[PATCH v5 07/23] aarch64: Mark swapcontext with indirect_return

[Carlos O'Donell]

On 12/6/24 8:29 AM, Yury Khrustalev wrote:
> From: Szabolcs Nagy <szabolcs.nagy@arm.com>
> 

Very similar to CET.

LGTM.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  sysdeps/aarch64/bits/indirect-return.h | 36 ++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 sysdeps/aarch64/bits/indirect-return.h
> 
> diff --git a/sysdeps/aarch64/bits/indirect-return.h b/sysdeps/aarch64/bits/indirect-return.h
> new file mode 100644
> index 0000000000..99905f21fa
> --- /dev/null
> +++ b/sysdeps/aarch64/bits/indirect-return.h
> @@ -0,0 +1,36 @@
> +/* Definition of __INDIRECT_RETURN.  AArch64 version.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _UCONTEXT_H
> +# error "Never include <bits/indirect-return.h> directly; use <ucontext.h> instead."
> +#endif
> +
> +/* __INDIRECT_RETURN indicates that swapcontext may return via
> +   an indirect branch.  This happens when GCS is enabled, so
> +   add the attribute if available, otherwise returns_twice has
> +   a similar effect, but it prevents some code transformations
> +   that can cause build failures in some rare cases so it is
> +   only used when GCS is enabled.  */
> +#if __glibc_has_attribute (__indirect_return__)
> +# define __INDIRECT_RETURN __attribute__ ((__indirect_return__))
> +#elif __glibc_has_attribute (__returns_twice__) \
> +      && defined __ARM_FEATURE_GCS_DEFAULT
> +# define __INDIRECT_RETURN __attribute__ ((__returns_twice__))
> +#else
> +# define __INDIRECT_RETURN
> +#endif