From: Masahiro Yamada <masahiroy@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ard Biesheuvel <ardb@kernel.org>,
Guenter Roeck <linux@roeck-us.net>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Rich Felker <dalias@libc.org>, Arnd Bergmann <arnd@arndb.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Palmer Dabbelt <palmer@rivosinc.com>
Subject: Re: Linux 6.2-rc2
Date: Thu, 5 Jan 2023 22:44:09 +0900 [thread overview]
Message-ID: <CAK7LNAQz6f_1jsp22HRRQqwfb6jh8_BGMgyUtE9TK8ENoHzJxQ@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wg6K2qge_MWHX9DurBUpbd54ih482gV5rf8ts7v8TUipA@mail.gmail.com>
On Wed, Jan 4, 2023 at 3:34 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Tue, Jan 3, 2023 at 2:59 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > The purpose of this change is to prevent .note.GNU-stack from deciding
> > the section type of the .notes output section, and so keeping it in
> > its own section should be sufficient. E.g.,
> >
> > - /DISCARD/ : { *(.note.GNU-stack) } \
> > + .note.GNU-stack : { *(.note.GNU-stack) } \
>
> This seems to work for everybody, so let's go with this. Masahiro?
>
> Linus
Sorry for the delay, I completely missed this thread.
Tested-by: Masahiro Yamada <masahiroy@kernel.org>
It works for me, but the comment block above should be
changed accordingly, for example:
/*
- * Discard .note.GNU-stack, which is emitted as PROGBITS by the compiler.
+ * Separte note.GNU-stack, which is emitted as PROGBITS by the compiler.
* Otherwise, the type of .notes section would become PROGBITS
instead of NOTES.
*/
This change, however, leaves an empty .note.GNU-stack section in vmlinux.
I personally prefer discarding .note.GNU-stack entirely because
GNU linker does not leave empty .note.GNU-stack when linking
user-space programs.
Because I did not notice the discussion was happening in this thread,
I submitted a different approach for fixing s390, and it was quickly merged:
https://lore.kernel.org/lkml/20230105031306.1455409-1-masahiroy@kernel.org/
This approach requires RUNTIME_DISCARD_EXIT for each architecture, though.
I do not know how Michael will fix powerpc.
While I was looking into this issue,
I noticed the real issue is,
how to discard sections is up to arch maintainers.
[1] Most architectures discard .exit.* sections at run-time.
Just run
git grep EXIT_TEXT
or
find . -name vmlinux.lds.S | xargs grep "at runtime"
[2] If .exit.* is allocated, then later discarded, it is kept.
(the first occurrence wins, in other words,
the sections defined in /DISCARD/ are not necessarily discarded)
[3] Despite the fact of [1], many architectures forget to
define RUNTIME_DISCARD_EXIT.
They still work because they put DISCARD
at the end of their linker scripts.
[4] arm64 puts DISCARD at the beginning of the linker
script, and defines RUNTIME_DISCARD_EXIT because otherwise
.exit* are discarded due to the "first wins" rule.
[5] If we really want to discard more sections, we often end
up with moving DISCARD up, and at this point, we realize
that RUNTIME_DISCARD_EXIT is missing.
I think it is unreadable (and fragile)
to keep/discard sections depending on the particular
order in the linker scripts.
Is there any better approach to make sure to discard
sections defined in DISCARDS?
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2023-01-05 13:45 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-01 22:01 Linux 6.2-rc2 Linus Torvalds
2023-01-02 10:20 ` Build regressions/improvements in v6.2-rc2 Geert Uytterhoeven
2023-01-02 22:56 ` Linux 6.2-rc2 Guenter Roeck
2023-01-03 0:21 ` Linus Torvalds
2023-01-03 1:45 ` Guenter Roeck
2023-01-03 2:13 ` Linus Torvalds
2023-01-03 3:57 ` Guenter Roeck
2023-01-03 4:26 ` Nathan Chancellor
2023-01-03 9:14 ` Thorsten Leemhuis
2023-01-03 10:58 ` Ard Biesheuvel
2023-01-03 11:45 ` Conor Dooley
2023-01-03 12:22 ` Guenter Roeck
2023-01-03 18:26 ` Nathan Chancellor
2023-01-03 18:34 ` Linus Torvalds
2023-01-05 13:44 ` Masahiro Yamada [this message]
2023-01-04 10:34 ` Michael Ellerman
2023-01-10 0:32 ` SeongJae Park
2023-01-10 18:39 ` Masahiro Yamada
2023-01-10 19:14 ` SeongJae Park
2023-01-23 9:09 ` Masahiro Yamada
2023-01-23 18:27 ` SeongJae Park
2023-02-06 22:56 ` SeongJae Park
2023-02-08 1:27 ` Masahiro Yamada
2023-01-13 14:59 ` Tom Saeger
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