On Wed, 17 Jun 2020, H.J. Lu wrote:
> On Wed, Jun 17, 2020 at 1:59 AM Richard Biener
> <richard.guent...@gmail.com> wrote:
> >
> > On Mon, Jun 15, 2020 at 5:30 PM Matthias Klose <d...@ubuntu.com> wrote:
> > >
> > > PR lto/95604 was seen when checking for binaries without having CET
> > > support in a
> > > distro archive, for binaries built with LTO optimization. The hardening
> > > flag
> > > -fcf-protection=full is passed in CFLAGS, and maybe should be passed in
> > > LDFLAGS
> > > as well. However to make it work when not passed to the link step, it
> > > should be
> > > extracted from the options found in the lto opts section.
> > >
> > > Richard suggested two solutions offline. I checked that both fix the
> > > test case.
> > > Which one to install? Also ok for the 9 and 10 branches?
> >
> > I guess even though variant two is simpler it doesn't make much sense to
> > have differing settings of -fcf-protection between different functions? HJ?
>
> -fcf-protection is applied to a file, not a function since CET marker
> is per file.
>
> > So looking at variant one,
> >
> > @@ -287,6 +287,18 @@
> > foption->orig_option_with_args_text);
> > break;
> >
> > + case OPT_fcf_protection_:
> > + /* Append or check identical. */
> > + for (j = 0; j < *decoded_options_count; ++j)
> > + if ((*decoded_options)[j].opt_index == foption->opt_index)
> > + break;
> > + if (j == *decoded_options_count)
> > + append_option (decoded_options, decoded_options_count, foption);
> > + else if (strcmp ((*decoded_options)[j].arg, foption->arg))
> > + warning (input_location, "option %s with different values",
> > + foption->orig_option_with_args_text);
> > + break;
> >
> > you are always streaming a -fcf-protection option so the if (j ==
> > *decoded_options_count)
> > case shouldn't ever happen but I guess it's safe to leave the code
> > as-is. Can you
> > amend the warning with the option that prevails? Maybe
> >
> > + else if (strcmp ((*decoded_options)[j].arg, foption->arg))
> > {
> > static bool noted;
> > + warning (input_location, "option %s with different values",
> > + foption->orig_option_with_args_text);
> > if (!noted)
> > {
> > inform ("%s will be used instead",
> > (*decoded_options)[j].orig_option_with_args_text);
> > noted = true;
> > }
> >
> > I guess input_location is simply zero so the diagnostic doesn't
> > contain the actual file we're
> > looking at. Something to improve I guess (also applyign to other
> > diagnostics we emit).
> >
> > Otherwise looks OK.
> >
> > Please wait for HJ in case he'd like to go with option two.
> >
>
> I prefer option one. But what happens if input files are compiled
> with different -fcf-protection settings?
You get a warning and the first option setting wins (and I requested
to inform the user which that is).
Richard.
