[PATCH] moduleparam: fix alpha, ia64 and ppc64 compile failures

[PATCH] moduleparam: fix alpha, ia64 and ppc64 compile failures

[Ivan Kokshaysky]

On alpha, ia64 and ppc64 only relocations to local data can go into
read-only sections. The vast majority of module parameters use the global
generic param_set_*/param_get_* functions, so the 'const' attribute for
struct kernel_param is not only useless, but it also causes compile
failures due to 'section type conflict' in those rare cases where
param_set/get are local functions.

This fixes http://bugzilla.kernel.org/show_bug.cgi?id=8964

Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
---
 include/linux/moduleparam.h |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 8126e55..ec62438 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -62,6 +62,16 @@ struct kparam_array
 	void *elem;
 };
 
+/* On alpha, ia64 and ppc64 relocations to global data cannot go into
+   read-only sections (which is part of respective UNIX ABI on these
+   platforms). So 'const' makes no sense and even causes compile failures
+   with some compilers. */
+#if defined(CONFIG_ALPHA) || defined(CONFIG_IA64) || defined(CONFIG_PPC64)
+#define __moduleparam_const
+#else
+#define __moduleparam_const const
+#endif
+
 /* This is the fundamental function for registering boot/module
    parameters.  perm sets the visibility in sysfs: 000 means it's
    not there, read bits mean it's readable, write bits mean it's
@@ -71,7 +81,7 @@ struct kparam_array
 	static int __param_perm_check_##name __attribute__((unused)) =	\
 	BUILD_BUG_ON_ZERO((perm) < 0 || (perm) > 0777 || ((perm) & 2));	\
 	static const char __param_str_##name[] = prefix #name;		\
-	static struct kernel_param const __param_##name			\
+	static struct kernel_param __moduleparam_const __param_##name	\
 	__used								\
     __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
 	= { __param_str_##name, perm, set, get, { arg } }

Re: [PATCH] moduleparam: fix alpha, ia64 and ppc64 compile failures

[Andrew Morton]

On Sat, 9 Feb 2008 01:33:41 +0300
Ivan Kokshaysky <ink@jurassic.park.msu.ru> wrote:

> On alpha, ia64 and ppc64 only relocations to local data can go into
> read-only sections. The vast majority of module parameters use the global
> generic param_set_*/param_get_* functions, so the 'const' attribute for
> struct kernel_param is not only useless, but it also causes compile
> failures due to 'section type conflict' in those rare cases where
> param_set/get are local functions.
> 
> This fixes http://bugzilla.kernel.org/show_bug.cgi?id=8964
> 
> Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
> ---
>  include/linux/moduleparam.h |   12 +++++++++++-
>  1 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> index 8126e55..ec62438 100644
> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
> @@ -62,6 +62,16 @@ struct kparam_array
>  	void *elem;
>  };
>  
> +/* On alpha, ia64 and ppc64 relocations to global data cannot go into
> +   read-only sections (which is part of respective UNIX ABI on these
> +   platforms). So 'const' makes no sense and even causes compile failures
> +   with some compilers. */
> +#if defined(CONFIG_ALPHA) || defined(CONFIG_IA64) || defined(CONFIG_PPC64)
> +#define __moduleparam_const
> +#else
> +#define __moduleparam_const const
> +#endif
> +
>  /* This is the fundamental function for registering boot/module
>     parameters.  perm sets the visibility in sysfs: 000 means it's
>     not there, read bits mean it's readable, write bits mean it's
> @@ -71,7 +81,7 @@ struct kparam_array
>  	static int __param_perm_check_##name __attribute__((unused)) =	\
>  	BUILD_BUG_ON_ZERO((perm) < 0 || (perm) > 0777 || ((perm) & 2));	\
>  	static const char __param_str_##name[] = prefix #name;		\
> -	static struct kernel_param const __param_##name			\
> +	static struct kernel_param __moduleparam_const __param_##name	\
>  	__used								\
>      __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
>  	= { __param_str_##name, perm, set, get, { arg } }

I think it would have been better to define a new CONFIG_MODULEPARAM_CONST
for those three archictures, rather than muckying up the code like this.

But hey, I get to close a bugzilla report - I'm doing that amlonst monthly
now.  Thanks.

Re: [PATCH] moduleparam: fix alpha, ia64 and ppc64 compile failures

[Ivan Kokshaysky]

On Fri, Feb 08, 2008 at 02:46:15PM -0800, Andrew Morton wrote:
> I think it would have been better to define a new CONFIG_MODULEPARAM_CONST
> for those three archictures, rather than muckying up the code like this.

I'd prefer to keep this as is for now (sorta the uglier the better ;-)
I really hope it's the short term solution as we need some feedback from gcc
folks. We use named sections quite a lot, but gcc is sort of unfriendly with
these, and this particular problem is not the main one.
For instance, if someone dares to put a 'switch' statement into discarded
section (__exit), the final link fails (on any arch!), because gcc generates
a jump table in .rodata which references that discarded section...

Ivan.

Re: [PATCH] moduleparam: fix alpha, ia64 and ppc64 compile failures

[Daniel Drake]

Ivan Kokshaysky wrote:
> On alpha, ia64 and ppc64 only relocations to local data can go into
> read-only sections. The vast majority of module parameters use the global
> generic param_set_*/param_get_* functions, so the 'const' attribute for
> struct kernel_param is not only useless, but it also causes compile
> failures due to 'section type conflict' in those rare cases where
> param_set/get are local functions.
> 
> This fixes http://bugzilla.kernel.org/show_bug.cgi?id=8964

In case you weren't aware already, people seem to think this is actually 
a GCC bug (with a patch available):

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31490

Daniel