all: use LLVM=1 for building Linux with clang

This is the standard way now.

Since our configuration permits multiple parameter value combinations,
explicitly check for the compiler and linker that were to be passed via
CC and LD, and replace that with LLVM=1 if they were clang and ld.lld
correspondingly.

Update syz-kconf to rely on pkg/build's exported functionality for
generating Linux kernel build arguments.

3 files changed, 31 insertions, 19 deletions

diff --git a/pkg/build/linux.go b/pkg/build/linux.go
index 47c84c551..daf771e87 100644
--- a/pkg/build/linux.go
+++ b/pkg/build/linux.go
@@ -200,10 +200,17 @@ func LinuxMakeArgs(target *targets.Target, compiler, linker, ccache, buildDir st
 		if ccache != "" {
 			compiler = ccache + " " + compiler
 		}
-		args = append(args, "CC="+compiler)
 	}
-	if linker != "" {
-		args = append(args, "LD="+linker)
+	// The standard way to build Linux with clang is to pass LLVM=1 instead of CC= and LD=.
+	if compiler == targets.DefaultLLVMCompiler && (linker == "" || linker == targets.DefaultLLVMLinker) {
+		args = append(args, "LLVM=1")
+	} else {
+		if compiler != "" {
+			args = append(args, "CC="+compiler)
+		}
+		if linker != "" {
+			args = append(args, "LD="+linker)
+		}
 	}
 	if buildDir != "" {
 		args = append(args, "O="+buildDir)
diff --git a/sys/targets/targets.go b/sys/targets/targets.go
index 2cf001473..50f5c5121 100644
--- a/sys/targets/targets.go
+++ b/sys/targets/targets.go
@@ -881,6 +881,11 @@ func (target *Target) Timeouts(slowdown int) Timeouts {
 	return timeouts
 }
 
+const (
+	DefaultLLVMCompiler = "clang"
+	DefaultLLVMLinker   = "ld.lld"
+)
+
 func (target *Target) setCompiler(clang bool) {
 	// setCompiler may be called effectively twice for target.other,
 	// so first we remove flags the previous call may have added.
@@ -895,9 +900,9 @@ func (target *Target) setCompiler(clang bool) {
 	}
 	target.CFlags = target.CFlags[:pos]
 	if clang {
-		target.CCompiler = "clang"
-		target.KernelCompiler = "clang"
-		target.KernelLinker = "ld.lld"
+		target.CCompiler = DefaultLLVMCompiler
+		target.KernelCompiler = DefaultLLVMCompiler
+		target.KernelLinker = DefaultLLVMLinker
 		if target.Triple != "" {
 			target.CFlags = append(target.CFlags, "--target="+target.Triple)
 		}
diff --git a/tools/syz-kconf/kconf.go b/tools/syz-kconf/kconf.go
index ce39cd66a..9ba2bff06 100644
--- a/tools/syz-kconf/kconf.go
+++ b/tools/syz-kconf/kconf.go
@@ -18,6 +18,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/google/syzkaller/pkg/build"
 	"github.com/google/syzkaller/pkg/kconfig"
 	"github.com/google/syzkaller/pkg/osutil"
 	"github.com/google/syzkaller/pkg/tool"
@@ -444,22 +445,21 @@ clean:
 }
 
 func (ctx *Context) Make(args ...string) error {
-	args = append(args,
-		"O="+ctx.BuildDir,
-		"ARCH="+ctx.Target.KernelArch,
-		"-j", fmt.Sprint(runtime.NumCPU()),
-	)
-	if ctx.Target.Triple != "" {
-		args = append(args, "CROSS_COMPILE="+ctx.Target.Triple+"-")
-	}
+	compiler, linker := "", ""
 	if ctx.Inst.Compiler != "" {
-		args = append(args, "CC="+ctx.replaceVars(ctx.Inst.Compiler))
-	} else if ctx.Target.KernelCompiler != "" {
-		args = append(args, "CC="+ctx.Target.KernelCompiler)
+		compiler = ctx.replaceVars(ctx.Inst.Compiler)
 	}
 	if ctx.Inst.Linker != "" {
-		args = append(args, "LD="+ctx.replaceVars(ctx.Inst.Linker))
-	}
+		linker = ctx.replaceVars(ctx.Inst.Linker)
+	}
+	args = append(args, build.LinuxMakeArgs(
+		ctx.Target,
+		compiler,
+		linker,
+		"", // ccache
+		ctx.BuildDir,
+		runtime.NumCPU(),
+	)...)
 	_, err := osutil.RunCmd(10*time.Minute, ctx.SourceDir, "make", args...)
 	return err
 }