linux-kernel - [PATCH] Documentation: asm-annotation: clarify .L local symbol names

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Date:   Wed, 13 Jan 2021 09:46:20 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Documentation: asm-annotation: clarify .L local symbol names

Use more precise language and move the text to a region in the docs to
show that this constraint is not just for SYM_CODE_START*.

Suggested-by: Mark Brown <broonie@...nel.org>
Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Documentation/asm-annotations.rst | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/Documentation/asm-annotations.rst b/Documentation/asm-annotations.rst
index e711ff98102a..76424e0431f4 100644
--- a/Documentation/asm-annotations.rst
+++ b/Documentation/asm-annotations.rst
@@ -100,6 +100,11 @@ Instruction Macros
 ~~~~~~~~~~~~~~~~~~
 This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above.
 
+``objtool`` requires that all code must be contained in an ELF symbol. Symbol
+names that have a ``.L`` prefix do not emit symbol table entries. ``.L``
+prefixed symbols can be used within a code region, but should be avoided for
+denoting a range of code via ``SYM_*_START/END`` annotations.
+
 * ``SYM_FUNC_START`` and ``SYM_FUNC_START_LOCAL`` are supposed to be **the
   most frequent markings**. They are used for functions with standard calling
   conventions -- global and local. Like in C, they both align the functions to
@@ -153,15 +158,6 @@ This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above.
   To some extent, this category corresponds to deprecated ``ENTRY`` and
   ``END``. Except ``END`` had several other meanings too.
 
-  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``.
-
 * ``SYM_INNER_LABEL*`` is used to denote a label inside some
   ``SYM_{CODE,FUNC}_START`` and ``SYM_{CODE,FUNC}_END``.  They are very similar
   to C labels, except they can be made global. An example of use::
-- 
2.30.0.284.gd98b1dd5eaa7-goog