[PATCH] netlink: NL_SET_ERR_MSG - remove local static array

[PATCH] netlink: NL_SET_ERR_MSG - remove local static array

[Joe Perches]

The want was to have some separate object section for netlink messages
so all netlink messages could be specifically listed by some tool but
the effect is duplicating static const char arrays in the object code.

It seems unused presently so change the macro to avoid the local static
declarations until such time as these actually are wanted and used.

This reduces object size ~8KB in an x86-64 defconfig without modules.

$ size vmlinux.o*
   text	   data	    bss	    dec	    hex	filename
20110471	3460344	 741760	24312575	172faff	vmlinux.o.new
20119444	3460344	 741760	24321548	1731e0c	vmlinux.o.old

Signed-off-by: Joe Perches <joe@perches.com>
---
 include/linux/netlink.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 61b1c7fcc401e..4bb32ae134aa8 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -89,13 +89,12 @@ struct netlink_ext_ack {
  * to the lack of an output buffer.)
  */
 #define NL_SET_ERR_MSG(extack, msg) do {		\
-	static const char __msg[] = msg;		\
 	struct netlink_ext_ack *__extack = (extack);	\
 							\
-	do_trace_netlink_extack(__msg);			\
+	do_trace_netlink_extack(msg);			\
 							\
 	if (__extack)					\
-		__extack->_msg = __msg;			\
+		__extack->_msg = msg;			\
 } while (0)
 
 #define NL_SET_ERR_MSG_MOD(extack, msg)			\
@@ -111,13 +110,12 @@ struct netlink_ext_ack {
 #define NL_SET_BAD_ATTR(extack, attr) NL_SET_BAD_ATTR_POLICY(extack, attr, NULL)
 
 #define NL_SET_ERR_MSG_ATTR_POL(extack, attr, pol, msg) do {	\
-	static const char __msg[] = msg;			\
 	struct netlink_ext_ack *__extack = (extack);		\
 								\
-	do_trace_netlink_extack(__msg);				\
+	do_trace_netlink_extack(msg);				\
 								\
 	if (__extack) {						\
-		__extack->_msg = __msg;				\
+		__extack->_msg = msg;				\
 		__extack->bad_attr = (attr);			\
 		__extack->policy = (pol);			\
 	}							\

Re: [PATCH] netlink: NL_SET_ERR_MSG - remove local static array

[Jonathan Toppins]

On 8/9/21 1:04 PM, Joe Perches wrote:
> The want was to have some separate object section for netlink messages
> so all netlink messages could be specifically listed by some tool but
> the effect is duplicating static const char arrays in the object code.
> 
> It seems unused presently so change the macro to avoid the local static
> declarations until such time as these actually are wanted and used.
> 
> This reduces object size ~8KB in an x86-64 defconfig without modules.
> 
> $ size vmlinux.o*
>     text	   data	    bss	    dec	    hex	filename
> 20110471	3460344	 741760	24312575	172faff	vmlinux.o.new
> 20119444	3460344	 741760	24321548	1731e0c	vmlinux.o.old
> 
> Signed-off-by: Joe Perches <joe@perches.com>

Seems reasonable.

Acked-by: Jonathan Toppins <jtoppins@redhat.com>

Re: [PATCH] netlink: NL_SET_ERR_MSG - remove local static array

[Jakub Kicinski]

On Mon, 09 Aug 2021 10:04:00 -0700 Joe Perches wrote:
> The want was to have some separate object section for netlink messages
> so all netlink messages could be specifically listed by some tool but
> the effect is duplicating static const char arrays in the object code.
> 
> It seems unused presently so change the macro to avoid the local static
> declarations until such time as these actually are wanted and used.
> 
> This reduces object size ~8KB in an x86-64 defconfig without modules.
> 
> $ size vmlinux.o*
>    text	   data	    bss	    dec	    hex	filename
> 20110471	3460344	 741760	24312575	172faff	vmlinux.o.new
> 20119444	3460344	 741760	24321548	1731e0c	vmlinux.o.old
> 
> Signed-off-by: Joe Perches <joe@perches.com>

I guess we can bring it back when it's needed.

> diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> index 61b1c7fcc401e..4bb32ae134aa8 100644
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -89,13 +89,12 @@ struct netlink_ext_ack {
>   * to the lack of an output buffer.)
>   */
>  #define NL_SET_ERR_MSG(extack, msg) do {		\
> -	static const char __msg[] = msg;		\
>  	struct netlink_ext_ack *__extack = (extack);	\
>  							\
> -	do_trace_netlink_extack(__msg);			\
> +	do_trace_netlink_extack(msg);			\
>  							\
>  	if (__extack)					\
> -		__extack->_msg = __msg;			\
> +		__extack->_msg = msg;			\
>  } while (0)

But you've made us evaluate msg multiple times now.
Given extack is carefully evaluated only once this stands out.

