sphinx.addnodesdocument)}( rawsourcechildren]( translations LanguagesNode)}(hhh](h pending_xref)}(hhh]docutils.nodesTextChinese (Simplified)}parenthsba attributes}(ids]classes]names]dupnames]backrefs] refdomainstdreftypedoc reftarget,/translations/zh_CN/core-api/asm-annotationsmodnameN classnameN refexplicitutagnamehhh ubh)}(hhh]hChinese (Traditional)}hh2sbah}(h]h ]h"]h$]h&] refdomainh)reftypeh+ reftarget,/translations/zh_TW/core-api/asm-annotationsmodnameN classnameN refexplicituh1hhh ubh)}(hhh]hItalian}hhFsbah}(h]h ]h"]h$]h&] refdomainh)reftypeh+ reftarget,/translations/it_IT/core-api/asm-annotationsmodnameN classnameN refexplicituh1hhh ubh)}(hhh]hJapanese}hhZsbah}(h]h ]h"]h$]h&] refdomainh)reftypeh+ reftarget,/translations/ja_JP/core-api/asm-annotationsmodnameN classnameN refexplicituh1hhh ubh)}(hhh]hKorean}hhnsbah}(h]h ]h"]h$]h&] refdomainh)reftypeh+ reftarget,/translations/ko_KR/core-api/asm-annotationsmodnameN classnameN refexplicituh1hhh ubh)}(hhh]hPortuguese (Brazilian)}hhsbah}(h]h ]h"]h$]h&] refdomainh)reftypeh+ reftarget,/translations/pt_BR/core-api/asm-annotationsmodnameN classnameN refexplicituh1hhh ubh)}(hhh]hSpanish}hhsbah}(h]h ]h"]h$]h&] refdomainh)reftypeh+ reftarget,/translations/sp_SP/core-api/asm-annotationsmodnameN classnameN refexplicituh1hhh ubeh}(h]h ]h"]h$]h&]current_languageEnglishuh1h hh _documenthsourceNlineNubhsection)}(hhh](htitle)}(hAssembler Annotationsh]hAssembler Annotations}(hhhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhhhF/var/lib/git/docbuild/linux/Documentation/core-api/asm-annotations.rsthKubh paragraph)}(h"Copyright (c) 2017-2019 Jiri Slabyh]h"Copyright (c) 2017-2019 Jiri Slaby}(hhhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhKhhhhubh)}(hThis document describes the new macros for annotation of data and code in assembly. In particular, it contains information about ``SYM_FUNC_START``, ``SYM_FUNC_END``, ``SYM_CODE_START``, and similar.h](hThis document describes the new macros for annotation of data and code in assembly. In particular, it contains information about }(hhhhhNhNubhliteral)}(h``SYM_FUNC_START``h]hSYM_FUNC_START}(hhhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhubh, }(hhhhhNhNubh)}(h``SYM_FUNC_END``h]h SYM_FUNC_END}(hhhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhubh, }(hhhhhNhNubh)}(h``SYM_CODE_START``h]hSYM_CODE_START}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhhubh, and similar.}(hhhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhhhhubh)}(hhh](h)}(h Rationaleh]h Rationale}(hj$hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj!hhhhhK ubh)}(hX Some code like entries, trampolines, or boot code needs to be written in assembly. The same as in C, such code is grouped into functions and accompanied with data. Standard assemblers do not force users into precisely marking these pieces as code, data, or even specifying their length. Nevertheless, assemblers provide developers with such annotations to aid debuggers throughout assembly. On top of that, developers also want to mark some functions as *global* in order to be visible outside of their translation units.h](hXSome code like entries, trampolines, or boot code needs to be written in assembly. The same as in C, such code is grouped into functions and accompanied with data. Standard assemblers do not force users into precisely marking these pieces as code, data, or even specifying their length. Nevertheless, assemblers provide developers with such annotations to aid debuggers throughout assembly. On top of that, developers also want to mark some functions as }(hj2hhhNhNubhemphasis)}(h*global*h]hglobal}(hj<hhhNhNubah}(h]h ]h"]h$]h&]uh1j:hj2ubh; in order to be visible outside of their translation units.