From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758041AbcBXObr (ORCPT ); Wed, 24 Feb 2016 09:31:47 -0500 Received: from ozlabs.org ([103.22.144.67]:47241 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753007AbcBXO2v (ORCPT ); Wed, 24 Feb 2016 09:28:51 -0500 From: Michael Ellerman To: Cc: bsingharora@gmail.com, duwe@lst.de, , 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 Subject: [PATCH 03/12] powerpc/module: Create a special stub for ftrace_caller() Date: Thu, 25 Feb 2016 01:28:26 +1100 Message-Id: <1456324115-21144-3-git-send-email-mpe@ellerman.id.au> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1456324115-21144-1-git-send-email-mpe@ellerman.id.au> References: <1456324115-21144-1-git-send-email-mpe@ellerman.id.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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; + 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; -- 2.5.0