cmd/go: skip writing dwarf debug info for ephemeral binaries

Update issue 6853

For an ephemeral binary - one created, run, and then deleted -
there is no need to write dwarf debug information, since the
binary will not be used with gdb. In this case, instruct the linker
not to spend time and disk space generating the debug information
by passing the -w flag to the linker.

Omitting dwarf information reduces the size of most binaries by 25%.
We may be more aggressive about this in the future.

LGTM=bradfitz, r
R=r, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/65890043

4 files changed, 7 insertions, 0 deletions

diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index 824351b7e..dcc24d99c 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -1714,6 +1714,10 @@ func (gcToolchain) ld(b *builder, p *Package, out string, allactions []*action,
 	if buildContext.InstallSuffix != "" {
 		ldflags = append(ldflags, "-installsuffix", buildContext.InstallSuffix)
 	}
+	if p.omitDWARF {
+		ldflags = append(ldflags, "-w")
+	}
+
 	// If the user has not specified the -extld option, then specify the
 	// appropriate linker. In case of C++ code, use the compiler named
 	// by the CXX environment variable or defaultCXX if CXX is not set.
diff --git a/src/cmd/go/pkg.go b/src/cmd/go/pkg.go
index 0190b6784..3ff386270 100644
--- a/src/cmd/go/pkg.go
+++ b/src/cmd/go/pkg.go
@@ -89,6 +89,7 @@ type Package struct {
 	exeName      string               // desired name for temporary executable
 	coverMode    string               // preprocess Go source files with the coverage tool in this mode
 	coverVars    map[string]*CoverVar // variables created by coverage analysis
+	omitDWARF    bool                 // tell linker not to write DWARF information
 }
 
 // CoverVar holds the name of the generated coverage variables targeting the named file.
diff --git a/src/cmd/go/run.go b/src/cmd/go/run.go
index e6dadd229..8d42622b8 100644
--- a/src/cmd/go/run.go
+++ b/src/cmd/go/run.go
@@ -58,6 +58,7 @@ func runRun(cmd *Command, args []string) {
 	if p.Error != nil {
 		fatalf("%s", p.Error)
 	}
+	p.omitDWARF = true
 	for _, err := range p.DepsErrors {
 		errorf("%s", err)
 	}
diff --git a/src/cmd/go/test.go b/src/cmd/go/test.go
index dcba12e11..26b7f87f4 100644
--- a/src/cmd/go/test.go
+++ b/src/cmd/go/test.go
@@ -654,6 +654,7 @@ func (b *builder) test(p *Package) (buildAction, runAction, printAction *action,
 		pkgdir:     testDir,
 		fake:       true,
 		Stale:      true,
+		omitDWARF:  !testC && !testNeedBinary,
 	}
 	if pxtest != nil {
 		pmain.imports = append(pmain.imports, pxtest)