}(hj2hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhK hj!hhubh)}(hXnOver time, the Linux kernel has adopted macros from various projects (like ``binutils``) to facilitate such annotations. So for historic reasons, developers have been using ``ENTRY``, ``END``, ``ENDPROC``, and other annotations in assembly. Due to the lack of their documentation, the macros are used in rather wrong contexts at some locations. Clearly, ``ENTRY`` was intended to denote the beginning of global symbols (be it data or code). ``END`` used to mark the end of data or end of special functions with *non-standard* calling convention. In contrast, ``ENDPROC`` should annotate only ends of *standard* functions.h](hKOver time, the Linux kernel has adopted macros from various projects (like }(hjThhhNhNubh)}(h ``binutils``h]hbinutils}(hj\hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubhV) to facilitate such annotations. So for historic reasons, developers have been using }(hjThhhNhNubh)}(h ``ENTRY``h]hENTRY}(hjnhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubh, }(hjThhhNhNubh)}(h``END``h]hEND}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubh, }hjTsbh)}(h ``ENDPROC``h]hENDPROC}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubh, and other annotations in assembly. Due to the lack of their documentation, the macros are used in rather wrong contexts at some locations. Clearly, }(hjThhhNhNubh)}(h ``ENTRY``h]hENTRY}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubhN was intended to denote the beginning of global symbols (be it data or code). }(hjThhhNhNubh)}(h``END``h]hEND}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubh? used to mark the end of data or end of special functions with }(hjThhhNhNubj;)}(h*non-standard*h]h non-standard}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1j:hjTubh" calling convention. In contrast, }(hjThhhNhNubh)}(h ``ENDPROC``h]hENDPROC}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjTubh should annotate only ends of }(hjThhhNhNubj;)}(h *standard*h]hstandard}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1j:hjTubh functions.}(hjThhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhj!hhubh)}(hWhen these macros are used correctly, they help assemblers generate a nice object with both sizes and types set correctly. For example, the result of ``arch/x86/lib/putuser.S``::h](hWhen these macros are used correctly, they help assemblers generate a nice object with both sizes and types set correctly. For example, the result of }(hjhhhNhNubh)}(h``arch/x86/lib/putuser.S``h]harch/x86/lib/putuser.S}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh:}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhj!hhubh literal_block)}(hXPNum: Value Size Type Bind Vis Ndx Name 25: 0000000000000000 33 FUNC GLOBAL DEFAULT 1 __put_user_1 29: 0000000000000030 37 FUNC GLOBAL DEFAULT 1 __put_user_2 32: 0000000000000060 36 FUNC GLOBAL DEFAULT 1 __put_user_4 35: 0000000000000090 37 FUNC GLOBAL DEFAULT 1 __put_user_8h]hXPNum: Value Size Type Bind Vis Ndx Name 25: 0000000000000000 33 FUNC GLOBAL DEFAULT 1 __put_user_1 29: 0000000000000030 37 FUNC GLOBAL DEFAULT 1 __put_user_2 32: 0000000000000060 36 FUNC GLOBAL DEFAULT 1 __put_user_4 35: 0000000000000090 37 FUNC GLOBAL DEFAULT 1 __put_user_8}hj&sbah}(h]h ]h"]h$]h&] xml:spacepreserveuh1j$hhhK#hj!hhubh)}(hXThis is not only important for debugging purposes. When there are properly annotated objects like this, tools can be run on them to generate more useful information. In particular, on properly annotated objects, ``objtool`` can be run to check and fix the object if needed. Currently, ``objtool`` can report missing frame pointer setup/destruction in functions. It can also automatically generate annotations for the ORC unwinder (Documentation/arch/x86/orc-unwinder.rst) for most code. Both of these are especially important to support reliable stack traces which are in turn necessary for kernel live patching (Documentation/livepatch/livepatch.rst).h](hThis is not only important for debugging purposes. When there are properly annotated objects like this, tools can be run on them to generate more useful information. In particular, on properly annotated objects, }(hj6hhhNhNubh)}(h ``objtool``h]hobjtool}(hj>hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj6ubh> can be run to check and fix the object if needed. Currently, }(hj6hhhNhNubh)}(h ``objtool``h]hobjtool}(hjPhhhNhNubah}(h]h ]h"]h$]h&]uh1hhj6ubhXd can report missing frame pointer setup/destruction in functions. It can also automatically generate annotations for the ORC unwinder (Documentation/arch/x86/orc-unwinder.rst) for most code. Both of these are especially important to support reliable stack traces which are in turn necessary for kernel live patching (Documentation/livepatch/livepatch.rst).