commit db126ae243cd70e4f68fd50a7c619740e90e1dc6
Author: Daniel Kiss <daniel.kiss@arm.com>
Date:   Wed Aug 11 10:11:30 2021 +0200

    [Arm][Unwind][libc++abi] Add _Unwind_ForcedUnwind to EHABI.
    
    _Unwind_ForcedUnwind is not mandated by the EHABI but for compatibilty
    reasons adding so the interface to higher layers would be the same.
    Dropping EHABI specific _Unwind_Stop_Fn definition since it is not defined by EHABI.
    
    Reviewed By: MaskRay
    
    Differential Revision: https://reviews.llvm.org/D89570

diff --git a/libunwind/include/unwind.h b/libunwind/include/unwind.h
index e8d114854325..87c3cf6c804e 100644
--- a/libunwind/include/unwind.h
+++ b/libunwind/include/unwind.h
@@ -61,6 +61,14 @@ typedef struct _Unwind_Context _Unwind_Context;   // opaque
 #include "unwind_itanium.h"
 #endif
 
+typedef _Unwind_Reason_Code (*_Unwind_Stop_Fn)
+    (int version,
+     _Unwind_Action actions,
+     uint64_t exceptionClass,
+     _Unwind_Exception* exceptionObject,
+     struct _Unwind_Context* context,
+     void* stop_parameter);
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/libunwind/include/unwind_arm_ehabi.h b/libunwind/include/unwind_arm_ehabi.h
index 58444d14eb8d..5ad088722560 100644
--- a/libunwind/include/unwind_arm_ehabi.h
+++ b/libunwind/include/unwind_arm_ehabi.h
@@ -26,7 +26,7 @@ typedef uint32_t _Unwind_EHT_Header;
 
 struct _Unwind_Control_Block;
 typedef struct _Unwind_Control_Block _Unwind_Control_Block;
-typedef struct _Unwind_Control_Block _Unwind_Exception; /* Alias */
+#define _Unwind_Exception _Unwind_Control_Block /* Alias */
 
 struct _Unwind_Control_Block {
   uint64_t exception_class;
@@ -63,11 +63,6 @@ struct _Unwind_Control_Block {
   long long int :0; /* Enforce the 8-byte alignment */
 } __attribute__((__aligned__(8)));
 
-typedef _Unwind_Reason_Code (*_Unwind_Stop_Fn)
-      (_Unwind_State state,
-       _Unwind_Exception* exceptionObject,
-       struct _Unwind_Context* context);
-
 typedef _Unwind_Reason_Code (*_Unwind_Personality_Fn)(
     _Unwind_State state, _Unwind_Exception *exceptionObject,
     struct _Unwind_Context *context);
diff --git a/libunwind/include/unwind_itanium.h b/libunwind/include/unwind_itanium.h
index 1e1389c7f0da..eeb45f622832 100644
--- a/libunwind/include/unwind_itanium.h
+++ b/libunwind/include/unwind_itanium.h
@@ -39,14 +39,6 @@ struct _Unwind_Exception {
   // alignment for the target"; so do we.
 } __attribute__((__aligned__));
 
-typedef _Unwind_Reason_Code (*_Unwind_Stop_Fn)
-    (int version,
-     _Unwind_Action actions,
-     uint64_t exceptionClass,
-     _Unwind_Exception* exceptionObject,
-     struct _Unwind_Context* context,
-     void* stop_parameter );
-
 typedef _Unwind_Reason_Code (*_Unwind_Personality_Fn)(
     int version, _Unwind_Action actions, uint64_t exceptionClass,
     _Unwind_Exception *exceptionObject, struct _Unwind_Context *context);
diff --git a/libunwind/src/Unwind-EHABI.cpp b/libunwind/src/Unwind-EHABI.cpp
index 8843db7f54c3..ba6064d3ef00 100644
--- a/libunwind/src/Unwind-EHABI.cpp
+++ b/libunwind/src/Unwind-EHABI.cpp
@@ -602,7 +602,7 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor
     // If there is a personality routine, tell it we are unwinding.
     if (frameInfo.handler != 0) {
       _Unwind_Personality_Fn p =
-          (_Unwind_Personality_Fn)(long)(frameInfo.handler);
+          (_Unwind_Personality_Fn)(intptr_t)(frameInfo.handler);
       struct _Unwind_Context *context = (struct _Unwind_Context *)(cursor);
       // EHABI #7.2
       exception_object->pr_cache.fnstart = frameInfo.start_ip;
@@ -670,6 +670,112 @@ static _Unwind_Reason_Code unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor
   return _URC_FATAL_PHASE2_ERROR;
 }
 
