syz-ci: clean kernel dir before patch test build

This leads to false errors when we are switching between gcc and clang:

kernel build failed: failed to run /usr/bin/make [make bzImage -j 32 CC=/syzkaller/clang-kmsan/bin/clang]: exit status 2
arch/x86/Makefile:184: *** Compiler lacks asm-goto support..  Stop.

Fixes #568

2 files changed, 15 insertions, 0 deletions

diff --git a/pkg/kernel/kernel.go b/pkg/kernel/kernel.go
index f1bdcdc83..7fe3ef6d8 100644
--- a/pkg/kernel/kernel.go
+++ b/pkg/kernel/kernel.go
@@ -52,6 +52,18 @@ func Build(dir, compiler, config string) error {
 	return err
 }
 
+func Clean(dir string) error {
+	cmd := osutil.Command("make", "distclean")
+	if err := osutil.Sandbox(cmd, true, true); err != nil {
+		return err
+	}
+	cmd.Dir = dir
+	if _, err := osutil.Run(10*time.Minute, cmd); err != nil {
+		return err
+	}
+	return nil
+}
+
 // CreateImage creates a disk image that is suitable for syzkaller.
 // Kernel is taken from kernelDir, userspace system is taken from userspaceDir.
 // If cmdlineFile is not empty, contents of the file are appended to the kernel command line.
diff --git a/syz-ci/jobs.go b/syz-ci/jobs.go
index 68d69010f..42f8e585a 100644
--- a/syz-ci/jobs.go
+++ b/syz-ci/jobs.go
@@ -228,6 +228,9 @@ func (jp *JobProcessor) buildImage(job *Job) error {
 	resp.Build.KernelCommitTitle = kernelCommit.Title
 	resp.Build.KernelCommitDate = kernelCommit.Date
 
+	if err := kernel.Clean(kernelDir); err != nil {
+		return fmt.Errorf("kernel clean failed: %v", err)
+	}
 	if err := git.Patch(kernelDir, req.Patch); err != nil {
 		return err
 	}