Re: [Xen-devel] [PATCH v9 01/28] linkage: Introduce new macros for assembler symbols

["Rafael J. Wysocki" <rafael@xxxxxxxxxx>]

On Fri, Oct 11, 2019 at 1:53 PM Jiri Slaby <jslaby@xxxxxxx> 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:
>
> a) Support macros for the ones below
>    SYM_T_FUNC -- type used by assembler to mark functions
>    SYM_T_OBJECT -- type used by assembler to mark data
>    SYM_T_NONE -- type used by assembler to mark entries of unknown type
>
>    They are defined as STT_FUNC, STT_OBJECT, and STT_NOTYPE
>    respectively. According to the gas manual, this is the most portable
>    way. I am not sure about other assemblers, so this can be switched
>    back to %function and %object if this turns into a problem.
>    Architectures can also override them by something like ", @function"
>    if they need.
>
>    SYM_A_ALIGN, SYM_A_NONE -- align the symbol?
>    SYM_L_GLOBAL, SYM_L_WEAK, SYM_L_LOCAL -- linkage of symbols
>
> b) Mostly internal annotations, used by the ones below
>    SYM_ENTRY -- use only if you have to (for non-paired symbols)
>    SYM_START -- use only if you have to (for paired symbols)
>    SYM_END -- use only if you have to (for paired symbols)
>
> c) Annotations for code
>    SYM_INNER_LABEL_ALIGN -- only for labels in the middle of code
>    SYM_INNER_LABEL -- only for labels in the middle of code
>
>    SYM_FUNC_START_LOCAL_ALIAS -- use where there are two local names for
>         one function
>    SYM_FUNC_START_ALIAS -- use where there are two global names for one
>         function
>    SYM_FUNC_END_ALIAS -- the end of LOCAL_ALIASed or ALIASed function
>
>    SYM_FUNC_START -- use for global functions
>    SYM_FUNC_START_NOALIGN -- use for global functions, w/o alignment
>    SYM_FUNC_START_LOCAL -- use for local functions
>    SYM_FUNC_START_LOCAL_NOALIGN -- use for local functions, w/o
>         alignment
>    SYM_FUNC_START_WEAK -- use for weak functions
>    SYM_FUNC_START_WEAK_NOALIGN -- use for weak functions, w/o alignment
>    SYM_FUNC_END -- the end of SYM_FUNC_START_LOCAL, SYM_FUNC_START,
>         SYM_FUNC_START_WEAK, ...
>
>    For functions with special (non-C) calling conventions:
>    SYM_CODE_START -- use for non-C (special) functions
>    SYM_CODE_START_NOALIGN -- use for non-C (special) functions, w/o
>         alignment
>    SYM_CODE_START_LOCAL -- use for local non-C (special) functions
>    SYM_CODE_START_LOCAL_NOALIGN -- use for local non-C (special)
>         functions, w/o alignment
>    SYM_CODE_END -- the end of SYM_CODE_START_LOCAL or SYM_CODE_START
>
> d) For data
>    SYM_DATA_START -- global data symbol
>    SYM_DATA_START_LOCAL -- local data symbol
>    SYM_DATA_END -- the end of the SYM_DATA_START symbol
>    SYM_DATA_END_LABEL -- the labeled end of SYM_DATA_START symbol
>    SYM_DATA -- start+end wrapper around simple global data
>    SYM_DATA_LOCAL -- start+end wrapper around simple local data
>
> ==========
>
> The macros allow to pair starts and ends of functions and mark functions
> correctly in the output ELF objects.
>
> All users of the old macros in x86 are converted to use these in further
> patches.
>
> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: hpa@xxxxxxxxx
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: jpoimboe@xxxxxxxxxx
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-pm@xxxxxxxxxxxxxxx
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: mingo@xxxxxxxxxx
> Cc: Pavel Machek <pavel@xxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

for all the changes in the series affecting the power management code
maintained by me.

Thanks!

