[PATCH] libgcc/CET: Skip signal frames when unwinding shadow stack

[H.J. Lu]

When -fcf-protection -mcet is used, I got

FAIL: g++.dg/eh/sighandle.C

(gdb) bt
 #0  _Unwind_RaiseException (exc=exc@entry=0x416ed0)
    at /export/gnu/import/git/sources/gcc/libgcc/unwind.inc:140
 #1  0x00007ffff7d9936b in __cxxabiv1::__cxa_throw (obj=<optimized out>,
    tinfo=0x403dd0 <typeinfo for int@@CXXABI_1.3>, dest=0x0)
    at /export/gnu/import/git/sources/gcc/libstdc++-v3/libsupc++/eh_throw.cc:90
 #2  0x0000000000401255 in sighandler (signo=11, si=0x7fffffffd6f8,
    uc=0x7fffffffd5c0)
    at /export/gnu/import/git/sources/gcc/gcc/testsuite/g++.dg/eh/sighandle.C:9
 #3  <signal handler called> <<<< Signal frame which isn't on shadow stack
 #4  dosegv ()
    at /export/gnu/import/git/sources/gcc/gcc/testsuite/g++.dg/eh/sighandle.C:14
 #5  0x00000000004012e3 in main ()
    at /export/gnu/import/git/sources/gcc/gcc/testsuite/g++.dg/eh/sighandle.C:30
(gdb) p frames
$6 = 5
(gdb)

frame count should be 4, not 5.  This patch skips signal frames when
unwinding shadow stack.

Tested on i686 and x86-64.  OK for trunk?

H.J.
----
        PR libgcc/85334
        * unwind-generic.h (_Unwind_Frames_Increment): New.
        * config/i386/shadow-stack-unwind.h (_Unwind_Frames_Increment):
        Likewise.
        * unwind.inc (_Unwind_RaiseException_Phase2): Increment frame
        count with _Unwind_Frames_Increment.
        (_Unwind_ForcedUnwind_Phase2): Likewise.
---
 libgcc/config/i386/shadow-stack-unwind.h | 5 +++++
 libgcc/unwind-generic.h                  | 3 +++
 libgcc/unwind.inc                        | 6 ++++--
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/libgcc/config/i386/shadow-stack-unwind.h 
b/libgcc/config/i386/shadow-stack-unwind.h
index 40f48df2aec..a32f3e74b52 100644
--- a/libgcc/config/i386/shadow-stack-unwind.h
+++ b/libgcc/config/i386/shadow-stack-unwind.h
@@ -49,3 +49,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If 
not, see
        }                                       \
     }                                          \
     while (0)
+
+/* Increment frame count.  Skip signal frames.  */
+#undef _Unwind_Frames_Increment
+#define _Unwind_Frames_Increment(context, frames) \
+  if (!_Unwind_IsSignalFrame (context)) frames++
diff --git a/libgcc/unwind-generic.h b/libgcc/unwind-generic.h
index b5e3568e1bc..639c96f438e 100644
--- a/libgcc/unwind-generic.h
+++ b/libgcc/unwind-generic.h
@@ -291,4 +291,7 @@ EXCEPTION_DISPOSITION _GCC_specific_handler 
(PEXCEPTION_RECORD, void *,
 /* Additional actions to unwind number of stack frames.  */
 #define _Unwind_Frames_Extra(frames)
 
+/* Increment frame count.  */
+#define _Unwind_Frames_Increment(context, frames) frames++
+
 #endif /* unwind.h */
diff --git a/libgcc/unwind.inc b/libgcc/unwind.inc
index 68c08964d30..b49f8797009 100644
--- a/libgcc/unwind.inc
+++ b/libgcc/unwind.inc
@@ -72,8 +72,9 @@ _Unwind_RaiseException_Phase2(struct _Unwind_Exception *exc,
       /* Don't let us unwind past the handler context.  */
       gcc_assert (!match_handler);
 
+      _Unwind_Frames_Increment (context, frames);
+
       uw_update_context (context, &fs);
-      frames++;
     }
 
   *frames_p = frames;
@@ -187,10 +188,11 @@ _Unwind_ForcedUnwind_Phase2 (struct _Unwind_Exception 
*exc,
            return _URC_FATAL_PHASE2_ERROR;
        }
 
+      _Unwind_Frames_Increment (context, frames);
+
       /* Update cur_context to describe the same frame as fs, and discard
         the previous context if necessary.  */
       uw_advance_context (context, &fs);
-      frames++;
     }
 
   *frames_p = frames;
-- 
2.14.3