 193 if err := cmd.Run(); err != nil { 194 base.Fatalf("%s: %v\n%s%s", desc, err, stdout.Bytes(), stderr.Bytes()) 195 } 196 197 line := stdout.String() 198 f := strings.Fields(line) 199 if len(f) < 3 || f[0] != name && path != VetTool || f[1] != "version" || f[2] == "devel" && !strings.HasPrefix(f[len(f)-1], "buildID=") { 200 base.Fatalf("%s -V=full: unexpected output:\n\t%s", desc, line) 201 } 202 if f[2] == "devel" { 203 // On the development branch, use the content ID part of the build ID. 204 id = contentID(f[len(f)-1]) 205 } else { 206 // For a release, the output is like: "compile version go1.9.1 X:framepointer". 207 // Use the whole line. 208 id = strings.TrimSpace(line) 209 } 210 211 b.id.Lock() 212 b.toolIDCache[name] = id 213 b.id.Unlock() 214 215 return id 216 } 217 218 // gccToolID returns the unique ID to use for a tool that is invoked 219 // by the GCC driver. This is used particularly for gccgo, but this can also 220 // be used for gcc, g++, gfortran, etc.; those tools all use the GCC 221 // driver under different names. The approach used here should also 222 // work for sufficiently new versions of clang. Unlike toolID, the 223 // name argument is the program to run. The language argument is the 224 // type of input file as passed to the GCC driver's -x option. 225 // 226 // For these tools we have no -V=full option to dump the build ID, 227 // but we can run the tool with -v -### to reliably get the compiler proper 228 // and hash that. That will work in the presence of -toolexec. 229 // 230 // In order to get reproducible builds for released compilers, we 231 // detect a released compiler by the absence of "experimental" in the 232 // --version output, and in that case we just use the version string. 233 func (b *Builder) gccgoToolID(name, language string) (string, error) { 234 key := name + "." + language 235 b.id.Lock() 236 id := b.toolIDCache[key] 237 b.id.Unlock() 238 239 if id != "" { 240 return id, nil 241 } 242 243 // Invoke the driver with -### to see the subcommands and the 244 // version strings. Use -x to set the language. Pretend to 245 // compile an empty file on standard input. 246 cmdline := str.StringList(cfg.BuildToolexec, name, "-###", "-x", language, "-c", "-") 247 cmd := exec.Command(cmdline[0], cmdline[1:]...) 248 cmd.Env = base.EnvForDir(cmd.Dir, os.Environ()) 249 // Force untranslated output so that we see the string "version". 250 cmd.Env = append(cmd.Env, "LC_ALL=C") 251 out, err := cmd.CombinedOutput() 252 if err != nil { 253 return "", fmt.Errorf("%s: %v; output: %q", name, err, out) 254 } 255 256 version := "" 257 lines := strings.Split(string(out), "\n") 258 for _, line := range lines { 259 if fields := strings.Fields(line); len(fields) > 1 && fields[1] == "version" { 260 version = line 261 break 262 } 263 } 264 if version == "" { 265 return "", fmt.Errorf("%s: can not find version number in %q", name, out) 266 } 267 268 if !strings.Contains(version, "experimental") { 269 // This is a release. Use this line as the tool ID. 270 id = version 271 } else { 272 // This is a development version. The first line with 273 // a leading space is the compiler proper. 274 compiler := "" 275 for _, line := range lines { 276 if len(line) > 1 && line[0] == ' ' { 277 compiler = line 278 break 279 } 280 } 281 if compiler == "" { 282 return "", fmt.Errorf("%s: can not find compilation command in %q", name, out) 283 } 284 285 fields := strings.Fields(compiler) 286 if len(fields) == 0 { 287 return "", fmt.Errorf("%s: compilation command confusion %q", name, out) 288 } 289 exe := fields[0] 290 if !strings.ContainsAny(exe, `/\`) { 291 if lp, err := exec.LookPath(exe); err == nil { 292 exe = lp 293 } 294 } 295 if _, err := os.Stat(exe); err != nil { 296 return "", fmt.Errorf("%s: can