> ---
>
> Notes:
>     [v2]
>     * use SYM_ prefix and sane names
>     * add SYM_START and SYM_END and parametrize all the macros
>
>     [v3]
>     * add SYM_DATA, SYM_DATA_LOCAL, and SYM_DATA_END_LABEL
>
>     [v4]
>     * add _NOALIGN versions of some macros
>     * add _CODE_ derivates of _FUNC_ macros
>
>     [v5]
>     * drop "SIMPLE" from data annotations
>     * switch NOALIGN and ALIGN variants of inner labels
>     * s/visibility/linkage/; s@SYM_V_@SYM_L_@
>     * add Documentation
>
>     [v6]
>     * fixed typos found by Randy Dunlap
>     * remove doubled INNER_LABEL macros, one pair was unused
>
>     [v8]
>     * use lkml.kernel.org for links
>     * link the docs from index.rst (by Boris)
>     * fixed typos on the docs
>
>     [v9]
>     * updated the docs as requested by Boris
>
>  Documentation/asm-annotations.rst | 216 ++++++++++++++++++++++++++
>  Documentation/index.rst           |   8 +
>  arch/x86/include/asm/linkage.h    |  10 +-
>  include/linux/linkage.h           | 245 +++++++++++++++++++++++++++++-
>  4 files changed, 468 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..29ccd6e61fe5
> --- /dev/null
> +++ b/Documentation/asm-annotations.rst
> @@ -0,0 +1,216 @@
> +Assembler Annotations
> +=====================
> +
> +Copyright (c) 2017-2019 Jiri Slaby
> +
> +This document describes the new macros for annotation of data and code in
> +assembly. In particular, it contains information about ``SYM_FUNC_START``,
> +``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, such code is grouped into functions and
> +accompanied 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 annotations to aid
> +debuggers throughout assembly. On top of that, developers also want to mark
> +some functions as *global* in order to be visible outside of their 
> translation
> +units.
> +
> +Over time, the Linux kernel has adopted macros from various projects (like
> +``binutils``) to facilitate such annotations. So for historic reasons,
> +developers 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 to denote the beginning of global symbols (be it data or code).
> +``END`` used to mark the end of data or end of special functions with
> +*non-standard* calling convention. In contrast, ``ENDPROC`` should annotate
> +only ends of *standard* functions.
> +
> +When these macros are used correctly, they help assemblers generate a nice
> +object with both sizes and types set correctly. For example, the result of
> +``arch/x86/lib/putuser.S``::
> +
> +   Num:    Value          Size Type    Bind   Vis      Ndx Name
> +    25: 0000000000000000    33 FUNC    GLOBAL DEFAULT    1 __put_user_1
> +    29: 0000000000000030    37 FUNC    GLOBAL DEFAULT    1 __put_user_2
> +    32: 0000000000000060    36 FUNC    GLOBAL DEFAULT    1 __put_user_4
> +    35: 0000000000000090    37 FUNC    GLOBAL DEFAULT    1 __put_user_8
> +
> +This is not only important for debugging purposes. When there are properly
> +annotated objects like this, tools can be run on them to generate more useful
> +information. In particular, on properly annotated objects, ``objtool`` can be
> +run to check and fix the object if needed. Currently, ``objtool`` can report
> +missing frame pointer setup/destruction in functions. It can also
> +automatically generate annotations for :doc:`ORC unwinder <x86/orc-unwinder>`
> +for most code. Both of these are especially important to support reliable
> +stack traces which are in turn necessary for :doc:`Kernel live patching
> +<livepatch/livepatch>`.
> +
> +Caveat and Discussion
> +---------------------
> +As one might realize, there were only three macros previously. That is indeed
> +insufficient to cover all the combinations of cases:
> +
> +* standard/non-standard function
> +* code/data
> +* global/local symbol
> +
> +There was a discussion_ and instead of extending the current ``ENTRY/END*``
> +macros, it was decided that brand new macros should be introduced instead::
> +
> +    So how about using macro names that actually show the purpose, instead
> +    of importing all the crappy, historic, essentially randomly chosen
> +    debug symbol macro names from the binutils and older kernels?