}(hj6hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhK)hj!hhubeh}(h] rationaleah ]h"] rationaleah$]h&]uh1hhhhhhhhK ubh)}(hhh](h)}(hCaveat and Discussionh]hCaveat and Discussion}(hjshhhNhNubah}(h]h ]h"]h$]h&]uh1hhjphhhhhK5ubh)}(hAs one might realize, there were only three macros previously. That is indeed insufficient to cover all the combinations of cases:h]hAs one might realize, there were only three macros previously. That is indeed insufficient to cover all the combinations of cases:}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhK6hjphhubh bullet_list)}(hhh](h list_item)}(hstandard/non-standard functionh]h)}(hjh]hstandard/non-standard function}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhK9hjubah}(h]h ]h"]h$]h&]uh1jhjhhhhhNubj)}(h code/datah]h)}(hjh]h code/data}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhK:hjubah}(h]h ]h"]h$]h&]uh1jhjhhhhhNubj)}(hglobal/local symbol h]h)}(hglobal/local symbolh]hglobal/local symbol}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhK;hjubah}(h]h ]h"]h$]h&]uh1jhjhhhhhNubeh}(h]h ]h"]h$]h&]bullet*uh1jhhhK9hjphhubh)}(hThere was a discussion_ and instead of extending the current ``ENTRY/END*`` macros, it was decided that brand new macros should be introduced instead::h](h There was a }(hjhhhNhNubh reference)}(h discussion_h]h discussion}(hjhhhNhNubah}(h]h ]h"]h$]h&]name discussionrefuri?https://lore.kernel.org/r/20170217104757.28588-1-jslaby@suse.czuh1jhjresolvedKubh& and instead of extending the current }(hjhhhNhNubh)}(h``ENTRY/END*``h]h ENTRY/END*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubhK macros, it was decided that brand new macros should be introduced instead:}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhK=hjphhubj%)}(hSo how about using macro names that actually show the purpose, instead of importing all the crappy, historic, essentially randomly chosen debug symbol macro names from the binutils and older kernels?h]hSo how about using macro names that actually show the purpose, instead of importing all the crappy, historic, essentially randomly chosen debug symbol macro names from the binutils and older kernels?}hjsbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhK@hjphhubhtarget)}(hO.. _discussion: https://lore.kernel.org/r/20170217104757.28588-1-jslaby@suse.czh]h}(h] discussionah ]h"] discussionah$]h&]jjuh1j+hKDhjphhhhʌ referencedKubeh}(h]caveat-and-discussionah ]h"]caveat and discussionah$]h&]uh1hhhhhhhhK5ubh)}(hhh](h)}(hMacros Descriptionh]hMacros Description}(hjEhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjBhhhhhKGubh)}(h_The new macros are prefixed with the ``SYM_`` prefix and can be divided into three main groups:h](h%The new macros are prefixed with the }(hjShhhNhNubh)}(h``SYM_``h]hSYM_}(hj[hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjSubh2 prefix and can be divided into three main groups:}(hjShhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKIhjBhhubhenumerated_list)}(hhh](j)}(hXS``SYM_FUNC_*`` -- to annotate C-like functions. This means functions with standard C calling conventions. For example, on x86, this means that 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. h](h)}(hX``SYM_FUNC_*`` -- to annotate C-like functions. This means functions with standard C calling conventions. For example, on x86, this means that 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.h](h)}(h``SYM_FUNC_*``h]h SYM_FUNC_*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhj|ubhXx -- to annotate C-like functions. This means functions with standard C calling conventions. For example, on x86, this means that the stack contains a return address at the predefined place and a return from the function can happen in a standard way. When frame pointers are enabled, save/restore of frame pointer shall happen at the start/end of a function, respectively, too.