From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by sourceware.org (Postfix) with ESMTPS id 27E613857C45 for ; Wed, 23 Sep 2020 19:04:05 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 27E613857C45 Received: by mail-il1-x141.google.com with SMTP id s88so662121ilb.6 for ; Wed, 23 Sep 2020 12:04:05 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=k4CDO37pf9yto/M5am4TtM3P4bXLqbK/iVRlBy2zavE=; b=TPm/BJneBGoFcp0Zmvc68Rylf983TLbIBOtPPUmcxWSYnhUybsN6eXS1fFc6PRg0eN LyqeRNxt1yslGfwDGumMwAsDKjL5jW57ODsAyS9mUqt/nv8JJ2rmmcnhLc+0E4xnJoZA XACzEz3+7jq1jx1BwINOKNha1vUfiKryCInTD2N20DPQ//exE7tgHt1DV8rY79EUJt/S bufQoT46UwTfuJROdR6nfNuC/rTB+itlWawBghxRIDbbOgxK2iiCK4AIPqEXsnq7k5+D 5HGwqgTbfFmdp3dxH472b+1/QlLReKTF2TqfgPSCg0i/eAfcFCQEboCOYd56npJOFXZn n92A== X-Gm-Message-State: AOAM532kBdxbroG3v4603qR89kVI+MyhKWgB/iKa7afpn2B74o4bMoOc B9eqpxuNDAkUmIpRWh72J1g/Pbhj0AryMZA14AnUx58w+80= X-Google-Smtp-Source: ABdhPJzm6o1s5uNKs/kUq5kXPuokGlyS3di31oU+htK69J372F78KKufMa7WiPrkknzwe+It9sAAzLKjn8Fi4l3puQE= X-Received: by 2002:a92:c882:: with SMTP id w2mr1036185ilo.151.1600887844560; Wed, 23 Sep 2020 12:04:04 -0700 (PDT) MIME-Version: 1.0 References: <20200923010930.xtc4mgmxsoesohkn@gmail.com> <20200923095818.npbwybrm63vb4ejm@jozef-acer-manjaro> <20200923165211.fr4rqzp5uqqmrufq@jozef-acer-manjaro> <20200923184735.4k2tji4yro452bep@jozef-acer-manjaro> In-Reply-To: <20200923184735.4k2tji4yro452bep@jozef-acer-manjaro> From: "H.J. Lu" Date: Wed, 23 Sep 2020 12:03:28 -0700 Message-ID: Subject: Re: [PATCH] Support SHF_GNU_RETAIN ELF section flag To: Michael Matz , Binutils Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: binutils@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Binutils mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Sep 2020 19:04:06 -0000 On Wed, Sep 23, 2020 at 11:47 AM Jozef Lawrynowicz wrote: > > On Wed, Sep 23, 2020 at 10:13:37AM -0700, H.J. Lu via Binutils wrote: > > On Wed, Sep 23, 2020 at 9:52 AM Jozef Lawrynowicz > > wrote: > > > > > > On Wed, Sep 23, 2020 at 01:51:56PM +0000, Michael Matz wrote: > > > > Hello, > > > > > > > > On Wed, 23 Sep 2020, H.J. Lu via Binutils wrote: > > > > > > > > > > I think that: > > > > > > > > > > > > > .section .text,"ax" > > > > > > > ... > > > > > > > foo: > > > > > > > ... > > > > > > > .retain > > > > > > > retained_fn: > > > > > > > ... > > > > > > > > > > > > is some nice syntactic sugar compared to: > > > > > > > > > > > > > .section .text,"ax" > > > > > > > ... > > > > > > > foo: > > > > > > > ... > > > > > > > .section .text,"axR" > > > > > > > retained_fn: > > > > > > > ... > > > > > > > > > > > > It's also partly for convenience; we have other directives which are > > > > > > synonyms or short-hand for each other. > > > > > > > > > > > > > > > > You don't need to keep the whole section when only one symbol should > > > > > be kept. Please drop the .retain directive. GCC, as and ld should do the > > > > > right thing with > > > > > > > > > > .section .text,"ax" > > > > > ... > > > > > foo: > > > > > ... > > > > > .section .text,"axR" > > > > > > > > > > retained_fn: > > > > > > > > > > where foo can be dropped and retained_fn will be kept. > > > > > > > > This is not what we discussed at the ABI list, the flag is per section, so > > > > either the whole section is retained or not. What you describe is > > > > something else that would work on a per symbol basis, which would have to > > > > be specified in a different way and might or might not be a good idea. > > > > But let's not conflate these two. > > > > > > Also, the linker cannot currently dissect a section and remove a > > > particular unused symbol anyway. Since garbage collection only operates > > > on the section level, marking the section itself as "retained" seems > > > most appropriate. > > > > It can be done. If you put your branch on > > > > https://gitlab.com/x86-binutils/binutils-gdb > > > > I can help you implement it. > > It's not something I have time to look into at the moment, for now the > aim is just to prevent garbage collection of sections. Linker and assembler already support it. You just need to add SHF_GNU_RETAIN to the framework. Check how SHF_GNU_MBIND works. > However, it would certainly be a useful enhancement for the linker, and > is something I would be interested in working on in the future, so I > appreciate the offer. > -- H.J.