> +
> +.. _discussion: 
> https://lkml.kernel.org/r/20170217104757.28588-1-jslaby@xxxxxxx
> +
> +Macros Description
> +------------------
> +
> +The new macros are prefixed with the ``SYM_`` prefix and can be divided into
> +three main groups:
> +
> +1. ``SYM_FUNC_*`` -- to annotate C-like functions. This means functions with
> +   standard C calling conventions, i.e. the stack contains a return address 
> at
> +   the predefined place and a return from the function can happen in a
> +   standard way. When frame pointers are enabled, save/restore of frame
> +   pointer shall happen at the start/end of a function, respectively, too.
> +
> +   Checking tools like ``objtool`` should ensure such marked functions 
> conform
> +   to these rules. The tools can also easily annotate these functions with
> +   debugging information (like *ORC data*) automatically.
> +
> +2. ``SYM_CODE_*`` -- special functions called with special stack. Be it
> +   interrupt handlers with special stack content, trampolines, or startup
> +   functions.
> +
> +   Checking tools mostly ignore checking of these functions. But some debug
> +   information still can be generated automatically. For correct debug data,
> +   this code needs hints like ``UNWIND_HINT_REGS`` provided by developers.
> +
> +3. ``SYM_DATA*`` -- obviously data belonging to ``.data`` sections and not to
> +   ``.text``. Data do not contain instructions, so they have to be treated
> +   specially by the tools: they should not treat the bytes as instructions,
> +   nor assign any debug information to them.
> +
> +Instruction Macros
> +~~~~~~~~~~~~~~~~~~
> +This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above.
> +
> +* ``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
> +  architecture specific ``__ALIGN`` bytes. There are also ``_NOALIGN`` 
> variants
> +  for special cases where developers do not want this implicit alignment.
> +
> +  ``SYM_FUNC_START_WEAK`` and ``SYM_FUNC_START_WEAK_NOALIGN`` markings are
> +  also offered as an assembler counterpart to the *weak* attribute known from
> +  C.
> +
> +  All of these **shall** be coupled with ``SYM_FUNC_END``. First, it marks
> +  the sequence of instructions as a function and computes its size to the
> +  generated object file. Second, it also eases checking and processing such
> +  object files as the tools can trivially find exact function boundaries.
> +
> +  So in most cases, developers should write something like in the following
> +  example, having some asm instructions in between the macros, of course::
> +
> +    SYM_FUNC_START(function_hook)
> +        ... asm insns ...
> +    SYM_FUNC_END(function_hook)
> +
> +  In fact, this kind of annotation corresponds to the now deprecated 
> ``ENTRY``
> +  and ``ENDPROC`` macros.
> +
> +* ``SYM_FUNC_START_ALIAS`` and ``SYM_FUNC_START_LOCAL_ALIAS`` serve for those
> +  who decided to have two or more names for one function. The typical use 
> is::
> +
> +    SYM_FUNC_START_ALIAS(__memset)
> +    SYM_FUNC_START(memset)
> +        ... asm insns ...
> +    SYM_FUNC_END(memset)
> +    SYM_FUNC_END_ALIAS(__memset)
> +
> +  In this example, one can call ``__memset`` or ``memset`` with the same
> +  result, except the debug information for the instructions is generated to
> +  the object file only once -- for the non-``ALIAS`` case.
> +
> +* ``SYM_CODE_START`` and ``SYM_CODE_START_LOCAL`` should be used only in
> +  special cases -- if you know what you are doing. This is used exclusively
> +  for interrupt handlers and similar where the calling convention is not the 
> C
> +  one. ``_NOALIGN`` variants exist too. The use is the same as for the 
> ``FUNC``
> +  category above::
> +
> +    SYM_CODE_START_LOCAL(bad_put_user)
> +        ... asm insns ...
> +    SYM_CODE_END(bad_put_user)
> +
> +  Again, every ``SYM_CODE_START*`` **shall** be coupled by ``SYM_CODE_END``.
