targets: syz-extract: add Clang support for Linux builds

Allow targets.go use Clang instead of the default Linux compiler by
setting the SYZ_CLANG=1 env var. Doing so changes the compiler to
"clang" and the linker to "ld.ldd", assuming they are in $PATH, and adds
the --target and -ferror-limit CFLAGS.

Target also exports KernelCompiler and KernelLinker fields now, which allows
overriding the compiler and linker in the kernel make invocation.

Signed-off-by: Alexander Potapenko <glider@google.com>

2 files changed, 18 insertions, 0 deletions

diff --git a/sys/syz-extract/linux.go b/sys/syz-extract/linux.go
index 5eca07daf..29d99d1de 100644
--- a/sys/syz-extract/linux.go
+++ b/sys/syz-extract/linux.go
@@ -96,6 +96,12 @@ func (*linux) prepareArch(arch *Arch) error {
 	if target.Triple != "" {
 		makeArgs = append(makeArgs, "CROSS_COMPILE="+target.Triple+"-")
 	}
+	if target.KernelCompiler != "" {
+		makeArgs = append(makeArgs, "CC="+target.KernelCompiler)
+	}
+	if target.KernelLinker != "" {
+		makeArgs = append(makeArgs, "LD="+target.KernelLinker)
+	}
 	out, err := osutil.RunCmd(time.Hour, kernelDir, "make", append(makeArgs, "defconfig")...)
 	if err != nil {
 		return fmt.Errorf("make defconfig failed: %v\n%s", err, out)
diff --git a/sys/targets/targets.go b/sys/targets/targets.go
index 1395b13ff..0bcba8a21 100644
--- a/sys/targets/targets.go
+++ b/sys/targets/targets.go
@@ -26,6 +26,8 @@ type Target struct {
 	CFlags           []string
 	Triple           string
 	CCompiler        string
+	KernelCompiler   string // override CC when running kernel make
+	KernelLinker     string // override LD when running kernel make
 	KernelArch       string
 	KernelHeaderArch string
 	BrokenCompiler   string
@@ -466,6 +468,15 @@ func initTarget(target *Target, OS, arch string) {
 			target.CCompiler = target.Triple + "-" + target.CCompiler
 		}
 	}
+	if useClang {
+		target.CCompiler = "clang"
+		target.KernelCompiler = "clang"
+		target.KernelLinker = "ld.lld"
+		if target.Triple != "" {
+			target.CFlags = append(target.CFlags, "--target="+target.Triple)
+		}
+		target.CFlags = append(target.CFlags, "-ferror-limit=0")
+	}
 	if target.CPP == "" {
 		target.CPP = "cpp"
 	}
@@ -541,6 +552,7 @@ func checkFlagSupported(target *Target, flag string) bool {
 }
 
 var runningOnCI = os.Getenv("CI") != ""
+var useClang = os.Getenv("SYZ_CLANG") != ""
 
 // <algorithm> is included by executor, so we test is as well.
 const simpleProg = `