Force unwind frame with user-defined personality.

[logan]

Summary

If libcxxabi is compiled as a shared library, and the
executable references the user-defined personality routines
(e.g. gxx_personality_v0), then the pointer comparison in
Unwind-EHABI.cpp won't work. This is due to the fact that
the PREL31 will point to the PLT stubs for the personality
routines (in the executable), while the gxx_personality_v0
symbol reference is yet another (different) PLT stub (in the
libunwind.)

This will cause _Unwind_Backtrace() stops to unwind the frame
whenever it reaches __gxx_personality_v0(). This CL fix the
problem by calling the user-defined personality routines
with an undocumented API for force unwinding.

[rengolin]

I'll leave this one for @jroelofs... :)

[jroelofs]

src/Unwind/UnwindLevel1-gcc-ext.c

107

would be nice to re-use signExtendPrel31 instead.

144

which part specifically are you calling out as undocumented here? (would be useful info in the comment)

161

I think you want _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND here.

[jroelofs]

LGTM with those changes.

[logan]

Address the review comments.

[logan]

src/Unwind/UnwindLevel1-gcc-ext.c

107

Done.

144

Revised. Mentioned the undocumented flag _US_FORCE_UNWIND in the next revision.

161

Done.

[logan]

Update.

[logan]

Thanks. Committed as rL226822.

src/Unwind/Unwind-EHABI.h

+//===------------------------- Unwind-EHABI.hpp ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __UNWIND_EHABI_H__
+#define __UNWIND_EHABI_H__
+
+#include <stdint.h>
+#include <unwind.h>
+
+// Unable to unwind in the ARM index table (section 5 EHABI).
+#define UNW_EXIDX_CANTUNWIND 0x1
+
+static inline uint32_t signExtendPrel31(uint32_t data) {
+  return data | ((data & 0x40000000u) << 1);
+}
+
+static inline uint32_t readPrel31(const uint32_t *data) {
+  return (((uint32_t) data) + signExtendPrel31(*data));
+}
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+extern _Unwind_Reason_Code __aeabi_unwind_cpp_pr0(
+    _Unwind_State state, _Unwind_Control_Block *ucbp, _Unwind_Context *context);
+
+extern _Unwind_Reason_Code __aeabi_unwind_cpp_pr1(
+    _Unwind_State state, _Unwind_Control_Block *ucbp, _Unwind_Context *context);
+
+extern _Unwind_Reason_Code __aeabi_unwind_cpp_pr2(
+    _Unwind_State state, _Unwind_Control_Block *ucbp, _Unwind_Context *context);
+
+#if defined(__cplusplus)
+} // extern "C"
+#endif
+
+#endif  // __UNWIND_EHABI_H__

src/Unwind/Unwind-EHABI.cpp

 //===--------------------------- Unwind-EHABI.cpp -------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //
 //  Implements ARM zero-cost C++ exceptions
 //
 //===----------------------------------------------------------------------===//
 
+#include "Unwind-EHABI.h"
+
 #include <unwind.h>
 
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
const char* getNextWord(const char* data, uint32_t* out) {
   return data + 4;
 }
 
 const char* getNextNibble(const char* data, uint32_t* out) {
   *out = *reinterpret_cast<const uint16_t*>(data);
   return data + 2;
 }
 
-static inline uint32_t signExtendPrel31(uint32_t data) {
-  return data | ((data & 0x40000000u) << 1);
-}
-
 struct Descriptor {
    // See # 9.2
    typedef enum {
      SU16 = 0, // Short descriptor, 16-bit entries
      LU16 = 1, // Long descriptor,  16-bit entries
      LU32 = 3, // Long descriptor,  32-bit entries
      RESERVED0 =  4, RESERVED1 =  5, RESERVED2  = 6,  RESERVED3  =  7,
      RESERVED4 =  8, RESERVED5 =  9, RESERVED6  = 10, RESERVED7  = 11,
while (descriptorWord) {
     };
 
     getNextWord(descriptor, &descriptorWord);
   }
 
   return _URC_CONTINUE_UNWIND;
 }
 
-_Unwind_Reason_Code unwindOneFrame(
-    _Unwind_State state,
+static _Unwind_Reason_Code unwindOneFrame(_Unwind_State state,
                                           _Unwind_Control_Block* ucbp,
                                           struct _Unwind_Context* context) {
   // Read the compact model EHT entry's header # 6.3
   const uint32_t* unwindingData = ucbp->pr_cache.ehtp;
   assert((*unwindingData & 0xf0000000) == 0x80000000 && "Must be a compact entry");
   Descriptor::Format format =
       static_cast<Descriptor::Format>((*unwindingData & 0x0f000000) >> 24);
   size_t len = 0;
   size_t off = 0;
   unwindingData = decode_eht_entry(unwindingData, &off, &len);

