Re: [Xen-devel] [PATCH v5 14/28] x86, xsplice: Print payload's symbol name and payload name in backtraces

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> 04/06/16 4:39 AM >>>
>On Fri, Apr 01, 2016 at 09:23:15AM -0600, Jan Beulich wrote:
>> >>> On 24.03.16 at 21:00, <konrad.wilk@xxxxxxxxxx> wrote:
>> > @@ -331,16 +332,17 @@ static char *pointer(char *str, char *end, const 
>> > char **fmt_ptr,
>> >      {
>> >          unsigned long sym_size, sym_offset;
>> >          char namebuf[KSYM_NAME_LEN+1];
>> > +        bool_t payload = 0;
>> >  
>> >          /* Advance parents fmt string, as we have consumed 's' or 'S' */
>> >          ++*fmt_ptr;
>> >  
>> >          s = symbols_lookup((unsigned long)arg, &sym_size, &sym_offset, 
>> > namebuf);
>> > -
>> > -        /* If the symbol is not found, fall back to printing the address 
>> > */
>> > +        /* If the symbol is not found, fall back to printing the address. 
>> > */
>> >          if ( !s )
>> >              break;
>> > -
>> > +        if ( strncmp(namebuf, s, KSYM_NAME_LEN) )
>> > +            payload = 1;
>> 
>> What is this about? A comment is absolutely needed here, the
>> more that without context "payload" is also an unclear term.
>> And then - would simply comparing the two pointers suffice?
>
>Sadly no. The namebuf is defined on the stack (and the value copied in)
>while the 's' is a pointer to the char* in the symbols.

How does one being on the stack and the other in (I assume) a string table
prevent their pointers to be compared? Iirc for the in-hypervisor symbols
symbols_lookup() simply returns the passed in namebuf, and hence
s == namebuf above. Or I must be missing something...

Jan


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