Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752014AbbGMIGW (ORCPT ); Mon, 13 Jul 2015 04:06:22 -0400 Received: from smtprelay4.synopsys.com ([198.182.47.9]:46012 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751410AbbGMIGT convert rfc822-to-8bit (ORCPT ); Mon, 13 Jul 2015 04:06:19 -0400 From: Vineet Gupta To: Alexey Brodkin CC: "arc-linux-dev@synopsys.com" , "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] ARC: make sure instruction_pointer() returns unsigned value Thread-Topic: [PATCH] ARC: make sure instruction_pointer() returns unsigned value Thread-Index: AQHQvT0cxX2HeGW58ES7/6CuoW9l2Q== Date: Mon, 13 Jul 2015 08:05:59 +0000 Message-ID: References: <1436772317-3785-1-git-send-email-abrodkin@synopsys.com> Accept-Language: en-US, en-IN Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.12.197.226] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2555 Lines: 57 On Monday 13 July 2015 12:55 PM, Alexey Brodkin wrote: > Currently instruction_pointer() returns pt_regs->ret and so return value > is of type "long", which implicitly stands for "signed long". > > While that's perfectly fine when dealing with 32-bit values if return > value of instruction_pointer() gets assigned to 64-bit variable sign > extension may happen. > > And at least in one real use-case it happens already. > In perf_prepare_sample() return value of perf_instruction_pointer() > (which is an alias to instruction_pointer() in case of ARC) is assigned > to (struct perf_sample_data)->ip (which type is "u64"). > > And what we see if instuction pointer points to user-space application > that in case of ARC lays below 0x8000_0000 "ip" gets set properly with > leading 32 zeros. But if instruction pointer points to kernel address > space that starts from 0x8000_0000 then "ip" is set with 32 leadig > "f"-s. I.e. id instruction_pointer() returns 0x8100_0000, "ip" will be > assigned with 0xffff_ffff__8100_0000. Which is obviously wrong. > > In particular that issuse broke output of perf, because perf was unable > to associate addresses like 0xffff_ffff__8100_0000 with anything from > /proc/kallsyms. > > That's what we used to see: > ----------->8---------- > 6.27% ls [unknown] [k] 0xffffffff8046c5cc > 2.96% ls libuClibc-0.9.34-git.so [.] memcpy > 2.25% ls libuClibc-0.9.34-git.so [.] memset > 1.66% ls [unknown] [k] 0xffffffff80666536 > 1.54% ls libuClibc-0.9.34-git.so [.] 0x000224d6 > 1.18% ls libuClibc-0.9.34-git.so [.] 0x00022472 > ----------->8---------- > > With that change perf output looks much better now: > ----------->8---------- > 8.21% ls [kernel.kallsyms] [k] memset > 3.52% ls libuClibc-0.9.34-git.so [.] memcpy > 2.11% ls libuClibc-0.9.34-git.so [.] malloc > 1.88% ls libuClibc-0.9.34-git.so [.] memset > 1.64% ls [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore > 1.41% ls [kernel.kallsyms] [k] __d_lookup_rcu > ----------->8---------- > > Signed-off-by: Alexey Brodkin Thx Alexey - this solves a long standing mystery with some weird perf profiles. Applied ! Thx, -Vineet -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/