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71810db27c
The modversion symbol CRCs are emitted as ELF symbols, which allows us
to easily populate the kcrctab sections by relying on the linker to
associate each kcrctab slot with the correct value.
This has a couple of downsides:
- Given that the CRCs are treated as memory addresses, we waste 4 bytes
for each CRC on 64 bit architectures,
- On architectures that support runtime relocation, a R_<arch>_RELATIVE
relocation entry is emitted for each CRC value, which identifies it
as a quantity that requires fixing up based on the actual runtime
load offset of the kernel. This results in corrupted CRCs unless we
explicitly undo the fixup (and this is currently being handled in the
core module code)
- Such runtime relocation entries take up 24 bytes of __init space
each, resulting in a x8 overhead in [uncompressed] kernel size for
CRCs.
Switching to explicit 32 bit values on 64 bit architectures fixes most
of these issues, given that 32 bit values are not treated as quantities
that require fixing up based on the actual runtime load offset. Note
that on some ELF64 architectures [such as PPC64], these 32-bit values
are still emitted as [absolute] runtime relocatable quantities, even if
the value resolves to a build time constant. Since relative relocations
are always resolved at build time, this patch enables MODULE_REL_CRCS on
powerpc when CONFIG_RELOCATABLE=y, which turns the absolute CRC
references into relative references into .rodata where the actual CRC
value is stored.
So redefine all CRC fields and variables as u32, and redefine the
__CRC_SYMBOL() macro for 64 bit builds to emit the CRC reference using
inline assembler (which is necessary since 64-bit C code cannot use
32-bit types to hold memory addresses, even if they are ultimately
resolved using values that do not exceed 0xffffffff). To avoid
potential problems with legacy 32-bit architectures using legacy
toolchains, the equivalent C definition of the kcrctab entry is retained
for 32-bit architectures.
Note that this mostly reverts commit d4703aefdb ("module: handle ppc64
relocating kcrctabs when CONFIG_RELOCATABLE=y")
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
140 lines
4.2 KiB
C
140 lines
4.2 KiB
C
#ifndef _LINUX_EXPORT_H
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#define _LINUX_EXPORT_H
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/*
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* Export symbols from the kernel to modules. Forked from module.h
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* to reduce the amount of pointless cruft we feed to gcc when only
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* exporting a simple symbol or two.
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*
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* Try not to add #includes here. It slows compilation and makes kernel
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* hackers place grumpy comments in header files.
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*/
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/* Some toolchains use a `_' prefix for all user symbols. */
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#ifdef CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX
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#define __VMLINUX_SYMBOL(x) _##x
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#define __VMLINUX_SYMBOL_STR(x) "_" #x
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#else
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#define __VMLINUX_SYMBOL(x) x
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#define __VMLINUX_SYMBOL_STR(x) #x
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#endif
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/* Indirect, so macros are expanded before pasting. */
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#define VMLINUX_SYMBOL(x) __VMLINUX_SYMBOL(x)
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#define VMLINUX_SYMBOL_STR(x) __VMLINUX_SYMBOL_STR(x)
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#ifndef __ASSEMBLY__
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struct kernel_symbol
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{
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unsigned long value;
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const char *name;
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};
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#ifdef MODULE
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extern struct module __this_module;
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#define THIS_MODULE (&__this_module)
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#else
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#define THIS_MODULE ((struct module *)0)
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#endif
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#ifdef CONFIG_MODULES
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#if defined(__KERNEL__) && !defined(__GENKSYMS__)
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#ifdef CONFIG_MODVERSIONS
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/* Mark the CRC weak since genksyms apparently decides not to
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* generate a checksums for some symbols */
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#if defined(CONFIG_MODULE_REL_CRCS)
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#define __CRC_SYMBOL(sym, sec) \
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asm(" .section \"___kcrctab" sec "+" #sym "\", \"a\" \n" \
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" .weak " VMLINUX_SYMBOL_STR(__crc_##sym) " \n" \
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" .long " VMLINUX_SYMBOL_STR(__crc_##sym) " - . \n" \
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" .previous \n");
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#elif !defined(CONFIG_64BIT)
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#define __CRC_SYMBOL(sym, sec) \
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extern __visible void *__crc_##sym __attribute__((weak)); \
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static const unsigned long __kcrctab_##sym \
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__used \
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__attribute__((section("___kcrctab" sec "+" #sym), used)) \
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= (unsigned long) &__crc_##sym;
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#else
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#define __CRC_SYMBOL(sym, sec) \
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asm(" .section \"___kcrctab" sec "+" #sym "\", \"a\" \n" \
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" .weak " VMLINUX_SYMBOL_STR(__crc_##sym) " \n" \
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" .long " VMLINUX_SYMBOL_STR(__crc_##sym) " \n" \
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" .previous \n");
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#endif
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#else
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#define __CRC_SYMBOL(sym, sec)
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#endif
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/* For every exported symbol, place a struct in the __ksymtab section */
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#define ___EXPORT_SYMBOL(sym, sec) \
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extern typeof(sym) sym; \
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__CRC_SYMBOL(sym, sec) \
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static const char __kstrtab_##sym[] \
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__attribute__((section("__ksymtab_strings"), aligned(1))) \
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= VMLINUX_SYMBOL_STR(sym); \
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static const struct kernel_symbol __ksymtab_##sym \
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__used \
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__attribute__((section("___ksymtab" sec "+" #sym), used)) \
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= { (unsigned long)&sym, __kstrtab_##sym }
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#if defined(__KSYM_DEPS__)
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/*
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* For fine grained build dependencies, we want to tell the build system
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* about each possible exported symbol even if they're not actually exported.
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* We use a string pattern that is unlikely to be valid code that the build
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* system filters out from the preprocessor output (see ksym_dep_filter
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* in scripts/Kbuild.include).
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*/
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#define __EXPORT_SYMBOL(sym, sec) === __KSYM_##sym ===
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#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
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#include <generated/autoksyms.h>
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#define __EXPORT_SYMBOL(sym, sec) \
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__cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
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#define __cond_export_sym(sym, sec, conf) \
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___cond_export_sym(sym, sec, conf)
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#define ___cond_export_sym(sym, sec, enabled) \
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__cond_export_sym_##enabled(sym, sec)
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#define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec)
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#define __cond_export_sym_0(sym, sec) /* nothing */
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#else
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#define __EXPORT_SYMBOL ___EXPORT_SYMBOL
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#endif
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#define EXPORT_SYMBOL(sym) \
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__EXPORT_SYMBOL(sym, "")
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#define EXPORT_SYMBOL_GPL(sym) \
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__EXPORT_SYMBOL(sym, "_gpl")
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#define EXPORT_SYMBOL_GPL_FUTURE(sym) \
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__EXPORT_SYMBOL(sym, "_gpl_future")
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#ifdef CONFIG_UNUSED_SYMBOLS
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#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused")
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#define EXPORT_UNUSED_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_unused_gpl")
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#else
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#define EXPORT_UNUSED_SYMBOL(sym)
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#define EXPORT_UNUSED_SYMBOL_GPL(sym)
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#endif
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#endif /* __GENKSYMS__ */
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#else /* !CONFIG_MODULES... */
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#define EXPORT_SYMBOL(sym)
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#define EXPORT_SYMBOL_GPL(sym)
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#define EXPORT_SYMBOL_GPL_FUTURE(sym)
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#define EXPORT_UNUSED_SYMBOL(sym)
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#define EXPORT_UNUSED_SYMBOL_GPL(sym)
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#endif /* CONFIG_MODULES */
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#endif /* !__ASSEMBLY__ */
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#endif /* _LINUX_EXPORT_H */
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