Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933464AbcCIR2c (ORCPT ); Wed, 9 Mar 2016 12:28:32 -0500 Received: from verein.lst.de ([213.95.11.211]:49245 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750922AbcCIR2X (ORCPT ); Wed, 9 Mar 2016 12:28:23 -0500 Date: Wed, 9 Mar 2016 18:28:21 +0100 From: Torsten Duwe To: Petr Mladek Cc: jeyu@redhat.com, jkosina@suse.cz, jikos@kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, kamalesh@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org, live-patching@vger.kernel.org, mbenes@suse.cz Subject: [PATCH 1/2] ppc64le live patch: clear out storage location(s) in mini stack frame Message-ID: <20160309172821.GC27913@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1788 Lines: 43 This can be applied on top of Petr Mladek's v4 rework of the ppc64le live patching. Inspired by Balbir Singh's v5, information about the callee's r2 is stored in a "reserved" 32 bit location in the caller's stack frame, instead of 64 bits in the newly created mini frame 24(r1). It only needs to work for a local call, when caller's TOC == callee's TOC, and along with the return address (LR) it's all within a 4GiB range (+-31 bits). If the original call already was global, we are allowed to restore any nonsense into r2, because the global caller will restore its TOC anyway from the ABI compliant location 24(r1) right after return. Signed-off-by: Torsten Duwe --- This is only the preparation for dumping the mini stack frame. It shouldn't break anything, bisecting-wise. --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -1284,8 +1284,9 @@ ftrace_call: * lr and LRSAVE(r1) contain the address of klp_return_helper. * We loaded ctr with the address of the patched function earlier */ + subf r0, r0, r2 /* Calculate offset from current TOC to LR */ + stw r0, 12(r1) /* and save it in CR+4 */ stdu r1, -32(r1) /* open new mini stack frame */ - std r2, 24(r1) /* save TOC now, unconditionally. */ bl 5f 5: mflr r12 addi r12, r12, (klp_return_helper + 4 - .)@l @@ -1323,9 +1324,10 @@ _GLOBAL(ftrace_stub) * maybe inserting a klp_return_helper frame or not. */ klp_return_helper: - ld r2, 24(r1) /* restore TOC (saved by ftrace_caller) */ addi r1, r1, 32 /* destroy mini stack frame */ + lwa r2, 12(r1) /* Load from CR+4, offset of TOC w.r.t LR */ ld r0, LRSAVE(r1) /* get the real return address */ + add r2, r2, r0 /* Add the current LR to offset */ mtlr r0 blr #endif