}(hj|hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKLhjxubh)}(hChecking 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.h](hChecking tools like }(hjhhhNhNubh)}(h ``objtool``h]hobjtool}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh should ensure such marked functions conform to these rules. The tools can also easily annotate these functions with debugging information (like }(hjhhhNhNubj;)}(h *ORC data*h]hORC data}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1j:hjubh) automatically.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKShjxubeh}(h]h ]h"]h$]h&]uh1jhjuhhhhhNubj)}(hXs``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. h](h)}(h``SYM_CODE_*`` -- special functions called with special stack. Be it interrupt handlers with special stack content, trampolines, or startup functions.h](h)}(h``SYM_CODE_*``h]h SYM_CODE_*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh -- special functions called with special stack. Be it interrupt handlers with special stack content, trampolines, or startup functions.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKWhjubh)}(hChecking 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.h](hChecking 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 }(hjhhhNhNubh)}(h``UNWIND_HINT_REGS``h]hUNWIND_HINT_REGS}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh provided by developers.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhK[hjubeh}(h]h ]h"]h$]h&]uh1jhjuhhhhhNubj)}(hX``SYM_DATA*`` -- obviously data belonging to ``.data`` sections and not to ``.text``. Data do not contain instructions, so they have to be treated specially by the tools: they should not treat the bytes as instructions, nor assign any debug information to them. h]h)}(hX``SYM_DATA*`` -- obviously data belonging to ``.data`` sections and not to ``.text``. Data do not contain instructions, so they have to be treated specially by the tools: they should not treat the bytes as instructions, nor assign any debug information to them.h](h)}(h ``SYM_DATA*``h]h SYM_DATA*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh -- obviously data belonging to }(hjhhhNhNubh)}(h ``.data``h]h.data}(hj0hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh sections and not to }(hjhhhNhNubh)}(h ``.text``h]h.text}(hjBhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh. 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.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhK_hjubah}(h]h ]h"]h$]h&]uh1jhjuhhhhhNubeh}(h]h ]h"]h$]h&]enumtypearabicprefixhsuffix.uh1jshjBhhhhhKLubh)}(hhh](h)}(hInstruction Macrosh]hInstruction Macros}(hjnhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjkhhhhhKeubh)}(hGThis section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above.h](hThis section covers }(hj|hhhNhNubh)}(h``SYM_FUNC_*``h]h SYM_FUNC_*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhj|ubh and }(hj|hhhNhNubh)}(h``SYM_CODE_*``h]h SYM_CODE_*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhj|ubh enumerated above.}(hj|hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKfhjkhhubh)}(hX!