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From: Mark Brown <broonie@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Fangrui Song <maskray@google.com>, Arnd Bergmann <arnd@arndb.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	Jiri Slaby <jirislaby@kernel.org>, Joe Perches <joe@perches.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com
Subject: Re: [PATCH v4] x86/entry: emit a symbol for register restoring thunk
Date: Tue, 12 Jan 2021 21:01:54 +0000
Message-ID: <20210112210154.GI4646@sirena.org.uk> (raw)
In-Reply-To: <20210112194625.4181814-1-ndesaulniers@google.com>


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On Tue, Jan 12, 2021 at 11:46:24AM -0800, Nick Desaulniers wrote:

This:

> when building with LLVM_IAS=1 (Clang's integrated assembler). Josh
> notes:

>   So basically, you can use an .L symbol *inside* a function or a code
>   segment, you just can't use the .L symbol to contain the code using a
>   SYM_*_START/END annotation pair.

is a stronger statement than this:

> +  Developers should avoid using local symbol names that are prefixed with
> +  ``.L``, as this has special meaning for the assembler; a symbol entry will
> +  not be emitted into the symbol table. This can prevent ``objtool`` from
> +  generating correct unwind info. Symbols with STB_LOCAL binding may still be
> +  used, and ``.L`` prefixed local symbol names are still generally useable
> +  within a function, but ``.L`` prefixed local symbol names should not be used
> +  to denote the beginning or end of code regions via
> +  ``SYM_CODE_START_LOCAL``/``SYM_CODE_END``.

and seems more what I'd expect - SYM_FUNC* is also affected for example.
Even though other usages are probably not very likely it seems better to
keep the stronger statement in case someone comes up with one, and to
stop anyone spending time wondering why only SYM_CODE_START_LOCAL is
affected.

This also looks like a good candiate for a checkpatch rule, but that can
be done separately of course.

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  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-23 23:21 [PATCH] x86/entry: use STB_GLOBAL " 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
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 [this message]
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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