Re: generating functions and eh region

["Vincent R." <forumer at smartmobili dot com>]

On Wed, 01 Apr 2009 07:54:20 -0700, Ian Lance Taylor <iant@google.com>
wrote:
> "Vincent R." <forumer@smartmobili.com> writes:
> 
>> Now the question is can we declare a function with an eh region and will
>> it
>> construct prologue and epilogue ?
> 
> The instructions are already in a function.  Why do you need a separate
> prologue and epilogue for them?
> 
> Maybe I am missing the point here.  It seems to me that the __except
> keyword as you described it can be implemented by a transformation from
> C++ to C++.  gcc already knows how to handle exception regions; you
> don't have to teach it anything in that area.  You just have to generate
> the correct GIMPLE or GENERIC in the frontend.  You are talking about
> creating a new function, but I just don't see any reason to do so.  You
> already have a function, and you can just create exception regions in
> that function.  The code in the exception region can call other
> functions, etc.  What am I missing?
> 
> Ian

Yes I think I don't explain things very clearly, so what is important to
know is that the __except keyword
can be passed instructions(case 1) or directly a function(case 2).

in the case 1)  ie if you declare something like :

...
__except( printf("hello gcc"), 1)

and I look at asm generated I can notice that the instructions inside the
patenthesis will be put inside a function
because I can notice a prologue and epilogue.



int main()
{
...
  __except(puts("in filter"), EXCEPTION_EXECUTE_HANDLER)
  {
    ...
  }
} // main
...


So on a arm plateform here is the annoted asm (asm + source code), I have
only pasted the __except part :
And we can see that just after the closing } for main there is a prologue
followed by the instructions
originally in the __except and then the epilogue.


// main }
; 128  : 	__except(puts("in filter"), EXCEPTION_EXECUTE_HANDLER){

	str         lr, [sp, #-4]!  <<<< function prologue
|$LN8@wmain|
|$LN19@wmain|
	ldr         r0, [pc, #8]
	bl          puts
	mov         r0, #1
|$LN7@wmain|
	ldr         pc, [sp], #4 <<<< function epilogue


so instructions inside __except parenthesis are put in something that looks
like a function

Do I need to explain more ?