``objtool`` requires that all code must be contained in an ELF symbol. Symbol names that have a ``.L`` prefix do not emit symbol table entries. ``.L`` prefixed symbols can be used within a code region, but should be avoided for denoting a range of code via ``SYM_*_START/END`` annotations.h](h)}(h ``objtool``h]hobjtool}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubhU requires that all code must be contained in an ELF symbol. Symbol names that have a }(hjhhhNhNubh)}(h``.L``h]h.L}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh* prefix do not emit symbol table entries. }(hjhhhNhNubh)}(h``.L``h]h.L}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubhk prefixed symbols can be used within a code region, but should be avoided for denoting a range of code via }(hjhhhNhNubh)}(h``SYM_*_START/END``h]hSYM_*_START/END}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh annotations.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhhjkhhubj)}(hhh](j)}(hXx``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(memset) ... asm insns ... SYM_FUNC_END(memset) In fact, this kind of annotation corresponds to the now deprecated ``ENTRY`` and ``ENDPROC`` macros. h](h)}(hXw``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.h](h)}(h``SYM_FUNC_START``h]hSYM_FUNC_START}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh and }(hjhhhNhNubh)}(h``SYM_FUNC_START_LOCAL``h]hSYM_FUNC_START_LOCAL}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh are supposed to be }(hjhhhNhNubhstrong)}(h**the most frequent markings**h]hthe most frequent markings}(hj1hhhNhNubah}(h]h ]h"]h$]h&]uh1j/hjubh. They are used for functions with standard calling conventions -- global and local. Like in C, they both align the functions to architecture specific }(hjhhhNhNubh)}(h ``__ALIGN``h]h__ALIGN}(hjChhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh bytes. There are also }(hjhhhNhNubh)}(h ``_NOALIGN``h]h_NOALIGN}(hjUhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubhQ variants for special cases where developers do not want this implicit alignment.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKmhjubh)}(h``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.h](h)}(h``SYM_FUNC_START_WEAK``h]hSYM_FUNC_START_WEAK}(hjqhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjmubh and }(hjmhhhNhNubh)}(h``SYM_FUNC_START_WEAK_NOALIGN``h]hSYM_FUNC_START_WEAK_NOALIGN}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjmubh> markings are also offered as an assembler counterpart to the }(hjmhhhNhNubj;)}(h*weak*h]hweak}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1j:hjmubh attribute known from C.}(hjmhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKshjubh)}(hX"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.h](h All of these }(hjhhhNhNubj0)}(h **shall**h]hshall}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1j/hjubh be coupled with }(hjhhhNhNubh)}(h``SYM_FUNC_END``h]h SYM_FUNC_END}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh. 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.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKwhjubh)}(hSo in most cases, developers should write something like in the following example, having some asm instructions in between the macros, of course::h]hSo in most cases, developers should write something like in the following example, having some asm instructions in between the macros, of course:}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhK|hjubj%)}(hASYM_FUNC_START(memset) ... asm insns ... SYM_FUNC_END(memset)h]hASYM_FUNC_START(memset) ... asm insns ... SYM_FUNC_END(memset)}hjsbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhKhjubh)}(hdIn fact, this kind of annotation corresponds to the now deprecated ``ENTRY`` and ``ENDPROC`` macros.h](hCIn fact, this kind of annotation corresponds to the now deprecated }(hjhhhNhNubh)}(h ``ENTRY``h]hENTRY}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh and }(hjhhhNhNubh)}(h ``ENDPROC``h]hENDPROC}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh macros.