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// Package clang implements a simple wrapper for invoking clang to
// compile C to eBPF
package clang
import (
"fmt"
"io/ioutil"
"os"
"os/exec"
"path/filepath"
"strings"
"github.com/pkg/errors"
)
// CompileOpts configure how an XDP program is compiled / built
type Opts struct {
// clang binary to use
Clang string
// Header directories to include
Include []string
// Destination directory for compiled programs.
// Uses a temporary directory if empty.
Output string
// Emit DWARF debug info in the XDP elf.
// Required for BTF.
EmitDebug bool
}
// Compile compiles a C source string into an ELF
func Compile(source []byte, name string, opts Opts) ([]byte, error) {
var err error
outdir := opts.Output
if outdir == "" {
outdir, err = ioutil.TempDir("", "cbpfc-clang")
if err != nil {
return nil, errors.Wrap(err, "can't create output directory")
}
defer os.RemoveAll(outdir)
} else {
_ = os.Mkdir(outdir, 0755)
}
inputFile := fmt.Sprintf("%s.c", name)
outputFile := fmt.Sprintf("%s.elf", name)
err = ioutil.WriteFile(filepath.Join(outdir, inputFile), source, 0644)
if err != nil {
return nil, errors.Wrap(err, "can't write out program")
}
flags := []string{
"-O2",
"-Wall", "-Werror",
"-nostdinc",
"-c",
"-target", "bpf",
inputFile,
"-o", outputFile,
}
for _, include := range opts.Include {
// debug build script will be in a different directory, relative imports won't work
absInclude, err := filepath.Abs(include)
if err != nil {
return nil, errors.Wrapf(err, "can't get absolute path to include %s", include)
}
flags = append(flags, "-I", absInclude)
}
if opts.EmitDebug {
flags = append(flags, "-g")
}
cmd := exec.Command(opts.Clang, flags...)
// debug build script
if opts.Output != "" {
cmdline := cmd.Path + " " + strings.Join(flags, " ") + "\n"
err := ioutil.WriteFile(filepath.Join(outdir, "build"), []byte(cmdline), 0644)
if err != nil {
return nil, errors.Wrap(err, "can't write build cmdline")
}
}
cmd.Dir = outdir
_, err = cmd.Output()
if err != nil {
switch e := err.(type) {
case *exec.ExitError:
return nil, errors.Wrapf(e, "unable to compile C:\n%s", string(e.Stderr))
default:
return nil, errors.Wrapf(e, "unable to compile C")
}
}
elf, err := ioutil.ReadFile(filepath.Join(outdir, outputFile))
if err != nil {
return nil, errors.Wrap(err, "can't read ELF")
}
return elf, nil
}
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