github.com/zxy12/go_duplicate_112_new@v0.0.0-20200807091221-747231827200/src/cmd/go/internal/work/buildid.go (about) 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 avoids 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". Use the whole line. 207 id = f[2] 208 } 209 210 b.id.Lock() 211 b.toolIDCache[name] = id 212 b.id.Unlock() 213 214 return id 215 } 216 217 // gccToolID returns the unique ID to use for a tool that is invoked 218 // by the GCC driver. This is in particular gccgo, but this can also 219 // be used for gcc, g++, gfortran, etc.; those tools all use the GCC 220 // driver under different names. The approach used here should also 221 // work for sufficiently new versions of clang. Unlike toolID, the 222 // name argument is the program to run. The language argument is the 223 // type of input file as passed to the GCC driver's -x option. 224 // 225 // For these tools we have no -V=full option to dump the build ID, 226 // but we can run the tool with -v -### to reliably get the compiler proper 227 // and hash that. That will work in the presence of -toolexec. 228 // 229 // In order to get reproducible builds for released compilers, we 230 // detect a released compiler by the absence of "experimental" in the 231 // --version output, and in that case we just use the version string. 232 func (b *Builder) gccgoToolID(name, language string) (string, error) { 233 key := name + "." + language 234 b.id.Lock() 235 id := b.toolIDCache[key] 236 b.id.Unlock() 237 238 if id != "" { 239 return id, nil 240 } 241 242 // Invoke the driver with -### to see the subcommands and the 243 // version strings. Use -x to set the language. Pretend to 244 // compile an empty file on standard input. 245 cmdline := str.StringList(cfg.BuildToolexec, name, "-###", "-x", language, "-c", "-") 246 cmd := exec.Command(cmdline[0], cmdline[1:]...) 247 cmd.Env = base.EnvForDir(cmd.Dir, os.Environ()) 248 // Force untranslated output so that we see the string "version". 249 cmd.Env = append(cmd.Env, "LC_ALL=C") 250 out, err := cmd.CombinedOutput() 251 if err != nil { 252 return "", fmt.Errorf("%s: %v; output: %q", name, err, out) 253 } 254 255 version := "" 256 lines := strings.Split(string(out), "\n") 257 for _, line := range lines { 258 if fields := strings.Fields(line); len(fields) > 1 && fields[1] == "version" { 259 version = line 260 break 261 } 262 } 263 if version == "" { 264 return "", fmt.Errorf("%s: can not find version number in %q", name, out) 265 } 266 267 if !strings.Contains(version, "experimental") { 268 // This is a release. Use this line as the tool ID. 269 id = version 270 } else { 271 // This is a development version. The first line with 272 // a leading space is the compiler proper. 273 compiler := "" 274 for _, line := range lines { 275 if len(line) > 1 && line[0] == ' ' { 276 compiler = line 277 break 278 } 279 } 280 if compiler == "" { 281 return "", fmt.Errorf("%s: can not find compilation command in %q", name, out) 282 } 283 284 fields := strings.Fields(compiler) 285 if len(fields) == 0 { 286 return "", fmt.Errorf("%s: compilation command confusion %q", name, out) 287 } 288 exe := fields[0] 289 if !strings.ContainsAny(exe, `/\`) { 290 if lp, err := exec.LookPath(exe); err == nil { 291 exe = lp 292 } 293 } 294 if _, err := os.Stat(exe); err != nil { 295 return "", fmt.Errorf("%s: can not find compiler %q: %v; output %q", name, exe, err, out) 296 } 297 id = b.fileHash(exe) 298 } 299 300 b.id.Lock() 301 b.toolIDCache[name] = id 302 b.id.Unlock() 303 304 return id, 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" || 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 != "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 cfg.BuildN || cfg.BuildX { 358 for _, line := range bytes.Split(buf.Bytes(), []byte("\n")) { 359 b.Showcmd("", "echo '%s' >> %s", line, sfile) 360 } 361 if cfg.BuildN { 362 return sfile, nil 363 } 364 } 365 366 if err := ioutil.WriteFile(sfile, buf.Bytes(), 0666); err != nil { 367 return "", err 368 } 369 370 return sfile, nil 371 } 372 373 // buildID returns the build ID found in the given file. 374 // If no build