not find compiler %q: %v; output %q", name, exe, err, out) 297 } 298 id = b.fileHash(exe) 299 } 300 301 b.id.Lock() 302 b.toolIDCache[name] = id 303 b.id.Unlock() 304 305 return id, nil 306 } 307 308 // Check if assembler used by gccgo is GNU as. 309 func assemblerIsGas() bool { 310 cmd := exec.Command(BuildToolchain.compiler(), "-print-prog-name=as") 311 assembler, err := cmd.Output() 312 if err == nil { 313 cmd := exec.Command(strings.TrimSpace(string(assembler)), "--version") 314 out, err := cmd.Output() 315 return err == nil && strings.Contains(string(out), "GNU") 316 } else { 317 return false 318 } 319 } 320 321 // gccgoBuildIDFile creates an assembler file that records the 322 // action's build ID in an SHF_EXCLUDE section for ELF files or 323 // in a CSECT in XCOFF files. 324 func (b *Builder) gccgoBuildIDFile(a *Action) (string, error) { 325 sfile := a.Objdir + "_buildid.s" 326 327 var buf bytes.Buffer 328 if cfg.Goos == "aix" { 329 fmt.Fprintf(&buf, "\t.csect .go.buildid[XO]\n") 330 } else if (cfg.Goos != "solaris" && cfg.Goos != "illumos") || assemblerIsGas() { 331 fmt.Fprintf(&buf, "\t"+`.section .go.buildid,"e"`+"\n") 332 } else if cfg.Goarch == "sparc" || cfg.Goarch == "sparc64" { 333 fmt.Fprintf(&buf, "\t"+`.section ".go.buildid",#exclude`+"\n") 334 } else { // cfg.Goarch == "386" || cfg.Goarch == "amd64" 335 fmt.Fprintf(&buf, "\t"+`.section .go.buildid,#exclude`+"\n") 336 } 337 fmt.Fprintf(&buf, "\t.byte ") 338 for i := 0; i < len(a.buildID); i++ { 339 if i > 0 { 340 if i%8 == 0 { 341 fmt.Fprintf(&buf, "\n\t.byte ") 342 } else { 343 fmt.Fprintf(&buf, ",") 344 } 345 } 346 fmt.Fprintf(&buf, "%#02x", a.buildID[i]) 347 } 348 fmt.Fprintf(&buf, "\n") 349 if cfg.Goos != "solaris" && cfg.Goos != "illumos" && cfg.Goos != "aix" { 350 secType := "@progbits" 351 if cfg.Goarch == "arm" { 352 secType = "%progbits" 353 } 354 fmt.Fprintf(&buf, "\t"+`.section .note.GNU-stack,"",%s`+"\n", secType) 355 fmt.Fprintf(&buf, "\t"+`.section .note.GNU-split-stack,"",%s`+"\n", secType) 356 } 357 358 if cfg.BuildN || cfg.BuildX { 359 for _, line := range bytes.Split(buf.Bytes(), []byte("\n")) { 360 b.Showcmd("", "echo '%s' >> %s", line, sfile) 361 } 362 if cfg.BuildN { 363 return sfile, nil 364 } 365 } 366 367 if err := ioutil.WriteFile(sfile, buf.Bytes(), 0666); err != nil { 368 return "", err 369 } 370 371 return sfile, nil 372 } 373 374 // buildID returns the build ID found in the given file. 375 // If no build ID is found, buildID returns the content hash of the file. 376 func (b *Builder) buildID(file string) string { 377 b.id.Lock() 378 id := b.buildIDCache[file] 379 b.id.Unlock() 380 381 if id != "" { 382 return id 383 } 384 385 id, err := buildid.ReadFile(file) 386 if err != nil { 387 id = b.fileHash(file) 388 } 389 390 b.id.Lock() 391 b.buildIDCache[file] = id 392 b.id.Unlock() 393 394 return id 395 } 396 397 // fileHash returns the content hash of the named file. 398 func (b *Builder) fileHash(file string) string { 399 sum, err := cache.FileHash(file) 400 if err != nil { 401 return "" 402 } 403 return hashToString(sum) 404 } 405 406 // useCache tries to satisfy the action a, which has action ID actionHash, 407 // by using a cached result from an earlier build. At the moment, the only 408 // cached result is the installed package or binary at target. 409 // If useCache decides that the cache can be used, it sets a.buildID 410 // and a.built for use by parent actions and then returns true. 411 // Otherwise it sets a.buildID to a temporary build ID for use in the build 412 // and returns false. When useCache returns false the expectation is that 413 // the caller will build the target and then call updateBuildID to finish the 414 // build ID computation. 