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Date: Fri, 30 May 2003 20:32:00 -0000
From: Andrew Cagney <ac131313@redhat.com>
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To: Jim Blandy <jimb@redhat.com>
Cc: Mark Kettenis <kettenis@chello.nl>, mludvig@suse.cz,
	gdb@sources.redhat.com, Alexandre Oliva <aoliva@redhat.com>
Subject: Re: dwarf-frame.c question
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> Andrew Cagney <ac131313@redhat.com> writes:
> 
>> One idea (the origins of which are unknown) is for the compiler to
>> generate CFI info containing no addresses and have GDB look for that
>> dependant on the PC address being obtained using return or resume
>> (sigtramp, sentinel).
> 
> 
> I don't understand this.  Could you explain the idea in more detail?

A similar technique to the line number information where there are two 
line number entries for the start of function so that GDB can find the 
end of the function prologue given:

	int foo (int i) { int j = i * i; return j; }

In this case there would be two CFI entries covering the code at "1:" 
(assuming its possible):

> foo ()
> {
>     if (i)
>       abort (with, lots, of parameters)
>     do; normal; stuff;
> }
> 
> it can be turned into:
> 
>     branch !i, 1:
>     push with
>     push lots
>     push of
>     push parameters
>     call abort
> 1:
>     do
>     normal
>     stuff 

- [1:, 1:): describing the lost return instruction
- [1:, end-of-function) describing the real code

GDB could pick 'n' choose.

The other thing to do is to test this on an alternative compiler that 
generates CFI.

Andrew