On Wed, Apr 29, 2020 at 4:22 AM H.J. Lu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Allow -fcf-protection with external thunk since the external thunk can be
> made compatible with -fcf-protection.
>
> OK for master?
OK. I guess also OK for backporting to branches where CET support is
in a reasonable
state (not sure to what extent you backported the various fixes in this area).
Thanks,
Richard.
> Thanks.
>
> H.J.
> ---
> gcc/
>
> PR target/93654
> * config/i386/i386-options.c (ix86_set_indirect_branch_type):
> Allow -fcf-protection with -mindirect-branch=thunk-extern and
> -mfunction-return=thunk-extern.
> * doc/invoke.texi: Update notes for -fcf-protection=branch with
> -mindirect-branch=thunk-extern and -mindirect-return=thunk-extern.
>
> gcc/testsuite/
>
> PR target/93654
> * gcc.target/i386/pr93654.c: New test.
> ---
> gcc/config/i386/i386-options.c | 4 ++++
> gcc/doc/invoke.texi | 10 +++++++---
> gcc/testsuite/gcc.target/i386/pr93654.c | 9 +++++++++
> 3 files changed, 20 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/pr93654.c
>
> diff --git a/gcc/config/i386/i386-options.c b/gcc/config/i386/i386-options.c
> index e0be4932534..5c21fce06a4 100644
> --- a/gcc/config/i386/i386-options.c
> +++ b/gcc/config/i386/i386-options.c
> @@ -3083,6 +3083,8 @@ ix86_set_indirect_branch_type (tree fndecl)
> ? "thunk-extern" : "thunk"));
>
> if (cfun->machine->indirect_branch_type != indirect_branch_keep
> + && (cfun->machine->indirect_branch_type
> + != indirect_branch_thunk_extern)
> && (flag_cf_protection & CF_RETURN))
> error ("%<-mindirect-branch%> and %<-fcf-protection%> are not "
> "compatible");
> @@ -3126,6 +3128,8 @@ ix86_set_indirect_branch_type (tree fndecl)
> ? "thunk-extern" : "thunk"));
>
> if (cfun->machine->function_return_type != indirect_branch_keep
> + && (cfun->machine->function_return_type
> + != indirect_branch_thunk_extern)
> && (flag_cf_protection & CF_RETURN))
> error ("%<-mfunction-return%> and %<-fcf-protection%> are not "
> "compatible");
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index fed38e88ae5..5bb7d94833e 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -30097,9 +30097,9 @@ Note that @option{-mcmodel=large} is incompatible with
> @option{-mindirect-branch=thunk-extern} since the thunk function may
> not be reachable in the large code model.
>
> -Note that @option{-mindirect-branch=thunk-extern} is incompatible with
> -@option{-fcf-protection=branch} since the external thunk cannot be modified
> -to disable control-flow check.
> +Note that @option{-mindirect-branch=thunk-extern} is compatible with
> +@option{-fcf-protection=branch} since the external thunk can be made
> +to enable control-flow check.
>
> @item -mfunction-return=@var{choice}
> @opindex mfunction-return
> @@ -30112,6 +30112,10 @@ object file. You can control this behavior for a
> specific function by
> using the function attribute @code{function_return}.
> @xref{Function Attributes}.
>
> +Note that @option{-mindirect-return=thunk-extern} is compatible with
> +@option{-fcf-protection=branch} since the external thunk can be made
> +to enable control-flow check.
> +
> Note that @option{-mcmodel=large} is incompatible with
> @option{-mfunction-return=thunk} and
> @option{-mfunction-return=thunk-extern} since the thunk function may
> diff --git a/gcc/testsuite/gcc.target/i386/pr93654.c
> b/gcc/testsuite/gcc.target/i386/pr93654.c
> new file mode 100644
> index 00000000000..ec5bdce86a6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr93654.c
> @@ -0,0 +1,9 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fcf-protection -mfunction-return=thunk-extern
> -mindirect-branch=thunk-extern" } */
> +
> +int
> +bar (void (*foo) (void))
> +{
> + foo ();
> + return 0;
> +}
> --
> 2.25.4
>
