linux-kernel - Re: [PATCH] iwlwifi: pcie: make array prop static, shrinks object size

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Date:   Mon, 11 Jun 2018 12:40:55 -0700
From:   Joe Perches <joe@...ches.com>
To:     Colin King <colin.king@...onical.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Intel Linux Wireless <linuxwifi@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iwlwifi: pcie: make array prop static, shrinks object
 size

(adding Greg KH)

On Mon, 2018-06-11 at 18:15 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Don't populate the read-only array 'prop' on the stack but
> instead make it static. Makes the object code smaller by 20 bytes:
> 
> Before:
>    text    data     bss     dec     hex filename
>   71659   14614     576   86849   15341 trans.o
> 
> After:
>    text    data     bss     dec     hex filename
>   71479   14774     576   86829   1532d trans.o
> 
> (gcc version 7.3.0 x86_64)
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/net/wireless/intel/iwlwifi/pcie/trans.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
> index 7229991ae70d..c4626ebe5da1 100644
> --- a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
> +++ b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
> @@ -1946,7 +1946,7 @@ static void iwl_trans_pcie_removal_wk(struct work_struct *wk)
>  	struct iwl_trans_pcie_removal *removal =
>  		container_of(wk, struct iwl_trans_pcie_removal, work);
>  	struct pci_dev *pdev = removal->pdev;
> -	char *prop[] = {"EVENT=INACCESSIBLE", NULL};
> +	static char *prop[] = {"EVENT=INACCESSIBLE", NULL};
>  
>  	dev_err(&pdev->dev, "Device gone - attempting removal\n");
>  	kobject_uevent_env(&pdev->dev.kobj, KOBJ_CHANGE, prop);

Now what is happening is that prop is being reloaded
each invocation with the constant addresses of the strings.

It seems the prototype and function for kobject_uevent_env
should change as well to avoid this.

Perhaps this should become:
---
 drivers/net/wireless/intel/iwlwifi/pcie/trans.c | 2 +-
 include/linux/kobject.h                         | 2 +-
 lib/kobject_uevent.c                            | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
index 7229991ae70d..6668a8aad22e 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
@@ -1946,7 +1946,7 @@ static void iwl_trans_pcie_removal_wk(struct work_struct *wk)
 	struct iwl_trans_pcie_removal *removal =
 		container_of(wk, struct iwl_trans_pcie_removal, work);
 	struct pci_dev *pdev = removal->pdev;
-	char *prop[] = {"EVENT=INACCESSIBLE", NULL};
+	static const char * const prop[] = {"EVENT=INACCESSIBLE", NULL};
 
 	dev_err(&pdev->dev, "Device gone - attempting removal\n");
 	kobject_uevent_env(&pdev->dev.kobj, KOBJ_CHANGE, prop);
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 7f6f93c3df9c..9f5cf553dd1e 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -217,7 +217,7 @@ extern struct kobject *firmware_kobj;
 
 int kobject_uevent(struct kobject *kobj, enum kobject_action action);
 int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
-			char *envp[]);
+			const char * const envp[]);
 int kobject_synth_uevent(struct kobject *kobj, const char *buf, size_t count);
 
 __printf(2, 3)
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 63d0816ab23b..9107989a0cc8 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -452,7 +452,7 @@ static void zap_modalias_env(struct kobj_uevent_env *env)
  * corresponding error when it fails.
  */
 int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
-		       char *envp_ext[])
+		       const char * const envp_ext[])
 {
 	struct kobj_uevent_env *env;
 	const char *action_string = kobject_actions[action];