Commit 69a94abb authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

export.h, genksyms: do not make genksyms calculate CRC of trimmed symbols 



Arnd Bergmann reported false-positive modpost warnings detected by his
randconfig testing of linux-next.

Actually, this happens under the combination of CONFIG_MODVERSIONS
and CONFIG_TRIM_UNUSED_KSYMS since commit 15bfc234 ("modpost:
check for static EXPORT_SYMBOL* functions").

For example, arch/arm/config/multi_v7_defconfig + CONFIG_MODVERSIONS
+ CONFIG_TRIM_UNUSED_KSYMS produces the following false-positives:

WARNING: "__lshrdi3" [vmlinux] is a static (unknown)
WARNING: "__ashrdi3" [vmlinux] is a static (unknown)
WARNING: "__aeabi_lasr" [vmlinux] is a static (unknown)
WARNING: "__aeabi_llsr" [vmlinux] is a static (unknown)
WARNING: "ftrace_set_clr_event" [vmlinux] is a static (unknown)
WARNING: "__muldi3" [vmlinux] is a static (unknown)
WARNING: "__aeabi_ulcmp" [vmlinux] is a static (unknown)
WARNING: "__ucmpdi2" [vmlinux] is a static (unknown)
WARNING: "__aeabi_lmul" [vmlinux] is a static (unknown)
WARNING: "__bswapsi2" [vmlinux] is a static (unknown)
WARNING: "__bswapdi2" [vmlinux] is a static (unknown)
WARNING: "__ashldi3" [vmlinux] is a static (unknown)
WARNING: "__aeabi_llsl" [vmlinux] is a static (unknown)

The root cause of the problem is not in the modpost, but in the
implementation of CONFIG_TRIM_UNUSED_KSYMS.

If there is at least one untrimmed symbol in the file, genksyms is
invoked to calculate CRC of *all* the exported symbols in that file
even if some of them have been trimmed due to no caller existing.

As a result, .tmp_*.ver files contain CRC of trimmed symbols, thus
unneeded, orphan __crc* symbols are added to objects. It had been
harmless until recently.

With commit 15bfc234 ("modpost: check for static EXPORT_SYMBOL*
functions"), it is now harmful because the bogus __crc* symbols make
modpost call sym_update_crc() to add the symbols to the hash table,
but there is no one that clears the ->is_static member.

I gave Fixes to the first commit that uncovered the issue, but the
potential problem has long existed since commit f2355416
("export.h: allow for per-symbol configurable EXPORT_SYMBOL()").

Fixes: 15bfc234 ("modpost: check for static EXPORT_SYMBOL* functions")
Reported-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: default avatarArnd Bergmann <arnd@arndb.de>
parent a0469f98

include/linux/export.h

+16 −26
Original line number Diff line number Diff line
@@ -18,9 +18,6 @@ extern struct module __this_module; 
#define THIS_MODULE ((struct module *)0)

#endif



#ifdef CONFIG_MODULES



#if !defined(__GENKSYMS__)

#ifdef CONFIG_MODVERSIONS

/* Mark the CRC weak since genksyms apparently decides not to

 * generate a checksums for some symbols */
@@ -74,6 +71,12 @@ struct kernel_symbol { 
};

#endif



#ifdef __GENKSYMS__



#define ___EXPORT_SYMBOL(sym, sec)	__GENKSYMS_EXPORT_SYMBOL(sym)



#else



/* For every exported symbol, place a struct in the __ksymtab section */

#define ___EXPORT_SYMBOL(sym, sec)					\

	extern typeof(sym) sym;						\
@@ -83,7 +86,9 @@ struct kernel_symbol { 
	= #sym;								\

	__KSYMTAB_ENTRY(sym, sec)



#if defined(__DISABLE_EXPORTS)

#endif



#if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)



/*

 * Allow symbol exports to be disabled completely so that C code may
@@ -117,18 +122,14 @@ struct kernel_symbol { 
#define __cond_export_sym_0(sym, sec) /* nothing */



#else

#define __EXPORT_SYMBOL ___EXPORT_SYMBOL

#endif



#define EXPORT_SYMBOL(sym)					\

	__EXPORT_SYMBOL(sym, "")

#define __EXPORT_SYMBOL(sym, sec)	___EXPORT_SYMBOL(sym, sec)



#define EXPORT_SYMBOL_GPL(sym)					\

	__EXPORT_SYMBOL(sym, "_gpl")



#define EXPORT_SYMBOL_GPL_FUTURE(sym)				\

	__EXPORT_SYMBOL(sym, "_gpl_future")

#endif /* CONFIG_MODULES */



#define EXPORT_SYMBOL(sym)		__EXPORT_SYMBOL(sym, "")

#define EXPORT_SYMBOL_GPL(sym)		__EXPORT_SYMBOL(sym, "_gpl")

#define EXPORT_SYMBOL_GPL_FUTURE(sym)	__EXPORT_SYMBOL(sym, "_gpl_future")

#ifdef CONFIG_UNUSED_SYMBOLS

#define EXPORT_UNUSED_SYMBOL(sym)	__EXPORT_SYMBOL(sym, "_unused")

#define EXPORT_UNUSED_SYMBOL_GPL(sym)	__EXPORT_SYMBOL(sym, "_unused_gpl")
@@ -137,17 +138,6 @@ struct kernel_symbol { 
#define EXPORT_UNUSED_SYMBOL_GPL(sym)

#endif



#endif	/* __GENKSYMS__ */



#else /* !CONFIG_MODULES... */



#define EXPORT_SYMBOL(sym)

#define EXPORT_SYMBOL_GPL(sym)

#define EXPORT_SYMBOL_GPL_FUTURE(sym)

#define EXPORT_UNUSED_SYMBOL(sym)

#define EXPORT_UNUSED_SYMBOL_GPL(sym)



#endif /* CONFIG_MODULES */

#endif /* !__ASSEMBLY__ */



#endif /* _LINUX_EXPORT_H */

scripts/genksyms/keywords.c

+1 −5
Original line number Diff line number Diff line
@@ -3,11 +3,7 @@ static struct resword { 
	const char *name;

	int token;

} keywords[] = {

	{ "EXPORT_SYMBOL", EXPORT_SYMBOL_KEYW },

	{ "EXPORT_SYMBOL_GPL", EXPORT_SYMBOL_KEYW },

	{ "EXPORT_SYMBOL_GPL_FUTURE", EXPORT_SYMBOL_KEYW },

	{ "EXPORT_UNUSED_SYMBOL", EXPORT_SYMBOL_KEYW },

	{ "EXPORT_UNUSED_SYMBOL_GPL", EXPORT_SYMBOL_KEYW },

	{ "__GENKSYMS_EXPORT_SYMBOL", EXPORT_SYMBOL_KEYW },

	{ "__asm", ASM_KEYW },

	{ "__asm__", ASM_KEYW },

	{ "__attribute", ATTRIBUTE_KEYW },

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