[Bug target/84145] New: Wrong CET options processing

[igor.v.tsimbalist at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84145

            Bug ID: 84145
           Summary: Wrong CET options processing
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: igor.v.tsimbalist at intel dot com
  Target Milestone: ---

The gcc error message for not passing -mibt/-mshstk with -fcf-protection seems
confusing. It looks like it just checks that one of the options is present and
doesn’t check that it’s the option that is required by the protection
requested. So it's possible to do -fcf-protection=branch -mshstk and not get an
error, but not get any protection either.

Here is this part:

      if (!(TARGET_IBT_P (opts->x_ix86_isa_flags2)
            || TARGET_SHSTK_P (opts->x_ix86_isa_flags)))
        {
          if (flag_cf_protection == CF_FULL)
            {
              error ("%<-fcf-protection=full%> requires CET support "
                     "on this target. Use -mcet or one of -mibt, "
                     "-mshstk options to enable CET");
            }
          else if (flag_cf_protection == CF_BRANCH)
            {
              error ("%<-fcf-protection=branch%> requires CET support "
                     "on this target. Use -mcet or one of -mibt, "
                     "-mshstk options to enable CET");
            }
          else if (flag_cf_protection == CF_RETURN)
            {
              error ("%<-fcf-protection=return%> requires CET support "
                     "on this target. Use -mcet or one of -mibt, "
                     "-mshstk options to enable CET");
            }
          flag_cf_protection = CF_NONE;
          return false;
        }