> +
> +  To some extent, this category corresponds to deprecated ``ENTRY`` and
> +  ``END``. Except ``END`` had several other meanings too.
> +
> +* ``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::
> +
> +    SYM_CODE_START(ftrace_caller)
> +        /* save_mcount_regs fills in first two parameters */
> +        ...
> +
> +    SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
> +        /* Load the ftrace_ops into the 3rd parameter */
> +        ...
> +
> +    SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
> +        call ftrace_stub
> +        ...
> +        retq
> +    SYM_CODE_END(ftrace_caller)
> +
> +Data Macros
> +~~~~~~~~~~~
> +Similar to instructions, there is a couple of macros to describe data in the
> +assembly.
> +
> +* ``SYM_DATA_START`` and ``SYM_DATA_START_LOCAL`` mark the start of some data
> +  and shall be used in conjunction with either ``SYM_DATA_END``, or
> +  ``SYM_DATA_END_LABEL``. The latter adds also a label to the end, so that
> +  people can use ``lstack`` and (local) ``lstack_end`` in the following
> +  example::
> +
> +    SYM_DATA_START_LOCAL(lstack)
> +        .skip 4096
> +    SYM_DATA_END_LABEL(lstack, SYM_L_LOCAL, lstack_end)
> +
> +* ``SYM_DATA`` and ``SYM_DATA_LOCAL`` are variants for simple, mostly 
> one-line
> +  data::
> +
> +    SYM_DATA(HEAP,     .long rm_heap)
> +    SYM_DATA(heap_end, .long rm_stack)
> +
> +  In the end, they expand to ``SYM_DATA_START`` with ``SYM_DATA_END``
> +  internally.
> +
> +Support Macros
> +~~~~~~~~~~~~~~
> +All the above reduce themselves to some invocation of ``SYM_START``,
> +``SYM_END``, or ``SYM_ENTRY`` at last. Normally, developers should avoid 
> using
> +these.
> +
> +Further, in the above examples, one could see ``SYM_L_LOCAL``. There are also
> +``SYM_L_GLOBAL`` and ``SYM_L_WEAK``. All are intended to denote linkage of a
> +symbol marked by them. They are used either in ``_LABEL`` variants of the
> +earlier macros, or in ``SYM_START``.
> +
> +
> +Overriding Macros
> +~~~~~~~~~~~~~~~~~
> +Architecture can also override any of the macros in their own
> +``asm/linkage.h``, including macros specifying the type of a symbol
> +(``SYM_T_FUNC``, ``SYM_T_OBJECT``, and ``SYM_T_NONE``).  As every macro
> +described in this file is surrounded by ``#ifdef`` + ``#endif``, it is enough
> +to define the macros differently in the aforementioned architecture-dependent
> +header.
> diff --git a/Documentation/index.rst b/Documentation/index.rst
> index b843e313d2f2..2ceab197246f 100644
> --- a/Documentation/index.rst
> +++ b/Documentation/index.rst
> @@ -135,6 +135,14 @@ needed).
