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=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 7D80AC47082 for ; Mon, 7 Jun 2021 07:07:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 631136121E for ; Mon, 7 Jun 2021 07:07:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230198AbhFGHJb (ORCPT ); Mon, 7 Jun 2021 03:09:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:43884 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229436AbhFGHJ1 (ORCPT ); Mon, 7 Jun 2021 03:09:27 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2FAA561242 for ; Mon, 7 Jun 2021 07:07:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623049657; bh=LCovMA/WpeQPLJl1EPHBeVn/zjZbOdOtdU0vdT8DZj0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=AtT06Y8yIh0AbQlnWPYo7E1SKNDG5mobSDsxs7sJsCjpw7lP0QzfLfJwquZcPcSnn kM7mQz4XCFgt2c+CUxGm1TpkXn65UrGK14g54Le21/MGMK4kKHddEsWzjltQv8xzR1 di7fRXwVT1+PBlSMp4PEZPMDXvKbZlCAXSeJceJHVIzWRGVGoHOQfs46yO1DaSArSL VWQRoD3Kgwp9BaqyCUmNaLWj5RKpBqGfbRNsseapJjUtgjaxKEkbIExBf4JtjDruj9 UYq/KwEPgoIqq4VpbnSRQ8ZPa1j93w5Iv6A8oH8va9T5gqSq9LooQ7vrLvvGIBv4wg 7Bya1a+zXESNA== Received: by mail-oo1-f50.google.com with SMTP id d27-20020a4a3c1b0000b029024983ef66dbso1121828ooa.3 for ; Mon, 07 Jun 2021 00:07:37 -0700 (PDT) X-Gm-Message-State: AOAM531gx107/wGjfaSVuqhein+Lm3f71IBOYQ9RbRVti0MowkjkqQQ8 rJZA/Q6XFIflj2csXCEHktYsFxNXL/rEkOGb6iM= X-Google-Smtp-Source: ABdhPJy2kCYQwYjG0i1qYY2Ghb3U7Iy0TlG9MoCIcwelicr5YR1d2V/ah5ArlyZhVDqIf6fNCY6OKIyDR07ilfIwt5w= X-Received: by 2002:a4a:8706:: with SMTP id z6mr12433560ooh.41.1623049656460; Mon, 07 Jun 2021 00:07:36 -0700 (PDT) MIME-Version: 1.0 References: <20210607065948.31632-1-mark-pk.tsai@mediatek.com> In-Reply-To: <20210607065948.31632-1-mark-pk.tsai@mediatek.com> From: Ard Biesheuvel Date: Mon, 7 Jun 2021 09:07:25 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] recordmcount: avoid using ABS symbol as reference To: Mark-PK Tsai Cc: Linux ARM , Linux Kernel Mailing List , linux-mediatek@lists.infradead.org, Matthias Brugger , Matt Helsley , "Steven Rostedt (VMware)" , Sami Tolvanen , yj.chiang@mediatek.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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), > 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? > And in the symbol search loop in find_secsym_ndx(), get_symindex will > return 0xfff1 if the symbol is in ABS section. > > In this case, find_secsym_ndx() will return a absolute symbol as > base, which won't be relocate, if an ABS symbol is found before the > real symbol in section 65521. > I see your point here. > > > > > find_secsym_ndx, which use r_info in rela section to find the reference > > > symbol, may take ABS symbol as base. > > > > > > Symbol table '.symtab' contains 453285 entries: > > > Num: Value Size Type Bind Vis Ndx Name > > > 6: 0000000000000002 0 NOTYPE LOCAL DEFAULT ABS section_count > > > > > > Which cause an invalid address in __mcount_loc. > > > > > > > Could you give a better account of the error you are trying to address? > > > > Also, arm64 no longer defines a section_count symbol (since v5.11), so > > please make sure that the diagnostics of the issue you are addressing > > are accurate for mainline. > > > > My kernel version is 5.4.61. > But as I explained, I suppose mainline also have this issue. > Mainline is what we work on. So please base your changes (and your commit log) on mainline. > > > > > Signed-off-by: Mark-PK Tsai > > > --- > > > scripts/recordmcount.h | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h > > > index f9b19524da11..9b69167fb7ff 100644 > > > --- a/scripts/recordmcount.h > > > +++ b/scripts/recordmcount.h > > > @@ -526,6 +526,10 @@ static int find_secsym_ndx(unsigned const txtndx, > > > for (symp = sym0, t = nsym; t; --t, ++symp) { > > > unsigned int const st_bind = ELF_ST_BIND(symp->st_info); > > > > > > + /* avoid absolute symbols */ > > > + if (symp->st_shndx == SHN_ABS) > > > + continue; > > > + > > > if (txtndx == get_symindex(symp, symtab, symtab_shndx) > > > /* avoid STB_WEAK */ > > > && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {