[SOLVED] Assembler xbegin raise Illegal instruction

Assembler xbegin raise Illegal instruction

My assembly code raises Illegal Instruction when calls xbegin.

Is there any problem?

Here is my code.

main.c

if ( rtm_begin() == 0 ) {
    //do something.
}

rtm.S

rtm_begin:   
   xbegin 1f   
   mov $0, %rax      
   retq

1:
   mov $-1, %rax
   retq

   .globl rtm_end
   .type rtm_end, @function
   .section .text

Solution

First you need to check whether your version of assembler supports the TSX instructions or not.

Then it could be that your CPU doesn't have TSX feature. As per Intel® 64 and IA-32 architectures software developer’s manual, ch.16.3.1.2 Detection of RTM Support:

A processor supports RTM execution if CPUID.07H.EBX.RTM [bit 11] = 1. An application must check if the processor supports RTM before it uses the RTM instructions (XBEGI N, XEND, XABORT). These instructions will generate a #UD exception when used on a processor that does not support RTM.

Also to mitigate Zombieload 2 vulnerability, TSX could be disabled by the OS (related info for Windows, for Linux)