ID is found, buildID returns the content hash of the file. 375 func (b *Builder) buildID(file string) string { 376 b.id.Lock() 377 id := b.buildIDCache[file] 378 b.id.Unlock() 379 380 if id != "" { 381 return id 382 } 383 384 id, err := buildid.ReadFile(file) 385 if err != nil { 386 id = b.fileHash(file) 387 } 388 389 b.id.Lock() 390 b.buildIDCache[file] = id 391 b.id.Unlock() 392 393 return id 394 } 395 396 // fileHash returns the content hash of the named file. 397 func (b *Builder) fileHash(file string) string { 398 sum, err := cache.FileHash(file) 399 if err != nil { 400 return "" 401 } 402 return hashToString(sum) 403 } 404 405 // useCache tries to satisfy the action a, which has action ID actionHash, 406 // by using a cached result from an earlier build. At the moment, the only 407 // cached result is the installed package or binary at target. 408 // If useCache decides that the cache can be used, it sets a.buildID 409 // and a.built for use by parent actions and then returns true. 410 // Otherwise it sets a.buildID to a temporary build ID for use in the build 411 // and returns false. When useCache returns false the expectation is that 412 // the caller will build the target and then call updateBuildID to finish the 413 // build ID computation. 414 // When useCache returns false, it may have initiated buffering of output 415 // during a's work. The caller should defer b.flushOutput(a), to make sure 416 // that flushOutput is eventually called regardless of whether the action 417 // succeeds. The flushOutput call must happen after updateBuildID. 418 func (b *Builder) useCache(a *Action, p *load.Package, actionHash cache.ActionID, target string) bool { 419 // The second half of the build ID here is a placeholder for the content hash. 420 // It's important that the overall buildID be unlikely verging on impossible 421 // to appear in the output by chance, but that should be taken care of by 422 // the actionID half; if it also appeared in the input that would be like an 423 // engineered 96-bit partial SHA256 collision. 424 a.actionID = actionHash 425 actionID := hashToString(actionHash) 426 contentID := actionID // temporary placeholder, likely unique 427 a.buildID = actionID + buildIDSeparator + contentID 428 429 // Executable binaries also record the main build ID in the middle. 430 // See "Build IDs" comment above. 431 if a.Mode == "link" { 432 mainpkg := a.Deps[0] 433 a.buildID = actionID + buildIDSeparator + mainpkg.buildID + buildIDSeparator + contentID 434 } 435 436 // Check to see if target exists and matches the expected action ID. 437 // If so, it's up to date and we can reuse it instead of rebuilding it. 438 var buildID string 439 if target != "" && !cfg.BuildA { 440 buildID, _ = buildid.ReadFile(target) 441 if strings.HasPrefix(buildID, actionID+buildIDSeparator) { 442 a.buildID = buildID 443 a.built = target 444 // Poison a.Target to catch uses later in the build. 445 a.Target = "DO NOT USE - " + a.Mode 446 return true 447 } 448 } 449 450 // Special case for building a main package: if the only thing we 451 // want the package for is to link a binary, and the binary is 452 // already up-to-date, then to avoid a rebuild, report the package 453 // as up-to-date as well. See "Build IDs" comment above. 454 // TODO(rsc): Rewrite this code to use a TryCache func on the link action. 455 if target != "" && !cfg.BuildA && !b.NeedExport && a.Mode == "build" && len(a.triggers) == 1 && a.triggers[0].Mode == "link" { 456 buildID, err := buildid.ReadFile(target) 457 if err == nil { 458 id := strings.Split(buildID, buildIDSeparator) 459 if len(id) == 4 && id[1] == actionID { 460 // Temporarily assume a.buildID is the package build ID 461 // stored in the installed binary, and see if that makes 462 // the upcoming link action ID a match. If so, report that 463 // we built the package, safe in the knowledge that the 464 // link step will not ask us for the actual package file. 465 // Note that (*Builder).LinkAction arranged that all of 466 // a.triggers[0]'s dependencies other than a are also 467 // dependencies of a, so that we can be sure that, 468 // other than a.buildID, b.linkActionID is only accessing 469 // build IDs of completed actions. 