>     mic/index
>     scheduler/index
>
> +Architecture-agnostic documentation
> +-----------------------------------
> +
> +.. toctree::
> +   :maxdepth: 2
> +
> +   asm-annotations
> +
>  Architecture-specific documentation
>  -----------------------------------
>
> diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
> index 14caa9d9fb7f..e07188e8d763 100644
> --- a/arch/x86/include/asm/linkage.h
> +++ b/arch/x86/include/asm/linkage.h
> @@ -13,9 +13,13 @@
>
>  #ifdef __ASSEMBLY__
>
> -#define GLOBAL(name)   \
> -       .globl name;    \
> -       name:
> +/*
> + * GLOBAL is DEPRECATED
> + *
> + * use SYM_DATA_START, SYM_FUNC_START, SYM_INNER_LABEL, SYM_CODE_START, or
> + * similar
> + */
> +#define GLOBAL(name)   SYM_ENTRY(name, SYM_L_GLOBAL, SYM_A_NONE)
>
>  #if defined(CONFIG_X86_64) || defined(CONFIG_X86_ALIGNMENT_16)
>  #define __ALIGN                .p2align 4, 0x90
> diff --git a/include/linux/linkage.h b/include/linux/linkage.h
> index 7e020782ade2..f3ae8f3dea2c 100644
> --- a/include/linux/linkage.h
> +++ b/include/linux/linkage.h
> @@ -75,32 +75,58 @@
>
>  #ifdef __ASSEMBLY__
>
> +/* SYM_T_FUNC -- type used by assembler to mark functions */
> +#ifndef SYM_T_FUNC
> +#define SYM_T_FUNC                             STT_FUNC
> +#endif
> +
> +/* SYM_T_OBJECT -- type used by assembler to mark data */
> +#ifndef SYM_T_OBJECT
> +#define SYM_T_OBJECT                           STT_OBJECT
> +#endif
> +
> +/* SYM_T_NONE -- type used by assembler to mark entries of unknown type */
> +#ifndef SYM_T_NONE
> +#define SYM_T_NONE                             STT_NOTYPE
> +#endif
> +
> +/* SYM_A_* -- align the symbol? */
> +#define SYM_A_ALIGN                            ALIGN
> +#define SYM_A_NONE                             /* nothing */
> +
> +/* SYM_L_* -- linkage of symbols */
> +#define SYM_L_GLOBAL(name)                     .globl name
> +#define SYM_L_WEAK(name)                       .weak name
> +#define SYM_L_LOCAL(name)                      /* nothing */
> +
>  #ifndef LINKER_SCRIPT
>  #define ALIGN __ALIGN
>  #define ALIGN_STR __ALIGN_STR
>
> +/* === DEPRECATED annotations === */
> +
>  #ifndef GLOBAL
> +/* deprecated, use SYM_DATA*, SYM_ENTRY, or similar */
>  #define GLOBAL(name) \
>         .globl name ASM_NL \
>         name:
>  #endif
>
>  #ifndef ENTRY
> +/* deprecated, use SYM_FUNC_START */
>  #define ENTRY(name) \
> -       .globl name ASM_NL \
> -       ALIGN ASM_NL \
> -       name:
> +       SYM_FUNC_START(name)
>  #endif
>  #endif /* LINKER_SCRIPT */
>
>  #ifndef WEAK
> +/* deprecated, use SYM_FUNC_START_WEAK* */
>  #define WEAK(name)        \
> -       .weak name ASM_NL   \
> -       ALIGN ASM_NL \
> -       name:
> +       SYM_FUNC_START_WEAK(name)
>  #endif
>
>  #ifndef END
> +/* deprecated, use SYM_FUNC_END, SYM_DATA_END, or SYM_END */
>  #define END(name) \
>         .size name, .-name
>  #endif
> @@ -110,11 +136,214 @@
>   * static analysis tools such as stack depth analyzer.
>   */
>  #ifndef ENDPROC
> +/* deprecated, use SYM_FUNC_END */
>  #define ENDPROC(name) \
> -       .type name, @function ASM_NL \
> -       END(name)
> +       SYM_FUNC_END(name)
> +#endif
> +
> +/* === generic annotations === */
> +
> +/* SYM_ENTRY -- use only if you have to for non-paired symbols */
> +#ifndef SYM_ENTRY
> +#define SYM_ENTRY(name, linkage, align...)             \
> +       linkage(name) ASM_NL                            \
> +       align ASM_NL                                    \
> +       name:
> +#endif
> +
> +/* SYM_START -- use only if you have to */
> +#ifndef SYM_START
> +#define SYM_START(name, linkage, align...)             \
> +       SYM_ENTRY(name, linkage, align)
> +#endif
> +
> +/* SYM_END -- use only if you have to */
> +#ifndef SYM_END
> +#define SYM_END(name, sym_type)                                \
> +       .type name sym_type ASM_NL                      \
> +       .size name, .-name
> +#endif
> +
> +/* === code annotations === */
> +
> +/*
> + * FUNC -- C-like functions (proper stack frame etc.)
