src/UnwindLevel1-gcc-ext.c

//===--------------------- UnwindLevel1-gcc-ext.c -------------------------===//
//
//                     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 gcc extensions to the C++ ABI Exception Handling Level 1.
//
//===----------------------------------------------------------------------===//

#include <inttypes.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

#include "config.h"
#include "libunwind_ext.h"
#include "libunwind.h"
#include "Unwind-EHABI.h"
#include "unwind.h"

#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",
                       (void *)exception_object,
                       (long)exception_object->unwinder_cache.reserved1);
#else
  _LIBUNWIND_TRACE_API("_Unwind_Resume_or_Rethrow(ex_obj=%p), private_1=%ld\n",
                       (void *)exception_object,
                       (long)exception_object->private_1);
#endif

#if LIBCXXABI_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) {
    return _Unwind_RaiseException(exception_object);
    // Will return if there is no catch clause, so that __cxa_rethrow can call
    // std::terminate().
  }

  // Call through to _Unwind_Resume() which distiguishes between forced and
  // regular exceptions.
  _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
_Unwind_GetDataRelBase(struct _Unwind_Context *context) {
  (void)context;
  _LIBUNWIND_TRACE_API("_Unwind_GetDataRelBase(context=%p)\n", (void *)context);
  _LIBUNWIND_ABORT("_Unwind_GetDataRelBase() not implemented");
}


/// Called by personality handler during phase 2 to get base address for text
/// relative encodings.
_LIBUNWIND_EXPORT uintptr_t
_Unwind_GetTextRelBase(struct _Unwind_Context *context) {
  (void)context;
  _LIBUNWIND_TRACE_API("_Unwind_GetTextRelBase(context=%p)\n", (void *)context);
  _LIBUNWIND_ABORT("_Unwind_GetTextRelBase() not implemented");
}


/// Scans unwind information to find the function that contains the
/// specified code address "pc".
_LIBUNWIND_EXPORT void *_Unwind_FindEnclosingFunction(void *pc) {
  _LIBUNWIND_TRACE_API("_Unwind_FindEnclosingFunction(pc=%p)\n", pc);
  // This is slow, but works.
  // We create an unwind cursor then alter the IP to be pc
  unw_cursor_t cursor;
  unw_context_t uc;
  unw_proc_info_t info;
  unw_getcontext(&uc);
  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",
                       (void *)(uintptr_t)callback);

  // walk each frame
  while (true) {
    _Unwind_Reason_Code result;

    // ask libuwind to get next frame (skip over first frame which is
    // _Unwind_Backtrace())
    if (unw_step(&cursor) <= 0) {
      _LIBUNWIND_TRACE_UNWINDING(" _backtrace: ended because cursor reached "
                                 "bottom of stack, returning %d\n",
                                 _URC_END_OF_STACK);
      return _URC_END_OF_STACK;
    }

#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;
    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);
      unw_get_proc_info(&cursor, &frame);
      _LIBUNWIND_TRACE_UNWINDING(
          " _backtrace: start_ip=0x%llX, func=%s, lsda=0x%llX, context=%p\n",
          (long long)frame.start_ip, functionName, (long long)frame.lsda,
          (void *)&cursor);
    }

    // call trace function with this frame
    result = (*callback)((struct _Unwind_Context *)(&cursor), ref);
    if (result != _URC_NO_REASON) {
      _LIBUNWIND_TRACE_UNWINDING(
          " _backtrace: ended because callback returned %d\n", result);
      return result;
    }
  }
}


/// Find dwarf unwind info for an address 'pc' in some function.
_LIBUNWIND_EXPORT const void *_Unwind_Find_FDE(const void *pc,
                                               struct dwarf_eh_bases *bases) {
  // This is slow, but works.
  // We create an unwind cursor then alter the IP to be pc
  unw_cursor_t cursor;
  unw_context_t uc;
  unw_proc_info_t info;
  unw_getcontext(&uc);
  unw_init_local(&cursor, &uc);
  unw_set_reg(&cursor, UNW_REG_IP, (unw_word_t)(long) pc);
  unw_get_proc_info(&cursor, &info);
  bases->tbase = (uintptr_t)info.extra;
  bases->dbase = 0; // dbase not used on Mac OS X
  bases->func = (uintptr_t)info.start_ip;
  _LIBUNWIND_TRACE_API("_Unwind_Find_FDE(pc=%p) => %p\n", pc,
                  (void *)(long) info.unwind_info);
  return (void *)(long) info.unwind_info;
}