>  #define NL_SET_ERR_MSG_MOD(extack, msg)			\
> @@ -111,13 +110,12 @@ struct netlink_ext_ack {
>  #define NL_SET_BAD_ATTR(extack, attr) NL_SET_BAD_ATTR_POLICY(extack, attr, NULL)
>  
>  #define NL_SET_ERR_MSG_ATTR_POL(extack, attr, pol, msg) do {	\
> -	static const char __msg[] = msg;			\
>  	struct netlink_ext_ack *__extack = (extack);		\
>  								\
> -	do_trace_netlink_extack(__msg);				\
> +	do_trace_netlink_extack(msg);				\
>  								\
>  	if (__extack) {						\
> -		__extack->_msg = __msg;				\
> +		__extack->_msg = msg;				\
>  		__extack->bad_attr = (attr);			\
>  		__extack->policy = (pol);			\

Same here.

Re: [PATCH] netlink: NL_SET_ERR_MSG - remove local static array

[Joe Perches]

On Tue, 2021-08-10 at 13:30 -0700, Jakub Kicinski wrote:
> On Mon, 09 Aug 2021 10:04:00 -0700 Joe Perches wrote:
> > The want was to have some separate object section for netlink messages
> > so all netlink messages could be specifically listed by some tool but
> > the effect is duplicating static const char arrays in the object code.
> > 
> > It seems unused presently so change the macro to avoid the local static
> > declarations until such time as these actually are wanted and used.
> > 
> > This reduces object size ~8KB in an x86-64 defconfig without modules.
[]
> > diff --git a/include/linux/netlink.h b/include/linux/netlink.h
[]
> > @@ -89,13 +89,12 @@ struct netlink_ext_ack {
> >   * to the lack of an output buffer.)
> >   */
> >  #define NL_SET_ERR_MSG(extack, msg) do {		\
> > -	static const char __msg[] = msg;		\
> >  	struct netlink_ext_ack *__extack = (extack);	\
> >  							\
> > -	do_trace_netlink_extack(__msg);			\
> > +	do_trace_netlink_extack(msg);			\
> >  							\
> >  	if (__extack)					\
> > -		__extack->_msg = __msg;			\
> > +		__extack->_msg = msg;			\
> >  } while (0)
> 
> But you've made us evaluate msg multiple times now.
> Given extack is carefully evaluated only once this stands out.

msg is always a const char array so no evaluation is done.
It's just a pointer.

In fact, this could either become a static inline or a
simple function call to reduce object size even further.

For instance:

$ size vmlinux.o.nl_func.*
   text	   data	    bss	    dec	    hex	filename
19974564	3457991	 741312	24173867	170dd2b	vmlinux.o.nl_func.new
19992097	3457967	 741312	24191376	1712190	vmlinux.o.nl_func.old

---
 include/linux/netlink.h  | 29 ++++++++++-------------------
 net/netlink/af_netlink.c | 13 +++++++++++++
 2 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 61b1c7fcc401e..fe80c2704cc23 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -82,21 +82,16 @@ struct netlink_ext_ack {
 	u8 cookie_len;
 };
 
+void netlink_set_err_msg(struct netlink_ext_ack *extack, const char *msg);
 /* Always use this macro, this allows later putting the
  * message into a separate section or such for things
  * like translation or listing all possible messages.
  * Currently string formatting is not supported (due
  * to the lack of an output buffer.)
  */
-#define NL_SET_ERR_MSG(extack, msg) do {		\
-	static const char __msg[] = msg;		\
-	struct netlink_ext_ack *__extack = (extack);	\
-							\
-	do_trace_netlink_extack(__msg);			\
-							\
-	if (__extack)					\
-		__extack->_msg = __msg;			\
-} while (0)
+
+#define NL_SET_ERR_MSG(extack, msg)		\
+	netlink_set_err_msg(extack, msg)
 
 #define NL_SET_ERR_MSG_MOD(extack, msg)			\
 	NL_SET_ERR_MSG((extack), KBUILD_MODNAME ": " msg)
@@ -110,16 +105,12 @@ struct netlink_ext_ack {
 
 #define NL_SET_BAD_ATTR(extack, attr) NL_SET_BAD_ATTR_POLICY(extack, attr, NULL)
 
-#define NL_SET_ERR_MSG_ATTR_POL(extack, attr, pol, msg) do {	\
-	static const char __msg[] = msg;			\
-	struct netlink_ext_ack *__extack = (extack);		\
-								\
-	do_trace_netlink_extack(__msg);				\
-								\
-	if (__extack) {						\
-		__extack->_msg = __msg;				\
-		__extack->bad_attr = (attr);			\
-		__extack->policy = (pol);			\
+#define NL_SET_ERR_MSG_ATTR_POL(extack, attr, pol, msg)		\
+do {								\
+	netlink_set_err_msg(extack, msg);			\
+	if (extack) {						\
+		extack->bad_attr = (attr);			\
+		extack->policy = (pol);				\
 	}							\
 } while (0)
 
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 24b7cf447bc55..b6d035f0d343b 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2561,6 +2561,19 @@ int nlmsg_notify(struct sock *sk, struct sk_buff *skb, u32 portid,
 }
 EXPORT_SYMBOL(nlmsg_notify);
 
+/**
+ * nl_set_err_msg - 
+ */
+
+void netlink_set_err_msg(struct netlink_ext_ack *extack, const char *msg)
+{
+	do_trace_netlink_extack(msg);
+
+	if (extack)
+		extack->_msg = msg;
+}
+EXPORT_SYMBOL(netlink_set_err_msg);
+
 #ifdef CONFIG_PROC_FS
 struct nl_seq_iter {
 	struct seq_net_private p;