prog: support conditional fields

pkg/compiler restructures conditional fields in structures into unions,
so we only have to implement the support for unions.

Semantics is as follows:
If a union has conditions, syzkaller picks the first field whose
condition matches. Since we require the last union field to have no
conditions, we can always construct an object.

Changes from this commit aim at ensuring that the selected union fields
always follow the rule above.

1 files changed, 8 insertions, 1 deletions

diff --git a/prog/rand.go b/prog/rand.go
index c7f9053aa..742dbaa7c 100644
--- a/prog/rand.go
+++ b/prog/rand.go
@@ -27,6 +27,7 @@ type randGen struct {
 	*rand.Rand
 	target             *Target
 	inGenerateResource bool
+	inPatchConditional bool
 	recDepth           map[string]int
 }
 
@@ -598,8 +599,9 @@ func (r *randGen) generateParticularCall(s *state, meta *Syscall) (calls []*Call
 	}
 	c := MakeCall(meta, nil)
 	c.Args, calls = r.generateArgs(s, meta.Args, DirIn)
+	moreCalls, _ := r.patchConditionalFields(c, s)
 	r.target.assignSizesCall(c)
-	return append(calls, c)
+	return append(append(calls, moreCalls...), c)
 }
 
 // GenerateAllSyzProg generates a program that contains all pseudo syz_ calls for testing.
@@ -881,6 +883,11 @@ func (a *StructType) generate(r *randGen, s *state, dir Dir) (arg Arg, calls []*
 }
 
 func (a *UnionType) generate(r *randGen, s *state, dir Dir) (arg Arg, calls []*Call) {
+	if a.isConditional() {
+		// Conditions may reference other fields that may not have already
+		// been generated. We'll fill them in later.
+		return a.DefaultArg(dir), nil
+	}
 	index := r.Intn(len(a.Fields))
 	optType, optDir := a.Fields[index].Type, a.Fields[index].Dir(dir)
 	opt, calls := r.generateArg(s, optType, optDir)