  *
  * @param data Pointer to EHT.
  * @param[out] off Offset from return value (in bytes) to begin interpretation.
  * @param[out] len Number of bytes in unwind code.
  * @return Pointer to beginning of unwind code.
  */
 extern "C" const uint32_t*
 decode_eht_entry(const uint32_t* data, size_t* off, size_t* len) {
-  if ((*data & 0x80000000) == 0) {
-    // 6.2: Generic Model
-    // EHT entry is a prel31 pointing to the PR, followed by data understood only
-    // by the personality routine. Since EHABI doesn't guarantee the location or
-    // availability of the unwind opcodes in the generic model, we have to check
-    // for them on a case-by-case basis:
-    _Unwind_Reason_Code __gxx_personality_v0(int version, _Unwind_Action actions,
-                                             uint64_t exceptionClass,
-                                             _Unwind_Exception* unwind_exception,
-                                             _Unwind_Context* context);
-    void *PR = (void*)signExtendPrel31(*data);
-    if (PR == (void*)&__gxx_personality_v0) {
-      *off = 1; // First byte is size data.
-      *len = (((data[1] >> 24) & 0xff) + 1) * 4;
-    } else
-      return nullptr;
-    data++; // Skip the first word, which is the prel31 offset.
-  } else {
-    // 6.3: ARM Compact Model
-    // EHT entries here correspond to the __aeabi_unwind_cpp_pr[012] PRs indeded
-    // by format:
-    Descriptor::Format format =
-        static_cast<Descriptor::Format>((*data & 0x0f000000) >> 24);
-    switch (format) {
-      case Descriptor::SU16:
-        *len = 4;
-        *off = 1;
-        break;
-      case Descriptor::LU16:
-      case Descriptor::LU32:
-        *len = 4 + 4 * ((*data & 0x00ff0000) >> 16);
-        *off = 2;
-        break;
-      default:
-        return nullptr;
-    }
-  }
-
+  assert((*data & 0x80000000) != 0 &&
+         "decode_eht_entry() does not support user-defined personality");
+
   return data;
 }
 
 _Unwind_Reason_Code _Unwind_VRS_Interpret(
     _Unwind_Context* context,
     const uint32_t* data,
     size_t offset,
     size_t len) {

src/Unwind/UnwindCursor.hpp

 #include "libunwind.h"
 
 #include "AddressSpace.hpp"
 #include "Registers.hpp"
 #include "DwarfInstructions.hpp"
 #include "CompactUnwinder.hpp"
 #include "config.h"
 
+#if LIBCXXABI_ARM_EHABI
+#include "Unwind-EHABI.h"
+#endif
+
 namespace libunwind {
 
 #if _LIBUNWIND_SUPPORT_DWARF_UNWIND
 /// Cache of recently found FDEs.
 template <typename A>
 class _LIBUNWIND_HIDDEN DwarfFDECache {
   typedef typename A::pint_t pint_t;
 public:

 }
 
 #if LIBCXXABI_ARM_EHABI
 struct EHABIIndexEntry {
   uint32_t functionOffset;
   uint32_t data;
 };
 
-// Unable to unwind in the ARM index table (section 5 EHABI).
-#define UNW_EXIDX_CANTUNWIND 0x1
-
-static inline uint32_t signExtendPrel31(uint32_t data) {
-  return data | ((data & 0x40000000u) << 1);
-}
-
-extern "C" _Unwind_Reason_Code __aeabi_unwind_cpp_pr0(
-    _Unwind_State state, _Unwind_Control_Block *ucbp, _Unwind_Context *context);
-extern "C" _Unwind_Reason_Code __aeabi_unwind_cpp_pr1(
-    _Unwind_State state, _Unwind_Control_Block *ucbp, _Unwind_Context *context);
-extern "C" _Unwind_Reason_Code __aeabi_unwind_cpp_pr2(
-    _Unwind_State state, _Unwind_Control_Block *ucbp, _Unwind_Context *context);
-
 template<typename A>
 struct EHABISectionIterator {
   typedef EHABISectionIterator _Self;
 
   typedef std::random_access_iterator_tag iterator_category;
   typedef typename A::pint_t value_type;
   typedef typename A::pint_t* pointer;
   typedef typename A::pint_t& reference;

src/Unwind/UnwindLevel1-gcc-ext.c

 #include <stdio.h>
 #include <stdlib.h>
 
 #include "libunwind.h"
 #include "unwind.h"
 #include "libunwind_ext.h"
 #include "config.h"
 
