[Crash-utility] Another parsing bug -- likely confusion caused by open parenthesis

[Dave Anderson]

----- Original Message -----
> crash> p/x *(*(struct trace_page*)0xFFFF8804125CBA60).page | sed 's/^\$[0-9]* =/0xFFFF8804125CBA60 =/' >> trace-data.txt\n
> gdb: gdb request failed: p/x *(*(struct trace_page*)0xFFFF8804125CBA60).page | sed 's/^\$[0-9]* =/0xFFFF8804125CBA60 =/'
> crash> p/x *(*(struct trace_page*)0xFFFF8804125CBA60).page
> $1467 = {
>    flags = 0x200000000000000,
>    _count = {
>      counter = 0x1
>    },
>    {
>      _mapcount = {
>        counter = 0xffffffff
>      },
>      {
>        inuse = 0xffff,
>        objects = 0xffff
>      }
>    },
>    {
>      {
>        private = 0x0,
>        mapping = 0x0
>      },
>      ptl = {
>        raw_lock = {
>          slock = 0x0
>        }
>      },
>      slab = 0x0,
>      first_page = 0x0
>    },
>    {
>      index = 0x0,
>      freelist = 0x0,
>      reserve = 0x0,
>      frag_count = {
>        counter = 0x0
>      }
>    },
>    lru = {
>      next = 0xdead000000100100,
>      prev = 0xdead000000200200
>    }
> }

Bruce, 

I'm not sure what you mean about the "open parenthesis", but I think
this simpler example shows the problem, which is related to using
a native gdb command in conjunction with a pipe and a redirect.
  
The "p" command is sort of a "convenience" crash command that pretty 
much exists to be able to quickly change the output radix before passing
the request to the gdb module.  Using just "p" alone defaults to the
current output radix (decimal by default):
 
  crash> p jiffies
  jiffies = $12 = 4294754313
  crash>

The output radix can be changed by entering the "hex" alias,
and then the same command above.  Or alternatively, either 
"p -x" or the "px" alias can be used:

  crash> px jiffies
  jiffies = $13 = 0xfffcc009
  crash>

Piping the output works:

  crash> px jiffies | cat 
  jiffies = $14 = 0xfffcc009
  crash>

Piping the output, and then redirecting it works:

  crash> px jiffies | cat > /tmp/junk
  crash> !cat /tmp/junk
  jiffies = $15 = 0xfffcc009
  crash>

But using the gdb "p/x" command directly (bypassing the crash "p"
command), in conjunction with a pipe and a redirect, generates the
failure.  Just a pipe or a redirect alone works OK:

  crash> p/x jiffies | cat
  $16 = 0xfffcc009
  crash> p/x jiffies > /tmp/junk
  crash> !cat /tmp/junk
  $17 = 0xfffcc009
  crash>

But using a pipe and a redirect strips the redirect, but leaves the "| cat"
attached to the end of the command line sent to gdb:

  crash> p/x jiffies | cat > /tmp/junk
  gdb: gdb request failed: p/x jiffies | cat
  crash> 

Interesting that several pipes can be used, with the same bug
showing up:

  crash> p/x jiffies | cat | cat > /tmp/junk
  gdb: gdb request failed: p/x jiffies | cat | cat
  crash>

Not sure why just yet, other than there's a difference in the way 
native gdb commands and crash commands are processed.  Let me dig 
into it...
  
In the meantime, you should be able to use "px" instead of "p/x".
  
Dave