470 oldBuildID := a.buildID 471 a.buildID = id[1] + buildIDSeparator + id[2] 472 linkID := hashToString(b.linkActionID(a.triggers[0])) 473 if id[0] == linkID { 474 // Best effort attempt to display output from the compile and link steps. 475 // If it doesn't work, it doesn't work: reusing the cached binary is more 476 // important than reprinting diagnostic information. 477 if c := cache.Default(); c != nil { 478 showStdout(b, c, a.actionID, "stdout") // compile output 479 showStdout(b, c, a.actionID, "link-stdout") // link output 480 } 481 482 // Poison a.Target to catch uses later in the build. 483 a.Target = "DO NOT USE - main build pseudo-cache Target" 484 a.built = "DO NOT USE - main build pseudo-cache built" 485 return true 486 } 487 // Otherwise restore old build ID for main build. 488 a.buildID = oldBuildID 489 } 490 } 491 } 492 493 // Special case for linking a test binary: if the only thing we 494 // want the binary for is to run the test, and the test result is cached, 495 // then to avoid the link step, report the link as up-to-date. 496 // We avoid the nested build ID problem in the previous special case 497 // by recording the test results in the cache under the action ID half. 498 if !cfg.BuildA && len(a.triggers) == 1 && a.triggers[0].TryCache != nil && a.triggers[0].TryCache(b, a.triggers[0]) { 499 // Best effort attempt to display output from the compile and link steps. 500 // If it doesn't work, it doesn't work: reusing the test result is more 501 // important than reprinting diagnostic information. 502 if c := cache.Default(); c != nil { 503 showStdout(b, c, a.Deps[0].actionID, "stdout") // compile output 504 showStdout(b, c, a.Deps[0].actionID, "link-stdout") // link output 505 } 506 507 // Poison a.Target to catch uses later in the build. 508 a.Target = "DO NOT USE - pseudo-cache Target" 509 a.built = "DO NOT USE - pseudo-cache built" 510 return true 511 } 512 513 if b.IsCmdList { 514 // Invoked during go list to compute and record staleness. 515 if p := a.Package; p != nil && !p.Stale { 516 p.Stale = true 517 if cfg.BuildA { 518 p.StaleReason = "build -a flag in use" 519 } else { 520 p.StaleReason = "build ID mismatch" 521 for _, p1 := range p.Internal.Imports { 522 if p1.Stale && p1.StaleReason != "" { 523 if strings.HasPrefix(p1.StaleReason, "stale dependency: ") { 524 p.StaleReason = p1.StaleReason 525 break 526 } 527 if strings.HasPrefix(p.StaleReason, "build ID mismatch") { 528 p.StaleReason = "stale dependency: " + p1.ImportPath 529 } 530 } 531 } 532 } 533 } 534 535 // Fall through to update a.buildID from the build artifact cache, 536 // which will affect the computation of buildIDs for targets 537 // higher up in the dependency graph. 538 } 539 540 // Check the build artifact cache. 541 // We treat hits in this cache as being "stale" for the purposes of go list 542 // (in effect, "stale" means whether p.Target is up-to-date), 543 // but we're still happy to use results from the build artifact cache. 544 if c := cache.Default(); c != nil { 545 if !cfg.BuildA { 546 if file, _, err := c.GetFile(actionHash); err == nil { 547 if buildID, err := buildid.ReadFile(file); err == nil { 548 if err := showStdout(b, c, a.actionID, "stdout"); err == nil { 549 a.built = file 550 a.Target = "DO NOT USE - using cache" 551 a.buildID = buildID 552 if p := a.Package; p != nil { 553 // Clearer than explaining that something else is stale. 554 p.StaleReason = "not installed but available in build cache" 555 } 556 return true 557 } 558 } 559 } 560 } 561 562 // Begin saving output for later writing to cache. 