kernel / include / linux / init.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_INIT_H
#define _LINUX_INIT_H

#include <linux/build_bug.h>
#include <linux/compiler.h>
#include <linux/stringify.h>
#include <linux/types.h>

/* These macros are used to mark some functions or 
 * initialized data (doesn't apply to uninitialized data)
 * as `initialization' functions. The kernel can take this
 * as hint that the function is used only during the initialization
 * phase and free up used memory resources after
 *
 * Usage:
 * For functions:
 * 
 * You should add __init immediately before the function name, like:
 *
 * static void __init initme(int x, int y)
 * {
 *    extern int z; z = x * y;
 * }
 *
 * If the function has a prototype somewhere, you can also add
 * __init between closing brace of the prototype and semicolon:
 *
 * extern int initialize_foobar_device(int, int, int) __init;
 *
 * For initialized data:
 * You should insert __initdata or __initconst between the variable name
 * and equal sign followed by value, e.g.:
 *
 * static int init_variable __initdata = 0;
 * static const char linux_logo[] __initconst = { 0x32, 0x36, ... };
 *
 * Don't forget to initialize data not at file scope, i.e. within a function,
 * as gcc otherwise puts the data into the bss section and not into the init
 * section.
 */

/* These are for everybody (although not all archs will actually
   discard it in modules) */
#define __init		__section(".init.text") __cold __latent_entropy	\
						__no_kstack_erase
#define __initdata	__section(".init.data")
#define __initconst	__section(".init.rodata")
#define __exitdata	__section(".exit.data")
#define __exit_call	__used __section(".exitcall.exit")

/*
 * modpost check for section mismatches during the kernel build.
 * A section mismatch happens when there are references from a
 * code or data section to an init section (both code or data).
 * The init sections are (for most archs) discarded by the kernel
 * when early init has completed so all such references are potential bugs.
 * For exit sections the same issue exists.
 *
 * The following markers are used for the cases where the reference to
 * the *init / *exit section (code or data) is valid and will teach
 * modpost not to issue a warning.  Intended semantics is that a code or
 * data tagged __ref* can reference code or data from init section without
 * producing a warning (of course, no warning does not mean code is
 * correct, so optimally document why the __ref is needed and why it's OK).
 *
 * The markers follow same syntax rules as __init / __initdata.
 */
#define __ref            __section(".ref.text") noinline
#define __refdata        __section(".ref.data")
#define __refconst       __section(".ref.rodata")

#ifdef MODULE
#define __exitused
#else
#define __exitused  __used
#endif

#define __exit          __section(".exit.text") __exitused __cold notrace

#ifdef CONFIG_MEMORY_HOTPLUG
#define __meminit
#define __meminitdata
#define __meminitconst
#else
#define __meminit	__init
#define __meminitdata	__initdata
#define __meminitconst	__initconst
#endif

/* For assembly routines */
#define __HEAD		.section	".head.text","ax"
#define __INIT		.section	".init.text","ax"
#define __FINIT		.previous

#define __INITDATA	.section	".init.data","aw",%progbits
#define __INITRODATA	.section	".init.rodata","a",%progbits
#define __FINITDATA	.previous

/* silence warnings when references are OK */
#define __REF            .section       ".ref.text", "ax"
#define __REFDATA        .section       ".ref.data", "aw"
#define __REFCONST       .section       ".ref.rodata", "a"

#ifndef __ASSEMBLY__
/*
 * Used for initialization calls..
 */
typedef int (*initcall_t)(void);
typedef void (*exitcall_t)(void);

#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
typedef int initcall_entry_t;

static inline initcall_t initcall_from_entry(initcall_entry_t *entry)
{
	return offset_to_ptr(entry);
}
#else
typedef initcall_t initcall_entry_t;

static inline initcall_t initcall_from_entry(initcall_entry_t *entry)
{
	return *entry;
}
#endif

extern initcall_entry_t __con_initcall_start[], __con_initcall_end[];

/* Used for constructor calls. */
typedef void (*ctor_fn_t)(void);

struct file_system_type;

/* Defined in init/main.c */
extern int do_one_initcall(initcall_t fn);
extern char __initdata boot_command_line[];
extern char *saved_command_line;
extern unsigned int saved_command_line_len;
extern unsigned int reset_devices;

