On Tue, Apr 17, 2018 at 12:25 PM, H.J. Lu <hjl.to...@gmail.com> wrote: > On Tue, Apr 17, 2018 at 12:03 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >> On Tue, Apr 17, 2018 at 11:55 AM, Uros Bizjak <ubiz...@gmail.com> wrote: >>> On Tue, Apr 17, 2018 at 8:42 PM, H.J. Lu <hongjiu...@intel.com> wrote: >>>> -fcf-protection -mcet can't be used with IFUNC features, like symbol >>>> multiversioning or target clone, since IBT/SHSTK are applied to the whole >>>> program and they may be disabled in some functions. But -fcf-protection >>>> is implemented with multi-byte NOPs on all 64-bit processors as well as >>>> 32-bit processors starting with Pentium Pro. If -fcf-protection requires >>>> -mcet, IFUNC features can't be used on Linux when -fcf-protection is >>>> enabled by default. >>>> >>>> This patch changes -fcf-protection to to enable the NOP portion of CET >>>> ISAs unless IBT and/or SHSTK are disabled explicitly. The rest of CET >>>> ISAs, including intrinsics, still requires -mcet, -mibt or -mshstk. >>>> >>>> OK for trunk? >>> >>> As said in the PR, NOP sequences have non-zero cost in the executable >>> (they enlarge the executable), so I don't think this feature should be >>> enabled by default. >>> >>> There is always a configure option if someone wants their compiler to >>> always emit relevant multi-byte nops. >> >> What we need is an option to enable -fcf-function with multi-byte NOPs >> without -mcet which enables the full CET ISAs. A configure option >> without the corresponding the command-line option makes test and >> debug difficult. I can add >> >> --enable-cf-function-nop or --with-cf-function-nop >> >> with >> >> -fct-function-nop >> > > How about adding -mno-cet, which enables the NOP portion of CET
I meant -mnop-cet, not -mno-cet. > ISAs? > > -- > H.J. -- H.J.