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubeh}(h]h ]h"]h$]h&]uh1jhjhhhhhNubj)}(hX``SYM_FUNC_ALIAS``, ``SYM_FUNC_ALIAS_LOCAL``, and ``SYM_FUNC_ALIAS_WEAK`` can be used to define multiple names for a function. The typical use is:: SYM_FUNC_START(__memset) ... asm insns ... SYN_FUNC_END(__memset) SYM_FUNC_ALIAS(memset, __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. h](h)}(h``SYM_FUNC_ALIAS``, ``SYM_FUNC_ALIAS_LOCAL``, and ``SYM_FUNC_ALIAS_WEAK`` can be used to define multiple names for a function. The typical use is::h](h)}(h``SYM_FUNC_ALIAS``h]hSYM_FUNC_ALIAS}(hj;hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj7ubh, }(hj7hhhNhNubh)}(h``SYM_FUNC_ALIAS_LOCAL``h]hSYM_FUNC_ALIAS_LOCAL}(hjMhhhNhNubah}(h]h ]h"]h$]h&]uh1hhj7ubh, and }(hj7hhhNhNubh)}(h``SYM_FUNC_ALIAS_WEAK``h]hSYM_FUNC_ALIAS_WEAK}(hj_hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj7ubhI can be used to define multiple names for a function. The typical use is:}(hj7hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhj3ubj%)}(hfSYM_FUNC_START(__memset) ... asm insns ... SYN_FUNC_END(__memset) SYM_FUNC_ALIAS(memset, __memset)h]hfSYM_FUNC_START(__memset) ... asm insns ... SYN_FUNC_END(__memset) SYM_FUNC_ALIAS(memset, __memset)}hjwsbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhKhj3ubh)}(hIn 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.h](hIn this example, one can call }(hjhhhNhNubh)}(h ``__memset``h]h__memset}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh or }(hjhhhNhNubh)}(h ``memset``h]hmemset}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh with the same result, except the debug information for the instructions is generated to the object file only once -- for the non-}(hjhhhNhNubh)}(h ``ALIAS``h]hALIAS}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh case.}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhj3ubeh}(h]h ]h"]h$]h&]uh1jhjhhhhhNubj)}(hXc``SYM_CODE_START`` and ``SYM_CODE_START_LOCAL`` should be used only in special cases -- if you know what you are doing. This is used exclusively for interrupt handlers and similar where the calling convention is not the C one. ``_NOALIGN`` variants exist too. The use is the same as for the ``FUNC`` category above:: SYM_CODE_START_LOCAL(bad_put_user) ... asm insns ... SYM_CODE_END(bad_put_user) Again, every ``SYM_CODE_START*`` **shall** be coupled by ``SYM_CODE_END``. To some extent, this category corresponds to deprecated ``ENTRY`` and ``END``. Except ``END`` had several other meanings too. h](h)}(hX<``SYM_CODE_START`` and ``SYM_CODE_START_LOCAL`` should be used only in special cases -- if you know what you are doing. This is used exclusively for interrupt handlers and similar where the calling convention is not the C one. ``_NOALIGN`` variants exist too. The use is the same as for the ``FUNC`` category above::h](h)}(h``SYM_CODE_START``h]hSYM_CODE_START}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh and }(hjhhhNhNubh)}(h``SYM_CODE_START_LOCAL``h]hSYM_CODE_START_LOCAL}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh should be used only in special cases -- if you know what you are doing. This is used exclusively for interrupt handlers and similar where the calling convention is not the C one. }(hjhhhNhNubh)}(h ``_NOALIGN``h]h_NOALIGN}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh4 variants exist too. The use is the same as for the }(hjhhhNhNubh)}(h``FUNC``h]hFUNC}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh category above:}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubj%)}(hSSYM_CODE_START_LOCAL(bad_put_user) ... asm insns ... SYM_CODE_END(bad_put_user)h]hSSYM_CODE_START_LOCAL(bad_put_user) ... asm insns ... SYM_CODE_END(bad_put_user)}hj%sbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhKhjubh)}(hJAgain, every ``SYM_CODE_START*`` **shall** be coupled by ``SYM_CODE_END``.h](h Again, every }(hj3hhhNhNubh)}(h``SYM_CODE_START*``h]hSYM_CODE_START*}(hj;hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj3ubh }(hj3hhhNhNubj0)}(h **shall**h]hshall}(hjMhhhNhNubah}(h]h ]h"]h$]h&]uh1j/hj3ubh be coupled by }(hj3hhhNhNubh)}(h``SYM_CODE_END``h]h SYM_CODE_END}(hj_hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj3ubh.