Hi,

While trying to add a feature to strace related to -i, 
I was disappointed (a bit) about this option.

The man page explain:

  -i   Print the instruction pointer at  the  time  of  the system call.

Then add a note:

  The -i option is weakly supported


I think the note is not explicitly clear, at least under Linux.

As you may know (kidding :), under Linux, syscall are called through a
"vdso" (as reported in /proc/<pid>/maps) a.k.a. linux-gate.so.1 (as
reported by ldd). The instruction pointer at syscall time is always the
entry point in the vdso.

So the -i option really not useful. At least for me. People trying to
figure out what's done by an exploit or a rootkit would probably found
it more useful.

BTW, the manpage could be improved if something like this were added:

"The -i option is weakly supported: on some system, were syscalls are
call through a gate, like Linux, instruction pointer is likely to have a
fixed value"

Regards.

-- 
Yann Droneaud



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