Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1037380AbdDUJTt (ORCPT ); Fri, 21 Apr 2017 05:19:49 -0400 Received: from mail-wm0-f54.google.com ([74.125.82.54]:37095 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1037364AbdDUJT0 (ORCPT ); Fri, 21 Apr 2017 05:19:26 -0400 Subject: Re: [PATCH] Documentation: DocBook: kgdb: update CONFIG_STRICT_KERNEL_RWX info To: Li Qiang , Jonathan Corbet References: <1492567125-61756-1-git-send-email-liqiang6-s@360.cn> Cc: jason.wessel@windriver.com, labbott@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kgdb-bugreport@lists.sourceforge.net, Li Qiang From: Daniel Thompson Message-ID: <18c8a563-b160-a1c9-16c8-603b9e7ee273@linaro.org> Date: Fri, 21 Apr 2017 10:19:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3577 Lines: 94 On 21/04/17 03:26, Li Qiang wrote: > > @Daniel > > 2017-04-20 23:28 GMT+08:00 Daniel Thompson >: > > On 19/04/17 02:58, Li Qiang wrote: > > CONFIG_STRICT_KERNEL_RWX is no longer selectable on most > architectures. > Update this info to thedocumentation. > > > "git grep STRICT_KERNEL_RWX" comes up with nothing. > > > It was introduced in commit 0f5bf6d0afe4be6e1391908ff2d6dc9730e91550. Oops. I did the grep on the wrong machine :-( and therefore on an older kernel than I thought... > It is selectable on any architecture? If not we should remove it > entirely! > > The 'STRICT_KERNEL_RWX' is renamed from 'CONFIG_DEBUG_RODATA > '. The original option is selectable. > > I'm not sure is this selectable on any architecture. So... having found the right kernel, it looks to me like only arm, arm64, parisc, s390 and x86 define ARCH_HAS_STRICT_KERNEL_RWX. Of these five, only arm defines ARCH_OPTIONAL_KERNEL_RWX and makes it user selectable. > > @Jonathan > > On Tue, 18 Apr 2017 18:58:45 -0700 > Li Qiang > wrote: > > > CONFIG_STRICT_KERNEL_RWX is no longer selectable on most architectures. > > Update this info to the documentation. > > > > Signed-off-by: Li Qiang > > > --- > > Documentation/DocBook/kgdb.tmpl | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl > > index 856ac20..ef0b67b 100644 > > --- a/Documentation/DocBook/kgdb.tmpl > > +++ b/Documentation/DocBook/kgdb.tmpl > > @@ -121,7 +121,9 @@ > > If kgdb supports it for the architecture you are using, you can > > use hardware breakpoints if you desire to run with the > > CONFIG_STRICT_KERNEL_RWX option turned on, else you need to turn off > > - this option. > > + this option. In most architectures, this option is not selectable. > > + For this situation, it can be turned off by adding a runtime parameter > > + 'rodata=off'. > > So this is an improvement, I guess, though the paragraph remains kind of > confusing. Is there any chance we could actually just say which > architectures can use hardware breakpoints, and which should boot with > rodata=off? > > > I think this is unnecessary as it is not common to change the > default CONFIG_STRICT_KERNEL_RWX /add rodata=off. > We here give this hint because CONFIG_STRICT_KERNEL_RWX is renamed > from CONFIG_DEBUG_RODATA. > And the latter is selectable, this can help the peoples who > think CONFIG_STRICT_KERNEL_RWX is also selectable. Having looked at the earlier part of the paragraph I think the info about rodata actually needs to be introduced slightly earlier (and rodata should be presented as the primary way to do it because 4 of the 5 architectures don't make STRICT_KERNEL_RWX optional). Something like: If the architecture that you are using supports making the text section read-only (CONFIG_STRICT_KERNEL_RWX), you should consider turning it off by adding 'rodata=off' to the kernel commandline or, if your architecture makes CONFIG_STRICT_KERNEL_RWX optional, by disabling this config option. Alternatively, if your architecture supports hardware breakpoints, these can be used to provide limited breakpoint support if you desire to run with a read-only text section. Daniel.