id = 1372
title = "x86 BEXTR semantic bug"
state = "closed"
created_at = "2022-12-16T06:51:11.166Z"
closed_at = "2023-02-16T13:09:22.647Z"
labels = ["Closed::Fixed", "accel: TCG", "target: i386"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/1372"
host-os = "Windows 10 20H2"
host-arch = "x86"
qemu-version = "7.1.90 (v7.2.0-rc0)"
guest-os = "None"
guest-arch = "x86"
description = """The result of instruction BEXTR is different with from the CPU. The value of destination register is different. I think QEMU does not consider the operand size limit."""
reproduce = """1. Compile this code
```
void main() {
    asm("mov rax, 0x17b3693f77fb6e9");
    asm("mov rbx, 0x8f635a775ad3b9b4");
    asm("mov rcx, 0xb717b75da9983018");
    asm("bextr eax, ebx, ecx");
}
```
2. Execute and compare the result with the CPU.
    - CPU
        - RAX = 0x5a
    - QEMU
        - RAX = 0x635a775a"""
additional = """This bug is discovered by research conducted by KAIST SoftSec."""