From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758115AbcBYAJJ (ORCPT ); Wed, 24 Feb 2016 19:09:09 -0500 Received: from mail-pa0-f45.google.com ([209.85.220.45]:33746 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754407AbcBYAJF (ORCPT ); Wed, 24 Feb 2016 19:09:05 -0500 Subject: Re: [PATCH 03/12] powerpc/module: Create a special stub for ftrace_caller() To: Michael Ellerman , linuxppc-dev@ozlabs.org References: <1456324115-21144-1-git-send-email-mpe@ellerman.id.au> <1456324115-21144-3-git-send-email-mpe@ellerman.id.au> Cc: duwe@lst.de, linux-kernel@vger.kernel.org, rostedt@goodmis.org, kamalesh@linux.vnet.ibm.com, pmladek@suse.com, jeyu@redhat.com, jkosina@suse.cz, live-patching@vger.kernel.org, mbenes@suse.cz From: Balbir Singh Message-ID: <56CE4616.9080100@gmail.com> Date: Thu, 25 Feb 2016 11:08:54 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <1456324115-21144-3-git-send-email-mpe@ellerman.id.au> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/02/16 01:28, Michael Ellerman wrote: > In order to support the new -mprofile-kernel ABI, we need to be able to > call from the module back to ftrace_caller() (in the kernel) without > using the module's r2. That is because the function in this module which > is calling ftrace_caller() may not have setup r2, if it doesn't > otherwise need it (ie. it accesses no globals). > > To make that work we add a new stub which is used for calling > ftrace_caller(), which uses the kernel toc instead of the module toc. > > Signed-off-by: Michael Ellerman > --- > arch/powerpc/kernel/module_64.c | 48 ++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 47 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c > index 9629966e614b..e711d40a3b8f 100644 > --- a/arch/powerpc/kernel/module_64.c > +++ b/arch/powerpc/kernel/module_64.c > @@ -671,10 +671,56 @@ int apply_relocate_add(Elf64_Shdr *sechdrs, > } > > #ifdef CONFIG_DYNAMIC_FTRACE > + > +#define PACATOC offsetof(struct paca_struct, kernel_toc) > + > +static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me) > +{ > + struct ppc64_stub_entry *entry; > + unsigned int i, num_stubs; How about some comments on r2 r2 is still pointing to the module's toc, will be saved by ftrace_caller and restored by the instruction following bl ftrace_caller (after patching _mcount/nop) > + static u32 stub_insns[] = { > + 0xe98d0000 | PACATOC, /* ld r12,PACATOC(r13) */ > + 0x3d8c0000, /* addis r12,r12, */ > + 0x398c0000, /* addi r12,r12, */ > + 0x7d8903a6, /* mtctr r12 */ > + 0x4e800420, /* bctr */ > + }; > + long reladdr; > + > + num_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*entry); > + > + /* Find the next available stub entry */ > + entry = (void *)sechdrs[me->arch.stubs_section].sh_addr; > + for (i = 0; i < num_stubs && stub_func_addr(entry->funcdata); i++, entry++); > + > + if (i >= num_stubs) { > + pr_err("%s: Unable to find a free slot for ftrace stub.\n", me->name); > + return 0; > + } > + > + memcpy(entry->jump, stub_insns, sizeof(stub_insns)); > + > + /* Stub uses address relative to kernel_toc */ > + reladdr = (unsigned long)ftrace_caller - get_paca()->kernel_toc; > + if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) { > + pr_err("%s: Address of ftrace_caller out of range of kernel_toc.\n", me->name); > + return 0; > + } > + > + entry->jump[1] |= PPC_HA(reladdr); > + entry->jump[2] |= PPC_LO(reladdr); > + > + /* Eventhough we don't use funcdata in the stub, it's needed elsewhere. */ > + entry->funcdata = func_desc((unsigned long)ftrace_caller); > + entry->magic = STUB_MAGIC; > + > + return (unsigned long)entry; > +} > + > int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs) > { > mod->arch.toc = my_r2(sechdrs, mod); > - mod->arch.tramp = stub_for_addr(sechdrs, (unsigned long)ftrace_caller, mod); > + mod->arch.tramp = create_ftrace_stub(sechdrs, mod); > > if (!mod->arch.tramp) > return -ENOENT; Reviewed-by: Balbir Singh