FindBLX option on ReplaceBytes and ReplaceBytesNOP

pgaskin · Dec 15, 2018 · aec39b9 · aec39b9
1 parent 5e654ef
commit aec39b9
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Showing 3 changed files with 25 additions and 4 deletions.
diff --git a/patchfile/kobopatch/kobopatch.go b/patchfile/kobopatch/kobopatch.go
@@ -49,13 +49,15 @@ type instruction struct {
 		Offset   int32   `yaml:"Offset,omitempty"`
 		FindH    *string `yaml:"FindH,omitempty"`
 		ReplaceH *string `yaml:"ReplaceH,omitempty"`
+		FindBLX  *uint32 `yaml:"FindBLX,omitempty"`
 		Find     []byte  `yaml:"Find,omitempty"`
 		Replace  []byte  `yaml:"Replace,omitempty"`
 	} `yaml:"ReplaceBytes,omitempty"`
 	ReplaceBytesNOP *struct {
-		Offset int32   `yaml:"Offset,omitempty"`
-		FindH  *string `yaml:"FindH,omitempty"`
-		Find   []byte  `yaml:"Find,omitempty"`
+		Offset  int32   `yaml:"Offset,omitempty"`
+		FindH   *string `yaml:"FindH,omitempty"`
+		FindBLX *uint32 `yaml:"FindBLX,omitempty"`
+		Find    []byte  `yaml:"Find,omitempty"`
 	} `yaml:"ReplaceBytesNOP,omitempty"`
 	ReplaceZlib *struct {
 		Offset  int32  `yaml:"Offset,omitempty"`
@@ -340,10 +342,18 @@ func (ps *PatchSet) ApplyTo(pt *patchlib.Patcher) error {
 				err = pt.FindBaseAddressString(*i.FindBaseAddressString)
 			case i.ReplaceBytes != nil:
 				r := *i.ReplaceBytes
+				if r.FindBLX != nil {
+					r.Find = patchlib.BLX(uint32(pt.GetCur()+r.Offset), *r.FindBLX)
+					patchfile.Log("  ReplaceBytes.FindBLX -> Set ReplaceBytes.Find to BLX(0x%X, 0x%X) -> %X", pt.GetCur()+r.Offset, *r.FindBLX, r.Find)
+				}
 				patchfile.Log("  ReplaceBytes(%#v, %#v, %#v)\n", r.Offset, r.Find, r.Replace)
 				err = pt.ReplaceBytes(r.Offset, r.Find, r.Replace)
 			case i.ReplaceBytesNOP != nil:
 				r := *i.ReplaceBytesNOP
+				if r.FindBLX != nil {
+					r.Find = patchlib.BLX(uint32(pt.GetCur()+r.Offset), *r.FindBLX)
+					patchfile.Log("  ReplaceBytesNOP.FindBLX -> Set ReplaceBytesNOP.Find to BLX(0x%X, 0x%X) -> %X", pt.GetCur()+r.Offset, *r.FindBLX, r.Find)
+				}
 				patchfile.Log("  ReplaceBytesNOP(%#v, %#v)\n", r.Offset, r.Find)
 				err = pt.ReplaceBytesNOP(r.Offset, r.Find)
 			case i.ReplaceFloat != nil:

diff --git a/patchlib/blx.go b/patchlib/blx.go
@@ -33,6 +33,12 @@ func blx(pc, target uint32) uint32 {
 	return uint32(top)<<16 | uint32(bot)
 }
 
+// BLX assembles a BLX instruction and returns a byte slice which
+// can be patched directly into a binary.
+func BLX(pc, target uint32) []byte {
+	return mustBytes(toBEBin(blx(pc, target)))
+}
+
 func swapBytes(word uint16) uint16 {
 	a, b := word&0x00ff, word&0xff00
 	return a<<8 | b>>8

diff --git a/patchlib/patcher.go b/patchlib/patcher.go
@@ -309,7 +309,7 @@ func (p *Patcher) ReplaceBLX(offset int32, find, replace uint32) error {
 	if int32(len(p.buf)) < p.cur+offset {
 		return errors.New("offset past end of buf")
 	}
-	fi, ri := blx(uint32(p.cur+offset), find), blx(uint32(p.cur+offset), replace)
+	fi, ri := BLX(uint32(p.cur+offset), find), BLX(uint32(p.cur+offset), replace)
 	f, r := mustBytes(toBEBin(fi)), mustBytes(toBEBin(ri))
 	if len(f) != len(r) {
 		return errors.New("internal error: wrong blx length")
@@ -340,6 +340,11 @@ func (p *Patcher) ReplaceBytesNOP(offset int32, find []byte) error {
 	return nil
 }
 
+// GetCur gets the current base address.
+func (p *Patcher) GetCur() int32 {
+	return p.cur
+}
+
 // replaceValue encodes find and replace as little-endian binary and replaces the first
 // occurrence starting at cur. The lengths of the encoded find and replace must be the
 // same, or an error will be returned.