id = 2175
title = "Intel BLSI CF computation bug"
state = "closed"
created_at = "2024-02-19T05:00:51.360Z"
closed_at = "2024-08-21T05:08:10.856Z"
labels = ["Closed::Fixed", "accel: TCG", "target: i386"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/2175"
host-os = "Ubuntu 23.10"
host-arch = "x86_64"
qemu-version = "qemu-x86_64 version 8.2.1"
guest-os = "None"
guest-arch = "x86_64"
description = """CF flag computation of BLSI instruction is wrong. It seems #1370 was not completely fixed."""
reproduce = """1. Compile `example.c` using this command: `gcc -o example.bin example.c`. My gcc version is 12.3.0, but other versions may work.
```
int main() {
  __asm__ (
    "movq $0x1, %r8\\n"
    "mov $0xedbf530a, %r9\\n"
    "push $0x1\\n"
    "popf\\n"
    "blsi %r9d, %r8d\\n"
    "pushf\\n"
    "pop %rax\\n"
    "pop %rbp\\n"
    "ret\\n"
  );

  return 0;
}
```
2. Run `./example.bin`. Then check the return code using `echo $?`. It should be 3.
```
$ ./example.bin
$ echo $?
3
```
3. Run `./qemu-x86_64 ./example.bin`. Then check the return code using `echo $?`. It should be 2.
```
$ ./qemu-x86_64 ./example.bin
$ echo $?
2
```

The return code of `./example.bin` contains the value of the `RFLAGS` register after executing the `BLSI` instruction."""
additional = """"""