}(hj3hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubh)}(h}To some extent, this category corresponds to deprecated ``ENTRY`` and ``END``. Except ``END`` had several other meanings too.h](h8To some extent, this category corresponds to deprecated }(hjwhhhNhNubh)}(h ``ENTRY``h]hENTRY}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjwubh and }(hjwhhhNhNubh)}(h``END``h]hEND}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjwubh . Except }(hjwhhhNhNubh)}(h``END``h]hEND}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjwubh had several other meanings too.}(hjwhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubeh}(h]h ]h"]h$]h&]uh1jhjhhhhhNubj)}(hX ``SYM_INNER_LABEL*`` is used to denote a label inside some ``SYM_{CODE,FUNC}_START`` and ``SYM_{CODE,FUNC}_END``. They are very similar to C labels, except they can be made global. An example of use:: SYM_CODE_START(ftrace_caller) /* save_mcount_regs fills in first two parameters */ ... SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL) /* Load the ftrace_ops into the 3rd parameter */ ... SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) call ftrace_stub ... retq SYM_CODE_END(ftrace_caller) h](h)}(h``SYM_INNER_LABEL*`` is used to denote a label inside some ``SYM_{CODE,FUNC}_START`` and ``SYM_{CODE,FUNC}_END``. They are very similar to C labels, except they can be made global. An example of use::h](h)}(h``SYM_INNER_LABEL*``h]hSYM_INNER_LABEL*}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh' is used to denote a label inside some }(hjhhhNhNubh)}(h``SYM_{CODE,FUNC}_START``h]hSYM_{CODE,FUNC}_START}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh and }(hjhhhNhNubh)}(h``SYM_{CODE,FUNC}_END``h]hSYM_{CODE,FUNC}_END}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubhX. They are very similar to C labels, except they can be made global. An example of use:}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubj%)}(hX>SYM_CODE_START(ftrace_caller) /* save_mcount_regs fills in first two parameters */ ... SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL) /* Load the ftrace_ops into the 3rd parameter */ ... SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) call ftrace_stub ... retq SYM_CODE_END(ftrace_caller)h]hX>SYM_CODE_START(ftrace_caller) /* save_mcount_regs fills in first two parameters */ ... SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL) /* Load the ftrace_ops into the 3rd parameter */ ... SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) call ftrace_stub ... retq SYM_CODE_END(ftrace_caller)}hjsbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhKhjubeh}(h]h ]h"]h$]h&]uh1jhjhhhhhNubeh}(h]h ]h"]h$]h&]jjuh1jhhhKmhjkhhubeh}(h]instruction-macrosah ]h"]instruction macrosah$]h&]uh1hhjBhhhhhKeubh)}(hhh](h)}(h Data Macrosh]h Data Macros}(hj*hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj'hhhhhKubh)}(hVSimilar to instructions, there is a couple of macros to describe data in the assembly.h]hVSimilar to instructions, there is a couple of macros to describe data in the assembly.}(hj8hhhNhNubah}(h]h ]h"]h$]h&]uh1hhhhKhj'hhubj)}(hhh](j)}(hX``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) h](h)}(hX&``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::h](h)}(h``SYM_DATA_START``h]hSYM_DATA_START}(hjQhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjMubh and }(hjMhhhNhNubh)}(h``SYM_DATA_START_LOCAL``h]hSYM_DATA_START_LOCAL}(hjchhhNhNubah}(h]h ]h"]h$]h&]uh1hhjMubhJ mark the start of some data and shall be used in conjunction with either }(hjMhhhNhNubh)}(h``SYM_DATA_END``h]h SYM_DATA_END}(hjuhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjMubh, or }(hjMhhhNhNubh)}(h``SYM_DATA_END_LABEL``h]hSYM_DATA_END_LABEL}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjMubhB. The latter adds also a label to the end, so that people can use }(hjMhhhNhNubh)}(h ``lstack``h]hlstack}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjMubh and (local) }(hjMhhhNhNubh)}(h``lstack_end``h]h lstack_end}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjMubh in the following example:}(hjMhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjIubj%)}(h_SYM_DATA_START_LOCAL(lstack) .skip 