563 a.output = []byte{} 564 } 565 566 return false 567 } 568 569 func showStdout(b *Builder, c *cache.Cache, actionID cache.ActionID, key string) error { 570 stdout, stdoutEntry, err := c.GetBytes(cache.Subkey(actionID, key)) 571 if err != nil { 572 return err 573 } 574 575 if len(stdout) > 0 { 576 if cfg.BuildX || cfg.BuildN { 577 b.Showcmd("", "%s # internal", joinUnambiguously(str.StringList("cat", c.OutputFile(stdoutEntry.OutputID)))) 578 } 579 if !cfg.BuildN { 580 b.Print(string(stdout)) 581 } 582 } 583 return nil 584 } 585 586 // flushOutput flushes the output being queued in a. 587 func (b *Builder) flushOutput(a *Action) { 588 b.Print(string(a.output)) 589 a.output = nil 590 } 591 592 // updateBuildID updates the build ID in the target written by action a. 593 // It requires that useCache was called for action a and returned false, 594 // and that the build was then carried out and given the temporary 595 // a.buildID to record as the build ID in the resulting package or binary. 596 // updateBuildID computes the final content ID and updates the build IDs 597 // in the binary. 598 // 599 // Keep in sync with src/cmd/buildid/buildid.go 600 func (b *Builder) updateBuildID(a *Action, target string, rewrite bool) error { 601 if cfg.BuildX || cfg.BuildN { 602 if rewrite { 603 b.Showcmd("", "%s # internal", joinUnambiguously(str.StringList(base.Tool("buildid"), "-w", target))) 604 } 605 if cfg.BuildN { 606 return nil 607 } 608 } 609 610 // Cache output from compile/link, even if we don't do the rest. 611 if c := cache.Default(); c != nil { 612 switch a.Mode { 613 case "build": 614 c.PutBytes(cache.Subkey(a.actionID, "stdout"), a.output) 615 case "link": 616 // Even though we don't cache the binary, cache the linker text output. 617 // We might notice that an installed binary is up-to-date but still 618 // want to pretend to have run the linker. 619 // Store it under the main package's action ID 620 // to make it easier to find when that's all we have. 621 for _, a1 := range a.Deps { 622 if p1 := a1.Package; p1 != nil && p1.Name == "main" { 623 c.PutBytes(cache.Subkey(a1.actionID, "link-stdout"), a.output) 624 break 625 } 626 } 627 } 628 } 629 630 // Find occurrences of old ID and compute new content-based ID. 631 r, err := os.Open(target) 632 if err != nil { 633 return err 634 } 635 matches, hash, err := buildid.FindAndHash(r, a.buildID, 0) 636 r.Close() 637 if err != nil { 638 return err 639 } 640 newID := a.buildID[:strings.LastIndex(a.buildID, buildIDSeparator)] + buildIDSeparator + hashToString(hash) 641 if len(newID) != len(a.buildID) { 642 return fmt.Errorf("internal error: build ID length mismatch %q vs %q", a.buildID, newID) 643 } 644 645 // Replace with new content-based ID. 646 a.buildID = newID 647 if len(matches) == 0 { 648 // Assume the user specified -buildid= to override what we were going to choose. 649 return nil 650 } 651 652 if rewrite { 653 w, err := os.OpenFile(target, os.O_WRONLY, 0) 654 if err != nil { 655 return err 656 } 657 err = buildid.Rewrite(w, matches, newID) 658 if err != nil { 659 w.Close() 660 return err 661 } 662 if err := w.Close(); err != nil { 663 return err 664 } 665 } 666 667 // Cache package builds, but not binaries (link steps). 668 // The expectation is that binaries are not reused 669 // nearly as often as individual packages, and they're 670 // much larger, so the cache-footprint-to-utility ratio 671 // of binaries is much lower for binaries. 672 // Not caching the link step also makes sure that repeated "go run" at least 673 // always rerun the linker, so that they don't get too fast. 674 // (We don't want people thinking go is a scripting language.) 675 // Note also that if we start caching binaries, then we will 676 // copy the binaries out of the cache to run them, and then 677 // that will mean the go process is itself writing a binary 678 // and then executing it, so we will need to defend against 679 // ETXTBSY problems as discussed in exec.go and golang.org/issue/22220. 680 if c := cache.Default(); c != nil && a.Mode == "build" { 681 r, err := os.Open(target) 682 if err == nil { 683 if a.output == nil { 684 panic("internal error: a.output not set") 685 } 686 outputID, _, err := c.Put(a.actionID, r) 687 r.Close() 688 if err == nil && cfg.BuildX { 689 b.Showcmd("", "%s # internal", joinUnambiguously(str.StringList("cp", target, c.OutputFile(outputID)))) 690 } 691 if b.NeedExport { 692 if err != nil { 693 return err 694 } 695 a.Package.Export = c.OutputFile(outputID) 696 } 697 } 698 } 699 700 return nil 701 }