Re: Issues with current systemtap and example scripts

["Frank Ch. Eigler" <fche at redhat dot com>]

Hi -


> Looking at "perf list" there are individual syscalls:sys_entry_* and
> syscalls:sys_exit_* tracepoints that might be more efficent to use
> [...]

No, they aren't what they appear.  They are simply demultiplexed
(after-the-fact $id filtered) virtual tracepoints built upon the
same two enter/exit pair we use.


> [...]
> [wcohen@paketa systemtap]$ stap -e 'probe tp_syscall.open.return{ printf("tp %x %x %d %d\n", __tracepoint_arg_regs, $regs, _stp_syscall_nr(), returnval()); exit() }'
> ERROR: returnval() not defined in this context
> [...]

This is improved in error.stp.


> Newly added syscalls in recent kernels might be missing
> 
> Generating the syscalls tapsets is a manual process.  Occassionally
> new syscalls are added to the kernel.  [...]
>  cd tapset
>  ausyscall --dump|awk '{print $2}'|sort > ksyscalls
>  find -type f|egrep -E "\.(/x86_64)?/sysc_([_0-9a-zA-Z]+)"| sed "s/x86_64\///g"| sed "s/\.\/sysc_//g" |sed "s/\.stp//g" |sort > ssyscalls
>  diff -y ssyscalls ksyscalls

This sort of thing could go under scripts/.  See also dump-syscalls.sh
and tracepoint-diff there.


> Strive for context variable consistency between the syscall implementations
> 
> For example would like to have returnval() function working for
> nd_syscall.*.return, tp_syscall.*.return, and dw_syscall.*.return,
> since syscall.*.return may use any one of those implementations.
> [...]

More ideally, the tapset .return aliases could supply a variable like
retval, just as they supply retstr.


- FChE