Re: [Xen-devel] [PATCH v9 16/27] x86, xsplice: Print payload's symbol name and payload name in backtraces

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 04/26/2016 01:41 PM, Jan Beulich wrote:
> > > > On 26.04.16 at 13:06, <ross.lagerwall@xxxxxxxxxx> wrote:
> > On 04/25/2016 04:35 PM, Konrad Rzeszutek Wilk wrote:
> > > @@ -142,6 +145,55 @@ void *xsplice_symbols_lookup_by_name(const char *symname)
> > >        return 0;
> > >    }
> > >
> > > +static const char *xsplice_symbols_lookup(unsigned long addr,
> > > +                                          unsigned long *symbolsize,
> > > +                                          unsigned long *offset,
> > > +                                          char *namebuf)
> > > +{
> > > +    const struct payload *data;
> > > +    unsigned int i, best;
> > > +    const void *va = (const void *)addr;
> > > +    const char *n = NULL;
> > > +
> > > +    /*
> > > +     * Only RCU locking since this list is only ever changed during apply
> > > +     * or revert context. And in case it dies there we need an safe list.
> > > +     */
> > > +    rcu_read_lock(&rcu_applied_lock);
> > > +    list_for_each_entry_rcu ( data, &applied_list, applied_list )
> > > +    {
> > > +        if ( va < data->text_addr &&
> > > +             va >= (data->text_addr + data->pages * PAGE_SIZE) )
> > This calculation is wrong due to the use of void * and results in
> > incorrect backtrace results.
> When text_addr is void *, how is this calculation wrong then?
I'm sorry, ignore that. I temporarily forgot how void* arithmetic is 
defined for GCC.
The other two points are still valid and may result in incorrect 
backtraces with > 1 payload loaded.
> > > @@ -422,6 +475,13 @@ static int prepare_payload(struct payload *payload,
> > >            }
> > >        }
> > >
> > > +    /* Setup the virtual region with proper data. */
> > > +    region = &payload->region;
> > > +
> > > +    region->symbols_lookup = xsplice_symbols_lookup;
> > > +    region->start = payload->text_addr;
> > > +    region->end = payload->text_addr + payload->text_size;
> > This calculation is wrong due to the use of void *.
> And again - why?
>
> Jan

--
Ross Lagerwall

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