[PATCH 1/2] export.h: remove defined(__KERNEL__)

[PATCH 1/2] export.h: remove defined(__KERNEL__)

[Masahiro Yamada]

This line was touched by commit f235541699bc ("export.h: allow for
per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
not explain why.

CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 include/linux/export.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/export.h b/include/linux/export.h
index fd8711ed9ac4..cdd98a0d918c 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -20,7 +20,7 @@ extern struct module __this_module;
 
 #ifdef CONFIG_MODULES
 
-#if defined(__KERNEL__) && !defined(__GENKSYMS__)
+#if !defined(__GENKSYMS__)
 #ifdef CONFIG_MODVERSIONS
 /* Mark the CRC weak since genksyms apparently decides not to
  * generate a checksums for some symbols */
-- 
2.17.1

[PATCH 2/2] export.h, genksyms: do not make genksyms calculate CRC of trimmed symbols

[Masahiro Yamada]

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

  https://lkml.org/lkml/2019/9/6/619

Actually, this happens under the combination of CONFIG_MODVERSIONS=y
and CONFIG_TRIM_UNUSED_KSYMS=y since commit 15bfc2348d54 ("modpost:
check for static EXPORT_SYMBOL* functions").

For example, arch/arm/config/multi_v7_defconfig + CONFIG_MODVERSIONS=y
+ CONFIG_TRIM_UNUSED_KSYMS=y 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 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 __crc* symbols are added to objects. It has been harmless
until recently.

Since commit 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL*
functions"), it is harmful because the bogus __crc* symbols make
modpost call sym_update_crc(), and then new_symbol(), 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 f235541699bc
("export.h: allow for per-symbol configurable EXPORT_SYMBOL()").

Fixes: 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL* functions")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 include/linux/export.h      | 42 ++++++++++++++-----------------------
 scripts/genksyms/keywords.c |  6 +-----
 2 files changed, 17 insertions(+), 31 deletions(-)

diff --git a/include/linux/export.h b/include/linux/export.h
index cdd98a0d918c..7d8c112a8b61 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -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 */
diff --git a/scripts/genksyms/keywords.c b/scripts/genksyms/keywords.c
index c586d32dd2c3..7a85c4e21175 100644
--- a/scripts/genksyms/keywords.c
+++ b/scripts/genksyms/keywords.c
@@ -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 },
-- 
2.17.1

Re: [PATCH 2/2] export.h, genksyms: do not make genksyms calculate CRC of trimmed symbols

[Arnd Bergmann]

On Mon, Sep 9, 2019 at 12:53 PM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> Since commit 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL*
> functions"), it is harmful because the bogus __crc* symbols make
> modpost call sym_update_crc(), and then new_symbol(), 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 f235541699bc
> ("export.h: allow for per-symbol configurable EXPORT_SYMBOL()").
>
> Fixes: 15bfc2348d54 ("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>

Thanks for providing a proper fix!

       Arnd

Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)

[Nicolas Pitre]

On Mon, 9 Sep 2019, Masahiro Yamada wrote:

> This line was touched by commit f235541699bc ("export.h: allow for
> per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
> not explain why.
> 
> CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).

I'm pretty sure it was needed back then so not to interfere with users 
of this file. My fault for not documenting it.


Nicolas

Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)

[Masahiro Yamada]

Hi Nicolas,

On Mon, Sep 9, 2019 at 10:48 PM Nicolas Pitre <nico@fluxnic.net> wrote:
>
> On Mon, 9 Sep 2019, Masahiro Yamada wrote:
>
> > This line was touched by commit f235541699bc ("export.h: allow for
> > per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
> > not explain why.
> >
> > CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).
>
> I'm pretty sure it was needed back then so not to interfere with users
> of this file. My fault for not documenting it.

Hmm, I did not see a problem in my quick build test.

Do you remember which file was causing the problem?



-- 
Best Regards
Masahiro Yamada

Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)

[Nicolas Pitre]

On Mon, 9 Sep 2019, Masahiro Yamada wrote:

> Hi Nicolas,
> 
> On Mon, Sep 9, 2019 at 10:48 PM Nicolas Pitre <nico@fluxnic.net> wrote:
> >
> > On Mon, 9 Sep 2019, Masahiro Yamada wrote:
> >
> > > This line was touched by commit f235541699bc ("export.h: allow for
> > > per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
> > > not explain why.
> > >
> > > CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).
> >
> > I'm pretty sure it was needed back then so not to interfere with users
> > of this file. My fault for not documenting it.
> 
> Hmm, I did not see a problem in my quick build test.
> 
> Do you remember which file was causing the problem?

