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. Uros.
