linux-stable/scripts/mod/modpost.h
Masahiro Yamada ddb5cdbafa kbuild: generate KSYMTAB entries by modpost
Commit 7b4537199a ("kbuild: link symbol CRCs at final link, removing
CONFIG_MODULE_REL_CRCS") made modpost output CRCs in the same way
whether the EXPORT_SYMBOL() is placed in *.c or *.S.

For further cleanups, this commit applies a similar approach to the
entire data structure of EXPORT_SYMBOL().

The EXPORT_SYMBOL() compilation is split into two stages.

When a source file is compiled, EXPORT_SYMBOL() will be converted into
a dummy symbol in the .export_symbol section.

For example,

    EXPORT_SYMBOL(foo);
    EXPORT_SYMBOL_NS_GPL(bar, BAR_NAMESPACE);

will be encoded into the following assembly code:

    .section ".export_symbol","a"
    __export_symbol_foo:
            .asciz ""                      /* license */
            .asciz ""                      /* name space */
            .balign 8
            .quad foo                      /* symbol reference */
    .previous

    .section ".export_symbol","a"
    __export_symbol_bar:
            .asciz "GPL"                   /* license */
            .asciz "BAR_NAMESPACE"         /* name space */
            .balign 8
            .quad bar                      /* symbol reference */
    .previous

They are mere markers to tell modpost the name, license, and namespace
of the symbols. They will be dropped from the final vmlinux and modules
because the *(.export_symbol) will go into /DISCARD/ in the linker script.

Then, modpost extracts all the information about EXPORT_SYMBOL() from the
.export_symbol section, and generates the final C code:

    KSYMTAB_FUNC(foo, "", "");
    KSYMTAB_FUNC(bar, "_gpl", "BAR_NAMESPACE");

KSYMTAB_FUNC() (or KSYMTAB_DATA() if it is data) is expanded to struct
kernel_symbol that will be linked to the vmlinux or a module.

With this change, EXPORT_SYMBOL() works in the same way for *.c and *.S
files, providing the following benefits.

[1] Deprecate EXPORT_DATA_SYMBOL()

In the old days, EXPORT_SYMBOL() was only available in C files. To export
a symbol in *.S, EXPORT_SYMBOL() was placed in a separate *.c file.
arch/arm/kernel/armksyms.c is one example written in the classic manner.

Commit 22823ab419 ("EXPORT_SYMBOL() for asm") removed this limitation.
Since then, EXPORT_SYMBOL() can be placed close to the symbol definition
in *.S files. It was a nice improvement.

However, as that commit mentioned, you need to use EXPORT_DATA_SYMBOL()
for data objects on some architectures.

In the new approach, modpost checks symbol's type (STT_FUNC or not),
and outputs KSYMTAB_FUNC() or KSYMTAB_DATA() accordingly.

There are only two users of EXPORT_DATA_SYMBOL:

  EXPORT_DATA_SYMBOL_GPL(empty_zero_page)    (arch/ia64/kernel/head.S)
  EXPORT_DATA_SYMBOL(ia64_ivt)               (arch/ia64/kernel/ivt.S)

They are transformed as follows and output into .vmlinux.export.c

  KSYMTAB_DATA(empty_zero_page, "_gpl", "");
  KSYMTAB_DATA(ia64_ivt, "", "");

The other EXPORT_SYMBOL users in ia64 assembly are output as
KSYMTAB_FUNC().

EXPORT_DATA_SYMBOL() is now deprecated.

[2] merge <linux/export.h> and <asm-generic/export.h>

There are two similar header implementations:

  include/linux/export.h        for .c files
  include/asm-generic/export.h  for .S files

Ideally, the functionality should be consistent between them, but they
tend to diverge.

Commit 8651ec01da ("module: add support for symbol namespaces.") did
not support the namespace for *.S files.

This commit shifts the essential implementation part to C, which supports
EXPORT_SYMBOL_NS() for *.S files.

<asm/export.h> and <asm-generic/export.h> will remain as a wrapper of
<linux/export.h> for a while.

They will be removed after #include <asm/export.h> directives are all
replaced with #include <linux/export.h>.

[3] Implement CONFIG_TRIM_UNUSED_KSYMS in one-pass algorithm (by a later commit)

When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
the directory tree to determine which EXPORT_SYMBOL to trim. If an
EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the
second traverse, where some source files are recompiled with their
EXPORT_SYMBOL() tuned into a no-op.

We can do this better now; modpost can selectively emit KSYMTAB entries
that are really used by modules.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
2023-06-22 21:17:10 +09:00

