Re: [PATCH 1/2] tracing/syscalls: allow multiple syscall numbers per syscall

From: Steven Rostedt
Date: Tue Aug 30 2016 - 15:30:03 EST

On Tue, 30 Aug 2016 11:52:39 -0700
Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:

> Okay, I think I see what's going on. init_ftrace_syscalls() does:
> meta = find_syscall_meta(addr);
> Unless I'm missing some reason why this is a sensible thing to do,
> this seems overcomplicated and incorrect. There is exactly one caller
> of find_syscall_meta() and that caller knows the syscall number. Why
> doesn't it just look up the metadata by *number* instead of by syscall
> implementation address? There are plenty of architectures for which
> multiple logically different syscalls can share an implementation
> (e.g. pretty much everything that calls in_compat_syscall()).

The problem is that the meta data is created at the syscalls
themselves. Look at all the macro magic in include/linux/syscalls.h,
and search for __syscall_metadata. The meta data is created via linker
magic, and the find_syscall_meta() is what finds a specific system call
and the meta data associated with it.

Then it can use the number to system call mapping.

Yes, this code needs some loving.

-- Steve