From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751539AbdBFNCa (ORCPT ); Mon, 6 Feb 2017 08:02:30 -0500 Received: from foss.arm.com ([217.140.101.70]:57120 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750980AbdBFNC3 (ORCPT ); Mon, 6 Feb 2017 08:02:29 -0500 Date: Mon, 6 Feb 2017 13:02:29 +0000 From: Will Deacon To: Hekuang Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, mhiramat@kernel.org, jolsa@redhat.com, wangnan0@huawei.com, bintian.wang@huawei.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 1/3] perf tools: Use offset instead of dwarfnum in register table. Message-ID: <20170206130229.GI19939@arm.com> References: <20170203110607.97529-1-hekuang@huawei.com> <20170203130026.GF11585@arm.com> <589598D8.8050304@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <589598D8.8050304@huawei.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 04, 2017 at 05:03:20PM +0800, Hekuang wrote: > hi > > 在 2017/2/3 21:00, Will Deacon 写道: > >On Fri, Feb 03, 2017 at 11:06:05AM +0000, He Kuang wrote: > >>This patch changes the 'dwarfnum' to 'offset' in register table, so > >>the index of array becomes the dwarfnum (the index of each register > >>defined by DWARF) and the "offset" member means the byte-offset of the > >>register in (user_)pt_regs. This change makes the code consistent with > >>x86. > >> > >>Acked-by: Masami Hiramatsu > >>Signed-off-by: He Kuang > >>--- > >> tools/perf/arch/arm64/util/dwarf-regs.c | 107 ++++++++++++++++---------------- > >> 1 file changed, 52 insertions(+), 55 deletions(-) > >Thanks for splitting this up. Comment below. > > > >>diff --git a/tools/perf/arch/arm64/util/dwarf-regs.c b/tools/perf/arch/arm64/util/dwarf-regs.c > >>index d49efeb..090f36b 100644 > >>--- a/tools/perf/arch/arm64/util/dwarf-regs.c > >>+++ b/tools/perf/arch/arm64/util/dwarf-regs.c > >>@@ -9,72 +9,69 @@ > >> */ > >> #include > >>+#include /* for struct user_pt_regs */ > >> #include > >>-struct pt_regs_dwarfnum { > >>+struct pt_regs_offset { > >> const char *name; > >>- unsigned int dwarfnum; > >>+ int offset; > >> }; > >>-#define STR(s) #s > >>-#define REG_DWARFNUM_NAME(r, num) {.name = r, .dwarfnum = num} > >>-#define GPR_DWARFNUM_NAME(num) \ > >>- {.name = STR(%x##num), .dwarfnum = num} > >>-#define REG_DWARFNUM_END {.name = NULL, .dwarfnum = 0} > >>- > >> /* > >> * Reference: > >> * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0057b/IHI0057B_aadwarf64.pdf > >> */ > >>-static const struct pt_regs_dwarfnum regdwarfnum_table[] = { > >>- GPR_DWARFNUM_NAME(0), > >>- GPR_DWARFNUM_NAME(1), > >>- GPR_DWARFNUM_NAME(2), > >>- GPR_DWARFNUM_NAME(3), > >>- GPR_DWARFNUM_NAME(4), > >>- GPR_DWARFNUM_NAME(5), > >>- GPR_DWARFNUM_NAME(6), > >>- GPR_DWARFNUM_NAME(7), > >>- GPR_DWARFNUM_NAME(8), > >>- GPR_DWARFNUM_NAME(9), > >>- GPR_DWARFNUM_NAME(10), > >>- GPR_DWARFNUM_NAME(11), > >>- GPR_DWARFNUM_NAME(12), > >>- GPR_DWARFNUM_NAME(13), > >>- GPR_DWARFNUM_NAME(14), > >>- GPR_DWARFNUM_NAME(15), > >>- GPR_DWARFNUM_NAME(16), > >>- GPR_DWARFNUM_NAME(17), > >>- GPR_DWARFNUM_NAME(18), > >>- GPR_DWARFNUM_NAME(19), > >>- GPR_DWARFNUM_NAME(20), > >>- GPR_DWARFNUM_NAME(21), > >>- GPR_DWARFNUM_NAME(22), > >>- GPR_DWARFNUM_NAME(23), > >>- GPR_DWARFNUM_NAME(24), > >>- GPR_DWARFNUM_NAME(25), > >>- GPR_DWARFNUM_NAME(26), > >>- GPR_DWARFNUM_NAME(27), > >>- GPR_DWARFNUM_NAME(28), > >>- GPR_DWARFNUM_NAME(29), > >>- REG_DWARFNUM_NAME("%lr", 30), > >>- REG_DWARFNUM_NAME("%sp", 31), > >>- REG_DWARFNUM_END, > >>-}; > >>+#define REG_OFFSET_NAME(r, num) {.name = "%" #r, \ > >>+ .offset = offsetof(struct user_pt_regs, regs[num])} > >Whilst this works in practice, this is undefined behaviour for "sp", since > >you'll go off the end of the regs array. > > It's not undefined behaviour here, > struct user_pt_regs { > __u64 regs[31]; > __u64 sp; > __u64 pc; > __u64 pstate; > }; > user_pt_regs->regs[31] is user_pt_regs->sp and the offset value is correct. I think it's undefined from the C standard perspective. > > > >I still think you're better off sticking with the dwarfnum, then just having > >a dwarfnum2offset macro that multiplies by the size of a register. > > > >Will > I think add a ptregs_offset field is more suitable and makes the code > indepent > to struct user_pt_regs layout, for example if the structure changed to this: > > struct user_pt_regs { > __u64 sp; > __u64 pc; > __u64 pstate; > __u64 regs[31]; > }; We won't reorder a uapi structure because that would binary compatibility. Just send a patch using the dwarfnum as the index for the offset calculation, like I've been saying since you posted the first version. Will