On Mon, Jan 09, 2017 at 06:58:19AM -0800, Luis R. Rodriguez wrote: > Linux makes extensive use of custom ELF header sections, > documentation for these are well scatterred. Unify this is > documentation in a central place and provide helpers to > build custom Linux sections. This patch contains at least three logical changes and needs splitting: * unify documentation * adding helpers * MAINTAINERS addition Documentation and MAINTAINERS changes should go last in the patchset. Accordingly, the huuge commit message below should be spread around those three patches. > > This also generalizes sections code to enable avoiding > modifying the linker scripts when we want to add new > custom Linux sections. In order to make this generally > useful we need to ensure all architectures can make use of > core section helpers but that they can also override should > this be needed. Instead of relying on section.h this adds > a sections-core.h since this will be targetted to be safe > to be used on asm code, linker scripts and C code. > > v5: > > o Huge documentation revamp based on a careful review of the ELF > specifications. Includes documentation now also about usage of > two dots (..) when prefixing ELF program specific sections. > > o Replace macros for sections names in favor of just using > the section names explicitly in the linker script. This is > perhaps more work to grep but this is what folks seem to > currently prefer. > > o Fix .text and .rodata documentation to explain memory protection > strategies which architectures can embrace upon initialization > (documents CONFIG_DEBUG_RODATA and mark_rodata_ro()) > > o Skip the 'Linux section ordering' documentation section, we'll instead > add this on subsequent patch which will expand on it considerably > > o Dropped tree on MAINTAINERS -- as per discussions with Arnd, hpa and > Josh, its easier to just let changes for sections go in through the > respective tree that needs the changes. > > o Fix typos on documentation > > o Dropped SECTION_ALL(), __SECTION_CORE(), SECTION_CORE_ALL() macros > since we are favoring using explicit section names. These are > useless if we are being explicit. > > o Drop LINUX_SECTION_SIZE(), LINUX_SECTION_EMPTY() in favor of having > section ranges and linker tables define their own, to avoid confusion > and make code more readable. > > o Add __define_initcall() documentation and a small section describing > our current initcall levels. This should help also clarify what was > meant about keeping backward compatiblity. > > v4: > > o Port to shiny new sphinx documentation format This looks like a 4th patch ontop of the unifying documentation one. > > o fix a unicore32 build, turns out this actually fixes unicore32 > defconfig builds which were failing for a long while. unicore32 > does not seem to grok well the type passed on a section declaration, > this ignores it. > > o Use VMLINUX_SYMBOL() in more user symbols (extern C code), not doing > this was causing final linker issues with blackfin -- this is > a CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX=y architecture. The other one > being metatag. metatag is not supported on 0-day so I cannot confirm > compilation there. ... > +++ b/Documentation/sections/background.rst > @@ -0,0 +1,105 @@ > +====================== > +ELF section background > +====================== > + > +About > +===== > + > +The purpose of this chapter is to help those not familiar with ELF to brush up > +the latest ELF specifications in order to help understand how Linux uses and > +defines its own ELF sections. > + > +Standardized ELF > +================ > + > +The first publication documenting ELF was UNIX System Laboratories' (USL) > +*System V Release 4 Application Binary Interface* (`SRV4 ABI`_) specification. > +Originally ELF was only a small part of the SRV4 ABI, with time however new > +specifications only put focus on ELF, such was the case of the *TIS Portable > +Formats Specification version 1.2* (`TIS 1.2`_). As of TIS 1.2, ELF was > +supplemented with processor specific ELF addendums, available on the *Linux > +Foundation referenced specification page* (`LF ref page`_). The latest ELF > +specification is the *System V Application Binary Interface - DRAFT - 24 April > +2001* (`gabi4`_). > + > +.. _SRV4 ABI: http://www.sco.com/developers/devspecs/gabi41.pdf > +.. _TIS 1.2: https://refspecs.linuxbase.org/elf/elf.pdf > +.. _LF ref page: https://refspecs.linuxbase.org/ > +.. _gabi4: https://refspecs.linuxbase.org/elf/gabi4+/contents.html > + A pointer to the wikipedia page would suffice instead of us repeating ELF history here. > +ELF views on Linux > +================== > + > +There are two views which can be used for inspecting data in an ELF file, a > +Linking view, and an Execution view. A Section Header Table enables one to > +describe an object using the Linking view while a Program Header Table enables > +one to describe an object using the Execution view. The views are not mutually > +exclusive. For intance, vmlinux can be viewed under both views, ``readelf -S s/intance/instance/ > +vmlinux`` for the Linking view, and ``readelf -l vmlinux`` for the Execution > +view. In Linux only the vmlinux file will have an Execution view, even modules > +lack an Execution view given that vmlinux is the only file that describes how > +the the kernel runs from the start. All other Linux kernel object files have s/the // > +an available Linking view. s/n available// - "have a Linking view" is fine. > + > +Under the Linking view, the Section Header Table describes all available > +sections. The Section Header Table is an array of ELF section header data > +structures. If on a 32-bit system this is ``struct elf32_shd``, if on a 64-bit > +this is ``struct elf64_shdr``. "If on ... if on" doesn't work as a sentence. > Sections are only visible on object files that s/on/in/ > +have a Linking view, since all Linux kernel files have Linking view, all kernel > +objects have ELF sections. Btw, that last sentence is kinda funny and not really needed. Or do you wanna say that everything-code is in a section? > + > +Limitations on ELF sections ELF sections limitations > +=========================== > + > +We provide a summary on the limitations of ELF sections. Kill that sentence. > Refer to the public > +ELF specifications for details. Note that 64-bit limitations may depend > +on processor specific section attributes to be used, refer to your processsor "processsor" - the 's' button stuck? :-) > +specification if unsure. Better yet, kill that whole paragraph. > + > +Its worth ellaborating on the limitations on the name of an ELF section: "elaborating" > +ELF section names are stored as strings as per the ELF specification, and > +as can be expected, these don't have explicit limitations. The implicit > +limitation then depends on the size of an ELF object file and ELF section. > + > +If using really large kernels or objects with large amounts of sections one > +would still need to be sure that ELF loader in charge of loading the Linux > +kernel is properly updated to handle coping with the latest ELF extensions. > + > + .. flat-table:: Limitations on ELF Sections > + > + * - Section attribute > + - 32-bit > + - 64-bit > + > + * - ELF section name > + - Size of an ELF section > + - Size of an ELF section > + > + * - Size of an ELF section > + - 4 GiB > + - 16 EiB > + > + * - Max number of sections in an object file > + - 4 GiEntries (4294967296) > + - 16 EiEntries (18446744073709551616) > + > +Program specific ELF sections Program-specific > +============================= > + > +The ELF specification allows for a section type to be specified as > +*Program specific section*, defined as ``SHT_PROGBITS``. This sections type section > +enables programs to customize sections for their own use. In assembly this ^ is > +specified ``@progbits`` on most architectures, on ARM this is ``%progbits``. ^ ^ with the flag s/this is/it is called/ > + > +``SHT_PROGBITS`` is used by Linux for defining and using Linux ELF sections. > + > +Special ELF Sections > +==================== > + > +The ELF specification defines *Special ELF Sections* on chapter 4 (`gabi4 > +ch4`_). These are defined as sections which hold program and control > +information. Of these sections, a few have the section type as > +``SHT_PROGBITS``. This enables Linux to *further customize* use of the section > +beyond what the ELF specification suggests. > + > +.. _gabi4 ch4: https://refspecs.linuxbase.org/elf/gabi4+/ch4.sheader.html#special_sections > diff --git a/Documentation/sections/conf.py b/Documentation/sections/conf.py > new file mode 100644 > index 000000000000..faa1c57595e1 > --- /dev/null > +++ b/Documentation/sections/conf.py > @@ -0,0 +1,4 @@ > +# -*- coding: utf-8; mode: python -*- > + > +project = 'Linux Kernel ELF sections' > +html_search_language = 'en' > diff --git a/Documentation/sections/index.rst b/Documentation/sections/index.rst > new file mode 100644 > index 000000000000..f37511ef05e7 > --- /dev/null > +++ b/Documentation/sections/index.rst > @@ -0,0 +1,17 @@ > +========================= > +Linux Kernel ELF sections > +========================= > + > +This book documents the different ELF sections used on the Linux kernel. in > +We start off by providing references to how ELF was standardized, references > +to the standards on ELF sections, review limitations of ELF sections, and > +finally how Linux uses ELF sections in the Linux kernel. Certain important > +Linux ELF sections are documented carefully: we describe the goal of the > +ELF section, and address concurrency considerations when applicable. A few > +common a set of Linux helpers for ELF sections are also documented. s/few common a // > + > +.. toctree:: > + :maxdepth: 4 > + > + background > + section-core ... > diff --git a/arch/unicore32/include/asm/section-core.h b/arch/unicore32/include/asm/section-core.h > new file mode 100644 > index 000000000000..0b9c68429a1a > --- /dev/null > +++ b/arch/unicore32/include/asm/section-core.h > @@ -0,0 +1,19 @@ > +#ifndef __UNICORE_SECTION_CORE_ASM_H__ > +#define __UNICORE_SECTION_CORE_ASM_H__ > +/* > + * Copyright (C) 2016 Luis R. Rodriguez <mcgrof@xxxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms of copyleft-next (version 0.3.1 or later) as published > + * at http://copyleft-next.org/. Isn't all kernel code GPLv2? > + */ > + > +/* Unicore32 has known to not work properly with the type set, so ignore it */ > + > +#define __set_section_core_type(___section, ___core, ___name, \ > + ___level, ___flags, ___type) \ > + .section ___section..___core.___name.___level, ___flags > + > +#include <asm-generic/section-core.h> > + > +#endif /* __UNICORE_SECTION_CORE_ASM_H__ */ > diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild > index 2b892e2313a9..af975f21eeee 100644 > --- a/arch/x86/include/asm/Kbuild > +++ b/arch/x86/include/asm/Kbuild > @@ -12,3 +12,4 @@ generic-y += dma-contiguous.h > generic-y += early_ioremap.h > generic-y += mcs_spinlock.h > generic-y += mm-arch-hooks.h > +generic-y += section-core.h > diff --git a/arch/xtensa/include/asm/Kbuild b/arch/xtensa/include/asm/Kbuild > index b7fbaa56b51a..7879c31e66a7 100644 > --- a/arch/xtensa/include/asm/Kbuild > +++ b/arch/xtensa/include/asm/Kbuild > @@ -32,3 +32,4 @@ generic-y += topology.h > generic-y += trace_clock.h > generic-y += word-at-a-time.h > generic-y += xor.h > +generic-y += section-core.h > diff --git a/include/asm-generic/section-core.h b/include/asm-generic/section-core.h > new file mode 100644 > index 000000000000..bb16befc4251 > --- /dev/null > +++ b/include/asm-generic/section-core.h > @@ -0,0 +1,307 @@ > +#ifndef _ASM_GENERIC_SECTION_CORE_H_ > +#define _ASM_GENERIC_SECTION_CORE_H_ > +/* > + * Linux section core definitions > + * > + * Copyright (C) 2016 Luis R. Rodriguez <mcgrof@xxxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms of copyleft-next (version 0.3.1 or later) as published > + * at http://copyleft-next.org/. Ditto. > + */ > + > +/** > + * DOC: Linux ELF program specific sections > + * > + * Linux makes extensive use of ``SHT_PROGBITS`` to both extend use and definition ^^^^^^^^^^^^^^^^^^^^^^^^ needs rewording > of *Special ELF Sections* (`gabi4 ch4`_) and to define its own > + * sections. This