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

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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 15bfc2348d ("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 15bfc2348d ("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 f235541699
("export.h: allow for per-symbol configurable EXPORT_SYMBOL()").

Fixes: 15bfc2348d ("modpost: check for static EXPORT_SYMBOL* functions")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Arnd Bergmann <arnd@arndb.de>
This commit is contained in:
Masahiro Yamada 2019-09-09 19:53:17 +09:00
parent a0469f989f
commit 69a94abb82
2 changed files with 17 additions and 31 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

42
include/linux/export.h
View file

@ -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
@ -117,37 +122,22 @@ 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")
#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused")
#define EXPORT_UNUSED_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_unused_gpl")
#else
#define EXPORT_UNUSED_SYMBOL(sym)
#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 */

6
scripts/genksyms/keywords.c
View file

@ -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 },