If you build commit 7ec925701f5f with CONFIG_TRIM_UNUSED_KSYMS=y and the 
defined(__KERNEL__) test removed then you'll get:

  HOSTCC  scripts/mod/modpost.o
In file included from scripts/mod/modpost.c:24:
scripts/mod/../../include/linux/export.h:81:10: fatal error: linux/kconfig.h: No such file or directory


Nicolas

Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)

[Masahiro Yamada]

On Tue, Sep 10, 2019 at 1:06 AM Nicolas Pitre <nico@fluxnic.net> wrote:
>
> On Mon, 9 Sep 2019, Masahiro Yamada wrote:
>
> > Hi Nicolas,
> >
> > On Mon, Sep 9, 2019 at 10:48 PM Nicolas Pitre <nico@fluxnic.net> wrote:
> > >
> > > On Mon, 9 Sep 2019, Masahiro Yamada wrote:
> > >
> > > > This line was touched by commit f235541699bc ("export.h: allow for
> > > > per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
> > > > not explain why.
> > > >
> > > > CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).
> > >
> > > I'm pretty sure it was needed back then so not to interfere with users
> > > of this file. My fault for not documenting it.
> >
> > Hmm, I did not see a problem in my quick build test.
> >
> > Do you remember which file was causing the problem?
>
> If you build commit 7ec925701f5f with CONFIG_TRIM_UNUSED_KSYMS=y and the
> defined(__KERNEL__) test removed then you'll get:
>
>   HOSTCC  scripts/mod/modpost.o
> In file included from scripts/mod/modpost.c:24:
> scripts/mod/../../include/linux/export.h:81:10: fatal error: linux/kconfig.h: No such file or directory
>
>
> Nicolas


Thanks for explaining this.

It is not the case any more.


I will reword the commit message as follows:

------------------------>8---------------------------------------
export.h: remove defined(__KERNEL__), which is no longer needed

The conditional define(__KERNEL__) was added by commit f235541699bc
("export.h: allow for per-symbol configurable EXPORT_SYMBOL()").

It was needed at that time to avoid the build error of modpost
with CONFIG_TRIM_UNUSED_KSYMS=y.

Since commit b2c5cdcfd4bc ("modpost: remove symbol prefix support"),
modpost no longer includes linux/export.h, thus the define(__KERNEL__)
is unneeded.
------------------------>8---------------------------------------



--
Best Regards
Masahiro Yamada

Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)

[Nicolas Pitre]

On Tue, 10 Sep 2019, Masahiro Yamada wrote:

> On Tue, Sep 10, 2019 at 1:06 AM Nicolas Pitre <nico@fluxnic.net> wrote:
> >
> > On Mon, 9 Sep 2019, Masahiro Yamada wrote:
> >
> > > Hi Nicolas,
> > >
> > > On Mon, Sep 9, 2019 at 10:48 PM Nicolas Pitre <nico@fluxnic.net> wrote:
> > > >
> > > > On Mon, 9 Sep 2019, Masahiro Yamada wrote:
> > > >
> > > > > This line was touched by commit f235541699bc ("export.h: allow for
> > > > > per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
> > > > > not explain why.
> > > > >
> > > > > CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).
> > > >
> > > > I'm pretty sure it was needed back then so not to interfere with users
> > > > of this file. My fault for not documenting it.
> > >
> > > Hmm, I did not see a problem in my quick build test.
> > >
> > > Do you remember which file was causing the problem?
> >
> > If you build commit 7ec925701f5f with CONFIG_TRIM_UNUSED_KSYMS=y and the
> > defined(__KERNEL__) test removed then you'll get:
> >
> >   HOSTCC  scripts/mod/modpost.o
> > In file included from scripts/mod/modpost.c:24:
> > scripts/mod/../../include/linux/export.h:81:10: fatal error: linux/kconfig.h: No such file or directory
> >
> >
> > Nicolas
> 
> 
> Thanks for explaining this.
> 
> It is not the case any more.
> 
> 
> I will reword the commit message as follows:
> 
> ------------------------>8---------------------------------------
> export.h: remove defined(__KERNEL__), which is no longer needed
> 
> The conditional define(__KERNEL__) was added by commit f235541699bc
> ("export.h: allow for per-symbol configurable EXPORT_SYMBOL()").
> 
> It was needed at that time to avoid the build error of modpost
> with CONFIG_TRIM_UNUSED_KSYMS=y.
> 
> Since commit b2c5cdcfd4bc ("modpost: remove symbol prefix support"),
> modpost no longer includes linux/export.h, thus the define(__KERNEL__)
> is unneeded.
> ------------------------>8---------------------------------------
> 

Acked-by: Nicolas Pitre <nico@fluxnic.net>


Nicolas

Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)

[Masahiro Yamada]

On Mon, Sep 9, 2019 at 7:53 PM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> This line was touched by commit f235541699bc ("export.h: allow for
> per-symbol configurable EXPORT_SYMBOL()"), but the commit log did
> not explain why.
>
> CONFIG_TRIM_UNUSED_KSYMS works for me without defined(__KERNEL__).
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---

Both applied to linux-kbuild.


>  include/linux/export.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/export.h b/include/linux/export.h
> index fd8711ed9ac4..cdd98a0d918c 100644
> --- a/include/linux/export.h
> +++ b/include/linux/export.h
> @@ -20,7 +20,7 @@ extern struct module __this_module;
>
>  #ifdef CONFIG_MODULES
>
> -#if defined(__KERNEL__) && !defined(__GENKSYMS__)
> +#if !defined(__GENKSYMS__)
>  #ifdef CONFIG_MODVERSIONS
>  /* Mark the CRC weak since genksyms apparently decides not to
>   * generate a checksums for some symbols */
> --
> 2.17.1
>


-- 
Best Regards
Masahiro Yamada