+static _Unwind_Reason_Code
+unwind_phase2_forced(unw_context_t *uc, unw_cursor_t *cursor,
+                     _Unwind_Exception *exception_object, _Unwind_Stop_Fn stop,
+                     void *stop_parameter) {
+  // See comment at the start of unwind_phase1 regarding VRS integrity.
+  __unw_init_local(cursor, uc);
+  _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_force(ex_ojb=%p)",
+                             static_cast<void *>(exception_object));
+  // Walk each frame until we reach where search phase said to stop
+  while (true) {
+    // Update info about this frame.
+    unw_proc_info_t frameInfo;
+    if (__unw_get_proc_info(cursor, &frameInfo) != UNW_ESUCCESS) {
+      _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): __unw_step "
+                                 "failed => _URC_END_OF_STACK",
+                                 (void *)exception_object);
+      return _URC_FATAL_PHASE2_ERROR;
+    }
+
+    // When tracing, print state information.
+    if (_LIBUNWIND_TRACING_UNWINDING) {
+      char functionBuf[512];
+      const char *functionName = functionBuf;
+      unw_word_t offset;
+      if ((__unw_get_proc_name(cursor, functionBuf, sizeof(functionBuf),
+                               &offset) != UNW_ESUCCESS) ||
+          (frameInfo.start_ip + offset > frameInfo.end_ip))
+        functionName = ".anonymous.";
+      _LIBUNWIND_TRACE_UNWINDING(
+          "unwind_phase2_forced(ex_ojb=%p): start_ip=0x%" PRIxPTR
+          ", func=%s, lsda=0x%" PRIxPTR ", personality=0x%" PRIxPTR,
+          (void *)exception_object, frameInfo.start_ip, functionName,
+          frameInfo.lsda, frameInfo.handler);
+    }
+
+    // Call stop function at each frame.
+    _Unwind_Action action =
+        (_Unwind_Action)(_UA_FORCE_UNWIND | _UA_CLEANUP_PHASE);
+    _Unwind_Reason_Code stopResult =
+        (*stop)(1, action, exception_object->exception_class, exception_object,
+                (_Unwind_Context *)(cursor), stop_parameter);
+    _LIBUNWIND_TRACE_UNWINDING(
+        "unwind_phase2_forced(ex_ojb=%p): stop function returned %d",
+        (void *)exception_object, stopResult);
+    if (stopResult != _URC_NO_REASON) {
+      _LIBUNWIND_TRACE_UNWINDING(
+          "unwind_phase2_forced(ex_ojb=%p): stopped by stop function",
+          (void *)exception_object);
+      return _URC_FATAL_PHASE2_ERROR;
+    }
+
+    // If there is a personality routine, tell it we are unwinding.
+    if (frameInfo.handler != 0) {
+      _Unwind_Personality_Fn p =
+          (_Unwind_Personality_Fn)(uintptr_t)(frameInfo.handler);
+      struct _Unwind_Context *context = (struct _Unwind_Context *)(cursor);
+      // EHABI #7.2
+      exception_object->pr_cache.fnstart = frameInfo.start_ip;
+      exception_object->pr_cache.ehtp =
+          (_Unwind_EHT_Header *)frameInfo.unwind_info;
+      exception_object->pr_cache.additional = frameInfo.flags;
+      _Unwind_Reason_Code personalityResult =
+          (*p)(_US_FORCE_UNWIND | _US_UNWIND_FRAME_STARTING, exception_object,
+               context);
+      switch (personalityResult) {
+      case _URC_CONTINUE_UNWIND:
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned "
+                                   "_URC_CONTINUE_UNWIND",
+                                   (void *)exception_object);
+        // Destructors called, continue unwinding
+        break;
+      case _URC_INSTALL_CONTEXT:
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned "
+                                   "_URC_INSTALL_CONTEXT",
+                                   (void *)exception_object);
+        // We may get control back if landing pad calls _Unwind_Resume().
+        __unw_resume(cursor);
+        break;
+      default:
+        // Personality routine returned an unknown result code.
+        _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): "
+                                   "personality returned %d, "
+                                   "_URC_FATAL_PHASE2_ERROR",
+                                   (void *)exception_object, personalityResult);
+        return _URC_FATAL_PHASE2_ERROR;
+      }
+    }
+  }
+
+  // Call stop function one last time and tell it we've reached the end
+  // of the stack.
+  _LIBUNWIND_TRACE_UNWINDING("unwind_phase2_forced(ex_ojb=%p): calling stop "
+                             "function with _UA_END_OF_STACK",
+                             (void *)exception_object);
+  _Unwind_Action lastAction =
+      (_Unwind_Action)(_UA_FORCE_UNWIND | _UA_CLEANUP_PHASE | _UA_END_OF_STACK);
+  (*stop)(1, lastAction, exception_object->exception_class, exception_object,
+          (struct _Unwind_Context *)(cursor), stop_parameter);
+
+  // Clean up phase did not resume at the frame that the search phase said it
+  // would.
+  return _URC_FATAL_PHASE2_ERROR;
+}
+
 /// Called by __cxa_throw.  Only returns if there is a fatal error.
 _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_RaiseException(_Unwind_Exception *exception_object) {
@@ -717,10 +823,13 @@ _Unwind_Resume(_Unwind_Exception *exception_object) {
   unw_cursor_t cursor;
   __unw_getcontext(&uc);
 
