linux-kernel - Re: [PATCH v7 01/28] linkage: new macros for assembler symbols

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Message-ID: <20190131160019.GM6749@zn.tnic>
Date:   Thu, 31 Jan 2019 17:00:19 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     mingo@...hat.com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>, hpa@...or.com,
        Ingo Molnar <mingo@...nel.org>, jpoimboe@...hat.com,
        Juergen Gross <jgross@...e.com>,
        Len Brown <len.brown@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-pm@...r.kernel.org, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        xen-devel@...ts.xenproject.org, x86@...nel.org
Subject: Re: [PATCH v7 01/28] linkage: new macros for assembler symbols

On Wed, Jan 30, 2019 at 01:46:44PM +0100, Jiri Slaby wrote:
> Introduce new C macros for annotations of functions and data in
> assembly. There is a long-standing mess in macros like ENTRY, END,
> ENDPROC and similar. They are used in different manners and sometimes
> incorrectly.
> 
> So introduce macros with clear use to annotate assembly as follows:

...

> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: hpa@...or.com
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: jpoimboe@...hat.com
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-pm@...r.kernel.org
> Cc: mingo@...hat.com
> Cc: Pavel Machek <pavel@....cz>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: xen-devel@...ts.xenproject.org
> Cc: x86@...nel.org
> ---
>  Documentation/asm-annotations.rst | 217 ++++++++++++++++++++++++++

I guess you wanna integrate that into the doc hierarchy. Hunk ontop:

---
diff --git a/Documentation/index.rst b/Documentation/index.rst
index c858c2e66e36..754055d9565c 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -91,6 +91,14 @@ needed).
    vm/index
    bpf/index
 
+Architecture-agnostic documentation
+-----------------------------------
+
+.. toctree::
+   :maxdepth: 2
+
+   asm-annotations
+
 Architecture-specific documentation
 -----------------------------------
 

>  arch/x86/include/asm/linkage.h    |  10 +-
>  include/linux/linkage.h           | 245 +++++++++++++++++++++++++++++-
>  3 files changed, 461 insertions(+), 11 deletions(-)
>  create mode 100644 Documentation/asm-annotations.rst
> 
> diff --git a/Documentation/asm-annotations.rst b/Documentation/asm-annotations.rst
> new file mode 100644
> index 000000000000..265d64a1fc0b
> --- /dev/null
> +++ b/Documentation/asm-annotations.rst
> @@ -0,0 +1,217 @@
> +Assembler Annotations
> +=====================
> +
> +Copyright (c) 2017 Jiri Slaby
> +
> +This document describes the new macros for annotation of data and code in
> +assembler. In particular, it contains information about ``SYM_FUNC_START``,

s/assembler/assembly/

> +``SYM_FUNC_END``, ``SYM_CODE_START``, and similar.
> +
> +Rationale
> +---------
> +Some code like entries, trampolines, or boot code needs to be written in
> +assembly. The same as in C, we group such code into functions and accompany
> +them with data. Standard assemblers do not force users into precisely marking
> +these pieces as code, data, or even specifying their length. Nevertheless,
> +assemblers provide developers with such marks to aid debuggers throughout
> +assembly. On the top of that, developers also want to stamp some functions as
> +*global* to be visible outside of their translation units.
> +
> +Over the time, the Linux kernel took over macros from various projects (like

s/the //

> +``binutils``) to ease these markings. So for historic reasons, we have been
> +using ``ENTRY``, ``END``, ``ENDPROC``, and other annotations in assembly. Due
> +to the lack of their documentation, the macros are used in rather wrong
> +contexts at some locations. Clearly, ``ENTRY`` was intended for starts of
> +global symbols (be it data or code). ``END`` used to be the end of data or end
> +of special functions with *non-standard* calling convention. In contrast,
> +``ENDPROC`` should annotate only ends of *standard* functions.

...

-- 
Regards/Gruss,
    Boris.

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