Re: [PATCH 10/11] x86 - add speculation_barrier pattern
On Sat, Jul 28, 2018 at 1:25 AM, Uros Bizjak wrote: > On Fri, Jul 27, 2018 at 11:37 AM, Richard Earnshaw > wrote: >> >> This patch adds a speculation barrier for x86, based on my >> understanding of the required mitigation for that CPU, which is to use >> an lfence instruction. >> >> This patch needs some review by an x86 expert and if adjustments are >> needed, I'd appreciate it if they could be picked up by the port >> maintainer. This is supposed to serve as an example of how to deploy >> the new __builtin_speculation_safe_value() intrinsic on this >> architecture. >> >> * config/i386/i386.md (unspecv): Add UNSPECV_SPECULATION_BARRIER. >> (speculation_barrier): New insn. > > The implementation is OK, but someone from Intel (CC'd) should clarify > if lfence is the correct insn. > I checked with our people. lfence is OK. Thanks. -- H.J.
Re: [PATCH 10/11] x86 - add speculation_barrier pattern
On Fri, Jul 27, 2018 at 11:37 AM, Richard Earnshaw wrote: > > This patch adds a speculation barrier for x86, based on my > understanding of the required mitigation for that CPU, which is to use > an lfence instruction. > > This patch needs some review by an x86 expert and if adjustments are > needed, I'd appreciate it if they could be picked up by the port > maintainer. This is supposed to serve as an example of how to deploy > the new __builtin_speculation_safe_value() intrinsic on this > architecture. > > * config/i386/i386.md (unspecv): Add UNSPECV_SPECULATION_BARRIER. > (speculation_barrier): New insn. The implementation is OK, but someone from Intel (CC'd) should clarify if lfence is the correct insn. Uros.
[PATCH 10/11] x86 - add speculation_barrier pattern
This patch adds a speculation barrier for x86, based on my understanding of the required mitigation for that CPU, which is to use an lfence instruction. This patch needs some review by an x86 expert and if adjustments are needed, I'd appreciate it if they could be picked up by the port maintainer. This is supposed to serve as an example of how to deploy the new __builtin_speculation_safe_value() intrinsic on this architecture. * config/i386/i386.md (unspecv): Add UNSPECV_SPECULATION_BARRIER. (speculation_barrier): New insn. --- gcc/config/i386/i386.md | 10 ++ 1 file changed, 10 insertions(+) diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md index 559ad93..73948c1 100644 --- a/gcc/config/i386/i386.md +++ b/gcc/config/i386/i386.md @@ -301,6 +301,9 @@ (define_c_enum "unspecv" [ ;; For CLDEMOTE support UNSPECV_CLDEMOTE + + ;; For Speculation Barrier support + UNSPECV_SPECULATION_BARRIER ]) ;; Constants to represent rounding modes in the ROUND instruction @@ -20979,6 +20982,13 @@ (define_insn "cldemote" [(set_attr "type" "other") (set_attr "memory" "unknown")]) +(define_insn "speculation_barrier" + [(unspec_volatile [(const_int 0)] UNSPECV_SPECULATION_BARRIER)] + "" + "lfence" + [(set_attr "type" "other") + (set_attr "length" "3")]) + (include "mmx.md") (include "sse.md") (include "sync.md")
