RE: [PATCH v2 2/3] LAM: Enable tagged pointer support for watchpoints.

["Schimpe, Christina" <christina.schimpe@intel.com>]

> > > Or maybe we even want to warn if we find the string but can't
> > > convert it to a proper mask.
> >
> > As I said before I am not sure how we should handle those error
> conditions.
> > Maybe somebody else can help us here?
> 
> I think we want to warn or error out. You can look at existing GDB code.
> For example here GDB prints an error if it couldn't read an integer from a
> Linux file:
> https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/nat/linux-
> btrace.c;h=5715168d2f0887da2321694b5a8f3e21e74c4ad7;hb=8e8b2ab688b3
> d7e6035e6c782a2b42501d57c667#l601
> Not sure if there are other examples or counter examples, this just one I
> knew of.
> 
> In your case it is very unlikely that this will ever happen yes. But I think GDB
> is just much better off to check this. Otherwise the function might return
> some wrong mask silently. A warning or error makes it much easier to
> understand, if there ever is a bug.
> 
> Is the untag_mask string in the file, even if the default mask is "active"?
> In that case you could argue a warning is good enough, as we don't actually
> know if the watchpoint would be set to a wrong address.

As long as the kernel supports LAM the untag_mask string should be in the file,
even if LAM is not enabled.  So in practise we have to deal with both scenarios
with and without untag_mask string (older kernels).

> Though to be on the safe side, I lean towards an error.  We have the
> indication that LAM is supported (or even active), but can't read the mask.
> So we don't know if we can set a watchpoint on the right address.
> Yes this prevents users from setting watchpoints, but since it is an unlikely
> scenario I hope this is never a real problem for someone.

I am fine with an error here.

> And note that my code was just a rough sketch, please double check it.

Ok.

Christina
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