From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757261AbcHWJSC (ORCPT ); Tue, 23 Aug 2016 05:18:02 -0400 Received: from foss.arm.com ([217.140.101.70]:34620 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756699AbcHWJR7 (ORCPT ); Tue, 23 Aug 2016 05:17:59 -0400 Subject: Re: [PATCH 5/8] arm64: alternative: Add support for patching adrp instructions To: Ard Biesheuvel References: <1471525832-21209-1-git-send-email-suzuki.poulose@arm.com> <1471525832-21209-6-git-send-email-suzuki.poulose@arm.com> Cc: "linux-arm-kernel@lists.infradead.org" , Mark Rutland , Marc Zyngier , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Andre Przywara From: Suzuki K Poulose Message-ID: <3c727d40-0ea8-fb2d-7d51-3d47b96e96c4@arm.com> Date: Tue, 23 Aug 2016 10:16:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/08/16 12:45, Ard Biesheuvel wrote: > On 18 August 2016 at 15:10, Suzuki K Poulose wrote: >> adrp uses PC-relative address offset to a page (of 4K size) of >> a symbol. If it appears in an alternative code patched in, we >> should adjust the offset to reflect the address where it will >> be run from. This patch adds support for fixing the offset >> for adrp instructions. >> >> Cc: Will Deacon >> Cc: Marc Zyngier >> Cc: Andre Przywara >> Cc: Mark Rutland >> Signed-off-by: Suzuki K Poulose >> --- >> arch/arm64/kernel/alternative.c | 13 +++++++++++++ >> 1 file changed, 13 insertions(+) >> >> diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c >> index d2ee1b2..71c6962 100644 >> --- a/arch/arm64/kernel/alternative.c >> +++ b/arch/arm64/kernel/alternative.c >> @@ -80,6 +80,19 @@ static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr) >> offset = target - (unsigned long)insnptr; >> insn = aarch64_set_branch_offset(insn, offset); >> } >> + } else if (aarch64_insn_is_adrp(insn)) { >> + s32 orig_offset, new_offset; >> + unsigned long target; >> + >> + /* >> + * If we're replacing an adrp instruction, which uses PC-relative >> + * immediate addressing, adjust the offset to reflect the new >> + * PC. adrp operates on 4K aligned addresses. >> + */ >> + orig_offset = aarch64_insn_adrp_get_offset(insn); >> + target = ((unsigned long)altinsnptr & ~0xfffUL) + orig_offset; >> + new_offset = target - ((unsigned long)insnptr & ~0xfffUL); >> + insn = aarch64_insn_adrp_set_offset(insn, new_offset); > > Are orig_offset and new_offset guaranteed to be equal modulo 4 KB? > Otherwise, you will have to track down and patch the associated :lo12: > add/ldr instruction as well. We are modifying the alternative instruction to accommodate for the new PC, where this instruction will be executed from, while the referenced symbol remains the same. Hence the associated :lo12: doesn't change. Does that address your concern ? Or did I miss something ? Suzuki