/* used by init/main.c */
void setup_arch(char **);
void prepare_namespace(void);
void __init init_rootfs(void);

void init_IRQ(void);
void time_init(void);
void poking_init(void);
void pgtable_cache_init(void);

extern initcall_entry_t __initcall_start[];
extern initcall_entry_t __initcall0_start[];
extern initcall_entry_t __initcall1_start[];
extern initcall_entry_t __initcall2_start[];
extern initcall_entry_t __initcall3_start[];
extern initcall_entry_t __initcall4_start[];
extern initcall_entry_t __initcall5_start[];
extern initcall_entry_t __initcall6_start[];
extern initcall_entry_t __initcall7_start[];
extern initcall_entry_t __initcall_end[];

extern struct file_system_type rootfs_fs_type;

extern bool rodata_enabled;
void mark_rodata_ro(void);

extern void (*late_time_init)(void);

extern bool initcall_debug;

#ifdef MODULE
extern struct module __this_module;
#define THIS_MODULE (&__this_module)
#else
#define THIS_MODULE ((struct module *)0)
#endif

#endif
  
#ifndef MODULE

#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.
 *
 * The `id' arg to __define_initcall() is needed so that multiple initcalls
 * can point at the same handler without causing duplicate-symbol build errors.
 *
 * 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.
 */

/* Format: <modname>__<counter>_<line>_<fn> */
#define __initcall_id(fn)					\
	__PASTE(__KBUILD_MODNAME,				\
	__PASTE(__,						\
	__PASTE(__COUNTER__,					\
	__PASTE(_,						\
	__PASTE(__LINE__,					\
	__PASTE(_, fn))))))

/* Format: __<prefix>__<iid><id> */
#define __initcall_name(prefix, __iid, id)			\
	__PASTE(__,						\
	__PASTE(prefix,						\
	__PASTE(__,						\
	__PASTE(__iid, id))))

#ifdef CONFIG_LTO_CLANG
/*
 * With LTO, the compiler doesn't necessarily obey link order for
 * initcalls. In order to preserve the correct order, we add each
 * variable into its own section and generate a linker script (in
 * scripts/link-vmlinux.sh) to specify the order of the sections.
 */
#define __initcall_section(__sec, __iid)			\
	#__sec ".init.." #__iid

/*
 * With LTO, the compiler can rename static functions to avoid
 * global naming collisions. We use a global stub function for
 * initcalls to create a stable symbol name whose address can be
 * taken in inline assembly when PREL32 relocations are used.
 */
#define __initcall_stub(fn, __iid, id)				\
	__initcall_name(initstub, __iid, id)

#define __define_initcall_stub(__stub, fn)			\
	int __init __stub(void);				\
	int __init __stub(void)					\
	{ 							\
		return fn();					\
	}							\
	__ADDRESSABLE(__stub)
#else
#define __initcall_section(__sec, __iid)			\
	#__sec ".init"

#define __initcall_stub(fn, __iid, id)	fn

#define __define_initcall_stub(__stub, fn)			\
	__ADDRESSABLE(fn)
#endif

#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
#define ____define_initcall(fn, __stub, __name, __sec)		\
	__define_initcall_stub(__stub, fn)			\
	asm(".section	\"" __sec "\", \"a\"		\n"	\
	    __stringify(__name) ":			\n"	\
	    ".long	" __stringify(__stub) " - .	\n"	\
	    ".previous					\n");	\
	static_assert(__same_type(initcall_t, &fn));
#else
#define ____define_initcall(fn, __unused, __name, __sec)	\
	static initcall_t __name __used 			\
		__attribute__((__section__(__sec))) = fn;
#endif

#define __unique_initcall(fn, id, __sec, __iid)			\
	____define_initcall(fn,					\
		__initcall_stub(fn, __iid, id),			\
		__initcall_name(initcall, __iid, id),		\
		__initcall_section(__sec, __iid))

#define ___define_initcall(fn, id, __sec)			\
	__unique_initcall(fn, id, __sec, __initcall_id(fn))

#define __define_initcall(fn, id) ___define_initcall(fn, id, .initcall##id)

