Re: [Valgrind-users] Difference between "truss" and "valgrind --trace-syscalls=yes" on FreeBSD

[Ivo R. <ivo...@gm...>]

2015-09-08 1:35 GMT+02:00 Yue Chen <yc...@gm...>:

> I tried to use Valgrind syscall tracing utility on FreeBSD 10.1. I found
> that that the results of ``truss'' and ``valgrind --trace-syscalls=yes''
> are a little different. For example, the result of Valgrind has extra
> syscalls like sys_sysctl, sys_fstatfs6 and [async].
> Is it because Valgrind result contains the syscalls issued from the
> instrumentation code, or something else?
> Thanks.
>

Think of Valgrind as a virtual machine.
Truss observes behaviour of the host (Valgrind itself) while
--trace-syscalls traces behavior of the guest (your application).
Valgrind syscall machinery intercepts all syscalls from the application and
in general they are not mapped 1:1 to native ones.
Some of these might be changed or intercepted completely.
Valgrind will also issue syscalls on its own.
I.