[compiler-rt] [win/asan] GetInstructionSize: Fix `41 81 7c ...` to return 9. (PR #117828)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (bernhardu)

<details>
<summary>Changes</summary>

Trying to populate the recently added test for GetInstructionSize I stumbled over this.
gdb and bddisasm have the opinion this instruction is 9 bytes.
Also lldb shows this:
```
(lldb) disassemble --bytes --start-address 0x0000555555556004 --end-address 0x0000555555556024
    0x555555556004: 41 81 7b 73 74 75 76 77     cmpl   $0x77767574, 0x73(%r11)   ; imm = 0x77767574 
    0x55555555600c: 41 81 7c 73 74 75 76 77 78  cmpl   $0x78777675, 0x74(%r11,%rsi,2) ; imm = 0x78777675 
    0x555555556015: 41 81 7d 73 74 75 76 77     cmpl   $0x77767574, 0x73(%r13)   ; imm = 0x77767574 
    0x55555555601d: 00 00                       addb   %al, (%rax)
```

---
Full diff: https://github.com/llvm/llvm-project/pull/117828.diff


1 Files Affected:

- (modified) compiler-rt/lib/interception/interception_win.cpp (+4-1) 


``````````diff
diff --git a/compiler-rt/lib/interception/interception_win.cpp b/compiler-rt/lib/interception/interception_win.cpp
index 8767d8e79881c2..db9f922ba8b96b 100644
--- a/compiler-rt/lib/interception/interception_win.cpp
+++ b/compiler-rt/lib/interception/interception_win.cpp
@@ -808,7 +808,6 @@ static size_t GetInstructionSize(uptr address, size_t* rel_offset = nullptr) {
     case 0x798141:  // 41 81 79 XX YY YY YY YY : cmp DWORD PTR [r9+YY], XX XX XX XX
     case 0x7a8141:  // 41 81 7a XX YY YY YY YY : cmp DWORD PTR [r10+YY], XX XX XX XX
     case 0x7b8141:  // 41 81 7b XX YY YY YY YY : cmp DWORD PTR [r11+YY], XX XX XX XX
-    case 0x7c8141:  // 41 81 7c XX YY YY YY YY : cmp DWORD PTR [r12+YY], XX XX XX XX
     case 0x7d8141:  // 41 81 7d XX YY YY YY YY : cmp DWORD PTR [r13+YY], XX XX XX XX
     case 0x7e8141:  // 41 81 7e XX YY YY YY YY : cmp DWORD PTR [r14+YY], XX XX XX XX
     case 0x7f8141:  // 41 81 7f YY XX XX XX XX : cmp DWORD PTR [r15+YY], XX XX XX XX
@@ -835,6 +834,10 @@ static size_t GetInstructionSize(uptr address, size_t* rel_offset = nullptr) {
     case 0x2444c7:    // C7 44 24 XX YY YY YY YY
                       //   mov dword ptr [rsp + XX], YYYYYYYY
       return 8;
+
+    case 0x7c8141:  // 41 81 7c ZZ YY XX XX XX XX
+                    // cmp DWORD PTR [reg+reg*n+YY], XX XX XX XX
+      return 9;
   }
 
   switch (*(u32*)(address)) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/117828