[Bug libgcc/85334] Shadow stack isn't unwound properly through signal handler

[hjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85334

--- Comment #7 from hjl at gcc dot gnu.org <hjl at gcc dot gnu.org> ---
Author: hjl
Date: Wed Oct  3 16:55:06 2018
New Revision: 264814

URL: https://gcc.gnu.org/viewcvs?rev=264814&root=gcc&view=rev
Log:
i386: Remove _Unwind_Frames_Increment

CET kernel has been changed to place a restore token on shadow stack for
signal handler to enhance security.  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 remove _Unwind_Frames_Increment to pop the the restore token
from shadow stack.  Otherwise, we get

FAIL: g++.dg/torture/pr85334.C   -O0  execution test
FAIL: g++.dg/torture/pr85334.C   -O1  execution test
FAIL: g++.dg/torture/pr85334.C   -O2  execution test
FAIL: g++.dg/torture/pr85334.C   -O3 -g  execution test
FAIL: g++.dg/torture/pr85334.C   -Os  execution test
FAIL: g++.dg/torture/pr85334.C   -O2 -flto -fno-use-linker-plugin
-flto-partition=none  execution test

        Backport from mainline
        2018-07-27  H.J. Lu  <hongjiu.lu@intel.com>

        PR libgcc/85334
        * config/i386/shadow-stack-unwind.h (_Unwind_Frames_Increment):
        Removed.


Modified:
    branches/gcc-8-branch/libgcc/ChangeLog
    branches/gcc-8-branch/libgcc/config/i386/shadow-stack-unwind.h