loc2-test and stap disagree with each other

[Hien Nguyen]

I tried loc2c-test to figure out which variables are available at the 
probe point as follow

#./loc2c-test -k 0xc00000000036d048
kernel/sched.c (0x11)
        __kcrctab_wake_up_process     [443092]  long unsigned int const
        __kstrtab_wake_up_process     [4430b8]  char[] const

[.....]
       schedule (0x2e): 0xc00000000036c490 (kernel/sched.c:2865) .. 
0xc00000000036d2d8 (kernel/sched.c:4056)
            switch_count                  [43c0d6]      long int*
            prev                          [43c0e6]      task_t*
            next                          [43c0f6]      task_t*
            rq                            [43c106]      runqueue_t*
            array                         [43c115]      prio_array_t*
            queue                         [43c125]      list_head*
            now                           [43c131]      long long 
unsigned int
            run_time                      [43c141]      long unsigned int
            cpu                           [43c151]      int
            idx                           [43c161]      int
            new_prio                      [43c171]      int


Looks like loc2c-test indicates that the *prev* and *next* variables are 
available. However, stap failed to resolve those variable

#stap -p2 -vv -e 'probe 
kernel.statement("schedule@kernel/sched.c:3035"){ prev_task = 
$prev->pid; printf("%d\n", prev_task)}'

[....]Pass 1: parsed user script and 25 library script(s) in 
190usr/0sys/442real ms.
probe schedule@kernel/sched.c:3035 pc=0xc00000000036d048
semantic error: unresolved target-symbol expression: identifier '$prev' 
at <input>:1:69
semantic error: unresolved target-symbol expression: identifier '$prev' 
at <input>:1:69
semantic error: unresolved target-symbol expression: identifier '$prev' 
at <input>:1:69
semantic error: unresolved target-symbol expression: identifier '$prev' 
at <input>:1:69
Pass 2: analyzed script: 1 probe(s), 0 function(s), 0 global(s) in 
450usr/50sys/1130real ms.
Pass 2: analysis failed.  Try again with more '-v' (verbose) options.
Running rm -rf /tmp/stapGetF8h


Did I do something wrong?

Thanks, Hien.