cmd/go: drop fips140 build ID hacks

We were trying to keep all binaries stale in fips140 mode
so that every build would write and leave behind a fips.o
in the work directory for use by validating labs.
That breaks various staleness checks, including the one
in cmd/dist during GOFIPS140=latest ./make.bash.

Revert the fips140 hack. Validating labs will still be able
to find the fips.o when building against a clean cache.

Add the default godebug to the link hash though,
so that it is clear that GOFIPS140=latest
and GOFIPS140=off binaries have different hashes.
(The only effect is the default GODEBUG setting.)
They already had different hashes, because the
default GODEBUG ends up in p.Internal.BuildInfo,
and that gets hashed in a "modinfo" line,
but better to be explicit.

Fixes #70873.

Change-Id: I49a38c180208098c2b6720facef48f4e96d44c54
Reviewed-on: https://go-review.googlesource.com/c/go/+/637116
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/go/internal/fips140/fips140.go

@@ -40,14 +40,8 @@
 //
 //	GOFIPS140=latest go build -work my/binary
 //
-// will leave fips.o behind in $WORK/b001. Auditors like to be able to
-// see that file. Accordingly, when [Enabled] returns true,
-// [cmd/go/internal/work.Builder.useCache] arranges never to cache linker
-// output, so that the link step always runs, and fips.o is always left
-// behind in the link step. If this proves too slow, we could always
-// cache fips.o as an extra link output and then restore it when -work is
-// set, but we went a very long time never caching link steps at all, so
-// not caching them in FIPS mode seems perfectly fine.
+// will leave fips.o behind in $WORK/b001
+// (unless the build result is cached, of course).
 //
 // When GOFIPS140 is set to something besides off and latest, [Snapshot]
 // returns true, indicating that the build should replace the latest copy

src/cmd/go/internal/work/buildid.go

@@ -15,7 +15,6 @@ import (
 	"cmd/go/internal/base"
 	"cmd/go/internal/cache"
 	"cmd/go/internal/cfg"
-	"cmd/go/internal/fips140"
 	"cmd/go/internal/fsys"
 	"cmd/go/internal/str"
 	"cmd/internal/buildid"
@@ -447,19 +446,6 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string,
 		a.buildID = actionID + buildIDSeparator + mainpkg.buildID + buildIDSeparator + contentID
 	}
 
-	// In FIPS mode, we disable any link caching,
-	// so that we always leave fips.o in $WORK/b001.
-	// This makes sure that labs validating the FIPS
-	// implementation can always run 'go build -work'
-	// and then find fips.o in $WORK/b001/fips.o.
-	// We could instead also save the fips.o and restore it
-	// to $WORK/b001 from the cache,
-	// but we went years without caching binaries anyway,
-	// so not caching them for FIPS will be fine, at least to start.
-	if a.Mode == "link" && fips140.Enabled() && a.Package != nil && !strings.HasSuffix(a.Package.ImportPath, ".test") {
-		return false
-	}
-
 	// If user requested -a, we force a rebuild, so don't use the cache.
 	if cfg.BuildA {
 		if p := a.Package; p != nil && !p.Stale {
@@ -519,7 +505,7 @@ func (b *Builder) useCache(a *Action, actionHash cache.ActionID, target string,
 				oldBuildID := a.buildID
 				a.buildID = id[1] + buildIDSeparator + id[2]
 				linkID := buildid.HashToString(b.linkActionID(a.triggers[0]))
-				if id[0] == linkID && !fips140.Enabled() {
+				if id[0] == linkID {
 					// Best effort attempt to display output from the compile and link steps.
 					// If it doesn't work, it doesn't work: reusing the cached binary is more
 					// important than reprinting diagnostic information.

src/cmd/go/internal/work/exec.go

@@ -1374,6 +1374,7 @@ func (b *Builder) linkActionID(a *Action) cache.ActionID {
 	fmt.Fprintf(h, "buildmode %s goos %s goarch %s\n", cfg.BuildBuildmode, cfg.Goos, cfg.Goarch)
 	fmt.Fprintf(h, "import %q\n", p.ImportPath)
 	fmt.Fprintf(h, "omitdebug %v standard %v local %v prefix %q\n", p.Internal.OmitDebug, p.Standard, p.Internal.Local, p.Internal.LocalPrefix)
+	fmt.Fprintf(h, "defaultgodebug %q\n", p.DefaultGODEBUG)
 	if cfg.BuildTrimpath {
 		fmt.Fprintln(h, "trimpath")
 	}

src/cmd/go/testdata/script/fips.txt

@@ -20,12 +20,12 @@ go build -x -o x.exe
 go build -x -o x.exe
 ! stderr link
 
-# build with GOFIPS140=latest is NOT cached (need fipso)
+# build with GOFIPS140=latest is cached too
 env GOFIPS140=latest
 go build -x -o x.exe
 stderr link.*-fipso
 go build -x -o x.exe
-stderr link.*-fipso
+! stderr link.*-fipso
 
 # build test with GOFIPS140=off is cached
 env GOFIPS140=off
@@ -41,8 +41,6 @@ stderr link.*-fipso
 go test -x -c
 ! stderr link
 
-
-
 -- go.mod --
 module m
 -- x.go --

src/cmd/go/testdata/script/fipssnap.txt

@@ -47,11 +47,11 @@ stdout crypto/internal/fips140/$snap/sha256
 
 [short] skip
 
-# build with GOFIPS140=snap is NOT cached (need fipso)
+# build with GOFIPS140=snap is cached
 go build -x -o x.exe
 stderr link.*-fipso
 go build -x -o x.exe
-stderr link.*-fipso
+! stderr link.*-fipso
 
 # build test with GOFIPS140=snap is cached
 go test -x -c