linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Nick Desaulniers <ndesaulniers@google.com>
To: Michael Matz <matz@suse.de>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
	Fangrui Song <maskray@google.com>, Borislav Petkov <bp@alien8.de>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections from bzImage
Date: Mon, 24 Feb 2020 12:51:14 -0800	[thread overview]
Message-ID: <CAKwvOd=nCAyXtng1N-fvNYa=-NGD0yu+Rm6io9F1gs0FieatwA@mail.gmail.com> (raw)
In-Reply-To: <alpine.LSU.2.21.2002241319150.12812@wotan.suse.de>

On Mon, Feb 24, 2020 at 5:28 AM Michael Matz <matz@suse.de> wrote:
>
> Hello,
>
> On Sat, 22 Feb 2020, Nick Desaulniers wrote:
>
> > > > > In GNU ld, it seems that .shstrtab .symtab and .strtab are special
> > > > > cased. Neither the input section description *(.shstrtab) nor *(*)
> > > > > discards .shstrtab . I feel that this is a weird case (probably even a bug)
> > > > > that lld should not implement.
> > > >
> > > > Ok, forget what the tools do for a second: why is .shstrtab special and
> > > > why would one want to keep it?
> > > >
> > > > Because one still wants to know what the section names of an object are
> > > > or other tools need it or why?
> > > >
> > > > Thx.
> > > >
> > > > --
> > > > Regards/Gruss,
> > > >     Boris.
> > > >
> > > > https://people.kernel.org/tglx/notes-about-netiquette
> > >
> > > .shstrtab is required by the ELF specification. The e_shstrndx field in
> > > the ELF header is the index of .shstrtab, and each section in the
> > > section table is required to have an sh_name that points into the
> > > .shstrtab.
> >
> > Yeah, I can see it both ways.  That `*` doesn't glob all remaining
> > sections is surprising to me, but bfd seems to be "extra helpful" in
> > not discarding sections that are required via ELF spec.
>
> In a way the /DISCARD/ assignment should be thought of as applying to
> _input_ sections (as all such section references on the RHS), not
> necessarily to output sections.  What this then means for sections that
> are synthesized by the link editor is less clear.  Some of them are
> generated regardless (as you noted, e.g. the symbol table and associated
> string sections, including section name string table), some of them are
> suppressed, and either lead to an followup error (e.g. with .gnu.hash), or
> to invalid output (e.g. missing .dynsym for executables simply lead to
> segfaults when running them).
>
> That's the reason for the perceived inconsistency with behaviour on '*':
> it's application to synthesized sections.  Arguably bfd should be fixed to
> also not discard the other essential sections (or alternatively to give an
> error when an essential section is discarded).  The lld behaviour of e.g.
> discarding .shstrtab (or other synthesized sections necessary for valid
> ELF output) doesn't make much sense either, though.

Hi Michael, thank you for the precise feedback.  Do you have a list of
"synthesized sections necessary for valid ELF output?" Also, could you
point me to the documentation about `*` and its relation to
"synthesized sections necessary for valid ELF output?"  This will help
me file a precise bug against LLD.