415 // When useCache returns false, it may have initiated buffering of output 416 // during a's work. The caller should defer b.flushOutput(a), to make sure 417 // that flushOutput is eventually called regardless of whether the action 418 // succeeds. The flushOutput call must happen after updateBuildID. 419 func (b *Builder) useCache(a *Action, p *load.Package, actionHash cache.ActionID, target string) bool { 420 // The second half of the build ID here is a placeholder for the content hash. 421 // It's important that the overall buildID be unlikely verging on impossible 422 // to appear in the output by chance, but that should be taken care of by 423 // the actionID half; if it also appeared in the input that would be like an 424 // engineered 96-bit partial SHA256 collision. 425 a.actionID = actionHash 426 actionID := hashToString(actionHash) 427 if a.json != nil { 428 a.json.ActionID = actionID 429 } 430 contentID := actionID // temporary placeholder, likely unique 431 a.buildID = actionID + buildIDSeparator + contentID 432 433 // Executable binaries also record the main build ID in the middle. 434 // See "Build IDs" comment above. 435 if a.Mode == "link" { 436 mainpkg := a.Deps[0] 437 a.buildID = actionID + buildIDSeparator + mainpkg.buildID + buildIDSeparator + contentID 438 } 439 440 // Check to see if target exists and matches the expected action ID. 441 // If so, it's up to date and we can reuse it instead of rebuilding it. 442 var buildID string 443 if target != "" && !cfg.BuildA { 444 buildID, _ = buildid.ReadFile(target) 445 if strings.HasPrefix(buildID, actionID+buildIDSeparator) { 446 a.buildID = buildID 447 if a.json != nil { 448 a.json.BuildID = a.buildID 449 } 450 a.built = target 451 // Poison a.Target to catch uses later in the build. 452 a.Target = "DO NOT USE - " + a.Mode 453 return true 454 } 455 } 456 457 // Special case for building a main package: if the only thing we 458 // want the package for is to link a binary, and the binary is 459 // already up-to-date, then to avoid a rebuild, report the package 460 // as up-to-date as well. See "Build IDs" comment above. 461 // TODO(rsc): Rewrite this code to use a TryCache func on the link action. 462 if target != "" && !cfg.BuildA && !b.NeedExport && a.Mode == "build" && len(a.triggers) == 1 && a.triggers[0].Mode == "link" { 463 buildID, err := buildid.ReadFile(target) 464 if err == nil { 465 id := strings.Split(buildID, buildIDSeparator) 466 if len(id) == 4 && id[1] == actionID { 467 // Temporarily assume a.buildID is the package build ID 468 // stored in the installed binary, and see if that makes 469 // the upcoming link action ID a match. If so, report that 470 // we built the package, safe in the knowledge that the 471 // link step will not ask us for the actual package file. 472 // Note that (*Builder).LinkAction arranged that all of 473 // a.triggers[0]'s dependencies other than a are also 474 // dependencies of a, so that we can be sure that, 475 // other than a.buildID, b.linkActionID is only accessing 476 // build IDs of completed actions. 477 oldBuildID := a.buildID 478 a.buildID = id[1] + buildIDSeparator + id[2] 479 linkID := hashToString(b.linkActionID(a.triggers[0])) 480 if id[0] == linkID { 481 // Best effort attempt to display output from the compile and link steps. 482 // If it doesn't work, it doesn't work: reusing the cached binary is more 483 // important than reprinting diagnostic information. 484 if c := cache.Default(); c != nil { 485 showStdout(b, c, a.actionID, "stdout") // compile output 486 showStdout(b, c, a.actionID, "link-stdout") // link output 487 } 488 489 // Poison a.Target to catch uses later in the build. 490 a.Target = "DO NOT USE - main build pseudo-cache Target" 491 a.built = "DO NOT USE - main build pseudo-cache built" 492 if a.json != nil { 493 a.json.BuildID = a.buildID 494 } 495 return true 496 } 497 // Otherwise restore old build ID for main build. 