-  // _Unwind_RaiseException on EHABI will always set the reserved1 field to 0,
-  // which is in the same position as private_1 below.
-  // TODO(ajwong): Who wronte the above? Why is it true?
-  unwind_phase2(&uc, &cursor, exception_object, true);
+  if (exception_object->unwinder_cache.reserved1)
+    unwind_phase2_forced(
+        &uc, &cursor, exception_object,
+        (_Unwind_Stop_Fn)exception_object->unwinder_cache.reserved1,
+        (void *)exception_object->unwinder_cache.reserved3);
+  else
+    unwind_phase2(&uc, &cursor, exception_object, true);
 
   // Clients assume _Unwind_Resume() does not return, so all we can do is abort.
   _LIBUNWIND_ABORT("_Unwind_Resume() can't return");
@@ -967,6 +1076,27 @@ _Unwind_VRS_Pop(_Unwind_Context *context, _Unwind_VRS_RegClass regclass,
   _LIBUNWIND_ABORT("unsupported register class");
 }
 
+/// Not used by C++.
+/// Unwinds stack, calling "stop" function at each frame.
+/// Could be used to implement longjmp().
+_LIBUNWIND_EXPORT _Unwind_Reason_Code
+_Unwind_ForcedUnwind(_Unwind_Exception *exception_object, _Unwind_Stop_Fn stop,
+                     void *stop_parameter) {
+  _LIBUNWIND_TRACE_API("_Unwind_ForcedUnwind(ex_obj=%p, stop=%p)",
+                       (void *)exception_object, (void *)(uintptr_t)stop);
+  unw_context_t uc;
+  unw_cursor_t cursor;
+  __unw_getcontext(&uc);
+
+  // Mark that this is a forced unwind, so _Unwind_Resume() can do
+  // the right thing.
+  exception_object->unwinder_cache.reserved1 = (uintptr_t)stop;
+  exception_object->unwinder_cache.reserved3 = (uintptr_t)stop_parameter;
+
+  return unwind_phase2_forced(&uc, &cursor, exception_object, stop,
+                              stop_parameter);
+}
+
 /// Called by personality handler during phase 2 to find the start of the
 /// function.
 _LIBUNWIND_EXPORT uintptr_t
diff --git a/libunwind/src/UnwindLevel1-gcc-ext.c b/libunwind/src/UnwindLevel1-gcc-ext.c
index 310b836d129e..d69267ba25fe 100644
--- a/libunwind/src/UnwindLevel1-gcc-ext.c
+++ b/libunwind/src/UnwindLevel1-gcc-ext.c
@@ -25,31 +25,24 @@
 #if defined(_LIBUNWIND_BUILD_ZERO_COST_APIS)
 
 #if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
-#define private_1 private_[0]
+#define PRIVATE_1 private_[0]
+#elif defined(_LIBUNWIND_ARM_EHABI)
+#define PRIVATE_1 unwinder_cache.reserved1
+#else
+#define PRIVATE_1 private_1
 #endif
 
