On Wed, 29 Jul 2020, H.J. Lu wrote:
> On Wed, Jul 29, 2020 at 4:01 AM Richard Biener
> <richard.guent...@gmail.com> wrote:
> >
> > On Fri, Jul 17, 2020 at 5:32 PM H.J. Lu via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > On Fri, Jul 17, 2020 at 6:27 AM Richard Biener <rguent...@suse.de> wrote:
> > > >
> > > > On Fri, 17 Jul 2020, H.J. Lu wrote:
> > > >
> > > > > On Fri, Jul 17, 2020 at 12:08 AM Richard Biener <rguent...@suse.de>
> > > > > wrote:
> > > > > >
> > > > > > On Wed, 15 Jul 2020, Joseph Myers wrote:
> > > > > >
> > > > > > > On Wed, 15 Jul 2020, Richard Biener wrote:
> > > > > > >
> > > > > > > > But note one of the issues is that when not cross-compiling
> > > > > > > > we're
> > > > > > > > using a single libiberty for target and host objects (likewise
> > > > > > >
> > > > > > > There shouldn't be a target libiberty, since commit
> > > > > > > 8499116aa30a46993deff5acf73985df6b16fb8b (re PR regression/47836
> > > > > > > (Some
> > > > > > > Cross Compiler can't build target-libiberty or target-zlib), Wed
> > > > > > > Jun 22
> > > > > > > 19:40:45 2011 +0000). If something is causing target libiberty
> > > > > > > to be
> > > > > > > built, that's a bug that should be fixed.
> > > > > > >
> > > > > > > > That said, giving configury an idea whether it configures for
> > > > > > > > the host, the target or the build would be required here -
> > > > > > > > Joseph,
> > > > > > > > is there an existing mechanism for example libiberty can use
> > > > > > > > here?
> > > > > > >
> > > > > > > Makefile.def has some settings specific to host or build, e.g.
> > > > > > >
> > > > > > > build_modules= { module= libcpp;
> > > > > > > extra_configure_flags='--disable-nls
> > > > > > > am_cv_func_iconv=no';};
> > > > > > >
> > > > > > > or
> > > > > > >
> > > > > > > host_modules= { module= libiberty; bootstrap=true;
> > > > > > >
> > > > > > > extra_configure_flags='@extra_host_libiberty_configure_flags@';};
> > > > > >
> > > > > > Ah, OK. Looks like we should be able to add a
> > > > > > @extra_target_cet_configure_flags@, funnel that to the
> > > > > > target_modules
> > > > > > and keep CET disabled by default in the modules configury.
> > > > > >
> > > > > > Similarly (if HJ is correct) we'd need to add
> > > > > > @extra_{host,build}_cet_configure_flags@ for the purpose of
> > > > > > lto-plugin
> > > > > > which only has a host module (and for bootstrap host == build, so
> > > > > > it's
> > > > > > shared there but we still have separate libiberties for
> > > > > > host/build...)
> > > > > >
> > > > >
> > > > > We need -fcf-protection only on object files which will be dlopened on
> > > > > CET enabled build and host.
> > > >
> > > > Why is there a distinction between dlopen and execution? IIRC
> > > > ld falls back to non-CET operation when dlopening a non-CET shared
> > > > object?
> > >
> > > BTW, ld.so refuses to dlopen a legacy shared object after CET has been
> > > enabled.
> > > This behavior can be controlled when configuring glibc:
> > >
> > > '--enable-cet'
> > > '--enable-cet=permissive'
> > > Enable Intel Control-flow Enforcement Technology (CET) support.
