From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jessica Yu Subject: Re: livepatch: reuse module loader code to write relocations Date: Mon, 21 Mar 2016 14:07:43 -0400 Message-ID: <20160321180742.GA12357@packer-debian-8-amd64.digitalocean.com> References: <1458157628-8264-1-git-send-email-jeyu@redhat.com> <1458157628-8264-5-git-send-email-jeyu@redhat.com> <20160321163157.GG19401@pathway.suse.cz> <20160321164651.zautqklg7ng3jfbn@treble.redhat.com> <20160321173639.ooighgwwubuqv6le@treble.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Return-path: Content-Disposition: inline In-Reply-To: <20160321173639.ooighgwwubuqv6le@treble.redhat.com> Sender: linux-doc-owner@vger.kernel.org List-Archive: List-Post: To: Josh Poimboeuf Cc: Petr Mladek , Rusty Russell , Jiri Kosina , Jonathan Corbet , Miroslav Benes , linux-api@vger.kernel.org, live-patching@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-doc@vger.kernel.org List-ID: +++ Josh Poimboeuf [21/03/16 12:36 -0500]: >On Mon, Mar 21, 2016 at 11:46:51AM -0500, Josh Poimboeuf wrote: >> On Mon, Mar 21, 2016 at 05:31:57PM +0100, Petr Mladek wrote: >> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c >> > > index 780f00c..2aa20fa 100644 >> > > --- a/kernel/livepatch/core.c >> > > +++ b/kernel/livepatch/core.c >> > > +static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod) >> > > +{ >> > > + int i, cnt, vmlinux, ret; >> > > + struct klp_buf bufs = {0}; >> > > + Elf_Rela *relas; >> > > + Elf_Sym *sym; >> > > + char *symname; >> > > + unsigned long sympos; >> > > + >> > > + relas = (Elf_Rela *) relasec->sh_addr; >> > > + /* For each rela in this klp relocation section */ >> > > + for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) { >> > > + sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info); >> > > + if (sym->st_shndx != SHN_LIVEPATCH) >> > > + return -EINVAL; >> > > + >> > > + klp_clear_buf(&bufs); >> > > + >> > > + /* Format: .klp.sym.objname.symbol_name,sympos */ >> > > + symname = pmod->core_kallsyms.strtab + sym->st_name; >> > > + cnt = sscanf(symname, ".klp.sym.%64[^.].%128[^,],%lu", >> > > + bufs.objname, bufs.symname, &sympos); >> > >> > Note that MODULE_NAME_LEN even is not 64. It is defined by: >> > >> > #define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long)) >> > >> > I strongly suggest to use the proposal from Josh. >> >> Hm, looks like my suggestion to use __stringify(MODULE_NAME_LEN) doesn't >> work. It results in the string "MODULE_NAME_LEN". Which surprises me: >> isn't is supposed to resolve the macro before applying the '#' operation >> to it? > >Turns out I hadn't included module.h. When I do so, >__stringify(MODULE_NAME_LEN) becomes "(64 - sizeof(unsigned long))". >Which is still not going to work :-/ > Hm, we probably won't be able to make use of preprocessor tricks here, since I don't think the preprocessor can even evaluate that expression (esp. with that sizeof there). This might mean building the format string at runtime, which may be more trouble than it's worth... >> I was going to suggest another idea: hard-code it at 63 and then do >> something like >> >> BUILD_BUG_ON(MODULE_NAME_LEN != 64) >> >> But you're right... it's not even 64! >> >> Need to think on this some more... > >-- >Josh