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x86 BEXTR semantic bug
Description of problem
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.
Steps to reproduce
Compile this code
void main() {
asm("mov rax, 0x17b3693f77fb6e9");
asm("mov rbx, 0x8f635a775ad3b9b4");
asm("mov rcx, 0xb717b75da9983018");
asm("bextr eax, ebx, ecx");
}
Execute and compare the result with the CPU.
CPU
RAX = 0x5a
QEMU
RAX = 0x635a775a
Additional information
This bug is discovered by research conducted by KAIST SoftSec.
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