498 a.buildID = oldBuildID 499 } 500 } 501 } 502 503 // Special case for linking a test binary: if the only thing we 504 // want the binary for is to run the test, and the test result is cached, 505 // then to avoid the link step, report the link as up-to-date. 506 // We avoid the nested build ID problem in the previous special case 507 // by recording the test results in the cache under the action ID half. 508 if !cfg.BuildA && len(a.triggers) == 1 && a.triggers[0].TryCache != nil && a.triggers[0].TryCache(b, a.triggers[0]) { 509 // Best effort attempt to display output from the compile and link steps. 510 // If it doesn't work, it doesn't work: reusing the test result is more 511 // important than reprinting diagnostic information. 512 if c := cache.Default(); c != nil { 513 showStdout(b, c, a.Deps[0].actionID, "stdout") // compile output 514 showStdout(b, c, a.Deps[0].actionID, "link-stdout") // link output 515 } 516 517 // Poison a.Target to catch uses later in the build. 518 a.Target = "DO NOT USE - pseudo-cache Target" 519 a.built = "DO NOT USE - pseudo-cache built" 520 return true 521 } 522 523 if b.IsCmdList { 524 // Invoked during go list to compute and record staleness. 525 if p := a.Package; p != nil && !p.Stale { 526 p.Stale = true 527 if cfg.BuildA { 528 p.StaleReason = "build -a flag in use" 529 } else { 530 p.StaleReason = "build ID mismatch" 531 for _, p1 := range p.Internal.Imports { 532 if p1.Stale && p1.StaleReason != "" { 533 if strings.HasPrefix(p1.StaleReason, "stale dependency: ") { 534 p.StaleReason = p1.StaleReason 535 break 536 } 537 if strings.HasPrefix(p.StaleReason, "build ID mismatch") { 538 p.StaleReason = "stale dependency: " + p1.ImportPath 539 } 540 } 541 } 542 } 543 } 544 545 // Fall through to update a.buildID from the build artifact cache, 546 // which will affect the computation of buildIDs for targets 547 // higher up in the dependency graph. 548 } 549 550 // Check the build artifact cache. 551 // We treat hits in this cache as being "stale" for the purposes of go list 552 // (in effect, "stale" means whether p.Target is up-to-date), 553 // but we're still happy to use results from the build artifact cache. 554 if c := cache.Default(); c != nil { 555 if !cfg.BuildA { 556 if file, _, err := c.GetFile(actionHash); err == nil { 557 if buildID, err := buildid.ReadFile(file); err == nil { 558 if err := showStdout(b, c, a.actionID, "stdout"); err == nil { 559 a.built = file 560 a.Target = "DO NOT USE - using cache" 561 a.buildID = buildID 562 if a.json != nil { 563 a.json.BuildID = a.buildID 564 } 565 if p := a.Package; p != nil { 566 // Clearer than explaining that something else is stale. 567 p.StaleReason = "not installed but available in build cache" 568 } 569 return true 570 } 571 } 572 } 573 } 574 575 // Begin saving output for later writing to cache. 576 a.output = []byte{} 577 } 578 579 return false 580 } 581 582 func showStdout(b *Builder, c *cache.Cache, actionID cache.ActionID, key string) error { 583 stdout, stdoutEntry, err := c.GetBytes(cache.Subkey(actionID, key)) 584 if err != nil { 585 return err 586 } 587 588 if len(stdout) > 0 { 589 if cfg.BuildX || cfg.BuildN { 590 b.Showcmd("", "%s # internal", joinUnambiguously(str.StringList("cat", c.OutputFile(stdoutEntry.OutputID)))) 591 } 592 if !cfg.BuildN { 593 b.Print(string(stdout)) 594 } 595 } 596 return nil 597 } 598 599 // flushOutput flushes the output being queued in a. 600 func (b *Builder) flushOutput(a *Action) { 601 b.Print(string(a.output)) 602 a.output = nil 603 } 604 605 // updateBuildID updates the build ID in the target written by action a. 606 // It requires that useCache was called for action a and returned false, 607 // and that the build was then carried out and given the temporary 608 // a.buildID to record as the build ID in the resulting package or binary. 