chaper is dedicated to documenting Linux program specific "chapter" Please spellcheck the whole patchset before next submission. > + * sections and helpers available to make use of these easier to implement and > + * use. Huh, come again? This sentence is funny. > + * > + * .. _gabi4 ch4: https://refspecs.linuxbase.org/elf/gabi4+/ch4.sheader.html#special_sections > + */ > + > +/** > + * DOC: Linux linker script > + * > + * Linux uses a custom linker script to build the vmlinux binary, it uses it to > + * strategically place and define Linux ELF sections. Each architecture needs > + * to implement its own linker script, it is expected to reside in ... script which is expected ... > + * ``arch/$(ARCH)/kernel/vmlinux.lds.S``. Architecture Linux linker scripts in > + * turn include and use definitions from ``include/asm-generic/vmlinux.lds.h``, > + * as well as some helpers documented in this chapter. > + * > + * In assembly it is common practice to use dots (``.``) in labels to avoid > + * clashes with C symbols. Similarly, a dot (``.``) can be part of a section > + * name but not a C symbol. Historically then, two dots are used (``..``) > + * have been used in linker scripts when adding program specific sections are used .. have been used? > + * when there are concerns to avoid clashes with compiler generated sections. This last sentence needs simplifying. > + */ > + > +/** > + * DOC: Memory protection > + * > + * Linux allows architectures which support memory protection features to > + * take advantage of them by letting architectures define and enable > + * ``CONFIG_DEBUG_RODATA`` and implement a mark_rodata_ro() call. Simplify: "Architectures with memory protection features can define and enable CONFIG_DEBUG_RODATA... " > + * mark_rodata_ro() can be used for instance to mark specific sections as , for instance, > + * read-only or non-executable. > + * > + * Linux typically follows a convention to have the .rodata ELF section follow > + * after the .text ELF section, it does this to help architectures which . It does this... > + * support memory protection to mark both .text and .rodata as read-only in > + * one shot. > + * > + * For more details refer to mark_rodata_ro(). > + */ > + > +/** > + * DOC: .rodata > + * > + * ELF section used for data which must be protected from write access. > + */ > + > +/** > + * DOC: .text > + * > + * ELF section name used for code (functions) used during regular > + * kernel run time. > + */ > + > +/** > + * DOC: .data > + * > + * ELF section used for read-write data. > + */ > + > +/** > + * DOC: Linux init sections > + * > + * These sections are used for code and data structures used during boot or > + * module initialization. On architectures that support it (x86, x86_64), all > + * this code is freed up by the kernel right before the fist userspace init > + * process is called when built-in to the kernel, and if modular it is freed > + * after module initialization. Since the code is freed so early, in theory > + * there should be no races against freeing this code with other CPUs. Init > + * section code and data structures should never be exported with > + * EXPORT_SYMBOL*() as the code will quickly become unavailable to the kernel > + * after bootup. > + */ > + > +/** > + * DOC: .init.text > + * > + * ELF section for code (functions) used only during boot or driver > + * initialization. > + * > + */ > + > +/** > + * DOC: .init.data > + * > + * ELF section used for data structures used only during boot or driver > + * initialization. > + */ > + > +/** > + * DOC: .init.rodata > + * > + * ELF section used for read-only code (functions) used only during boot > + * or driver initialization. > + */ > + > +/** > + * DOC: .initcall > + * > + * ELF section used for subsystem init calls. There are init levels > + * representing different functionality in the kernel. For more details > + * refer to __define_initcall(). > + */ > + > +/** > + * DOC: Linux exit sections > + * > + * These sections are used to declare a functions and data structures which s/a // > + * are only required