On Wed, Apr 18, 2018 at 2:09 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> 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:
Yes, this is what I think should be the most appropriate approach.
Uros.
> 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