-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2020-02-24 20:51 UTC|newest]

Thread overview: 115+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-09 15:02 [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage Arvind Sankar
2020-01-09 15:02 ` [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections " Arvind Sankar
2020-02-06 11:44   ` Kees Cook
2020-02-19 16:55   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-02-22  5:08   ` [PATCH 2/2] " Nathan Chancellor
2020-02-22  6:55     ` Borislav Petkov
2020-02-22  7:02       ` Nathan Chancellor
2020-02-22  7:21         ` Fangrui Song
2020-02-22  7:42           ` Nathan Chancellor
2020-02-22 15:37             ` Arvind Sankar
2020-02-22 16:44               ` Arvind Sankar
2020-02-22 17:18                 ` [PATCH] x86/boot/compressed: Fix compressed kernel linking with lld Arvind Sankar
2020-02-22 18:14                   ` Nathan Chancellor
2020-02-22 18:58                     ` Fangrui Song
2020-02-22 20:17                       ` Arvind Sankar
2020-02-22 21:01                         ` Fangrui Song
2020-02-22 23:33                           ` Nick Desaulniers
2020-02-22 23:57                             ` Arvind Sankar
2020-02-23 19:37                               ` [PATCH 0/2] Stop generating .eh_frame sections Arvind Sankar
2020-02-24  4:15                                 ` Nathan Chancellor
2020-02-24 20:49                                 ` Nick Desaulniers
2020-02-24 21:53                                   ` Arvind Sankar
2020-02-24 22:01                                     ` Nick Desaulniers
2020-02-23 19:37                               ` [PATCH 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress " Arvind Sankar
2020-02-24 20:33                                 ` Nick Desaulniers
2020-02-24 21:05                                   ` Arvind Sankar
2020-02-24 21:12                                     ` Fangrui Song
2020-02-24 21:17                                       ` Nick Desaulniers
2020-02-24 21:22                                         ` Nick Desaulniers
2020-02-23 19:37                               ` [PATCH 2/2] arch/x86: Drop unneeded linker script discard of .eh_frame Arvind Sankar
2020-02-24 20:45                                 ` Nick Desaulniers
2020-02-24 21:33                                   ` Arvind Sankar
2020-02-24 21:58                                     ` Nick Desaulniers
2020-02-24 23:21                                       ` [PATCH v2 0/2] Stop generating .eh_frame sections Arvind Sankar
2020-02-24 23:21                                       ` [PATCH v2 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress " Arvind Sankar
2020-02-24 23:28                                         ` Nathan Chancellor
2020-02-24 23:30                                         ` Nick Desaulniers
2020-02-25  4:10                                         ` Kees Cook
2020-02-25 16:53                                         ` [tip: x86/boot] x86/*/Makefile: " tip-bot2 for Arvind Sankar
2020-02-24 23:21                                       ` [PATCH v2 2/2] arch/x86: Drop unneeded linker script discard of .eh_frame Arvind Sankar
2020-02-24 23:28                                         ` Nathan Chancellor
2020-02-24 23:33                                         ` Nick Desaulniers
2020-02-25  4:11                                         ` Kees Cook
2020-02-25 16:53                                         ` [tip: x86/boot] x86/vmlinux: " tip-bot2 for Arvind Sankar
2020-02-23 22:00                           ` [PATCH] x86/boot/compressed: Fix compressed kernel linking with lld Kees Cook
2020-02-24  6:06                             ` Fangrui Song
2020-02-22 17:29                 ` [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections from bzImage Borislav Petkov
2020-02-22 17:53                   ` Arvind Sankar
2020-02-22  7:42           ` Borislav Petkov
2020-02-22 16:22             ` Arvind Sankar
2020-02-22 23:20               ` Nick Desaulniers
2020-02-24 13:28                 ` Michael Matz
2020-02-24 20:51                   ` Nick Desaulniers [this message]
2020-02-24 21:28                     ` Fangrui Song
2020-02-24 21:48                       ` Arvind Sankar
2020-02-24 22:17                         ` Fangrui Song
2020-02-24 22:43                           ` Arvind Sankar
