On Wed, Apr 18, 2018 at 02:04:50PM +0200, Jakub Jelinek wrote:
> On Wed, Apr 18, 2018 at 04:57:41AM -0700, H.J. Lu wrote:
> > On Wed, Apr 18, 2018 at 4:55 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
> > > On Wed, Apr 18, 2018 at 1:39 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
> > >
> > >>>> Here is a patch to add -mnop and use it with -fcf-protection.
> > >>>
> > >>> +mnop
> > >>> +Target Report Var(flag_nop) Init(0)
> > >>> +Support multi-byte NOP code generation.
> > >>>
> > >>> the option name is incredibly bad and the documentation doesn't make it
> > >>> better either. The invoke.texi docs refer to duplicate {-mcet}.
> > >>>
> > >>> Isn't there a -fcf-protection sub-set that can be used to automatically
> > >>> enable this? Or simply do this mode by default when
> > >>> -fcf-protection is used but neither -mcet nor -mibt is enabled?
> > >>
> > >> Make -fcf-protection default to multi-byte NOPs works. Uros,
> > >> should I prepare a patch?
> > >
> > > Please make it an opt-in feature, so the compiler won't litter the
> > > executable with unnecessary nops without user consent.
> > >
> >
> > -fcf-protection is off by default. Users need to pass -fcf-protection
> > to enable it. I will work on such a patch.
>
> That is not true. When building gcc itself, config/cet.m4 makes
> -fcf-protection -mcet the default if assembler supports it.
> The request was to change --enable-cet configure option from having
> yes,no,default arguments with default autodetection and being a default
> if --enable-cet*/--disable-cet is not specified to say
> yes,no,auto arguments where no would be the default and auto would be the
> current default - enable it if as supports it, disable otherwise.
So untested patch would be something like:
2018-04-18 Jakub Jelinek <ja...@redhat.com>
* config/cet.m4 (GCC_CET_FLAGS): Default to --disable-cet, replace
--enable-cet=default with --enable-cet=auto.
* doc/install.texi: Document --disable-cet being the default and
--enable-cet=auto.
--- gcc/config/cet.m4.jj 2018-02-19 19:57:05.221280084 +0100
+++ gcc/config/cet.m4 2018-04-18 14:05:31.514859185 +0200
@@ -3,14 +3,14 @@ dnl GCC_CET_FLAGS
dnl (SHELL-CODE_HANDLER)
dnl
AC_DEFUN([GCC_CET_FLAGS],[dnl
-GCC_ENABLE(cet, default, ,[enable Intel CET in target libraries],
- permit yes|no|default)
+GCC_ENABLE(cet, no, ,[enable Intel CET in target libraries],
+ permit yes|no|auto)
AC_MSG_CHECKING([for CET support])
case "$host" in
i[[34567]]86-*-linux* | x86_64-*-linux*)
case "$enable_cet" in
- default)
+ auto)
# Check if target supports multi-byte NOPs
# and if assembler supports CET insn.
AC_COMPILE_IFELSE(
--- gcc/doc/install.texi.jj 2018-02-08 12:21:20.791749480 +0100
+++ gcc/doc/install.texi 2018-04-18 14:07:19.637901528 +0200
@@ -2103,10 +2103,11 @@ instrumentation, see @option{-fcf-protec
to add @option{-fcf-protection} and, if needed, other target
specific options to a set of building options.
-The option is enabled by default on Linux/x86 if target binutils
-supports @code{Intel CET} instructions. In this case the target
-libraries are configured to get additional @option{-fcf-protection}
-and @option{-mcet} options.
+The option is disabled by default on Linux/x86. When
+@code{--enable-cet=auto} is used, it is enabled if target binutils
+supports @code{Intel CET} instructions and disabled otherwise.
+In this case the target libraries are configured to get additional
+@option{-fcf-protection} and @option{-mcet} options.
@end table
@subheading Cross-Compiler-Specific Options
Jakub
