prog/target: add fetching function for syz_kfuzztest_run ID

All non-base variants of syz_kfuzztest_run (i.e., those that are
discovered dynamically) are encoded so that they map onto the base
variant which is defined in kfuzztest.txt, and known by the executor.

We add a function for fetching this, that is wrapped in a sync.once
block to avoid repeated iteration over the target's array of syscalls.

Signed-off-by: Ethan Graham <ethangraham@google.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/prog/target.go b/prog/target.go
index 5d35f7803..300a86a32 100644
--- a/prog/target.go
+++ b/prog/target.go
@@ -146,6 +146,10 @@ func (target *Target) lazyInit() {
 	target.initUselessHints()
 	target.initRelatedFields()
 	target.initArch(target)
+	// We ignore the return value here as they are cached, and it makes more
+	// sense to react to them when we attempt to execute a KFuzzTest call.
+	_, _ = target.KFuzzTestRunID()
+
 	// Give these 2 known addresses fixed positions and prepend target-specific ones at the end.
 	target.SpecialPointers = append([]uint64{
 		0x0000000000000000, // NULL pointer (keep this first because code uses special index=0 as NULL)
@@ -531,3 +535,24 @@ func (pg *Builder) Finalize() (*Prog, error) {
 	pg.p = nil
 	return p, nil
 }
+
+var kFuzzTestIDCache struct {
+	sync.Once
+	id  int
+	err error
+}
+
+// KFuzzTestRunID returns the ID for the syz_kfuzztest_run pseudo-syscall,
+// or an error if it is not found in the target.
+func (t *Target) KFuzzTestRunID() (int, error) {
+	kFuzzTestIDCache.Do(func() {
+		for _, call := range t.Syscalls {
+			if call.Attrs.KFuzzTest {
+				kFuzzTestIDCache.id = call.ID
+				return
+			}
+		}
+		kFuzzTestIDCache.err = fmt.Errorf("could not find ID for syz_kfuzztest_run - does it exist?")
+	})
+	return kFuzzTestIDCache.id, kFuzzTestIDCache.err
+}