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 X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7EDD5C4743F for ; Mon, 7 Jun 2021 13:18:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6928F61153 for ; Mon, 7 Jun 2021 13:18:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230302AbhFGNUt (ORCPT ); Mon, 7 Jun 2021 09:20:49 -0400 Received: from mailgw02.mediatek.com ([210.61.82.184]:59335 "EHLO mailgw02.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S230227AbhFGNUr (ORCPT ); Mon, 7 Jun 2021 09:20:47 -0400 X-UUID: d3af28efdb4e4da797687b36306ea06b-20210607 X-UUID: d3af28efdb4e4da797687b36306ea06b-20210607 Received: from mtkcas07.mediatek.inc [(172.21.101.84)] by mailgw02.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-SHA384 256/256) with ESMTP id 1502342600; Mon, 07 Jun 2021 21:18:53 +0800 Received: from MTKCAS06.mediatek.inc (172.21.101.30) by mtkmbs08n1.mediatek.inc (172.21.101.55) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 7 Jun 2021 21:18:51 +0800 Received: from mtksdccf07.mediatek.inc (172.21.84.99) by MTKCAS06.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Mon, 7 Jun 2021 21:18:45 +0800 From: Mark-PK Tsai To: CC: , , , , , , , , , , , Subject: Re: [PATCH] recordmcount: avoid using ABS symbol as reference Date: Mon, 7 Jun 2021 21:18:45 +0800 Message-ID: <20210607131845.3118-1-mark-pk.tsai@mediatek.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain X-MTK: N Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Mon, Jun 07, 2021 at 11:50:40AM +0200, Ard Biesheuvel wrote: > > On Mon, 7 Jun 2021 at 10:06, Mark-PK Tsai wrote: > > > > > > > > On Mon, 7 Jun 2021 at 08:59, Mark-PK Tsai wrote: > > > > > > > > > > > > > > On Mon, 7 Jun 2021 at 04:42, Mark-PK Tsai wrote: > > > > > > > > > > > > > > > > Avoid using ABS symbol, which won't be relocate, as reference. > > > > > > > > > > > > > > > > On arm64 platform, if there's shndx equals SHN_ABS(0xfff1). > > > > > > > > > > > > > > > > Section Headers: > > > > > > > > [Nr] Name Type Address Off Size ES Flg Lk Inf Al > > > > > > > > [65521] .text.n_tty_receive_buf PROGBITS 0000000000000000 3cdab520 000054 00 AX 0 0 4 > > > > > > > > [65522] .rela.text.n_tty_receive_buf RELA 0000000000000000 3cdab578 000030 18 I 152076 65521 8 > > > > > > > > > > > > > > > > > > > > > > A RELA section's r_info field points to the section to which it > > > > > > > applies. This is why in the example above section #65522 points to > > > > > > > section #65521. This has nothing to do with the numerical value of > > > > > > > SHN_ABS. > > > > > > > > > > > > If the r_info of RELA section is 65521(0xfff1), > > > > > > > > Oh sorry, I mean sh_info here. > > > > > > > > > > find_secsym_ndx() will use it to find the base symbol. > > > > > > > > > > > > > > > > But what does that have to do with the sh_info field of the RELA > > > > > section's Elf_Shdr struct? IOW, what is the relevance of section > > > > > #65521 here? > > > > > > > > > > > > > So what I mean is the problem occur if the sh_info of a RELA section > > > > is #65521. > > > > > > Actually the problem occur if the sh_info of a RELA section is in > > > the special section index range(SHN_LORESERVE ~ SHN_HIRESERVE). > > > Maybe I should add a is_shndx_special() to check this like > > > scripts/mod/modpost.h did? > > > > > > > So if I understand all of this correctly, we are running into a > > fundamental issue here, where the linker emits more sections than the > > sh_info field can describe, overflowing into the reserved range. > > > > I don't think papering over it like this is going to be maintainable > > going forward. > > There's an extended section header index section for just that. And > recordmcount actually seems to use that as well. > > I can't seem to find enough of the thread to figure out what the actual > problem is though. The lore archive doesn't have anything prior to this > message. > > One should only use st_shndx when >SHN_UDEF and SHN_XINDEX, then use .symtab_shndx. > > Apparently you've found a case where neither is true? In that case Yes, that's what my mean. get_symindex returns st_shndx directly even if st_shndx is in the reserve range. So either do not use get_symindex for those symbols or do extra handling for it like the patch you provide will solve the problem. > objtool seems to use shndx 0. A matching recordmcount patch would be > something like this. > > > diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h > index f9b19524da11..d99cc0aed6fe 100644 > --- a/scripts/recordmcount.h > +++ b/scripts/recordmcount.h > @@ -194,13 +194,18 @@ static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab, > unsigned long offset; > int index; > > - if (sym->st_shndx != SHN_XINDEX) > + if (sym->st_shndx > SHN_UDEF && > + sym->st_shndx < SHN_LORESERVE) > return w2(sym->st_shndx); > > - offset = (unsigned long)sym - (unsigned long)symtab; > - index = offset / sizeof(*sym); > + if (sym->st_shndx == SHN_XINDEX) { > + offset = (unsigned long)sym - (unsigned long)symtab; > + index = offset / sizeof(*sym); > > - return w(symtab_shndx[index]); > + return w(symtab_shndx[index]); > + } > + > + return 0; > } > > static unsigned int get_shnum(Elf_Ehdr const *ehdr, Elf_Shdr const *shdr0) Thanks for the suggestion. Skip all the symbols in the special sections seems fine because those sections should not be processed here.