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cmd/go: ignore -linkmode=external during cmd/cgo build

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cmd/cgo is special among the build tools because it is (re)built on demand
when needed for a package using cgo, to avoid additional bootstrap logic
elsewhere. (This is in contrast to cmd/compile, cmd/link, and so on, which
must be specially built before even invoking the go command.)

When the go command starts using content-based decisions about staleness,
it is important that the build of cmd/cgo never use -linkmode=external,
because that depends on runtime/cgo, which in turn depends on cmd/cgo.

Change-Id: I72a2be748606d1ed4b93a54f2a5c7084e87d5fbc
Reviewed-on: https://go-review.googlesource.com/67310
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Russ Cox 2017-07-16 13:42:12 -04:00
parent 3cdf6100f1
commit b78bce08e3
1 changed files with 33 additions and 1 deletions
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34
src/cmd/go/internal/work/build.go
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@ -2573,12 +2573,23 @@ func (gcToolchain) ld(b *Builder, root *Action, out, importcfg string, allaction
} else {
compiler = envList("CC", cfg.DefaultCC)
}
ldflags = setextld(ldflags, compiler)
ldflags = append(ldflags, "-buildmode="+ldBuildmode)
if root.Package.Internal.BuildID != "" {
ldflags = append(ldflags, "-buildid="+root.Package.Internal.BuildID)
}
ldflags = append(ldflags, cfg.BuildLdflags...)
if root.Package.Goroot {
// Cannot force -linkmode=external inside GOROOT.
// cmd/cgo cannot be linkmode=external,
// because that implies having runtime/cgo available,
// and runtime/cgo is built using cmd/cgo.
// It's possible the restriction can be limited to just cmd/cgo,
// but the whole-GOROOT prohibition matches the similar
// logic in ../load/pkg.go that decides whether to add an
// implicit runtime/cgo dependency.
ldflags = removeLinkmodeExternal(ldflags)
}
ldflags = setextld(ldflags, compiler)
// On OS X when using external linking to build a shared library,
// the argument passed here to -o ends up recorded in the final
@ -2595,6 +2606,27 @@ func (gcToolchain) ld(b *Builder, root *Action, out, importcfg string, allaction
return b.run(dir, root.Package.ImportPath, nil, cfg.BuildToolexec, base.Tool("link"), "-o", out, "-importcfg", importcfg, ldflags, mainpkg)
}
// removeLinkmodeExternal removes any attempt to set linkmode=external
// from ldflags, modifies ldflags in place, and returns ldflags.
func removeLinkmodeExternal(ldflags []string) []string {
out := ldflags[:0]
for i := 0; i < len(ldflags); i++ {
flag := ldflags[i]
if strings.HasPrefix(flag, "--") {
flag = flag[1:]
}
if flag == "-linkmode" && i+1 < len(ldflags) && ldflags[i+1] == "external" {
i++
continue
}
if flag == "-linkmode=external" {
continue
}
out = append(out, flag)
}
return out
}
func (gcToolchain) ldShared(b *Builder, toplevelactions []*Action, out, importcfg string, allactions []*Action) error {
ldflags := []string{"-installsuffix", cfg.BuildContext.InstallSuffix}
ldflags = append(ldflags, "-buildmode=shared")