On Wed, May 18, 2022 at 11:02 PM Richard Biener
<richard.guent...@gmail.com> wrote:
>
> On Wed, May 18, 2022 at 7:32 PM H.J. Lu via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Wed, May 11, 2022 at 1:52 PM H.J. Lu <hjl.to...@gmail.com> wrote:
> > >
> > > When -fcf-protection=branch is used, the compiler will generate jump
> > > tables for switch statements where the indirect jump is prefixed with
> > > the NOTRACK prefix, so it can jump to non-ENDBR targets. Since the
> > > indirect jump targets are generated by the compiler, they are always
> > > valid.
> > >
> > > Document -mcet-switch to generate jump tables for switch statements with
> > > ENDBR and skip the NOTRACK prefix for indirect jump. This option should
> > > be used when the NOTRACK prefix is disabled.
> > >
> > > PR target/104816
> > > * config/i386/i386.opt: Remove Undocumented.
> > > * doc/invoke.texi: Document -mcet-switch.
> > > ---
> > > gcc/config/i386/i386.opt | 2 +-
> > > gcc/doc/invoke.texi | 8 +++++++-
> > > 2 files changed, 8 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > > index a6b0e28f238..0dbaacb57ed 100644
> > > --- a/gcc/config/i386/i386.opt
> > > +++ b/gcc/config/i386/i386.opt
> > > @@ -1047,7 +1047,7 @@ Enable shadow stack built-in functions from
> > > Control-flow Enforcement
> > > Technology (CET).
> > >
> > > mcet-switch
> > > -Target Undocumented Var(flag_cet_switch) Init(0)
> > > +Target Var(flag_cet_switch) Init(0)
> > > Turn on CET instrumentation for switch statements that use a jump table
> > > and
> > > an indirect jump.
> > >
> > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> > > index 7a35d9613a4..968853690f9 100644
> > > --- a/gcc/doc/invoke.texi
> > > +++ b/gcc/doc/invoke.texi
> > > @@ -1420,7 +1420,8 @@ See RS/6000 and PowerPC Options.
> > > -msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop
> > > @gol
> > > -madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp
> > > @gol
> > > -mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg @gol
> > > --mshstk -mmanual-endbr -mforce-indirect-call -mavx512vbmi2 -mavx512bf16
> > > -menqcmd @gol
> > > +-mshstk -mmanual-endbr -mcet-switch -mforce-indirect-call @gol
> > > +-mavx512vbmi2 -mavx512bf16 -menqcmd @gol
> > > -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq
> > > @gol
> > > -mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid @gol
> > > -mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk@gol
> > > @@ -32641,6 +32642,11 @@ function attribute. This is useful when used
> > > with the option
> > > @option{-fcf-protection=branch} to control ENDBR insertion at the
> > > function entry.
> > >
> > > +@item -mcet-switch
> > > +@opindex mcet-switch
> > > +Turn on CET instrumentation for switch statements that use a jump table
> > > +and an indirect jump.
> > > +
>
> Can you explain the difference between -mcet-switch and -mno-cet-switch here
> please and indicate the default? The above doesn't sound useful to me.
How about this?
@item -mcet-switch
@opindex mcet-switch
By default, CET instrumentation is turned off on switch statements that
use a jump table and indirect branch track is disabled. This option
turns on CET instrumentation to enable indirect branch track for switch
statements with jump tables.
--
H.J.
