From 57799a834f68e87e4e6b19cf024f0803e8e74805 Mon Sep 17 00:00:00 2001
From: Dmitry Vyukov <dvyukov@google.com>
Date: Sat, 30 Jun 2018 13:28:11 +0200
Subject: prog: fix and improve fallback coverage

First we emitted fallbackSignalFlags inside of the loop,
while we need to this outside of the loop.
Second, make flags signal weaker otherwise we get all 256
signals for open, chmod, etc.
Third, simplify and speedup code.
---
 prog/analysis.go | 46 +++++++++++++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 19 deletions(-)

diff --git a/prog/analysis.go b/prog/analysis.go
index bb57ec463..3da9cba01 100644
--- a/prog/analysis.go
+++ b/prog/analysis.go
@@ -9,9 +9,6 @@
 package prog
 
 import (
-	"bytes"
-	"crypto/sha1"
-	"encoding/binary"
 	"fmt"
 )
 
@@ -206,10 +203,11 @@ func (p *Prog) FallbackSignal(info []CallInfo) {
 		})
 		// Specifically look only at top-level arguments,
 		// deeper arguments can produce too much false signal.
-		flags := new(bytes.Buffer)
+		flags := 0
 		for _, arg := range c.Args {
 			switch a := arg.(type) {
 			case *ResultArg:
+				flags <<= 1
 				if a.Res != nil {
 					ctor := resources[a.Res]
 					if ctor != nil {
@@ -217,35 +215,45 @@ func (p *Prog) FallbackSignal(info []CallInfo) {
 							encodeFallbackSignal(fallbackSignalCtor, id, ctor.Meta.ID))
 					}
 				} else {
-					for _, v := range a.Type().(*ResourceType).SpecialValues() {
-						if a.Val == v {
-							binary.Write(flags, binary.LittleEndian, v)
-						}
+					if a.Val != a.Type().(*ResourceType).SpecialValues()[0] {
+						flags |= 1
 					}
 				}
 			case *ConstArg:
+				const width = 3
+				flags <<= width
 				switch typ := a.Type().(type) {
 				case *FlagsType:
-					var mask uint64
-					for _, v := range typ.Vals {
-						mask |= v
+					if typ.BitMask {
+						for i, v := range typ.Vals {
+							if a.Val&v != 0 {
+								flags ^= 1 << (uint(i) % width)
+							}
+						}
+					} else {
+						for i, v := range typ.Vals {
+							if a.Val == v {
+								flags |= i % (1 << width)
+								break
+							}
+						}
 					}
-					binary.Write(flags, binary.LittleEndian, a.Val&mask)
 				case *LenType:
+					flags <<= 1
 					if a.Val == 0 {
-						flags.WriteByte(0x42)
+						flags |= 1
 					}
 				}
 			case *PointerArg:
+				flags <<= 1
 				if a.IsNull() {
-					flags.WriteByte(0x43)
+					flags |= 1
 				}
 			}
-			if flags.Len() != 0 {
-				hash := sha1.Sum(flags.Bytes())
-				inf.Signal = append(inf.Signal,
-					encodeFallbackSignal(fallbackSignalFlags, id, int(hash[0])))
-			}
+		}
+		if flags != 0 {
+			inf.Signal = append(inf.Signal,
+				encodeFallbackSignal(fallbackSignalFlags, id, flags))
 		}
 	}
 }
-- 
cgit mrf-deployment