linux-kernel - Re: [PATCH] Kbuild: Disable the -Wformat-security gcc flag

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Date:	Wed, 04 Feb 2009 14:26:45 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Floris Kraak <randakar@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Trivial Patch Monkey <trivial@...nel.org>
Subject: Re: [PATCH] Kbuild: Disable the -Wformat-security gcc flag

 > Before judging on this patch could you please post what warning it
 > triggers and one or a few patches to fix some of them.

The warnings are things like:

    init/main.c: In function 'start_kernel':
    init/main.c:557: warning: format not a string literal and no format arguments

where the patch to fix this would be:

diff --git a/init/main.c b/init/main.c
index 8442094..78fc0d8 100644
--- a/init/main.c
+++ b/init/main.c
@@ -554,7 +554,7 @@ asmlinkage void __init start_kernel(void)
 	boot_cpu_init();
 	page_address_init();
 	printk(KERN_NOTICE);
-	printk(linux_banner);
+	printk("%s", linux_banner);
 	setup_arch(&command_line);
 	mm_init_owner(&init_mm, &init_task);
 	setup_command_line(command_line);

with the impact:

add/remove: 0/0 grow/shrink: 1/0 up/down: 7/0 (7)
function                                     old     new   delta
start_kernel                                 689     696      +7


There are also many warnings like:

    drivers/char/mem.c: In function 'chr_dev_init':
    drivers/char/mem.c:994: warning: format not a string literal and no format arguments

which require a similar fix but show that we can't just restrict things
to some trick with printk():

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 3586b3b..ba3bf43 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -991,7 +991,7 @@ static int __init chr_dev_init(void)
 	for (i = 0; i < ARRAY_SIZE(devlist); i++)
 		device_create(mem_class, NULL,
 			      MKDEV(MEM_MAJOR, devlist[i].minor), NULL,
-			      devlist[i].name);
+			      "%s", devlist[i].name);
 
 	return 0;
 }
--
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