2020-02-24 22:50                             ` Fangrui Song
2020-02-24 23:08                               ` Arvind Sankar
2020-02-25  5:35                 ` --orphan-handling=warn (was Re: [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections) " Kees Cook
2020-02-25 16:42                   ` --orphan-handling=warn Arvind Sankar
2020-02-25 18:29                   ` --orphan-handling=warn Arvind Sankar
2020-02-25 19:42                     ` --orphan-handling=warn Kees Cook
2020-02-25 20:37                       ` --orphan-handling=warn Nick Desaulniers
2020-02-25 22:02                         ` --orphan-handling=warn Kees Cook
2020-02-26  1:56                           ` --orphan-handling=warn Fangrui Song
2020-02-26  5:35                             ` --orphan-handling=warn Kees Cook
2020-02-26 19:11                               ` --orphan-handling=warn Kristen Carlson Accardi
2020-02-26 19:26                                 ` --orphan-handling=warn Nick Desaulniers
2020-02-24 11:37   ` [tip: x86/boot] x86/boot/compressed: Remove .eh_frame section from bzImage tip-bot2 for Arvind Sankar
2020-02-24 16:41     ` Arvind Sankar
2020-02-24 17:16       ` Borislav Petkov
2020-02-24 17:28         ` Arvind Sankar
2020-02-05 16:29 ` [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable " Arvind Sankar
2020-02-18 18:03   ` Arvind Sankar
2020-02-19 12:09     ` Borislav Petkov
2020-02-19 17:57       ` Arvind Sankar
2020-02-19 18:22         ` Borislav Petkov
2020-02-19 19:06           ` Arvind Sankar
2020-02-06 11:18 ` Kees Cook
2020-02-19 16:55 ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-04-05 15:42 ` [PATCH 1/2] " Sergey Shatunov
2020-04-05 23:18   ` Arvind Sankar
2020-04-06  0:00     ` Sergey Shatunov
2020-04-06  3:51       ` Arvind Sankar
2020-04-06  7:32         ` Ard Biesheuvel
2020-04-06  8:47           ` Borislav Petkov
2020-04-06  9:11             ` Ard Biesheuvel
2020-04-06 11:20               ` Borislav Petkov
2020-04-06 13:22                 ` Arvind Sankar
2020-04-06 13:29                   ` Ard Biesheuvel
2020-04-06 16:01                     ` Arvind Sankar
2020-04-06 16:22                       ` Ard Biesheuvel
2020-04-06 16:52                         ` Arvind Sankar
2020-04-06 16:59                           ` Ard Biesheuvel
2020-04-06 18:06                             ` [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data Arvind Sankar
2020-04-06 18:06                               ` [PATCH 2/2] efi/x86: Always relocate the kernel for EFI handover entry Arvind Sankar
2020-04-14  8:20                                 ` [tip: efi/urgent] " tip-bot2 for Arvind Sankar
2020-04-06 18:29                               ` [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data Ard Biesheuvel
2020-04-08  7:43                               ` Dave Young
2020-04-08  7:49                                 ` Ard Biesheuvel
2020-04-09 14:39                                   ` Arvind Sankar
2020-04-09 14:47                                     ` Ard Biesheuvel
2020-04-09 16:35                                       ` Arvind Sankar
2020-04-10 14:47                                         ` Arvind Sankar
2020-04-10 15:26                                           ` Ard Biesheuvel
2020-04-14 14:57                                             ` Daniel Kiper
2020-04-10 11:26                               ` Thomas Meyer
2020-04-10 14:38                                 ` Arvind Sankar
2020-04-11  8:50                                   ` Thomas Meyer
2020-04-14  8:20                               ` [tip: efi/urgent] " tip-bot2 for Arvind Sankar
2020-04-06 17:21                     ` [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage Borislav Petkov
2020-04-06  8:44     ` Ard Biesheuvel
2020-04-06 12:36       ` Sergey Shatunov
2020-04-06 13:20         ` Ard Biesheuvel

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAKwvOd=nCAyXtng1N-fvNYa=-NGD0yu+Rm6io9F1gs0FieatwA@mail.gmail.com' \
    --to=ndesaulniers@google.com \
    --cc=bp@alien8.de \
    --cc=clang-built-linux@googlegroups.com \
    --cc=hpa@zytor.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=maskray@google.com \
    --cc=matz@suse.de \
    --cc=mingo@redhat.com \
    --cc=natechancellor@gmail.com \
    --cc=nivedita@alum.mit.edu \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).