[Crash-utility] right shift of the subtraction result

[Dave Anderson]

----- Original Message -----
> 
> 
> ----- Original Message -----
> > 
> > Hi Dave,
> > Does this sound like a bug, it need right shift of the subtraction result,
> > crash-git> pd (678324157984276 >> 32)
> > $10 = 157934
> > crash-git> pd ((681670518181331-678324157984276) >> 32)
> > p: gdb request failed: p ((681670518181331-678324157984276)
> > crash-git>
> > 
> > It might be lacking support of some advanced arithmetic, so what is a
> > proper
> > wayto do some arithmetic like this?
> 
> No, it is a crash bug.  If you turn on the console mode, you can see the
> string
> that is passed on to gdb.  Simple example:
>   
>   crash> !tty
>   /dev/pts/8
>   crash> set console /dev/pts/8
>   debug console [2850]: /dev/pts/8
>   console: /dev/pts/8
>   crash> set debug 1
>   debug: 1
>   crash>
>   
> The simple shift case works, and you can see the string that gets passed
> to gdb on the 2nd line of output, in the bracket after gdb_pass_through:
>   
>   crash> pd (15 >> 1)
>   error() trace: 467e99 => 51c147 => 518ca6 => 46eaff
>   gdb_pass_through: [p (15 >> 1)]
>   p: per_cpu_symbol_search((15 >> 1)): NULL
>   $9 = 7
>   crash>
>   
> But by adding the internal set of parentheses, the string gets
> clipped, and just "p ((15+1)" gets passed to gdb:
>   
>   crash> pd ((15+1) >> 1)
>   error() trace: 467e99 => 51c147 => 518ca6 => 46eaff
>   p: per_cpu_symbol_search(((15+1)): NULL
>   gdb_pass_through: [p ((15+1)]
>   error() trace: 467e99 => 51c1e7 => 51a7d5 => 46eaff
>   p: gdb request failed: p ((15+1)
>   crash>
> 
> So it's either related to the crash command line redirection code,
> or in the process_gdb_output() function.  (Feel free to debug it
> if you have the time...)
> 
> Thanks,
>   Dave

FWIW, because of C operator precedence, you can work around the bug by
removing the inner parentheses:

  crash> pd ((681670518181331-678324157984276) >> 32)
  p: gdb request failed: p ((681670518181331-678324157984276)
  crash> pd (681670518181331-678324157984276 >> 32)
  $1 = 779
  crash> 

Dave