/*
 * Early initcalls run before initializing SMP.
 *
 * Only for built-in code, not modules.
 */
#define early_initcall(fn)		__define_initcall(fn, early)

/*
 * A "pure" initcall has no dependencies on anything else, and purely
 * initializes variables that couldn't be statically initialized.
 *
 * This only exists for built-in code, not for modules.
 * Keep main.c:initcall_level_names[] in sync.
 */
#define pure_initcall(fn)		__define_initcall(fn, 0)

#define core_initcall(fn)		__define_initcall(fn, 1)
#define core_initcall_sync(fn)		__define_initcall(fn, 1s)
#define postcore_initcall(fn)		__define_initcall(fn, 2)
#define postcore_initcall_sync(fn)	__define_initcall(fn, 2s)
#define arch_initcall(fn)		__define_initcall(fn, 3)
#define arch_initcall_sync(fn)		__define_initcall(fn, 3s)
#define subsys_initcall(fn)		__define_initcall(fn, 4)
#define subsys_initcall_sync(fn)	__define_initcall(fn, 4s)
#define fs_initcall(fn)			__define_initcall(fn, 5)
#define fs_initcall_sync(fn)		__define_initcall(fn, 5s)
#define rootfs_initcall(fn)		__define_initcall(fn, rootfs)
#define device_initcall(fn)		__define_initcall(fn, 6)
#define device_initcall_sync(fn)	__define_initcall(fn, 6s)
#define late_initcall(fn)		__define_initcall(fn, 7)
#define late_initcall_sync(fn)		__define_initcall(fn, 7s)

#define __initcall(fn) device_initcall(fn)

#define __exitcall(fn)						\
	static exitcall_t __exitcall_##fn __exit_call = fn

#define console_initcall(fn)	___define_initcall(fn, con, .con_initcall)

struct obs_kernel_param {
	const char *str;
	int (*setup_func)(char *);
	int early;
};

extern const struct obs_kernel_param __setup_start[], __setup_end[];

/*
 * Only for really core code.  See moduleparam.h for the normal way.
 *
 * Force the alignment so the compiler doesn't space elements of the
 * obs_kernel_param "array" too far apart in .init.setup.
 */
#define __setup_param(str, unique_id, fn, early)			\
	static const char __setup_str_##unique_id[] __initconst		\
		__aligned(1) = str; 					\
	static struct obs_kernel_param __setup_##unique_id		\
		__used __section(".init.setup")				\
		__aligned(__alignof__(struct obs_kernel_param))		\
		= { __setup_str_##unique_id, fn, early }

/*
 * NOTE: __setup functions return values:
 * @fn returns 1 (or non-zero) if the option argument is "handled"
 * and returns 0 if the option argument is "not handled".
 */
#define __setup(str, fn)						\
	__setup_param(str, fn, fn, 0)

/*
 * NOTE: @fn is as per module_param, not __setup!
 * I.e., @fn returns 0 for no error or non-zero for error
 * (possibly @fn returns a -errno value, but it does not matter).
 * Emits warning if @fn returns non-zero.
 */
#define early_param(str, fn)						\
	__setup_param(str, fn, fn, 1)

#define early_param_on_off(str_on, str_off, var, config)		\
									\
	int var = IS_ENABLED(config);					\
									\
	static int __init parse_##var##_on(char *arg)			\
	{								\
		var = 1;						\
		return 0;						\
	}								\
	early_param(str_on, parse_##var##_on);				\
									\
	static int __init parse_##var##_off(char *arg)			\
	{								\
		var = 0;						\
		return 0;						\
	}								\
	early_param(str_off, parse_##var##_off)

/* Relies on boot_command_line being set */
void __init parse_early_param(void);
void __init parse_early_options(char *cmdline);
#endif /* __ASSEMBLY__ */

#else /* MODULE */

#define __setup_param(str, unique_id, fn)	/* nothing */
#define __setup(str, func) 			/* nothing */
#endif

/* Data marked not to be saved by software suspend */
#define __nosavedata __section(".data..nosave")

#ifdef MODULE
#define __exit_p(x) x
#else
#define __exit_p(x) NULL
#endif

#endif /* _LINUX_INIT_H */