on exit, the function or data structure will be dropped > + * if the code declaring this section is not compiled as a module on > + * architectures that support this (x86, x86_64). There is no special case > + * handling for this code when built-in to the kernel. > + */ > + > +/** > + * DOC: .exit.text > + * > + * ELF section used to for code (functions) used only during module unload. > + */ > + > +/** > + * DOC: .exit.data > + * > + * ELF section used to for data structures used only during module > + * unload. > + */ > + > +/** > + * DOC: .exitcall.exit > + * > + * ELF section used for exit routines, order is important and maintained by > + * link order. > + */ > + > +/** > + * DOC: Linux references to init sections > + * > + * These sections are used to teach modpost to not warn about possible > + * misuses of init section code from other sections. If you use this > + * your use case should document why you are certain such use of init > + * sectioned code is valid. For more details refer to ``include/linux/init.h`` > + * ``__ref``, ``__refdata``, and ``__refconst`` documentation. > + */ > + > +/** > + * DOC: .ref.text > + * > + * ELF section used to annotate code (functions) which has been vetteed as vetted? > + * valid for its reference or use of other code (functions) or data structures > + * which are part of the init sections. > + */ > + > +/** > + * DOC: .ref.data > + * > + * ELF section used for data structures which have been vetteed for its ditto. > + * reference or use of other code (functions) or data structures part of the > + * init sections. > + */ > + > +/** > + * DOC: .ref.rodata > + * > + * ELF section used to annotate const code (functions) const data structures > + * which has been vetteed for its reference or use of other code (functions) ditto. > + * or data structures part of the init sections. > + */ > + > +/* Can be used on foo.S for instance */ What does that comment mean? > +#ifndef __set_section_core_type > +# define __set_section_core_type(___section, ___core, ___name, \ > + ___level, ___flags, ___type) \ > + .section ___section..___core.___name.___level, ___flags, ___type Are you sure we need 4 levels of hierarchy? If so, we should document what all those section, core, name and level mean and how the whole sections hierarchy is supposed to look like. > +#endif > + > +#ifndef __set_section_core > +# define __set_section_core(___section, ___core, ___name, ___level, ___flags) \ > + .section ___section..___core.___name.___level, ___flags > +#endif > + > +#ifndef __push_section_core > +# define __push_section_core(__section, __core, __name, __level, __flags) \ > + .pushsection __section..__core.__name.__level, __flags > +#endif > + > +#ifdef __KERNEL__ > +#include <linux/stringify.h> > +#endif > + > +#if defined(__ASSEMBLER__) || defined(__ASSEMBLY__) > + > +# ifndef LINKER_SCRIPT > + > +# ifndef push_section_core > +# define push_section_core(__section, __core, __name, __level, __flags) \ > + __push_section_core(__section, __core, __name, \ > + __level, __stringify(__flags)) > +# endif > + > +# ifndef set_section_core > +# define set_section_core(__section, __core, __name, \ > + __level, __flags) \ > + __set_section_core(__section, __core, __name, \ > + __level, __stringify(__flags)) > +# endif > + > +# ifndef set_section_core_type > +# define set_section_core_type(__section, __core, __name, \ > + __level, __flags, __type) \ > + __set_section_core_type(__section, __core, __name, __level, \ > + __stringify(__flags), __type) > +# endif > + > +# endif /* LINKER_SCRIPT */ > +#else /* defined(__ASSEMBLER__) || defined(__ASSEMBLY__) */ > + > +/* > + * As per gcc's documentation a common asm separator is a new line followed > + * by tab [0], it however seems possible to also just use a newline as its . It, however, seems ... > + * the most commonly empirically observed semantic and folks seem to agree > + * this even works on S390. In case your architecture disagrees you may > + * override this and define your own and keep the rest of the macros. > + * > + * [0] https://gcc.gnu.org/onlinedocs/gcc/Basic-Asm.html#Basic-Asm > + */ > +# ifndef ASM_CMD_SEP > +# define ASM_CMD_SEP "\n" > +# endif > + > +# ifndef set_section_core > +# define set_section_core(__section, __core, __name, __level, __flags) \ > + __stringify(__set_section_core_type(__section, __core, __name, \ > + __level, __stringify(__flags))) \ > + ASM_CMD_SEP > +# endif > + > +/* > + * Some architectures (arm, and avr32 are two examples on kprobes) seem > + * currently explicitly specify the type [0] -- this can be any of the > + * optional constants on ELF: > + * > + * @progbits - section contains data > + * @nobits - section does not contain data (i.e., section only occupies space) > + * @note - section contains data which is used by things other than the program > + * @init_array - section contains an array of pointers to init functions > + * @fini_array - section contains an array of pointers to finish functions > + * @preinit_array - section contains an array of pointers to pre-init functions > + * > + * ARM requires % instead of @. > + * > + * At least as per nasm (x86/x86_64 only), in the absence of qualifiers the > + * defaults are as follows: > + * > + * section .text progbits alloc exec nowrite align=16 > + * section .rodata progbits alloc noexec nowrite align=4 > + * section .lrodata progbits alloc noexec nowrite align=4 > + * section .data progbits alloc noexec write align=4 > + * section .ldata progbits alloc noexec write align=4 > + * section .bss nobits alloc noexec write align=4 > + * section .lbss nobits alloc noexec write align=4 > + * section .tdata progbits alloc noexec write align=4 tls > + * section .tbss nobits alloc noexec write align=4 tls > + * section .comment progbits noalloc noexec nowrite align=1 > + * section other progbits alloc noexec nowrite align=1 > + * > + * gas should have sensible defaults for architectures... > + * > + * [0] http://www.nasm.us/doc/nasmdoc7.html > + */ > +# ifndef set_section_core_type > +# define set_section_core_type(__section, __core, __name, __level, \ > + __flags, __type) \ > + __stringify(__set_section_core_type(__section, __core, \ > + __name, __level, \ > + __stringify(__flags), \ > + __type)) \ > + ASM_CMD_SEP > +# endif > + > +# ifndef push_section_core > +# define push_section_core(__section, __core, __name, \ > + __level, __flags) \ > + __stringify(__push_section_core(__section, __core, \ > + __name, __level, \ > + __stringify(__flags))) \ > + ASM_CMD_SEP > +# endif > + > +#endif /* defined(__ASSEMBLER__) || defined(__ASSEMBLY__) */ > +#endif /* _ASM_GENERIC_SECTION_CORE_H_ */ > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h > index 4df64a1fc09e..b145ae8d9cbe 100644 > --- a/include/asm-generic/sections.h > +++ b/include/asm-generic/sections.h > @@ -1,6 +1,8 @@ > #ifndef _ASM_GENERIC_SECTIONS_H_ > #define _ASM_GENERIC_SECTIONS_H_ > > +#include <asm/section-core.h> > + > /* References to section boundaries */ > > #include <linux/compiler.h> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index 0968d13b3885..483f60c451f9 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -55,6 +55,7 @@ > #endif > > #include <linux/export.h> > +#include <asm/section-core.h> > > /* Align . to a 8 byte boundary equals to maximum function alignment. */ > #define ALIGN_FUNCTION() . = ALIGN(8) > diff --git a/include/linux/init.h b/include/linux/init.h > index 885c3e6d0f9d..116e3262332a 100644 > --- a/include/linux/init.h > +++ b/include/linux/init.h > @@ -130,6 +130,24 @@ int __init init_rootfs(void); > extern bool rodata_enabled; > #endif > #ifdef CONFIG_DEBUG_RODATA > +/** > + * mark_rodata_ro - implemement memory protection for ELF sections > + * > + * Architectures which support memory protection define a kernel configuration > + * entry for CONFIG_DEBUG_RODATA, That's just too many words for nothing. You can just as well say: "Architectures which support memory protection enable CONFIG_DEBUG_RODATA and implement mark_rodata_ro()." > enable it in and implement mark_rodata_ro(). > + * mark_rodata_ro() should strive to adjust the .rodata and .text ELF sections > + * with read-only memory protection