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- /* _Unwind_Frames_Extra with shadow stack for x86-64 and x86.
- Copyright (C) 2017-2022 Free Software Foundation, Inc.
- This file is part of GCC.
- GCC is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 3, or (at your option)
- any later version.
- GCC 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 General Public License for more details.
- Under Section 7 of GPL version 3, you are granted additional
- permissions described in the GCC Runtime Library Exception, version
- 3.1, as published by the Free Software Foundation.
- You should have received a copy of the GNU General Public License and
- a copy of the GCC Runtime Library Exception along with this program;
- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
- <http://www.gnu.org/licenses/>. */
- #include <x86gprintrin.h>
- /* Unwind the shadow stack for EH. */
- #undef _Unwind_Frames_Extra
- #define _Unwind_Frames_Extra(x) \
- do \
- { \
- _Unwind_Word ssp = _get_ssp (); \
- if (ssp != 0) \
- { \
- _Unwind_Word tmp = (x); \
- while (tmp > 255) \
- { \
- _inc_ssp (255); \
- tmp -= 255; \
- } \
- _inc_ssp (tmp); \
- } \
- } \
- while (0)
- /* Linux CET kernel places a restore token on shadow stack for signal
- handler to enhance security. The restore token is 8 byte and aligned
- to 8 bytes. It is usually transparent to user programs since kernel
- will pop the restore token when signal handler returns. But when an
- exception is thrown from a signal handler, now we need to pop the
- restore token from shadow stack. For x86-64, we just need to treat
- the signal frame as normal frame. For i386, we need to search for
- the restore token to check if the original shadow stack is 8 byte
- aligned. If the original shadow stack is 8 byte aligned, we just
- need to pop 2 slots, one restore token, from shadow stack. Otherwise,
- we need to pop 3 slots, one restore token + 4 byte padding, from
- shadow stack. */
- #ifndef __x86_64__
- #undef _Unwind_Frames_Increment
- #define _Unwind_Frames_Increment(context, frames) \
- if (_Unwind_IsSignalFrame (context)) \
- do \
- { \
- _Unwind_Word ssp, prev_ssp, token; \
- ssp = _get_ssp (); \
- if (ssp != 0) \
- { \
- /* Align shadow stack pointer to the next \
- 8 byte aligned boundary. */ \
- ssp = (ssp + 4) & ~7; \
- do \
- { \
- /* Look for a restore token. */ \
- token = (*(_Unwind_Word *) (ssp - 8)); \
- prev_ssp = token & ~7; \
- if (prev_ssp == ssp) \
- break; \
- ssp += 8; \
- } \
- while (1); \
- frames += (token & 0x4) ? 3 : 2; \
- } \
- } \
- while (0); \
- else \
- frames++;
- #endif
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