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 116FDC77B7C for ; Sun, 21 May 2023 16:05:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230075AbjEUQFU (ORCPT ); Sun, 21 May 2023 12:05:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55118 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230017AbjEUQFT (ORCPT ); Sun, 21 May 2023 12:05:19 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5E1E3CD; Sun, 21 May 2023 09:05:18 -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 E88F960F36; Sun, 21 May 2023 16:05:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 42A2BC4339E; Sun, 21 May 2023 16:05:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684685117; bh=fNR4CDXASXYl6s1DvjTHLO1BvaWuFWmKCQClVKnCc7s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=h9MbM1JfV/RDfTfTvRsMuDs9iyR1i4Yb5uoJ/nLE4syQQxu7iQkF89kxdZiYsxWTD ZTD8cLNzJFauyIFbbMVl6tlYJpeU5kl7o+GStYWQU/u94eqU4c4bQAk2M1YrBy7jiY JLMZbn/012F3GlLcshbLfhRgjMSyvGJSIRjkIBH/tWKm+3nv469IVUcZ7iEdUoaLzv CW0Rpe7UC2E6KcTkujjKuy6x7tc5/OJfi+mW37CbhZKOZTeCZCsKo7KS0TntbvUI/y e+p0GFNB5Sofu6R+77TzNg080f2tjm3Zk2oxf8Ljr51NoZ6y8U8C/WaCcy8CRwtA5y Y/GwpNMgFlU4w== From: Masahiro Yamada To: linux-kbuild@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Nathan Chancellor , Nick Desaulniers , Nicolas Schier , Masahiro Yamada Subject: [PATCH v6 02/20] modpost: fix section mismatch message for R_ARM_ABS32 Date: Mon, 22 May 2023 01:04:07 +0900 Message-Id: <20230521160426.1881124-3-masahiroy@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230521160426.1881124-1-masahiroy@kernel.org> References: <20230521160426.1881124-1-masahiroy@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org addend_arm_rel() processes R_ARM_ABS32 in a wrong way. Here, simple test code. [test code 1] #include int __initdata foo; int get_foo(int x) { return foo; } If you compile it with ARM versatile_defconfig, modpost will show the symbol name, (unknown). WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> (unknown) (section: .init.data) If you compile it for other architectures, modpost will show the correct symbol name. WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> foo (section: .init.data) For R_ARM_ABS32, addend_arm_rel() sets r->r_addend to a wrong value. I just mimicked the code in arch/arm/kernel/module.c. However, there is more difficulty for ARM. Here, test code. [test code 2] #include int __initdata foo; int get_foo(int x) { return foo; } int __initdata bar; int get_bar(int x) { return bar; } With this commit applied, modpost will show the following messages for ARM versatile_defconfig: WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> foo (section: .init.data) WARNING: modpost: vmlinux.o: section mismatch in reference: get_bar (section: .text) -> foo (section: .init.data) The reference from 'get_bar' to 'foo' seems wrong. I have no solution for this because it is true in assembly level. In the following output, relocation at 0x1c is no longer associated with 'bar'. The two relocation entries point to the same symbol, and the offset to 'bar' is encoded in the instruction 'r0, [r3, #4]'. Disassembly of section .text: 00000000 : 0: e59f3004 ldr r3, [pc, #4] @ c 4: e5930000 ldr r0, [r3] 8: e12fff1e bx lr c: 00000000 .word 0x00000000 00000010 : 10: e59f3004 ldr r3, [pc, #4] @ 1c 14: e5930004 ldr r0, [r3, #4] 18: e12fff1e bx lr 1c: 00000000 .word 0x00000000 Relocation section '.rel.text' at offset 0x244 contains 2 entries: Offset Info Type Sym.Value Sym. Name 0000000c 00000c02 R_ARM_ABS32 00000000 .init.data 0000001c 00000c02 R_ARM_ABS32 00000000 .init.data When find_elf_symbol() gets into a situation where relsym->st_name is zero, there is no guarantee to get the symbol name as written in C. I am keeping the current logic because it is useful in many architectures, but the symbol name is not always correct depending on the optimization of the relocation. I left some comments in find_tosym(). Fixes: 56a974fa2d59 ("kbuild: make better section mismatch reports on arm") Signed-off-by: Masahiro Yamada --- Changes in v6: - More detailed commit log scripts/mod/modpost.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 71de14544432..34fbbd85bfde 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -1124,6 +1124,10 @@ static Elf_Sym *find_tosym(struct elf_info *elf, Elf64_Sword addr, if (relsym->st_name != 0) return relsym; + /* + * Strive to find a better symbol name, but the resulting name does not + * always match the symbol referenced in the original code. + */ relsym_secindex = get_secindex(elf, relsym); for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) { if (get_secindex(elf, sym) != relsym_secindex) @@ -1306,12 +1310,12 @@ static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r) static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r) { unsigned int r_typ = ELF_R_TYPE(r->r_info); + Elf_Sym *sym = elf->symtab_start + ELF_R_SYM(r->r_info); + unsigned int inst = TO_NATIVE(*reloc_location(elf, sechdr, r)); switch (r_typ) { case R_ARM_ABS32: - /* From ARM ABI: (S + A) | T */ - r->r_addend = (int)(long) - (elf->symtab_start + ELF_R_SYM(r->r_info)); + r->r_addend = inst + sym->st_value; break; case R_ARM_PC24: case R_ARM_CALL: -- 2.39.2