From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Ellerman Subject: Re: [PATCH 3/5] powerpc64: Add .opd based function descriptor dereference Date: Wed, 20 Sep 2017 11:51:49 +1000 Message-ID: <878tha9lxm.fsf@concordia.ellerman.id.au> References: <20170916035347.19705-1-sergey.senozhatsky@gmail.com> <20170916035347.19705-4-sergey.senozhatsky@gmail.com> <20170916094345.d332z3odceqiyrll@naverao1-tp.localdomain> <87shfjkmxe.fsf@concordia.ellerman.id.au> <20170919103154.GC401@jagdpanzerIV.localdomain> Mime-Version: 1.0 Content-Type: text/plain Cc: "Naveen N. Rao" , Sergey Senozhatsky , Tony Luck , Fenghua Yu , Benjamin Herrenschmidt , Paul Mackerras , "James E . J . Bottomley" , Helge Deller , Petr Mladek , linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, Alexei Starovoitov , Steven Rostedt , linux-kernel@vger.kernel.org, Jessica Yu , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin To: Sergey Senozhatsky Return-path: In-Reply-To: <20170919103154.GC401@jagdpanzerIV.localdomain> List-ID: List-Id: linux-parisc.vger.kernel.org Sergey Senozhatsky writes: > On (09/19/17 20:22), Michael Ellerman wrote: >> > On 2017/09/16 12:53PM, Sergey Senozhatsky wrote: >> >> We are moving towards separate kernel and module function descriptor >> >> dereference callbacks. This patch enables it for powerpc64. >> >> >> >> For pointers that belong to the kernel >> >> - Added __start_opd and __end_opd pointers, to track the kernel >> >> .opd section address range; >> >> >> >> - Added dereference_kernel_function_descriptor(). Now we >> >> will dereference only function pointers that are within >> >> [__start_opd, __end_opd]; >> >> >> >> For pointers that belong to a module >> >> - Added dereference_module_function_descriptor() to handle module >> >> function descriptor dereference. Now we will dereference only >> >> pointers that are within [module->opd.start, module->opd.end]. >> > >> > Would it be simpler to just use kernel_text_address() and dereference >> > everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only >> > dereference function descriptor for non-text symbols") for a related >> > patch. >> >> Yeah that would be a lot simpler and probably work perfectly well. > > unlike ppc_function_entry(), printk() can get called on any symbol, > not just function pointers. > > for example, > > cat /proc/kallsyms | grep shrinker_rwsem > ffffffff81a4b1e0 d shrinker_rwsem Yep, good point. So your patch is probably good then. Maybe someone other than me can find time to test it ;) cheers From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Ellerman Date: Wed, 20 Sep 2017 01:51:49 +0000 Subject: Re: [PATCH 3/5] powerpc64: Add .opd based function descriptor dereference Message-Id: <878tha9lxm.fsf@concordia.ellerman.id.au> List-Id: References: <20170916035347.19705-1-sergey.senozhatsky@gmail.com> <20170916035347.19705-4-sergey.senozhatsky@gmail.com> <20170916094345.d332z3odceqiyrll@naverao1-tp.localdomain> <87shfjkmxe.fsf@concordia.ellerman.id.au> <20170919103154.GC401@jagdpanzerIV.localdomain> In-Reply-To: <20170919103154.GC401@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Sergey Senozhatsky Cc: "Naveen N. Rao" , Sergey Senozhatsky , Tony Luck , Fenghua Yu , Benjamin Herrenschmidt , Paul Mackerras , "James E . J . Bottomley" , Helge Deller , Petr Mladek , linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, Alexei Starovoitov , Steven Rostedt , linux-kernel@vger.kernel.org, Jessica Yu , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin Sergey Senozhatsky writes: > On (09/19/17 20:22), Michael Ellerman wrote: >> > On 2017/09/16 12:53PM, Sergey Senozhatsky wrote: >> >> We are moving towards separate kernel and module function descriptor >> >> dereference callbacks. This patch enables it for powerpc64. >> >> >> >> For pointers that belong to the kernel >> >> - Added __start_opd and __end_opd pointers, to track the kernel >> >> .opd section address range; >> >> >> >> - Added dereference_kernel_function_descriptor(). Now we >> >> will dereference only function pointers that are within >> >> [__start_opd, __end_opd]; >> >> >> >> For pointers that belong to a module >> >> - Added dereference_module_function_descriptor() to handle module >> >> function descriptor dereference. Now we will dereference only >> >> pointers that are within [module->opd.start, module->opd.end]. >> > >> > Would it be simpler to just use kernel_text_address() and dereference >> > everything else? See commit 83e840c770f2c5 ("powerpc64/elfv1: Only >> > dereference function descriptor for non-text symbols") for a related >> > patch. >> >> Yeah that would be a lot simpler and probably work perfectly well. > > unlike ppc_function_entry(), printk() can get called on any symbol, > not just function pointers. > > for example, > > cat /proc/kallsyms | grep shrinker_rwsem > ffffffff81a4b1e0 d shrinker_rwsem Yep, good point. So your patch is probably good then. Maybe someone other than me can find time to test it ;) cheers