RE: [PATCH] btrace: kernel address filtering

["Metzger, Markus T" <markus dot t dot metzger at intel dot com>]

> -----Original Message-----
> From: Pedro Alves [mailto:palves@redhat.com]
> Sent: Tuesday, September 8, 2015 12:25 PM
> To: Metzger, Markus T
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH] btrace: kernel address filtering
> 
> On 09/01/2015 04:42 PM, Markus Metzger wrote:
> 
> > --- a/gdb/nat/linux-btrace.h
> > +++ b/gdb/nat/linux-btrace.h
> > @@ -101,10 +101,11 @@ struct btrace_target_info
> >    } variant;
> >  #endif /* HAVE_LINUX_PERF_EVENT_H */
> >
> > -  /* The size of a pointer in bits for this thread.
> > -     The information is used to identify kernel addresses in order to skip
> > -     records from/to kernel space.  */
> > -  int ptr_bits;
> > +  /* The kernel start address.
> > +     The information is used to tell kernel addresses from user addresses in
> > +     order to skip records from kernel space.  We assume that any address
> > +     smaller than KERNEL_START is in user space.  */
> > +  uint64_t kernel_start;
> 
> Is there a reason we need to store the kernel's start address on every
> thread?

I don't think we need to store it, at all.  We had to store the ptr_bits since we
needed to fill them in later.  But the kernel start address is computed, cached,
and used in nat/linux-btrace.c.

I'll send an updated patch.

thanks,
Markus.

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