Date: Fri, 01 Sep 2006 18:39:34 +1000 From: Peter Chubb <peterc@chubb.wattle.id.au> To: Robert Watson <rwatson@FreeBSD.org> Cc: marcel@FreeBSD.org, ia64@FreeBSD.org, Peter Chubb <peterc@gelato.unsw.edu.au>, ppc@FreeBSD.org Subject: Re: IA64, PPC system call path audit patches Message-ID: <87hczsasl5.wl%peterc@quokka.chubb.wattle.id.au> In-Reply-To: <20060901092636.E4921@fledge.watson.org> References: <20060901080402.W97485@fledge.watson.org> <87irk8at9i.wl%peterc@quokka.chubb.wattle.id.au> <20060901092636.E4921@fledge.watson.org>
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>>>>> "Robert" == Robert Watson <rwatson@FreeBSD.org> writes: Robert> On Fri, 1 Sep 2006, Peter Chubb wrote: >> You've only caught the IA64 slow path system call entries. The >> fast path is highly optimised assembly language inside >> arch/ia64/kernel/fsys.S, that avoids doing a trap at all. >> >> With a modern libc, syscall_via_break is only called for a very few >> system calls. Robert> Hmm. I'm confused by the above comment -- I'm catching system Robert> calls on the kernel side of the system call invocation around Robert> the system call, not on the libc side. I only see two system Robert> call demux points in the src/sys/ia64 tree: Sure. Original libcs call the system call using break 0x10000, which ends up in the code you saw. Recent libcs call via a gate page with an epc (execute privileged code) instruction that vectors direcgtly to the syscall implementation. Robert> ./ia32/ia32_trap.c: error = (*callp->sy_call)(td, args64); Robert> ./ia64/trap.c: error = (*callp->sy_call)(td, args); Take a look in gate.S, symbol _kernel_syscall_via_epc There's assembly language there that loads the function descriptor from the table and branches to it. THere are two kinds of system call implementations: fast (implemented directly in assembly language in fsys.S) and slow (the code in fsys.S `bubbles down' into kernel space and then invokes the syscall directly. Robert> Both of which are covered in the patch I attached. I'm under Robert> the impression that the different mechanisms to enter the Robert> kernel system call path converge prior to the system call Robert> table evaluation, in the kernel trap code. Do I Robert> misunderstand? Robert> Robert N M Watson Computer Laboratory University of Cambridge
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