215 lines
5.6 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <elf.h>
#include "list.h"
#include "elfconfig.h"
/* On BSD-alike OSes elf.h defines these according to host's word size */
#undef ELF_ST_BIND
#undef ELF_ST_TYPE
#undef ELF_R_SYM
#undef ELF_R_TYPE
#if KERNEL_ELFCLASS == ELFCLASS32
#define Elf_Ehdr Elf32_Ehdr
#define Elf_Shdr Elf32_Shdr
#define Elf_Sym Elf32_Sym
#define Elf_Addr Elf32_Addr
#define Elf_Section Elf32_Half
#define ELF_ST_BIND ELF32_ST_BIND
#define ELF_ST_TYPE ELF32_ST_TYPE
#define Elf_Rel Elf32_Rel
#define Elf_Rela Elf32_Rela
#define ELF_R_SYM ELF32_R_SYM
#define ELF_R_TYPE ELF32_R_TYPE
#else
#define Elf_Ehdr Elf64_Ehdr
#define Elf_Shdr Elf64_Shdr
#define Elf_Sym Elf64_Sym
#define Elf_Addr Elf64_Addr
#define Elf_Section Elf64_Half
#define ELF_ST_BIND ELF64_ST_BIND
#define ELF_ST_TYPE ELF64_ST_TYPE
#define Elf_Rel Elf64_Rel
#define Elf_Rela Elf64_Rela
#define ELF_R_SYM ELF64_R_SYM
#define ELF_R_TYPE ELF64_R_TYPE
#endif
/* The 64-bit MIPS ELF ABI uses an unusual reloc format. */
typedef struct
{
Elf32_Word r_sym; /* Symbol index */
unsigned char r_ssym; /* Special symbol for 2nd relocation */
unsigned char r_type3; /* 3rd relocation type */
unsigned char r_type2; /* 2nd relocation type */
unsigned char r_type1; /* 1st relocation type */
} _Elf64_Mips_R_Info;
typedef union
{
Elf64_Xword r_info_number;
_Elf64_Mips_R_Info r_info_fields;
} _Elf64_Mips_R_Info_union;
#define ELF64_MIPS_R_SYM(i) \
((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_sym)
#define ELF64_MIPS_R_TYPE(i) \
((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_type1)
#if KERNEL_ELFDATA != HOST_ELFDATA
static inline void __endian(const void *src, void *dest, unsigned int size)
{
unsigned int i;
for (i = 0; i < size; i++)
((unsigned char*)dest)[i] = ((unsigned char*)src)[size - i-1];
}
#define TO_NATIVE(x) \
({ \
typeof(x) __x; \
__endian(&(x), &(__x), sizeof(__x)); \
__x; \
})
#else /* endianness matches */
#define TO_NATIVE(x) (x)
#endif
#define NOFAIL(ptr) do_nofail((ptr), #ptr)
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
void *do_nofail(void *ptr, const char *expr);
struct buffer {
char *p;
int pos;
int size;
};
void __attribute__((format(printf, 2, 3)))
buf_printf(struct buffer *buf, const char *fmt, ...);
void
buf_write(struct buffer *buf, const char *s, int len);
struct module {
struct list_head list;
struct list_head exported_symbols;
struct list_head unresolved_symbols;
bool is_gpl_compatible;
bool from_dump; /* true if module was loaded from *.symvers */
bool is_vmlinux;
bool seen;
bool has_init;
bool has_cleanup;
struct buffer dev_table_buf;
char srcversion[25];
// Missing namespace dependencies
struct list_head missing_namespaces;
// Actual imported namespaces
struct list_head imported_namespaces;
char name[];
};
struct elf_info {
size_t size;
Elf_Ehdr *hdr;
Elf_Shdr *sechdrs;
Elf_Sym *symtab_start;
Elf_Sym *symtab_stop;
unsigned int export_symbol_secndx; /* .export_symbol section */
char *strtab;
char *modinfo;
unsigned int modinfo_len;
/* support for 32bit section numbers */
unsigned int num_sections; /* max_secindex + 1 */
unsigned int secindex_strings;
/* if Nth symbol table entry has .st_shndx = SHN_XINDEX,
* take shndx from symtab_shndx_start[N] instead */
Elf32_Word *symtab_shndx_start;
Elf32_Word *symtab_shndx_stop;
};
/* Accessor for sym->st_shndx, hides ugliness of "64k sections" */
static inline unsigned int get_secindex(const struct elf_info *info,
const Elf_Sym *sym)
{
unsigned int index = sym->st_shndx;
/*
* Elf{32,64}_Sym::st_shndx is 2 byte. Big section numbers are available
* in the .symtab_shndx section.
*/
if (index == SHN_XINDEX)
return info->symtab_shndx_start[sym - info->symtab_start];
/*
* Move reserved section indices SHN_LORESERVE..SHN_HIRESERVE out of
* the way to UINT_MAX-255..UINT_MAX, to avoid conflicting with real
* section indices.
*/
if (index >= SHN_LORESERVE && index <= SHN_HIRESERVE)
return index - SHN_HIRESERVE - 1;
return index;
}
/* file2alias.c */
void handle_moddevtable(struct module *mod, struct elf_info *info,
Elf_Sym *sym, const char *symname);
void add_moddevtable(struct buffer *buf, struct module *mod);
/* sumversion.c */
void get_src_version(const char *modname, char sum[], unsigned sumlen);
/* from modpost.c */
char *read_text_file(const char *filename);
char *get_line(char **stringp);
void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym);
enum loglevel {
LOG_WARN,
LOG_ERROR,
LOG_FATAL
};
void modpost_log(enum loglevel loglevel, const char *fmt, ...);
/*
* warn - show the given message, then let modpost continue running, still
* allowing modpost to exit successfully. This should be used when
* we still allow to generate vmlinux and modules.
*
* error - show the given message, then let modpost continue running, but fail
* in the end. This should be used when we should stop building vmlinux
* or modules, but we can continue running modpost to catch as many
* issues as possible.
*
* fatal - show the given message, and bail out immediately. This should be
* used when there is no point to continue running modpost.
*/
#define warn(fmt, args...) modpost_log(LOG_WARN, fmt, ##args)
#define error(fmt, args...) modpost_log(LOG_ERROR, fmt, ##args)
#define fatal(fmt, args...) modpost_log(LOG_FATAL, fmt, ##args)