Makefile: enable -Wunused-const-variable

See discussion in PR #942.
Extend support for optional flags in sys/targets
as this flag is not supported by gcc 5.
Make flags consistent across Makefile and pkg/csource.

1 files changed, 46 insertions, 19 deletions

diff --git a/sys/targets/targets.go b/sys/targets/targets.go
index b5acb68d7..5c2222808 100644
--- a/sys/targets/targets.go
+++ b/sys/targets/targets.go
@@ -60,7 +60,7 @@ func Get(OS, arch string) *Target {
 		return nil
 	}
 	target.init.Do(func() {
-		checkStaticBuild(target)
+		checkOptionalFlags(target)
 	})
 	return target
 }
@@ -172,13 +172,11 @@ var List = map[string]map[string]*Target{
 	},
 	"freebsd": {
 		"amd64": {
-			PtrSize:     8,
-			PageSize:    4 << 10,
-			CFlags:      []string{"-m64"},
-			CrossCFlags: []string{"-m64", "-static"},
-			NeedSyscallDefine: func(uint64) bool {
-				return false
-			},
+			PtrSize:           8,
+			PageSize:          4 << 10,
+			CFlags:            []string{"-m64"},
+			CrossCFlags:       []string{"-m64", "-static"},
+			NeedSyscallDefine: dontNeedSyscallDefine,
 		},
 	},
 	"netbsd": {
@@ -352,6 +350,22 @@ var oses = map[string]osCommon{
 	},
 }
 
+var (
+	commonCFlags = []string{
+		"-O2",
+		"-pthread",
+		"-Wall",
+		"-Werror",
+		"-Wparentheses",
+		"-Wunused-const-variable",
+		"-Wframe-larger-than=8192",
+	}
+	optionalCFlags = map[string]bool{
+		"-static":                 true, // some distributions don't have static libraries
+		"-Wunused-const-variable": true, // gcc 5 does not support this flag
+	}
+)
+
 func init() {
 	for OS, archs := range List {
 		for arch, target := range archs {
@@ -400,23 +414,36 @@ func initTarget(target *Target, OS, arch string) {
 		target.CCompiler = fmt.Sprintf("cant-build-%v-on-%v", target.OS, runtime.GOOS)
 		target.CPP = target.CCompiler
 	}
+	target.CrossCFlags = append(append([]string{}, commonCFlags...), target.CrossCFlags...)
 }
 
-func checkStaticBuild(target *Target) {
-	for i, flag := range target.CrossCFlags {
-		if flag == "-static" {
-			// Some distributions don't have static libraries.
-			if !supportsStatic(target) {
-				copy(target.CrossCFlags[i:], target.CrossCFlags[i+1:])
-				target.CrossCFlags = target.CrossCFlags[:len(target.CrossCFlags)-1]
-			}
-			break
+func checkOptionalFlags(target *Target) {
+	flags := make(map[string]*bool)
+	var wg sync.WaitGroup
+	for _, flag := range target.CrossCFlags {
+		if !optionalCFlags[flag] {
+			continue
+		}
+		flags[flag] = new(bool)
+		flag, res := flag, flags[flag]
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			*res = checkFlagSupported(target, flag)
+		}()
+	}
+	wg.Wait()
+	for i := 0; i < len(target.CrossCFlags); i++ {
+		if res := flags[target.CrossCFlags[i]]; res != nil && !*res {
+			copy(target.CrossCFlags[i:], target.CrossCFlags[i+1:])
+			target.CrossCFlags = target.CrossCFlags[:len(target.CrossCFlags)-1]
+			i--
 		}
 	}
 }
 
-func supportsStatic(target *Target) bool {
-	cmd := exec.Command(target.CCompiler, "-x", "c", "-", "-o", "/dev/null", "-static")
+func checkFlagSupported(target *Target, flag string) bool {
+	cmd := exec.Command(target.CCompiler, "-x", "c", "-", "-o", "/dev/null", flag)
 	cmd.Stdin = strings.NewReader("int main(){}")
 	return cmd.Run() == nil
 }