From patchwork Fri Dec 2 10:55:58 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arnd Bergmann X-Patchwork-Id: 9458233 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 8843860585 for ; Fri, 2 Dec 2016 10:57:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6DB2228539 for ; Fri, 2 Dec 2016 10:57:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 623202853D; Fri, 2 Dec 2016 10:57:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CA00D28539 for ; Fri, 2 Dec 2016 10:57:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759542AbcLBK5f (ORCPT ); Fri, 2 Dec 2016 05:57:35 -0500 Received: from mout.kundenserver.de ([212.227.126.131]:59256 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751786AbcLBK5d (ORCPT ); Fri, 2 Dec 2016 05:57:33 -0500 Received: from wuerfel.localnet ([78.43.21.235]) by mrelayeu.kundenserver.de (mreue003 [212.227.15.129]) with ESMTPSA (Nemesis) id 0LaYbD-1cyWGj3wn1-00mK9V; Fri, 02 Dec 2016 11:56:03 +0100 From: Arnd Bergmann To: Linus Torvalds Cc: Adam Borowski , Greg Kroah-Hartman , Linux Kbuild mailing list , Michal Marek , Ben Hutchings , Debian kernel maintainers , "linux-arch@vger.kernel.org" , Ingo Molnar , Nicholas Piggin , Linux Kernel Mailing List , Alan Modra Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Date: Fri, 02 Dec 2016 11:55:58 +0100 Message-ID: <14455987.OWjnZpEEup@wuerfel> User-Agent: KMail/5.1.3 (Linux/4.4.0-34-generic; KDE/5.18.0; x86_64; ; ) In-Reply-To: References: <20161129131922.GA31466@angband.pl> <2899250.iZaPagXLk8@wuerfel> MIME-Version: 1.0 X-Provags-ID: V03:K0:IZqzDrWMacRL7DzVdUSrCuxYMSW0rQS7CQIY7PavCfGhcBwVRzj 0S3LaG0sOcCxPRftYemR+i9+q+8OJ/IcJHIscO9SWErhpIoDfveqSzMqzAHELn4cdPR/Mqn O0nrUhgf8QBJglw45Lhl4t0JRwhJEcN3fAmmzyo9gbkTVCu/KKesgOHrDrIYg+JgvwtKqNM yOX/nAAEF3DX7bVIBVjHA== X-UI-Out-Filterresults: notjunk:1; V01:K0:JCsFMOpnlsM=:mvypwcfB8Sg1U08/vtgLTh MfHXQSSJljtFjJnI0wEu+UAK3f3DbsXPPZ4EnDYVlVvByPQIzW/OHXVtE7LVx9y+jaFWAAGhS 3xgCk/4eyZxUdiTRJQpa5M8SxcYfp4wVN3dNdxhu5RbRXOwpEiVL/lwIVIV4naSyoK1CLbhG1 oQDCn+iItAayg1IS+mO364yaBIhwPFSkZvvwP08BCbNOjeBN2wYojD28/Yo5SEd/wW6FURQZ2 Gyj+jRIl+eDiPCYTlfwlw760SEGBVFDDUdrfnW7MAcVCZ2+KuaZRy/xrF3SLasE7YKb96tJ54 iTn1Plw12fncT0vb16ZKZecRosBC1msaG2Ys1Pxlii+IGZjqjJnPAO3eJ4xiwups7DUYDS087 FG14wZ3RLQupbnAAP49fArYZX6QciAJHdgPSZme0brewlFtL2vQSk6mnMwShZyaPegc+JZzpU pna5/GhvRzGT8veyfntYzXO/CQnAF1sZhbFWXazJ0xNX/VqAKsC4lh0WWlqy2YxW+SPpMc7Ll nWGyAov0fIFiGp+tojQCf1qPeQtXGMz4dacQ7BGIpxS2Xo0FHSMS+WvojbBpGF/vnl7+kkG0g s2FWaQtepTKo+azHy8X7gPcxulGF8vT/2xvAjEXzxnM5HNHB21WzaZoFHbAb0WqT51GQL0aob 82Adz6uuazFM8UFD4dFQBYoh6Mfs/YmXhws+imMIOYJzBKyZZ2DGOKCjpfzXCy7cCGSNm8lue dWSP79XTv6r87yiV Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Thursday, December 1, 2016 10:26:07 AM CET Linus Torvalds wrote: > On Thu, Dec 1, 2016 at 5:58 AM, Arnd Bergmann wrote: > > > > WARNING: EXPORT symbol "mcount" [arch/x86/entry/built-in.ko] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "mcount" [arch/x86/built-in.ko] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "cmpxchg8b_emu" [vmlinux] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "empty_zero_page" [vmlinux] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "mcount" [vmlinux] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "cmpxchg8b_emu" [vmlinux] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "empty_zero_page" [vmlinux] version generation failed, symbol will not be versioned. > > WARNING: EXPORT symbol "mcount" [vmlinux] version generation failed, symbol will not be versioned. > > > > Out of 12 randconfig builds that had CONFIG_MODVERSIONS enabled, all 12 > > had this problem, though not always with all the symbols. > > Well, the good news is that pretty fundamentally, if it's just the asm > symbls, those really don't have ABI's that change (or if they change, > it's such a fundamental change that everything else will likely have > changed too and we don't need to worry about one asm symbol crc - the > change will be caught by other symbols). Yes, it's always been just the assembly symbols