From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3CA21C7EE26 for ; Wed, 24 May 2023 00:05:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236229AbjEXAFc (ORCPT ); Tue, 23 May 2023 20:05:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34968 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229539AbjEXAFa (ORCPT ); Tue, 23 May 2023 20:05:30 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAF10E5; Tue, 23 May 2023 17:05:27 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 75D4562FBF; Wed, 24 May 2023 00:05:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D318FC4339B; Wed, 24 May 2023 00:05:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684886726; bh=c87dWfVIQm/nlzRv/KMLKVrwTHENHNLcmE0pdAdLe9o=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=OW1pb27yVUhopPe1LpHaPewR4l6jjgc68XiZBzRUDCFDtWBYe5+2rF0+MlsizNFEM 7XpiUYVuQImePtZ8HpkX45RrIH18oN8XnMu4opd3CW+nnHVGUEjDaYVGz4RD53XuAa jDZ8hBNRhU0bQjAnwk8rXBySv4L88NXN2Lam8iwowvuYnYZyV3f5cPmua6mCZa7MDt s9qyrMc7QR/ZoknEI/dw7UHhPou/p9WyHNTaYfajSg+lItMX3Q7T6f36TftE30h8eF 5C7pEBXvK+d5m+tBF/qMuk6eidHH/9AV0TZVCRV7ILixxh6xzu5g5UfBtUmtYByjsR My9THfihL2S/w== Received: by mail-oi1-f182.google.com with SMTP id 5614622812f47-39810ce3e13so310159b6e.2; Tue, 23 May 2023 17:05:26 -0700 (PDT) X-Gm-Message-State: AC+VfDzOXhFR70nR59lKbl9ikwiF22YbkTl+Y2oNVHCcGHRL+ZJTp0Fw i8Qg6BVTMw5eYV9tNu9/f6DIxeNt2aKwLoXk8Xw= X-Google-Smtp-Source: ACHHUZ5zgeo+bl4IlfyfI42y83apWO7cSnlKyUWFgBeMURoyHPsQMVQekNPkCs7jFSTpHTmO7uHYiJOUqtQ3Z9ciU1E= X-Received: by 2002:aca:6747:0:b0:398:3671:9bfe with SMTP id b7-20020aca6747000000b0039836719bfemr1685268oiy.31.1684886726117; Tue, 23 May 2023 17:05:26 -0700 (PDT) MIME-Version: 1.0 References: <20230521160426.1881124-1-masahiroy@kernel.org> <20230521160426.1881124-4-masahiroy@kernel.org> In-Reply-To: From: Masahiro Yamada Date: Wed, 24 May 2023 09:04:49 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v6 03/20] modpost: detect section mismatch for R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS To: Nick Desaulniers Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Nathan Chancellor , Nicolas Schier , Linux ARM , Ard Biesheuvel , Fangrui Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org On Tue, May 23, 2023 at 3:03=E2=80=AFAM Nick Desaulniers wrote: > > + linux-arm-kernel > > On Sun, May 21, 2023 at 9:05=E2=80=AFAM Masahiro Yamada wrote: > > > > ARM defconfig misses to detect some section mismatches. > > > > [test code] > > > > #include > > > > int __initdata foo; > > int get_foo(int x) { return foo; } > > > > It is apparently a bad reference, but modpost does not report anything > > for ARM defconfig (i.e. multi_v7_defconfig). > > > > The test code above produces the following relocations. > > > > Relocation section '.rel.text' at offset 0x200 contains 2 entries: > > Offset Info Type Sym.Value Sym. Name > > 00000000 0000062b R_ARM_MOVW_ABS_NC 00000000 .LANCHOR0 > > 00000004 0000062c R_ARM_MOVT_ABS 00000000 .LANCHOR0 > > > > Relocation section '.rel.ARM.exidx' at offset 0x210 contains 2 entrie= s: > > Offset Info Type Sym.Value Sym. Name > > 00000000 0000022a R_ARM_PREL31 00000000 .text > > 00000000 00001000 R_ARM_NONE 00000000 __aeabi_unwind_cpp_pr= 0 > > > > Currently, R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS are just skipped. > > > > Add code to handle them. I checked arch/arm/kernel/module.c to learn > > how the offset is encoded in the instruction. > > > > The referenced symbol in relocation might be a local anchor. > > If is_valid_name() returns false, let's search for a better symbol name= . > > > > Signed-off-by: Masahiro Yamada > > --- > > > > scripts/mod/modpost.c | 12 ++++++++++-- > > 1 file changed, 10 insertions(+), 2 deletions(-) > > > > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c > > index 34fbbd85bfde..ed2301e951a9 100644 > > --- a/scripts/mod/modpost.c > > +++ b/scripts/mod/modpost.c > > @@ -1108,7 +1108,7 @@ static inline int is_valid_name(struct elf_info *= elf, Elf_Sym *sym) > > /** > > * Find symbol based on relocation record info. > > * In some cases the symbol supplied is a valid symbol so > > - * return refsym. If st_name !=3D 0 we assume this is a valid symbol. > > + * return refsym. If is_valid_name() =3D=3D true, we assume this is a = valid symbol. > > * In other cases the symbol needs to be looked up in the symbol table > > * based on section and address. > > * **/ > > @@ -1121,7 +1121,7 @@ static Elf_Sym *find_tosym(struct elf_info *elf, = Elf64_Sword addr, > > Elf64_Sword d; > > unsigned int relsym_secindex; > > > > - if (relsym->st_name !=3D 0) > > + if (is_valid_name(elf, relsym)) > > return relsym; > > > > /* > > @@ -1312,11 +1312,19 @@ static int addend_arm_rel(struct elf_info *elf,= Elf_Shdr *sechdr, Elf_Rela *r) > > unsigned int r_typ =3D ELF_R_TYPE(r->r_info); > > Elf_Sym *sym =3D elf->symtab_start + ELF_R_SYM(r->r_info); > > unsigned int inst =3D TO_NATIVE(*reloc_location(elf, sechdr, r)= ); > > + int offset; > > > > switch (r_typ) { > > case R_ARM_ABS32: > > r->r_addend =3D inst + sym->st_value; > > break; > > + case R_ARM_MOVW_ABS_NC: > > + case R_ARM_MOVT_ABS: > > + offset =3D ((inst & 0xf0000) >> 4) | (inst & 0xfff); > > + offset =3D (offset ^ 0x8000) - 0x8000; > > The code in arch/arm/kernel/module.c then right shifts the offset by > 16 for R_ARM_MOVT_ABS. Is that necessary? I replied to Ard's email, but just in case. modpost does not need to write back the fixed instruction. modpost is only interested in the offset address. So, the right-shift by 16 is unneeded. --=20 Best Regards Masahiro Yamada