> > > When the GNU C Library is built with '--enable-cet' or
> > > '--enable-cet=permissive', the resulting library is protected with
> > > indirect branch tracking (IBT) and shadow stack (SHSTK). When CET
> > > is enabled, the GNU C Library is compatible with all existing
> > > executables and shared libraries. This feature is currently
> > > supported on i386, x86_64 and x32 with GCC 8 and binutils 2.29 or
> > > later. Note that when CET is enabled, the GNU C Library requires
> > > CPUs capable of multi-byte NOPs, like x86-64 processors as well as
> > > Intel Pentium Pro or newer. With '--enable-cet', it is an error to
> > > dlopen a non CET enabled shared library in CET enabled application.
> > > With '--enable-cet=permissive', CET is disabled when dlopening a
> > > non CET enabled shared library in CET enabled application.
> >
> > So getting back to this one of the issues is that --enable-cet is used
> > for both GCC_CET_FLAGS and GCC_CET_HOST_FLAGS where
> > for the host flag part I'd use --enable-cet=auto but for the target library
> > part I definitely want to know if --enable-cet cannot be honored.
> >
> > Your current patch would still prohibit a non-bootstrap build with a host
> > compiler not supporting CET and requesting CET enabled target libraries,
> > thus
> >
> > ../configure --enable-cet --disable-bootstrap
> >
> > would fail. Shouldn't we - for the host part - simply treat 'yes' equal
> > to 'auto'? If not, then we should have --enable-cet-host. Which would
> > be somewhat misleading since cc1 isn't built CET enabled, just
> > lto-plugin.so is, so better --enable-lto-plugin-cet?
> >
> > Thus I'd go with the simpler of both:
> >
> > diff --git a/config/cet.m4 b/config/cet.m4
> > index d9608699cd5..fb4e4275413 100644
> > --- a/config/cet.m4
> > +++ b/config/cet.m4
> > @@ -64,7 +64,7 @@ case "$host" in
> > save_CFLAGS="$CFLAGS"
> > CFLAGS="$CFLAGS -fcf-protection"
> > case "$enable_cet" in
> > - auto)
> > + auto|yes)
> > # Check if target supports multi-byte NOPs
> > # and if assembler supports CET insn.
> > AC_COMPILE_IFELSE(
> > @@ -80,15 +80,6 @@ asm ("setssbsy");
> > [enable_cet=yes],
> > [enable_cet=no])
> > ;;
> > - yes)
> > - # Check if assembler supports CET.
> > - AC_COMPILE_IFELSE(
> > - [AC_LANG_PROGRAM(
> > - [],
> > - [asm ("setssbsy");])],
> > - [],
> > - [AC_MSG_ERROR([assembler with CET support is required for
> > --enable-cet])])
> > - ;;
> > esac
> > CFLAGS="$save_CFLAGS"
> > ;;
> >
> > is that OK with you?
> >
>
> How about this one instead?
It still has
+ && (test ! -f ../stage_current \
+ || test `cat ../stage_current` != "stage1"); then
which I find ugly since it depends on directory layout.
Thinking about the LTO plugin issue again I wonder in which case
we end up using the stage1 lto-plugin? Shouldn't stage2-gcc
use the stage2 lto-plugin which should pass the CET test? Thus,
a extra_stage1_configure_flags=--disable-cet for the libiberty
and lto-plugin modules should work, too, with Makefile.tpl
getting taught about this via
[+ IF extra_stage[+id+]_configure_flags +] \
[+extra_stage[+id+]_configure_flags+][+ ENDIF
extra_stage[+id+]_configure_flags +]
where it hopefully supports nested [+ +], otherwise some
IF id == 1 and expanding [+extra_stage1_configure_flags+] only.
For the non-bootstrap case there's another place where
extra_configure_flags is expanded which we might run into
with --disable-bootstrap (not sure).
The other idea was to make sth like POSTSTAGE1 available
in the environment so your test above can check for that
instead. There's already POSTSTAGE1_FLAGS_TO_PAS and
STAGE1_FLAGS_TO_PASS (extra arguments to make), adding
POSTSTAGE1=1 to POSTSTAGE1_FLAGS_TO_PASS might be enough.
Richard.
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