that broke, these were the ones that Al's original patch changed and that ended up with no version information. > So I think the whole "we don't really care" approach should work fine. > The "let's make every symbol always be versioned" may just be too much > pain for no real gain. I have managed to bisect the link failure to a specific binutils commit by Alan Modra now: d983c8c ("Strip undefined symbols from .symtab") went into binutils-2_26 and was reverted in a82e3ef ("Revert "Strip undefined symbols from .symtab"") after the release branch for 2.26 was started, so that version ended up being fine. However, the 2.27 version never saw the revert and causes loadable kernel modules to become unusable when they refer to a weak symbol in vmlinux. This works with 2.26 and lower: $ nm obj-arm/vmlinux | grep __gnu_mcount_nc w __crc___gnu_mcount_nc c031ed58 T __gnu_mcount_nc c0ef4590 r __kcrctab___gnu_mcount_nc c0efb4f5 r __kstrtab___gnu_mcount_nc c0ee68bc R __ksymtab___gnu_mcount_nc and this is breaks with 2.27 and higher: $ make modules 2>&1 | tail -n 1 WARNING: "__gnu_mcount_nc" [drivers/ata/ahci_platform.ko] has no CRC! $ nm obj-arm/vmlinux | grep __gnu_mcount_nc c031ed58 T __gnu_mcount_nc c0ef4590 r __kcrctab___gnu_mcount_nc c0efb4f5 r __kstrtab___gnu_mcount_nc c0ee68bc R __ksymtab___gnu_mcount_nc Applying the patch below on top of today's binutils master branch makes it work again. The real patch will also have to fix the testsuite. Arnd --- commit 9a48071533f311ff1f567361874fab141bd77230 Author: Arnd Bergmann Date: Fri Dec 2 11:31:34 2016 +0100 Revert "Strip undefined symbols from .symtab" This reverts commit d983c8c5503d680c6d4955ceb610a9beebc64460. Signed-off-by: Arnd Bergmann -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/bfd/elflink.c b/bfd/elflink.c index 5f87f87..57c4d42 100644 --- a/bfd/elflink.c +++ b/bfd/elflink.c @@ -9354,9 +9354,8 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data) a regular file, or that we have been told to strip. However, if h->indx is set to -2, the symbol is used by a reloc and we must output it. */ - strip = FALSE; if (h->indx == -2) - ; + strip = FALSE; else if ((h->def_dynamic || h->ref_dynamic || h->root.type == bfd_link_hash_new) @@ -9382,13 +9381,14 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data) && h->root.u.undef.abfd != NULL && (h->root.u.undef.abfd->flags & BFD_PLUGIN) != 0) strip = TRUE; + else + strip = FALSE; type = h->type; /* If we're stripping it, and it's not a dynamic symbol, there's - nothing else to do. However, if it is a forced local symbol or - an ifunc symbol we need to give the backend finish_dynamic_symbol - function a chance to make it dynamic. */ + nothing else to do unless it is a forced local symbol or a + STT_GNU_IFUNC symbol. */ if (strip && h->dynindx == -1 && type != STT_GNU_IFUNC @@ -9691,18 +9691,9 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data) } } - /* If the symbol is undefined, and we didn't output it to .dynsym, - strip it from .symtab too. Obviously we can't do this for - relocatable output or when needed for --emit-relocs. */ - else if (input_sec == bfd_und_section_ptr - && h->indx != -2 - && !bfd_link_relocatable (flinfo->info)) - return TRUE; - /* Also strip others that we couldn't earlier due to dynamic symbol - processing. */ - if (strip) - return TRUE; - if ((input_sec->flags & SEC_EXCLUDE) != 0) + /* If we're stripping it, then it was just a dynamic symbol, and + there's nothing else to do. */ + if (strip || (input_sec->flags & SEC_EXCLUDE) != 0) return TRUE; /* Output a FILE symbol so that following locals are not associated @@ -9952,9 +9943,8 @@ elf_link_input_bfd (struct elf_final_link_info *flinfo, bfd *input_bfd) *ppsection = isec; - /* Don't output the first, undefined, symbol. In fact, don't - output any undefined local symbol. */ - if (isec == bfd_und_section_ptr) + /* Don't output the first, undefined, symbol. */ + if (ppsection == flinfo->sections) continue; if (ELF_ST_TYPE (isym->st_info) == STT_SECTION)