/// Returns the CFA (call frame area, or stack pointer at start of function)
/// for the current context.
_LIBUNWIND_EXPORT uintptr_t _Unwind_GetCFA(struct _Unwind_Context *context) {
  unw_cursor_t *cursor = (unw_cursor_t *)context;
  unw_word_t result;
  unw_get_reg(cursor, UNW_REG_SP, &result);
  _LIBUNWIND_TRACE_API("_Unwind_GetCFA(context=%p) => 0x%" PRIx64 "\n",
                       (void *)context, (uint64_t)result);
  return (uintptr_t)result;
}


/// Called by personality handler during phase 2 to get instruction pointer.
/// ipBefore is a boolean that says if IP is already adjusted to be the call
/// site address.  Normally IP is the return address.
_LIBUNWIND_EXPORT uintptr_t _Unwind_GetIPInfo(struct _Unwind_Context *context,
                                              int *ipBefore) {
  _LIBUNWIND_TRACE_API("_Unwind_GetIPInfo(context=%p)\n", (void *)context);
  *ipBefore = 0;
  return _Unwind_GetIP(context);
}

#if _LIBUNWIND_SUPPORT_DWARF_UNWIND

/// Called by programs with dynamic code generators that want
/// to register a dynamically generated FDE.
/// This function has existed on Mac OS X since 10.4, but
/// was broken until 10.6.
_LIBUNWIND_EXPORT void __register_frame(const void *fde) {
  _LIBUNWIND_TRACE_API("__register_frame(%p)\n", fde);
  _unw_add_dynamic_fde((unw_word_t)(uintptr_t) fde);
}


/// Called by programs with dynamic code generators that want
/// to unregister a dynamically generated FDE.
/// This function has existed on Mac OS X since 10.4, but
/// was broken until 10.6.
_LIBUNWIND_EXPORT void __deregister_frame(const void *fde) {
  _LIBUNWIND_TRACE_API("__deregister_frame(%p)\n", fde);
  _unw_remove_dynamic_fde((unw_word_t)(uintptr_t) fde);
}


// The following register/deregister functions are gcc extensions.
// They have existed on Mac OS X, but have never worked because Mac OS X
// before 10.6 used keymgr to track known FDEs, but these functions
// never got updated to use keymgr.
// For now, we implement these as do-nothing functions to keep any existing
// applications working.  We also add the not in 10.6 symbol so that nwe
// application won't be able to use them.

#if _LIBUNWIND_SUPPORT_FRAME_APIS
_LIBUNWIND_EXPORT void __register_frame_info_bases(const void *fde, void *ob,
                                                   void *tb, void *db) {
  (void)fde;
  (void)ob;
  (void)tb;
  (void)db;
 _LIBUNWIND_TRACE_API("__register_frame_info_bases(%p,%p, %p, %p)\n",
                            fde, ob, tb, db);
  // do nothing, this function never worked in Mac OS X
}

_LIBUNWIND_EXPORT void __register_frame_info(const void *fde, void *ob) {
  (void)fde;
  (void)ob;
  _LIBUNWIND_TRACE_API("__register_frame_info(%p, %p)\n", fde, ob);
  // do nothing, this function never worked in Mac OS X
}

_LIBUNWIND_EXPORT void __register_frame_info_table_bases(const void *fde,
                                                         void *ob, void *tb,
                                                         void *db) {
  (void)fde;
  (void)ob;
  (void)tb;
  (void)db;
  _LIBUNWIND_TRACE_API("__register_frame_info_table_bases"
                             "(%p,%p, %p, %p)\n", fde, ob, tb, db);
  // do nothing, this function never worked in Mac OS X
}

_LIBUNWIND_EXPORT void __register_frame_info_table(const void *fde, void *ob) {
  (void)fde;
  (void)ob;
  _LIBUNWIND_TRACE_API("__register_frame_info_table(%p, %p)\n", fde, ob);
  // do nothing, this function never worked in Mac OS X
}

_LIBUNWIND_EXPORT void __register_frame_table(const void *fde) {
  (void)fde;
  _LIBUNWIND_TRACE_API("__register_frame_table(%p)\n", fde);
  // do nothing, this function never worked in Mac OS X
}

_LIBUNWIND_EXPORT void *__deregister_frame_info(const void *fde) {
  (void)fde;
  _LIBUNWIND_TRACE_API("__deregister_frame_info(%p)\n", fde);
  // do nothing, this function never worked in Mac OS X
  return NULL;
}

_LIBUNWIND_EXPORT void *__deregister_frame_info_bases(const void *fde) {
  (void)fde;
  _LIBUNWIND_TRACE_API("__deregister_frame_info_bases(%p)\n", fde);
  // do nothing, this function never worked in Mac OS X
  return NULL;
}
#endif // _LIBUNWIND_SUPPORT_FRAME_APIS

#endif // _LIBUNWIND_SUPPORT_DWARF_UNWIND

#endif // _LIBUNWIND_BUILD_ZERO_COST_APIS