linux-kernel - Re: [PATCH] x86/boot/compressed: Fix compressed kernel linking with lld

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Message-ID: <20200224060618.blsbhilbmm6b23a2@google.com>
Date:   Sun, 23 Feb 2020 22:06:18 -0800
From:   Fangrui Song <maskray@...gle.com>
To:     Kees Cook <keescook@...omium.org>,
        Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Borislav Petkov <bp@...en8.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com, Michael Matz <matz@...e.de>
Subject: Re: [PATCH] x86/boot/compressed: Fix compressed kernel linking with
 lld

On 2020-02-23, Kees Cook wrote:
>On Sat, Feb 22, 2020 at 1:01 PM 'Fangrui Song' via Clang Built Linux
><clang-built-linux@...glegroups.com> wrote:
>> https://github.com/torvalds/linux/commit/83a092cf95f28696ddc36c8add0cf03ac034897f
>> added -Wl,--orphan-handling=warn to arch/powerpc/Makefile .
>> x86 can follow if that is appropriate.
>
>I've been playing with a series to do this, here:
>
>https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=linker/orphans/x86-arm
>
>There's some work to be done still...

Thanks for investigating this! There are a number of compiler options
which can add ad-hoc sections. They may need caution.


I just filed https://sourceware.org/bugzilla/show_bug.cgi?id=25591 "Should /DISCARD/ : { *(.symtab) *(.strtab) } work?"
Let's see what GNU ld will do...

Note that * can be refined to SHF_ALLOC sections
(https://sourceware.org/binutils/docs/ld/Input-Section-Basics.html):

   SECTIONS {
     .text : { *(.text) }
     /* This excludes .strtab / .symtab / .shstrtab */
     /* https://reviews.llvm.org/D72756 implemented INPUT_SECTION_FLAGS. Not included in LLVM release/10.* */
     /DISCARD/ : { INPUT_SECTION_FLAGS(SHF_ALLOC) *(*) }
   }


Just realized that this was reported as https://bugs.llvm.org/show_bug.cgi?id=44452
Looks like we will probably close it as wontfix.