to prevent modifications of these sections "mark_rodata_ro() marks .rodata and .text section read-only..." Simple. > + * after bootup. It can also try to use memory protection to prevent execution > + * on the .rodata ELF section. > + * > + * In order to help architectures set both .text and .rodata as read-only with > + * memory protections in one shot Linux has typically followed the convention > + * to have the .rodata ELF section follow the .text ELF section on the vmlinux in > + * linker script. > + * > + * Linux calls mark_rodata_ro() after freeing .init code and prior to calling > + * the first init userspace process. "first init userspace process" either say "prior to calling init" or "prior to calling the first userspace process" but both is jambalayed into something confusing. > + */ > void mark_rodata_ro(void); > #endif > > @@ -140,25 +158,70 @@ extern bool initcall_debug; > #endif > > #ifndef MODULE > +/** > + * DOC: Initcall levels > + * > + * When Linux boots the kernel do_initcalls() iterates over each Linux When Linux boots the kernel?!? You're joking, right? Just do "During boot, do_initcalls() ..." > + * initialization level ID and calls all routines embedded on each level ID. > + * Prior to v2.5.2.3 Linux had only one init level onto which all init > + * functions folded onto using __initcall(). After v2.5.2.4 Linux split up > + * initcalls into 7 separate initcall subsection levels, each level describing > + * different functionality part of the kernel (commit `9d6ba121b7e17085`_ > + * (v2.5.2.3 -> v2.5.2.4)). In order to remain backward compatible __initcall() > + * calls were left mapped to device_initcall(). And why do we need all that git archeology here? > + * Each init level consists of a dedicated ELF section, init functions are > + * associated to an init level by linking it into the respective level's with > + * ELF section. > + * > + * Lower order init levels run prior to higher order init levels. Ordering > + * inside each initcall level is determined by respective link order. Those last two sentences are enough. > + * > + * .. _9d6ba121b7e17085: https://git.kernel.org/cgit/linux/kernel/git/history/history.git/commit/?id=9d6ba121b7e17085c95139233686b27a4d4c650e That's one ugly footnote. Also, the git commit id suffices, you don't need the URL. > + */ > > #ifndef __ASSEMBLY__ > > -/* > - * initcalls are now grouped by functionality into separate > - * subsections. Ordering inside the subsections is determined > - * by link order. > - * For backwards compatibility, initcall() puts the call in > - * the device init subsection. > +/** > + * __define_initcall - wrapper for definiting init levels () also s/definiting/defining/ Also, this is not what __define_initcall() does. It is not defining init levels. > * > - * The `id' arg to __define_initcall() is needed so that multiple initcalls > - * can point at the same handler without causing duplicate-symbol build errors. > + * @fn: init routine > + * @id: init level > * > - * Initcalls are run by placing pointers in initcall sections that the > - * kernel iterates at runtime. The linker can do dead code / data elimination > - * and remove that completely, so the initcall sections have to be marked > - * as KEEP() in the linker script. > + * Defines a kernel initialization level. A respective linker script entry > + * is required to ensure the init level is accounted for and to ensure symbols > + * exist for iterating over all functions in the init level. A init level An > + * represents a series of functionality in the kernel. That sounds yucky. An init level is a bunch of functions which are called after init_level - 1 and before init_level + 1. > + * > + * Ordering within an initialization level is determined by link order, so > + * for instance if a Makefile had:: > + * > + * obj-y += foo.o > + * obj-y += bar.o > + * > + * And foo.c:: > + * > + * subsys_initcall(foo_init); > + * > + * And bar.c had:: > + * > + * subsys_initcall(bar_init); > + * > + * foo_init() would be called prior to bar_init(). > + * > + * Note that @id in __define_initcall() also