Re: [MinGW] RFC/RFA: Get Partial Stack Traces on Windows

[Andrew Haley <aph at redhat dot com>]

Ranjit Mathew writes:
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 > [Bryce, CC-ing you explicitly to get your opinion on the
 > fallback_backtrace() changes.]
 > 
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 > Index: ChangeLog
 > from  Ranjit Mathew  <rmathew@gcc.gnu.org>
 > 
 > 	* sysdep/i386/backtrace.h (fallback_backtrace): Check that a potential
 > 	frame pointer value is 32-bit word-aligned.  Use operand of the CALL
 > 	instruction calling the current function to find its starting address.
 > 	* stacktrace.cc: Include platform.h.
 > 	(_Jv_StackTrace::getLineNumberForFrame): Use VirtualQuery() trick on
 > 	Windows to find the module containing a given address.
 > 	(_Jv_StackTrace::GetStackTraceElements): Use nCodeMap even for Windows.
 > 	(_Jv_StackTrace::GetClassContext): Use fallback_backtrace() for
 > 	targets with SJLJ exceptions instead of using _Unwind_Backtrace().
 > 	(_Jv_StackTrace::GetFirstNonSystemClassLoader): Likewise.

What happens with -findirect-dispatch?

 > Index: sysdep/i386/backtrace.h
 > ===================================================================
 > --- sysdep/i386/backtrace.h	(revision 114838)
 > +++ sysdep/i386/backtrace.h	(working copy)
 > @@ -1,6 +1,6 @@
 >  // backtrace.h - Fallback backtrace implementation. i386 implementation.
 >  
 > -/* Copyright (C) 2005  Free Software Foundation
 > +/* Copyright (C) 2005, 2006  Free Software Foundation
 >  
 >     This file is part of libgcj.
 >  
 > @@ -29,12 +29,37 @@ fallback_backtrace (_Jv_UnwindState *sta
 >         rfp && i < state->length;
 >         rfp = *(unsigned int **)rfp)
 >      {
 > +      /* Sanity checks to eliminate dubious-looking frame pointer chains.
 > +         The frame pointer should be a 32-bit word-aligned stack address.
 > +         Since the stack grows downwards on x86, the frame pointer must have
 > +         a value greater than the current value of the stack pointer, it
 > +         should not be below the supposed next frame pointer and it should
 > +         not be too far off from the supposed next frame pointer.  */
 >        int diff = *rfp - (unsigned int)rfp;
 > -      if ((void*)rfp < _esp || diff > 4 * 1024 || diff < 0)
 > +      if (((unsigned int)rfp & 0x00000003) != 0 || (void*)rfp < _esp

Don't use unsigned int for a pointer; instead use 
int __attribute__((mode(pointer))).  This is an int that is exactly the
same size as a pointer.

Andrew.