From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756803AbdADSAc (ORCPT ); Wed, 4 Jan 2017 13:00:32 -0500 Received: from 92-243-34-74.adsl.nanet.at ([92.243.34.74]:43325 "EHLO mail.osadl.at" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751599AbdADR7g (ORCPT ); Wed, 4 Jan 2017 12:59:36 -0500 Date: Wed, 4 Jan 2017 17:58:23 +0000 From: Nicholas Mc Guire To: Dave Young Cc: Vivek Goyal , Nicholas Mc Guire , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Baoquan He Subject: Re: [PATCH RFC V2] purgatory: fix up declarations Message-ID: <20170104175823.GA641@osadl.at> References: <1482493387-30168-1-git-send-email-hofrat@osadl.org> <20170103153814.GC29807@redhat.com> <20170103163422.GB24542@osadl.at> <20170104061620.GA19466@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170104061620.GA19466@dhcp-128-65.nay.redhat.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 Wed, Jan 04, 2017 at 02:16:20PM +0800, Dave Young wrote: > Vivek, thanks for ccing me.. > > On 01/03/17 at 04:34pm, Nicholas Mc Guire wrote: > > On Tue, Jan 03, 2017 at 10:38:14AM -0500, Vivek Goyal wrote: > > > On Fri, Dec 23, 2016 at 12:43:07PM +0100, Nicholas Mc Guire wrote: > > > > Add the missing declarations of basic purgatory functions and variables > > > > used with kexec_purgatory_get_set_symbol() to allow a clean build. > > > > > > > > Fixes: commit 8fc5b4d4121c ("purgatory: core purgatory functionality") > > > > Signed-off-by: Nicholas Mc Guire > > > > --- > > > > > > > > V2: after kbuild test robot reported a build failure > > > > removed incorrect declaration of copy_backup_region which is static > > > > anyway. > > > > > > > > sparse complained about: > > > > CHECK arch/x86/purgatory/purgatory.c > > > > arch/x86/purgatory/purgatory.c:21:15: warning: symbol 'backup_dest' was not declared. Should it be static? > > > > arch/x86/purgatory/purgatory.c:22:15: warning: symbol 'backup_src' was not declared. Should it be static? > > > > arch/x86/purgatory/purgatory.c:23:15: warning: symbol 'backup_sz' was not declared. Should it be static? > > > > arch/x86/purgatory/purgatory.c:25:4: warning: symbol 'sha256_digest' was not declared. Should it be static? > > > > arch/x86/purgatory/purgatory.c:27:19: warning: symbol 'sha_regions' was not declared. Should it be static? > > > > arch/x86/purgatory/purgatory.c:42:5: warning: symbol 'verify_sha256_digest' was not declared. Should it be static? > > > > arch/x86/purgatory/purgatory.c:61:6: warning: symbol 'purgatory' was not declared. Should it be static? > > > > CC arch/x86/purgatory/purgatory.o > > > > > > > > Numerous sparse messages regarding functions not being declared, these > > > > functions are resolved via kexec_purgatory_get_set_symbol() and not > > > > directly called anywhere. > > > > > > Hi Nicholas, > > > > > > So purgatory() is a separate piece of small binary which does not link > > > against kernel. And we don't want these symbols static as kernel > > > obtains the values of these symbols and modifies binary in place on > > > the fly. I am assuming if we make them static, then we will lose this > > > capability to be able to read elf headers and be able to modify value > > > of these symbols. > > > > I donīt understand why this would be lost - the symbols are not being > > used by kernel code other than kexec code it self - in what way > > would declaring them extern change there handling ? > > kexec_purgatory_find_symbol is using the elf header to resolve the > > symbol location and declaring it extern should not change that in any > > way - am I overlooking something ? > > > > > > > > Now question is how to supress warnings from sparse. If just declaring > > > them extern in header file and including that header file in some other > > > .c file make the sparse warning go away, so be it. Atleast we need > > > to make explicit comment that this is being done just to take care > > > of sparse warning. > > > > > > I am not very happy with the solution though. In future it