[all-commits] [llvm/llvm-project] 213c90: [win/asan] GetInstructionSize: Fix `41 81 7c ...` ...

bernhardu via All-commits all-commits at lists.llvm.org
Mon Dec 9 09:15:17 PST 2024


  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 213c90d3c1f1517eb7a75ecf834f1faf90c288a8
      https://github.com/llvm/llvm-project/commit/213c90d3c1f1517eb7a75ecf834f1faf90c288a8
  Author: bernhardu <bernhardu at mailbox.org>
  Date:   2024-12-09 (Mon, 09 Dec 2024)

  Changed paths:
    M compiler-rt/lib/interception/interception_win.cpp
    M compiler-rt/lib/interception/tests/interception_win_test.cpp

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

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)
```

There is also a handy tool in llvm to directly feed in the byte sequence
- `41 81 7c` also uses 9 bytes here:
```
$ echo -n -e "0x41, 0x81, 0x7b, 0x73, 0x74, 0x75, 0x76, 0x77, 0x90" | ./llvm/build/bin/llvm-mc --disassemble --show-encoding
        .text
        cmpl    $2004252020, 115(%r11)          # encoding: [0x41,0x81,0x7b,0x73,0x74,0x75,0x76,0x77]
                                        # imm = 0x77767574
        nop                                     # encoding: [0x90]
$ echo -n -e "0x41, 0x81, 0x7c, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x90" | ./llvm/build/bin/llvm-mc --disassemble --show-encoding
        .text
        cmpl    $2021095029, 116(%r11,%rsi,2)   # encoding: [0x41,0x81,0x7c,0x73,0x74,0x75,0x76,0x77,0x78]
                                        # imm = 0x78777675
        nop                                     # encoding: [0x90]
```



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