From: Nick Desaulniers <ndesaulniers@google.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Fāng-ruì Sòng" <maskray@google.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>, "Arnd Bergmann" <arnd@arndb.de>,
"Josh Poimboeuf" <jpoimboe@redhat.com>, "X86 ML" <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Nathan Chancellor" <natechancellor@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v3] x86/entry: emit a symbol for register restoring thunk
Date: Mon, 11 Jan 2021 17:13:16 -0800 [thread overview]
Message-ID: <CAKwvOdmGS97e4Rj_oW+RnkYAMjycTFQiiPJAfCvKTdxgv2KfEA@mail.gmail.com> (raw)
In-Reply-To: <20210112010010.GA8239@zn.tnic>
On Mon, Jan 11, 2021 at 5:00 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Mon, Jan 11, 2021 at 04:41:52PM -0800, Fāng-ruì Sòng wrote:
> > To be fair: we cannot use
>
> Who's "we"?
>
> > .L-prefixed local because of the objtool limitation.
>
> What objtool limitation? I thought clang's assembler removes .text which
> objtool uses. It worked fine with GNU as so far.
I don't think we need to completely stop using .L prefixes in the
kernel, just this one location since tracking the control flow seems a
little tricky for objtool. Maybe Josh can clarify more if needed?
>
> > The LLVM integrated assembler behavior is a good one
>
> Please explain what "good one" means in that particular context.
>
> > and binutils global maintainers have agreed so H.J. went ahead and
> > implemented it for GNU as x86.
>
> But they don't break old behavior, do they? Or are they removing .text
> unconditionally now too?
Unconditionally. See
https://sourceware.org/pipermail/binutils/2021-January/114700.html
where that flag was rejected and the optimization was adopted as the
optimization was obvious to GNU binutils developers. So I suspect this
will become a problem for GNU binutils users as well after the latest
release that contains
https://sourceware.org/pipermail/binutils/attachments/20210105/75dd4a9d/attachment-0001.bin.
> > --generate-unused-section-symbols=[yes|no] as an assembler option has
> > been rejected.
>
> Meaning what exactly? There's no way for clang's integrated assembler to
> even get a cmdline option to not strip .text?
I can clean that up in v5; The section symbols were not generated then
stripped; they were simply never generated.
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2021-01-12 1:14 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-23 23:21 [PATCH] x86/entry: use STB_GLOBAL for register restoring thunk Nick Desaulniers
2020-12-24 4:55 ` Josh Poimboeuf
2021-01-06 0:43 ` [PATCH v2] " Nick Desaulniers
2021-01-06 1:58 ` Josh Poimboeuf
2021-01-11 20:38 ` [PATCH v3] x86/entry: emit a symbol " Nick Desaulniers
2021-01-11 20:58 ` Fangrui Song
2021-01-11 22:09 ` Josh Poimboeuf
2021-01-11 22:16 ` Fāng-ruì Sòng
2021-01-11 22:12 ` Josh Poimboeuf
2021-01-12 0:38 ` Borislav Petkov
2021-01-12 0:41 ` Fāng-ruì Sòng
2021-01-12 1:00 ` Borislav Petkov
2021-01-12 1:13 ` Nick Desaulniers [this message]
2021-01-12 1:59 ` Josh Poimboeuf
2021-01-12 11:54 ` Borislav Petkov
2021-01-12 19:46 ` [PATCH v4] " Nick Desaulniers
2021-01-12 21:01 ` Mark Brown
2021-01-13 16:59 ` Josh Poimboeuf
2021-01-13 17:46 ` [PATCH] Documentation: asm-annotation: clarify .L local symbol names Nick Desaulniers
2021-01-13 19:56 ` Mark Brown
2021-01-13 17:56 ` [PATCH v4] x86/entry: emit a symbol for register restoring thunk Nick Desaulniers
2021-01-14 10:39 ` Borislav Petkov
2021-01-14 11:36 ` Peter Zijlstra
2021-01-14 13:28 ` [PATCH] x86/entry: Remove put_ret_addr_in_rdi THUNK macro argument Borislav Petkov
2021-01-14 15:53 ` Peter Zijlstra
2021-01-19 10:12 ` [tip: x86/entry] " tip-bot2 for Borislav Petkov
2021-01-14 15:14 ` [PATCH v4] x86/entry: emit a symbol for register restoring thunk Josh Poimboeuf
2021-01-13 11:52 ` [tip: x86/entry] x86/entry: Emit " tip-bot2 for Nick Desaulniers
2021-01-19 10:12 ` tip-bot2 for Nick Desaulniers
2021-01-12 11:47 ` [PATCH v3] x86/entry: emit " Borislav Petkov
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