 ///  Called by __cxa_rethrow().
 _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_Resume_or_Rethrow(_Unwind_Exception *exception_object) {
-#if defined(_LIBUNWIND_ARM_EHABI)
-  _LIBUNWIND_TRACE_API("_Unwind_Resume_or_Rethrow(ex_obj=%p), private_1=%ld",
-                       (void *)exception_object,
-                       (long)exception_object->unwinder_cache.reserved1);
-#else
-  _LIBUNWIND_TRACE_API("_Unwind_Resume_or_Rethrow(ex_obj=%p), private_1=%" PRIdPTR,
-                       (void *)exception_object,
-                       (intptr_t)exception_object->private_1);
-#endif
+  _LIBUNWIND_TRACE_API(
+      "_Unwind_Resume_or_Rethrow(ex_obj=%p), private_1=%" PRIdPTR,
+      (void *)exception_object, (intptr_t)exception_object->PRIVATE_1);
 
-#if defined(_LIBUNWIND_ARM_EHABI)
-  // _Unwind_RaiseException on EHABI will always set the reserved1 field to 0,
-  // which is in the same position as private_1 below.
-  return _Unwind_RaiseException(exception_object);
-#else
   // If this is non-forced and a stopping place was found, then this is a
   // re-throw.
   // Call _Unwind_RaiseException() as if this was a new exception
-  if (exception_object->private_1 == 0) {
+  if (exception_object->PRIVATE_1 == 0) {
     return _Unwind_RaiseException(exception_object);
     // Will return if there is no catch clause, so that __cxa_rethrow can call
     // std::terminate().
@@ -60,10 +53,8 @@ _Unwind_Resume_or_Rethrow(_Unwind_Exception *exception_object) {
   _Unwind_Resume(exception_object);
   _LIBUNWIND_ABORT("_Unwind_Resume_or_Rethrow() called _Unwind_RaiseException()"
                    " which unexpectedly returned");
-#endif
 }
 
-
 /// Called by personality handler during phase 2 to get base address for data
 /// relative encodings.
 _LIBUNWIND_EXPORT uintptr_t
diff --git a/libunwind/test/forceunwind.pass.cpp b/libunwind/test/forceunwind.pass.cpp
new file mode 100644
index 000000000000..e74aa3faa080
--- /dev/null
+++ b/libunwind/test/forceunwind.pass.cpp
@@ -0,0 +1,68 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: linux
+
+// Basic test for _Unwind_ForcedUnwind.
+// See libcxxabi/test/forced_unwind* tests too.
+
+#include <assert.h>
+#include <dlfcn.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <unwind.h>
+
+void foo();
+_Unwind_Exception ex;
+
+_Unwind_Reason_Code stop(int version, _Unwind_Action actions,
+                         uint64_t exceptionClass,
+                         _Unwind_Exception *exceptionObject,
+                         struct _Unwind_Context *context,
+                         void *stop_parameter) {
+  assert(version == 1);
+  assert((actions & _UA_FORCE_UNWIND) != 0);
+  (void)exceptionClass;
+  assert(exceptionObject == &ex);
+  assert(stop_parameter == &foo);
+
+  Dl_info info = {0, 0, 0, 0};
+
+  // Unwind util the main is reached, above frames depend on the platform and
+  // architecture.
+  if (dladdr(reinterpret_cast<void *>(_Unwind_GetIP(context)), &info) &&
+      info.dli_sname && !strcmp("main", info.dli_sname)) {
+    _Exit(0);
+  }
+  return _URC_NO_REASON;
+}
+
+__attribute__((noinline)) void foo() {
+
+  // Arm EHABI defines struct _Unwind_Control_Block as exception
+  // object. Ensure struct _Unwind_Exception* work there too,
+  // because _Unwind_Exception in this case is just an alias.
+  struct _Unwind_Exception *e = &ex;
+#if defined(_LIBUNWIND_ARM_EHABI)
+  // Create a mock exception object.
+  memset(e, '\0', sizeof(*e));
+  e->exception_class = 0x434C4E47554E5700; // CLNGUNW\0
+#endif
+  _Unwind_ForcedUnwind(e, stop, (void *)&foo);
+}
+
+int main() {
+  foo();
+  return -2;
+}