609 // updateBuildID computes the final content ID and updates the build IDs 610 // in the binary. 611 // 612 // Keep in sync with src/cmd/buildid/buildid.go 613 func (b *Builder) updateBuildID(a *Action, target string, rewrite bool) error { 614 if cfg.BuildX || cfg.BuildN { 615 if rewrite { 616 b.Showcmd("", "%s # internal", joinUnambiguously(str.StringList(base.Tool("buildid"), "-w", target))) 617 } 618 if cfg.BuildN { 619 return nil 620 } 621 } 622 623 // Cache output from compile/link, even if we don't do the rest. 624 if c := cache.Default(); c != nil { 625 switch a.Mode { 626 case "build": 627 c.PutBytes(cache.Subkey(a.actionID, "stdout"), a.output) 628 case "link": 629 // Even though we don't cache the binary, cache the linker text output. 630 // We might notice that an installed binary is up-to-date but still 631 // want to pretend to have run the linker. 632 // Store it under the main package's action ID 633 // to make it easier to find when that's all we have. 634 for _, a1 := range a.Deps { 635 if p1 := a1.Package; p1 != nil && p1.Name == "main" { 636 c.PutBytes(cache.Subkey(a1.actionID, "link-stdout"), a.output) 637 break 638 } 639 } 640 } 641 } 642 643 // Find occurrences of old ID and compute new content-based ID. 644 r, err := os.Open(target) 645 if err != nil { 646 return err 647 } 648 matches, hash, err := buildid.FindAndHash(r, a.buildID, 0) 649 r.Close() 650 if err != nil { 651 return err 652 } 653 newID := a.buildID[:strings.LastIndex(a.buildID, buildIDSeparator)] + buildIDSeparator + hashToString(hash) 654 if len(newID) != len(a.buildID) { 655 return fmt.Errorf("internal error: build ID length mismatch %q vs %q", a.buildID, newID) 656 } 657 658 // Replace with new content-based ID. 659 a.buildID = newID 660 if a.json != nil { 661 a.json.BuildID = a.buildID 662 } 663 if len(matches) == 0 { 664 // Assume the user specified -buildid= to override what we were going to choose. 665 return nil 666 } 667 668 if rewrite { 669 w, err := os.OpenFile(target, os.O_WRONLY, 0) 670 if err != nil { 671 return err 672 } 673 err = buildid.Rewrite(w, matches, newID) 674 if err != nil { 675 w.Close() 676 return err 677 } 678 if err := w.Close(); err != nil { 679 return err 680 } 681 } 682 683 // Cache package builds, but not binaries (link steps). 684 // The expectation is that binaries are not reused 685 // nearly as often as individual packages, and they're 686 // much larger, so the cache-footprint-to-utility ratio 687 // of binaries is much lower for binaries. 688 // Not caching the link step also makes sure that repeated "go run" at least 689 // always rerun the linker, so that they don't get too fast. 690 // (We don't want people thinking go is a scripting language.) 691 // Note also that if we start caching binaries, then we will 692 // copy the binaries out of the cache to run them, and then 693 // that will mean the go process is itself writing a binary 694 // and then executing it, so we will need to defend against 695 // ETXTBSY problems as discussed in exec.go and golang.org/issue/22220. 696 if c := cache.Default(); c != nil && a.Mode == "build" { 697 r, err := os.Open(target) 698 if err == nil { 699 if a.output == nil { 700 panic("internal error: a.output not set") 701 } 702 outputID, _, err := c.Put(a.actionID, r) 703 r.Close() 704 if err == nil && cfg.BuildX { 705 b.Showcmd("", "%s # internal", joinUnambiguously(str.StringList("cp", target, c.OutputFile(outputID)))) 706 } 707 if b.NeedExport { 708 if err != nil { 709 return err 710 } 711 a.Package.Export = c.OutputFile(outputID) 712 } 713 } 714 } 715 716 return nil 717 } 718