From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755059AbcHVLTY (ORCPT ); Mon, 22 Aug 2016 07:19:24 -0400 Received: from foss.arm.com ([217.140.101.70]:51016 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754167AbcHVLTW (ORCPT ); Mon, 22 Aug 2016 07:19:22 -0400 Date: Mon, 22 Aug 2016 12:19:22 +0100 From: Will Deacon To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, andre.przywara@arm.com, Marc Zyngier Subject: Re: [PATCH 5/8] arm64: alternative: Add support for patching adrp instructions Message-ID: <20160822111921.GC14680@arm.com> References: <1471525832-21209-1-git-send-email-suzuki.poulose@arm.com> <1471525832-21209-6-git-send-email-suzuki.poulose@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1471525832-21209-6-git-send-email-suzuki.poulose@arm.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 Thu, Aug 18, 2016 at 02:10:29PM +0100, 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); The masking with ~0xfffUL might be nicer if you write it as align_down(ptr, SZ_4K); > + insn = aarch64_insn_adrp_set_offset(insn, new_offset); > } > > return insn; I wonder if we shouldn't have a catch-all for any instructions performing PC-relative operations here, because silent corruption of the instruction stream is pretty horrible. What other instructions are there? ADR, LDR (literal), ... ? Will