enables multiple initcalls > + * to be created using the same handler for different init levels without > + * causing duplicate-symbol build errors. > + * > + * Initcalls are run by placing start symbols to initcall levels inside ELF > + * sections, the kernel in turn uses these symbols to iterate over each init > + * level at runtime with do_initcall_level(). The end of each init level is > + * marked by the subsequent's symbol's start address until we reach the symbol > + * ``__initcall_end``. Needlessly complex, simplify. > The linker can do dead code / data elimination and each > + * init level start symbol could be removed completely in this process, to . To <-- new sentence > + * avoid this each init level start symbols must be marked as 'KEEP()' in the > + * linker script to avoid any linker optimization heuristic on initcalls. > */ > - > #define __define_initcall(fn, id) \ > static initcall_t __initcall_##fn##id __used \ > __attribute__((__section__(".initcall" #id ".init"))) = fn; > diff --git a/include/linux/sections.h b/include/linux/sections.h > new file mode 100644 > index 000000000000..6771c727bcd1 > --- /dev/null > +++ b/include/linux/sections.h > @@ -0,0 +1,87 @@ > +#ifndef _LINUX_SECTIONS_H > +#define _LINUX_SECTIONS_H > +/* > + * Linux de-facto sections Useless. > + * > + * Copyright (C) 2016 Luis R. Rodriguez <mcgrof@xxxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms of copyleft-next (version 0.3.1 or later) as published > + * at http://copyleft-next.org/. > + */ > + > +#include <asm/section-core.h> > +#include <linux/export.h> > + > +#ifndef __ASSEMBLY__ > + > +/** > + * DOC: Introduction > + * > + * Linux defines a set of common helpers which can be used to against its use ^^^^^^^^^^^^^^^^^^^^^^^^^^ ?? > + * of standard or custom Linux sections, this section is dedicated to these this section is talking about sections, that's too much. > + * helpers. > + */ > + > +/** > + * LINUX_SECTION_ALIGNMENT - get section alignment > + * > + * @name: section name > + * > + * Gives you the alignment for the section. > + */ > +#define LINUX_SECTION_ALIGNMENT(name) __alignof__(*VMLINUX_SYMBOL(name)) Eeww, too long and it is a getter but doesn't have "GET" in its name. How about GET_SECTION_ALIGN() ? And what's with the "LINUX_" prefix - that's like useless use of screen real estate. > + > +/** > + * LINUX_SECTION_START - get address of start of section GET_SECTION_START() - get address of section start > + * > + * @name: section name > + * > + * This gives you the start address of the section. > + * This should give you the address of the first entry. Huh? > + * > + */ > +#define LINUX_SECTION_START(name) VMLINUX_SYMBOL(name) Ditto. > + > +/** > + * LINUX_SECTION_END - get address of end of the section > + * > + * @name: section name > + * > + * This gives you the end address of the section. > + * This should give you the address of the end of the > + * section. This will match the start address if the > + * section is empty. > + */ > +#define LINUX_SECTION_END(name) VMLINUX_SYMBOL(name##__end) > + > +/** > + * DECLARE_LINUX_SECTION - Declares a custom Linux section DECLARE_SECTION() is perfectly fine IMO. > + * > + * @type: type of custom Linux section > + * @name: custom section name > + * > + * Declares a read-write custom Linux section > + */ > +#define DECLARE_LINUX_SECTION(type, name) \ > + extern type VMLINUX_SYMBOL(name)[], \ > + VMLINUX_SYMBOL(name##__end)[] > + > +/** > + * DECLARE_LINUX_SECTION_RO - Declares a read-only custom Linux section DECLARE_SECTION_RO() > + * > + * @type: type of custom Linux section > + * @name: custom section name > + * > + * Declares a read-only custom Linux section > + */ > +#define DECLARE_LINUX_SECTION_RO(type, name) \ > + extern const type VMLINUX_SYMBOL(name)[], \ > + VMLINUX_SYMBOL(name##__end)[] > + > +#define __SECTION_CORE(section, core, name, level) \ > + #section ".." #core "." #name "." #level > + > +#endif /* __ASSEMBLY__ */ > + > +#endif /* _LINUX_SECTIONS_H */ > -- -- Regards/Gruss, Boris. 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