4096 SYM_DATA_END_LABEL(lstack, SYM_L_LOCAL, lstack_end)h]h_SYM_DATA_START_LOCAL(lstack) .skip 4096 SYM_DATA_END_LABEL(lstack, SYM_L_LOCAL, lstack_end)}hjsbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhKhjIubeh}(h]h ]h"]h$]h&]uh1jhjFhhhhhNubj)}(h``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. h](h)}(hS``SYM_DATA`` and ``SYM_DATA_LOCAL`` are variants for simple, mostly one-line data::h](h)}(h ``SYM_DATA``h]hSYM_DATA}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh and }(hjhhhNhNubh)}(h``SYM_DATA_LOCAL``h]hSYM_DATA_LOCAL}(hjhhhNhNubah}(h]h ]h"]h$]h&]uh1hhjubh/ are variants for simple, mostly one-line data:}(hjhhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubj%)}(hDSYM_DATA(HEAP, .long rm_heap) SYM_DATA(heap_end, .long rm_stack)h]hDSYM_DATA(HEAP, .long rm_heap) SYM_DATA(heap_end, .long rm_stack)}hj sbah}(h]h ]h"]h$]h&]j4j5uh1j$hhhKhjubh)}(hOIn the end, they expand to ``SYM_DATA_START`` with ``SYM_DATA_END`` internally.h](hIn the end, they expand to }(hj hhhNhNubh)}(h``SYM_DATA_START``h]hSYM_DATA_START}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubh with }(hj hhhNhNubh)}(h``SYM_DATA_END``h]h SYM_DATA_END}(hj1 hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubh internally.}(hj hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhjubeh}(h]h ]h"]h$]h&]uh1jhjFhhhhhNubeh}(h]h ]h"]h$]h&]jjuh1jhhhKhj'hhubeh}(h] data-macrosah ]h"] data macrosah$]h&]uh1hhjBhhhhhKubh)}(hhh](h)}(hSupport Macrosh]hSupport Macros}(hj` hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj] hhhhhKubh)}(hAll the above reduce themselves to some invocation of ``SYM_START``, ``SYM_END``, or ``SYM_ENTRY`` at last. Normally, developers should avoid using these.h](h6All the above reduce themselves to some invocation of }(hjn hhhNhNubh)}(h ``SYM_START``h]h SYM_START}(hjv hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjn ubh, }(hjn hhhNhNubh)}(h ``SYM_END``h]hSYM_END}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjn ubh, or }(hjn hhhNhNubh)}(h ``SYM_ENTRY``h]h SYM_ENTRY}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhjn ubh8 at last. Normally, developers should avoid using these.}(hjn hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhj] hhubh)}(hX 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``.h](h.Further, in the above examples, one could see }(hj hhhNhNubh)}(h``SYM_L_LOCAL``h]h SYM_L_LOCAL}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubh. There are also }(hj hhhNhNubh)}(h``SYM_L_GLOBAL``h]h SYM_L_GLOBAL}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubh and }(hj hhhNhNubh)}(h``SYM_L_WEAK``h]h SYM_L_WEAK}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubhY. All are intended to denote linkage of a symbol marked by them. They are used either in }(hj hhhNhNubh)}(h ``_LABEL``h]h_LABEL}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubh' variants of the earlier macros, or in }(hj hhhNhNubh)}(h ``SYM_START``h]h SYM_START}(hj hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj ubh.}(hj hhhNhNubeh}(h]h ]h"]h$]h&]uh1hhhhKhj] hhubeh}(h]support-macrosah ]h"]support macrosah$]h&]uh1hhjBhhhhhKubh)}(hhh](h)}(hOverriding Macrosh]hOverriding Macros}(hj% hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj" hhhhhKubh)}(hXmArchitecture 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.h](h>Architecture can also override any of the macros in their own }(hj3 hhhNhNubh)}(h``asm/linkage.h``h]h asm/linkage.h}(hj; hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj3 ubh4, including macros specifying the type of a symbol (}(hj3 hhhNhNubh)}(h``SYM_T_FUNC``h]h SYM_T_FUNC}(hjM hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj3 ubh, }(hj3 hhhNhNubh)}(h``SYM_T_OBJECT``h]h SYM_T_OBJECT}(hj_ hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj3 ubh, and }(hj3 hhhNhNubh)}(h``SYM_T_NONE``h]h SYM_T_NONE}(hjq hhhNhNubah}(h]h ]h"]h$]h&]uh1hhj3 ubh;). 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