From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [PATCH 1/2] tracing/syscalls: allow multiple syscall numbers per syscall Date: Tue, 30 Aug 2016 15:29:55 -0400 Message-ID: <20160830152955.17633511@gandalf.local.home> References: <1472463007-6469-1-git-send-email-marcin.nowakowski@imgtec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Andy Lutomirski Cc: Marcin Nowakowski , Linux API , Ingo Molnar , open list , Linux MIPS Mailing List List-Id: linux-api@vger.kernel.org On Tue, 30 Aug 2016 11:52:39 -0700 Andy Lutomirski 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