+#if LIBCXXABI_ARM_EHABI
+#include "Unwind-EHABI.h"
+#endif
+
 #if _LIBUNWIND_BUILD_ZERO_COST_APIS
 
 ///  Called by __cxa_rethrow().
 _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_Resume_or_Rethrow(_Unwind_Exception *exception_object) {
 #if LIBCXXABI_ARM_EHABI
   _LIBUNWIND_TRACE_API("_Unwind_Resume_or_Rethrow(ex_obj=%p), "
                        "private_1=%ld\n",
_LIBUNWIND_EXPORT void *_Unwind_FindEnclosingFunction(void *pc) {
   unw_init_local(&cursor, &uc);
   unw_set_reg(&cursor, UNW_REG_IP, (unw_word_t)(long) pc);
   if (unw_get_proc_info(&cursor, &info) == UNW_ESUCCESS)
     return (void *)(long) info.start_ip;
   else
     return NULL;
 }
 
-
 /// Walk every frame and call trace function at each one.  If trace function
 /// returns anything other than _URC_NO_REASON, then walk is terminated.
 _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_Backtrace(_Unwind_Trace_Fn callback, void *ref) {
   unw_cursor_t cursor;
   unw_context_t uc;
   unw_getcontext(&uc);
   unw_init_local(&cursor, &uc);
 
   _LIBUNWIND_TRACE_API("_Unwind_Backtrace(callback=%p)\n", callback);

 #if LIBCXXABI_ARM_EHABI
     // Get the information for this frame.
     unw_proc_info_t frameInfo;
     if (unw_get_proc_info(&cursor, &frameInfo) != UNW_ESUCCESS) {
       return _URC_END_OF_STACK;
     }
 
     struct _Unwind_Context *context = (struct _Unwind_Context *)&cursor;
-    size_t off;
-    size_t len;
     const uint32_t* unwindInfo = (uint32_t *) frameInfo.unwind_info;
+    if ((*unwindInfo & 0x80000000) == 0) {
+      // 6.2: Generic Model
+      // EHT entry is a prel31 pointing to the PR, followed by data understood
+      // only by the personality routine. Since EHABI doesn't guarantee the
+      // location or availability of the unwind opcodes in the generic model,
+      // we have to call personality functions with (_US_VIRTUAL_UNWIND_FRAME |
+      // _US_FORCE_UNWIND) state.
+
+      // Create a mock exception object for force unwinding.
+      _Unwind_Exception ex;
+      ex.exception_class = 0x434C4E47554E5700; // CLNGUNW\0
+      ex.pr_cache.fnstart = frameInfo.start_ip;
+      ex.pr_cache.ehtp = (_Unwind_EHT_Header *) unwindInfo;
+      ex.pr_cache.additional= frameInfo.flags;
+
+      // Get and call the personality function to unwind the frame.
+      __personality_routine pr = (__personality_routine) readPrel31(unwindInfo);
+      if (pr(_US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND, &ex, context) !=
+              _URC_CONTINUE_UNWIND) {
+        return _URC_END_OF_STACK;
+      }
+    } else {
+      size_t off, len;
       unwindInfo = decode_eht_entry(unwindInfo, &off, &len);
       if (unwindInfo == NULL) {
         return _URC_FAILURE;
       }
 
       result = _Unwind_VRS_Interpret(context, unwindInfo, off, len);
       if (result != _URC_CONTINUE_UNWIND) {
         return _URC_END_OF_STACK;
       }
+    }
 #endif // LIBCXXABI_ARM_EHABI
 
     // debugging
     if (_LIBUNWIND_TRACING_UNWINDING) {
       char functionName[512];
       unw_proc_info_t frame;
       unw_word_t offset;
       unw_get_proc_name(&cursor, functionName, 512, &offset);