> + * CODE -- non-C code (e.g. irq handlers with different, special stack etc.)
> + *
> + * Objtool validates stack for FUNC, but not for CODE.
> + * Objtool generates debug info for both FUNC & CODE, but needs special
> + * annotations for each CODE's start (to describe the actual stack frame).
> + *
> + * ALIAS -- does not generate debug info -- the aliased function will
> + */
> +
> +/* SYM_INNER_LABEL_ALIGN -- only for labels in the middle of code */
> +#ifndef SYM_INNER_LABEL_ALIGN
> +#define SYM_INNER_LABEL_ALIGN(name, linkage)   \
> +       .type name SYM_T_NONE ASM_NL                    \
> +       SYM_ENTRY(name, linkage, SYM_A_ALIGN)
> +#endif
> +
> +/* SYM_INNER_LABEL -- only for labels in the middle of code */
> +#ifndef SYM_INNER_LABEL
> +#define SYM_INNER_LABEL(name, linkage)         \
> +       .type name SYM_T_NONE ASM_NL                    \
> +       SYM_ENTRY(name, linkage, SYM_A_NONE)
> +#endif
> +
> +/*
> + * SYM_FUNC_START_LOCAL_ALIAS -- use where there are two local names for one
> + * function
> + */
> +#ifndef SYM_FUNC_START_LOCAL_ALIAS
> +#define SYM_FUNC_START_LOCAL_ALIAS(name)               \
> +       SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)
> +#endif
> +
> +/*
> + * SYM_FUNC_START_ALIAS -- use where there are two global names for one
> + * function
> + */
> +#ifndef SYM_FUNC_START_ALIAS
> +#define SYM_FUNC_START_ALIAS(name)                     \
> +       SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)
> +#endif
> +
> +/* SYM_FUNC_START -- use for global functions */
> +#ifndef SYM_FUNC_START
> +/*
> + * The same as SYM_FUNC_START_ALIAS, but we will need to distinguish these 
> two
> + * later.
> + */
> +#define SYM_FUNC_START(name)                           \
> +       SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)
> +#endif
> +
> +/* SYM_FUNC_START_NOALIGN -- use for global functions, w/o alignment */
> +#ifndef SYM_FUNC_START_NOALIGN
> +#define SYM_FUNC_START_NOALIGN(name)                   \
> +       SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)
> +#endif
> +
> +/* SYM_FUNC_START_LOCAL -- use for local functions */
> +#ifndef SYM_FUNC_START_LOCAL
> +/* the same as SYM_FUNC_START_LOCAL_ALIAS, see comment near SYM_FUNC_START */
> +#define SYM_FUNC_START_LOCAL(name)                     \
> +       SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)
>  #endif
>
> +/* SYM_FUNC_START_LOCAL_NOALIGN -- use for local functions, w/o alignment */
> +#ifndef SYM_FUNC_START_LOCAL_NOALIGN
> +#define SYM_FUNC_START_LOCAL_NOALIGN(name)             \
> +       SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)
>  #endif
>
> +/* SYM_FUNC_START_WEAK -- use for weak functions */
> +#ifndef SYM_FUNC_START_WEAK
> +#define SYM_FUNC_START_WEAK(name)                      \
> +       SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN)
>  #endif
> +
> +/* SYM_FUNC_START_WEAK_NOALIGN -- use for weak functions, w/o alignment */
> +#ifndef SYM_FUNC_START_WEAK_NOALIGN
> +#define SYM_FUNC_START_WEAK_NOALIGN(name)              \
> +       SYM_START(name, SYM_L_WEAK, SYM_A_NONE)
> +#endif
> +
> +/* SYM_FUNC_END_ALIAS -- the end of LOCAL_ALIASed or ALIASed function */
> +#ifndef SYM_FUNC_END_ALIAS
> +#define SYM_FUNC_END_ALIAS(name)                       \
> +       SYM_END(name, SYM_T_FUNC)
> +#endif
> +
> +/*
> + * SYM_FUNC_END -- the end of SYM_FUNC_START_LOCAL, SYM_FUNC_START,
> + * SYM_FUNC_START_WEAK, ...
