On Mon, Jan 8, 2018 at 1:56 AM, Martin Liška <mli...@suse.cz> wrote: > On 01/07/2018 11:59 PM, H.J. Lu wrote: >> Function return thunk is the same as memory thunk for -mindirect-branch= >> where the return address is at the top of the stack: >> >> __x86_return_thunk: >> call L2 >> L1: >> lfence >> jmp L1 >> L2: >> lea 8(%rsp), %rsp|lea 4(%esp), %esp >> ret >> >> and function return becomes >> >> jmp __x86_return_thunk > > Hello. > > Can you please explain more usage of the option? Is to prevent a speculative > execution of 'ret' instruction (which is an indirect call), as described in > [1]? > The paper mentions that return stack predictors are commonly implemented in > some form. > Looks that current version of Linux patches does not use the option. >
This option is requested by Linux kernel people. It may be used in the future. -- H.J.