will make > > > people scratch their head that why are we including this header file > > > and why some symbols are being declared extern. So if there is another > > > way to tell sparse to not worry about it, would be even better. > > > > > > > The assumtion was that these changes would be side-effect free - if they are > > not then this is probably the wrong path to go - the intent is to remove > > the sparse warnings only. > > Another way is do not include the header file, but declare them in the c > file just for avoiding the sparse warnings with some comments to explain > it. > ok - will go back and try that route - sounds a lot less invasive. > > > > > > > > > To resolve the sparse issues appropriate > > > > declarations were added to asm/kexec-bzimage64.h and the appropriate > > > > reference included in purgatory.c. Adding this to kexec-bzimage64.h > > > > was done as setup_purgatory() from machine_kexec_file_64.c uses > > > > these symbols - not sure if this is the proper place to add this. > > > > > > > > While at it the initialization of sha_regions to {{0,0}} was added. > > > > > > > > > > Is it really required. I thought all these global variable are will be > > > set to 0 without doing anything explicit. > > > > > > > No - technically it is not needed - but rather just a consistency > > issue as > > u8 sha256_digest[SHA256_DIGEST_SIZE] = { 0 }; > > is being initialized explicidly I just found it consostent to initialize > > struct sha_region sha_regions[16] = {}; > > explicidly as well - but that can be dropped if its usual practice. > > It can be in another patch, removing the explicit zero initializing > looks better.. > fine - that also achieves consistency - will put that into a separate patch then and repost. thanks for the review notes. thx! hofrat > > > > > > > Patch was compile tested with: x86_64_defconfig (implies CONFIG_KEXEC=y) > > > > > > > > Patch is against 4.9.0 (localversion-next is next-20161223) > > > > > > > > arch/x86/include/asm/kexec-bzimage64.h | 16 ++++++++++++++++ > > > > arch/x86/purgatory/purgatory.c | 8 ++------ > > > > 2 files changed, 18 insertions(+), 6 deletions(-) > > > > > > > > diff --git a/arch/x86/include/asm/kexec-bzimage64.h b/arch/x86/include/asm/kexec-bzimage64.h > > > > index d1b5d19..fd7f776 100644 > > > > --- a/arch/x86/include/asm/kexec-bzimage64.h > > > > +++ b/arch/x86/include/asm/kexec-bzimage64.h > > > > @@ -1,6 +1,21 @@ > > > > #ifndef _ASM_KEXEC_BZIMAGE64_H > > > > #define _ASM_KEXEC_BZIMAGE64_H > > > > > > > > +struct sha_region { > > > > + unsigned long start; > > > > + unsigned long len; > > > > +}; > > > > + > > > > extern struct kexec_file_ops kexec_bzImage64_ops; > > > > > > > > +/* needed for kexec_purgatory_get_set_symbol() */ > > > > +extern unsigned long backup_dest; > > > > +extern unsigned long backup_src; > > > > +extern unsigned long backup_sz; > > > > +extern u8 sha256_digest[]; > > > > +extern struct sha_region sha_regions[]; > > > > + > > > > +void purgatory(void); > > > > +int verify_sha256_digest(void); > > > > + > > > > #endif /* _ASM_KEXE_BZIMAGE64_H */ > > > > diff --git a/arch/x86/purgatory/purgatory.c b/arch/x86/purgatory/purgatory.c > > > > index 25e068b..26c8367 100644 > > > > --- a/arch/x86/purgatory/purgatory.c > > > > +++ b/arch/x86/purgatory/purgatory.c > > > > @@ -12,11 +12,7 @@ > > > > > > > > #include "sha256.h" > > > > #include "../boot/string.h" > > > > - > > > > -struct sha_region { > > > > - unsigned long start; > > > > - unsigned long len; > > > > -}; > > > > +#include > > > > > > > > unsigned long backup_dest = 0; > > > > unsigned long backup_src = 0; > > > > @@ -24,7 +20,7 @@ unsigned long backup_sz = 0; > > > > > > > > u8 sha256_digest[SHA256_DIGEST_SIZE] = { 0 }; > > > > > > > > -struct sha_region sha_regions[16] = {}; > > > > +struct sha_region sha_regions[16] = { { 0, 0 } }; > > > > > > > > /* > > > > * On x86, second kernel requries first 640K of memory to boot. Copy > > > > -- > > > > 2.1.4 > > Thanks > Dave