> + */
> +#ifndef SYM_FUNC_END
> +/* the same as SYM_FUNC_END_ALIAS, see comment near SYM_FUNC_START */
> +#define SYM_FUNC_END(name)                             \
> +       SYM_END(name, SYM_T_FUNC)
> +#endif
> +
> +/* SYM_CODE_START -- use for non-C (special) functions */
> +#ifndef SYM_CODE_START
> +#define SYM_CODE_START(name)                           \
> +       SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)
> +#endif
> +
> +/* SYM_CODE_START_NOALIGN -- use for non-C (special) functions, w/o 
> alignment */
> +#ifndef SYM_CODE_START_NOALIGN
> +#define SYM_CODE_START_NOALIGN(name)                   \
> +       SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)
> +#endif
> +
> +/* SYM_CODE_START_LOCAL -- use for local non-C (special) functions */
> +#ifndef SYM_CODE_START_LOCAL
> +#define SYM_CODE_START_LOCAL(name)                     \
> +       SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)
> +#endif
> +
> +/*
> + * SYM_CODE_START_LOCAL_NOALIGN -- use for local non-C (special) functions,
> + * w/o alignment
> + */
> +#ifndef SYM_CODE_START_LOCAL_NOALIGN
> +#define SYM_CODE_START_LOCAL_NOALIGN(name)             \
> +       SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)
> +#endif
> +
> +/* SYM_CODE_END -- the end of SYM_CODE_START_LOCAL, SYM_CODE_START, ... */
> +#ifndef SYM_CODE_END
> +#define SYM_CODE_END(name)                             \
> +       SYM_END(name, SYM_T_NONE)
> +#endif
> +
> +/* === data annotations === */
> +
> +/* SYM_DATA_START -- global data symbol */
> +#ifndef SYM_DATA_START
> +#define SYM_DATA_START(name)                           \
> +       SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)
> +#endif
> +
> +/* SYM_DATA_START -- local data symbol */
> +#ifndef SYM_DATA_START_LOCAL
> +#define SYM_DATA_START_LOCAL(name)                     \
> +       SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)
> +#endif
> +
> +/* SYM_DATA_END -- the end of SYM_DATA_START symbol */
> +#ifndef SYM_DATA_END
> +#define SYM_DATA_END(name)                             \
> +       SYM_END(name, SYM_T_OBJECT)
> +#endif
> +
> +/* SYM_DATA_END_LABEL -- the labeled end of SYM_DATA_START symbol */
> +#ifndef SYM_DATA_END_LABEL
> +#define SYM_DATA_END_LABEL(name, linkage, label)       \
> +       linkage(label) ASM_NL                           \
> +       .type label SYM_T_OBJECT ASM_NL                 \
> +       label:                                          \
> +       SYM_END(name, SYM_T_OBJECT)
> +#endif
> +
> +/* SYM_DATA -- start+end wrapper around simple global data */
> +#ifndef SYM_DATA
> +#define SYM_DATA(name, data...)                                \
> +       SYM_DATA_START(name) ASM_NL                             \
> +       data ASM_NL                                             \
> +       SYM_DATA_END(name)
> +#endif
> +
> +/* SYM_DATA_LOCAL -- start+end wrapper around simple local data */
> +#ifndef SYM_DATA_LOCAL
> +#define SYM_DATA_LOCAL(name, data...)                  \
> +       SYM_DATA_START_LOCAL(name) ASM_NL                       \
> +       data ASM_NL                                             \
> +       SYM_DATA_END(name)
> +#endif
> +
> +#endif /* __ASSEMBLY__ */
> +
> +#endif /* _LINUX_LINKAGE_H */
> --
> 2.23.0
>

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