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Re: [PATCH 3/5] x86: Add -mfunction-return=
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.
Thanks,
Martin
[1] https://support.google.com/faqs/answer/7625886