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loc2-test and stap disagree with each other


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.


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