Re: kgdb support in vanilla 2.6.2

[Andi Kleen]

On Wed, 11 Feb 2004 17:34:13 -0800
George Anzinger <george@xxxxxxxxxx> wrote:


> > The latest binutils should support .cfi_* for i386 too. I don't see much sense
> > in making the code more ugly just for staying backwards compatible with older versions for the 
> > debug case (without CONFIG_DEBUG_INFO it should be compatible though).
> > You need a fairly new gdb too anyways for it.
> 
> Well, yes, the CVS version I mentioned in my patch is needed as I found a bug in 
> the expression analizer.  I am NOT trying to say compatable with old tools.  I 
> AM trying to do something the CURRENT tools make hard to impossible.
> 
> The problem with the gas CFI support is that it does not provide a way to define 
> CFI expressions which are needed to determine if the CFI address should be zero 
> (i.e. the return is to user space) or the current adjusted stack address.

Michal, can you comment? 
 
> I suppose the open ended .cfi_ thing could be used but it requires that you 
> compute your own sleb128 and uleb128 values.  It is also not clear how you tell 
> this thing if you want a word or a half word as the dwarf2 spec requires.  More 
> info on this would be very "nice".  I really would like to do this with out the 
> dwarf2 macros, but, please understand, one of the main reasons for the effort 
> was to tie off the bottom of the stack and that seems to require an expression 
> capability for the asm code in entry.S.

The one issue that required expression support on x86-64 (switching between the
interrupt stack and the process stack) was handled by a dummy base register
with a single ifdef. This turned out to be relatively clean.

-Andi

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