bpf2go: Allow multiple commands inside BPF2GO_CC

Allow multiple commands to be specified inside BPF2GO_CC. Example:

```
BPF2GO_CC="ccache clang" go generate ../pkg/a/b
```

Signed-off-by: Jordan Rife <[email protected]>

Author: jrife

cmd/bpf2go/gen/compile.go

@@ -7,14 +7,15 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 )
 
 type CompileArgs struct {
 	// Which compiler to use.
 	CC string
 	// Command used to strip DWARF from the ELF.
 	Strip string
-	// Flags to pass to the compiler.
+	// Flags to pass to the compiler. This may contain positional arguments as well.
 	Flags []string
 	// Absolute working directory
 	Workdir string
@@ -27,9 +28,8 @@ type CompileArgs struct {
 	DisableStripping bool
 }
 
-// Compile C to a BPF ELF file.
-func Compile(args CompileArgs) error {
-	// Default cflags that can be overridden by args.cFlags
+func insertDefaultFlags(flags []string) []string {
+	// Default cflags that can be overridden by the user.
 	overrideFlags := []string{
 		// Code needs to be optimized, otherwise the verifier will often fail
 		// to understand it.
@@ -40,7 +40,26 @@ func Compile(args CompileArgs) error {
 		"-mcpu=v1",
 	}
 
-	cmd := exec.Command(args.CC, append(overrideFlags, args.Flags...)...)
+	insert := 0
+
+	// Find the first non-positional argument to support CC commands with
+	// multiple components. E.g.: BPF2GO_CC="ccache clang" ...
+	for ; insert < len(flags); insert++ {
+		if strings.HasPrefix(flags[insert], "-") {
+			break
+		}
+	}
+
+	result := append([]string(nil), flags[:insert]...)
+	result = append(result, overrideFlags...)
+	result = append(result, flags[insert:]...)
+
+	return result
+}
+
+// Compile C to a BPF ELF file.
+func Compile(args CompileArgs) error {
+	cmd := exec.Command(args.CC, insertDefaultFlags(args.Flags)...)
 	cmd.Stderr = os.Stderr
 
 	inputDir := filepath.Dir(args.Source)

cmd/bpf2go/main.go

@@ -155,9 +155,12 @@ func newB2G(stdout io.Writer, args []string) (*bpf2go, error) {
 		return nil, errors.New("missing package, you should either set the go-package flag or the GOPACKAGE env")
 	}
 
-	if b2g.cc == "" {
+	// Allow CC like "ccache clang" to work.
+	ccParts := strings.Fields(b2g.cc)
+	if len(ccParts) == 0 {
 		return nil, errors.New("no compiler specified")
 	}
+	b2g.cc = ccParts[0]
 
 	args, cFlags := splitCFlagsFromArgs(fs.Args())
 
@@ -178,7 +181,7 @@ func newB2G(stdout io.Writer, args []string) (*bpf2go, error) {
 		}
 	}
 
-	b2g.cFlags = cFlags[:len(cFlags):len(cFlags)]
+	b2g.cFlags = append(ccParts[1:], cFlags[:len(cFlags):len(cFlags)]...)
 
 	if len(args) < 2 {
 		return nil, errors.New("expected at least two arguments")