Re: [cxx-abi-dev] Flaws in spec for __cxa_begin_catch

[Cary Coutant <cary@xxxxxxxxxx>]

> That seems like a good strategy.  Would you care to submit a patch to 
> the ABI spec?
All right, I took a stab at it. You may want to do some wordsmithing.

-cary


*** abi-eh.html	Fri Nov 19 09:55:12 2004
--- abi-eh-041119.html	Fri Nov 19 10:49:10 2004
***************
*** 13,23 ****
  C++ ABI for Itanium: Exception Handling
  </b></i></font>

  <font size=-1>
  <p>
! <i>Revised 31 July 2001.
  <a href=#revisions>Revision history</a> at end of document.
  </i>

  </center>

--- 13,23 ----
  C++ ABI for Itanium: Exception Handling
  </b></i></font>

  <font size=-1>
  <p>
! <i>Revised 19 November 2004.
  <a href=#revisions>Revision history</a> at end of document.
  </i>

  </center>

*************** Multithreading behavior.
*** 1236,1250 ****
  <p>
  <a name=cxx-exc-object></a>
  <h5> 2.2.1  C++ Exception Objects </h5>

  <p>
! A <span class="change">complete</span>
  C++ exception object consists of a header,
  which is a wrapper around an unwind object header with additional C++
  specific information,
! followed by the <span class="change">thrown C++</span>
  exception object itself.
  The structure of the header is as follows:
  <code><pre>
        struct __cxa_exception {
  	std::type_info *	exceptionType;
--- 1236,1250 ----
  <p>
  <a name=cxx-exc-object></a>
  <h5> 2.2.1  C++ Exception Objects </h5>

  <p>
! A complete
  C++ exception object consists of a header,
  which is a wrapper around an unwind object header with additional C++
  specific information,
! followed by the thrown C++
  exception object itself.
  The structure of the header is as follows:
  <code><pre>
        struct __cxa_exception {
  	std::type_info *	exceptionType;
*************** several things are considered <i>excepti
*** 1755,1778 ****

  Most of the behavior of a handler is implementation-defined.
  However, in order to allow maintenance of the exception stack,
  all handlers must make the following calls.

  <p>
  Upon entry, a handler must call:
  <code><pre>
! 	void __cxa_begin_catch ( void *exceptionObject );
  </pre></code>
  This routine:
  <ul>
  <li> Increment's the exception's handler count.
  <li> Places the exception on the stack of currently-caught exceptions
      if it is not already there,
      linking the exception to the previous top of the stack.
  <li> Decrements the uncaught_exception count.
  </ul>

  <p>
  When the personality routine encounters a termination condition,
  it will call <code>__cxa_begin_catch()</code> to mark the exception
  as handled and then call <code>terminate()</code>,
  which shall not return to its caller.
--- 1755,1801 ----

  Most of the behavior of a handler is implementation-defined.
  However, in order to allow maintenance of the exception stack,
  all handlers must make the following calls.

+ <div class="change">
  <p>
  Upon entry, a handler must call:
  <code><pre>
! 	void *__cxa_get_exception_ptr ( void *exceptionObject );
! </pre></code>
! This routine returns the adjusted pointer to the exception object.
! (The adjusted pointer is typically computed by the personality routine
! during phase 1 and saved in the exception object.)
! </div>
!
! <p>
! <strike>Upon entry,</strike>
! <span class="change">Following initialization of the catch 
parameter,</span>
! a handler must call:
! <code><pre>
! 	void <span class="change">*</span>__cxa_begin_catch ( void 
*exceptionObject );
  </pre></code>
  This routine:
  <ul>
  <li> Increment's the exception's handler count.
  <li> Places the exception on the stack of currently-caught exceptions
      if it is not already there,
      linking the exception to the previous top of the stack.
  <li> Decrements the uncaught_exception count.
+ <li><span class="change">Returns the adjusted pointer to the 
exception object.</span>
  </ul>

+ <div class="change">
+ <p>
+ If the initialization of the catch parameter is trivial
+ (e,g., there is no formal catch parameter, or the parameter has no 
copy constructor),
+ the calls to <code>__cxa_get_exception_ptr()</code> and
+ <code>__cxa_begin_catch()</code> may be combined into a single call to
+ <code>__cxa_begin_catch()</code>.
+ </div>
+
  <p>
  When the personality routine encounters a termination condition,
  it will call <code>__cxa_begin_catch()</code> to mark the exception
  as handled and then call <code>terminate()</code>,
  which shall not return to its caller.
*************** This might be translated as follows:
*** 2253,2268 ****
--- 2276,2293 ----
  	[Cleanup code corresponding to exit of scope]
  	[enclosing the try block]
  	_Unwind_Resume();

  	H1: // Handler label
+ 	<span class="change">adjusted_exception_ptr = 
__cxa_get_exception_ptr(exception);</span>
  	[Initialize catch parameter]
  	__cxa_begin_catch(exception);
  	[User code]
  	goto R1;

  	H2:
+ 	<span class="change">adjusted_exception_ptr = 
__cxa_get_exception_ptr(exception);</span>
  	[Initialize catch parameter]
  	__cxa_begin_catch(exception);
  	[User code]
  	buz(); // Call attributes: Landing pad L2, action record A2
  	goto R1;
*************** and below.
*** 2304,2313 ****
--- 2329,2342 ----
  </font>


  <p><a name=revisions></a> <hr> <p>
  <h3> Appendix R:  Revisions </h3>
+
+ <p>
+ <font color="blue">[041119]</font>
+ Add __cxa_get_exception_ptr, add return value to __cxa_begin_catch.

  <p>
  <font color="blue">[011126]</font>
  Add __cxa_current_exception_type.