[PATCH] netlink: fix gcc -Wconversion compilation warning

[PATCH] netlink: fix gcc -Wconversion compilation warning

[Kirill A. Shutsemov]

From: Dmitry V. Levin <ldv@altlinux.org>

$ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
unsigned f(void) {return NLMSG_HDRLEN;}
EOF
<stdin>: In function 'f':
<stdin>:3:26: warning: negative integer implicitly converted to unsigned type

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 include/linux/netlink.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 1235669..e2b9e63 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -70,7 +70,7 @@ struct nlmsghdr {
    Check		NLM_F_EXCL
  */
 
-#define NLMSG_ALIGNTO	4
+#define NLMSG_ALIGNTO	4U
 #define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )
 #define NLMSG_HDRLEN	 ((int) NLMSG_ALIGN(sizeof(struct nlmsghdr)))
 #define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(NLMSG_HDRLEN))
-- 
1.7.3.3

Re: [PATCH] netlink: fix gcc -Wconversion compilation warning

[Eric W. Biederman]

"Kirill A. Shutsemov" <kirill@shutemov.name> writes:

> From: Dmitry V. Levin <ldv@altlinux.org>
>
> $ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
> unsigned f(void) {return NLMSG_HDRLEN;}
> EOF
> <stdin>: In function 'f':
> <stdin>:3:26: warning: negative integer implicitly converted to unsigned type
>
This doesn't look like a bad fix, but I believe things will fail if
we give NLMSG_ALIGN an unsigned long like size_t.  Say like sizeof.

Admittedly it has to be a huge size but still if we are going
to go fixing things...

And then there is the silliness that NLMSG_HDRLEN forces itself
to be an int, when it start out as a size_t.

So I think NLMSG_ALIGN either needs to operation exclusively
on unsigned longs aka size_t, or it needs to be type preserving.

Do you have time to look at this a bit more?


> Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> ---
>  include/linux/netlink.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> index 1235669..e2b9e63 100644
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -70,7 +70,7 @@ struct nlmsghdr {
>     Check		NLM_F_EXCL
>   */
>  
> -#define NLMSG_ALIGNTO	4
> +#define NLMSG_ALIGNTO	4U
>  #define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )
>  #define NLMSG_HDRLEN	 ((int) NLMSG_ALIGN(sizeof(struct nlmsghdr)))
>  #define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(NLMSG_HDRLEN))

Re: [PATCH] netlink: fix gcc -Wconversion compilation warning

[Kirill A. Shutemov]

On Mon, Dec 13, 2010 at 01:35:25PM -0800, Eric W. Biederman wrote:
> "Kirill A. Shutsemov" <kirill@shutemov.name> writes:
> 
> > From: Dmitry V. Levin <ldv@altlinux.org>
> >
> > $ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
> > unsigned f(void) {return NLMSG_HDRLEN;}
> > EOF
> > <stdin>: In function 'f':
> > <stdin>:3:26: warning: negative integer implicitly converted to unsigned type
> >
> This doesn't look like a bad fix, but I believe things will fail if
> we give NLMSG_ALIGN an unsigned long like size_t.  Say like sizeof.
> 
> Admittedly it has to be a huge size but still if we are going
> to go fixing things...
> 
> And then there is the silliness that NLMSG_HDRLEN forces itself
> to be an int, when it start out as a size_t.
> 
> So I think NLMSG_ALIGN either needs to operation exclusively
> on unsigned longs aka size_t, or it needs to be type preserving.
> 
> Do you have time to look at this a bit more?

Something like this? Untested.
---
>From 8b86073dc9697c0eff93c003d6331c1e4aeda60e Mon Sep 17 00:00:00 2001
From: Kirill A. Shutemov <kirill@shutemov.name>
Date: Tue, 14 Dec 2010 12:50:39 +0200
Subject: [PATCH] netlink: fix gcc -Wconversion compilation warning

$ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
unsigned f(void) {return NLMSG_HDRLEN;}
EOF
<stdin>: In function 'f':
<stdin>:3:26: warning: negative integer implicitly converted to unsigned type

Define NLMSG_ALIGNTO as size_t, NLMSG_ALIGN always returns size_t and
drop non-sense casting in NLMSG_HDRLEN. Now NLMSG_HDRLEN returns size_t.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 include/linux/netlink.h |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 1235669..db7d373 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -70,9 +70,9 @@ struct nlmsghdr {
    Check		NLM_F_EXCL
  */
 
-#define NLMSG_ALIGNTO	4
-#define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )
-#define NLMSG_HDRLEN	 ((int) NLMSG_ALIGN(sizeof(struct nlmsghdr)))
+#define NLMSG_ALIGNTO	((size_t) 4)
+#define NLMSG_ALIGN(len) ( ((size_t)(len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )
+#define NLMSG_HDRLEN	 NLMSG_ALIGN(sizeof(struct nlmsghdr))
 #define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(NLMSG_HDRLEN))
 #define NLMSG_SPACE(len) NLMSG_ALIGN(NLMSG_LENGTH(len))
 #define NLMSG_DATA(nlh)  ((void*)(((char*)nlh) + NLMSG_LENGTH(0)))
-- 
 Kirill A. Shutemov

Re: [PATCH] netlink: fix gcc -Wconversion compilation warning

[David Miller]

From: ebiederm@xmission.com (Eric W. Biederman)
Date: Mon, 13 Dec 2010 13:35:25 -0800

> "Kirill A. Shutsemov" <kirill@shutemov.name> writes:
> 
>> From: Dmitry V. Levin <ldv@altlinux.org>
>>
>> $ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
>> unsigned f(void) {return NLMSG_HDRLEN;}
>> EOF
>> <stdin>: In function 'f':
>> <stdin>:3:26: warning: negative integer implicitly converted to unsigned type
>>
> This doesn't look like a bad fix, but I believe things will fail if
> we give NLMSG_ALIGN an unsigned long like size_t.  Say like sizeof.

What are you talking about? That's exactly his test case,
look at what NLMSG_HDRLEN is defined to, it's exactly the
case you're worried "will fail", it passes sizeof() to
NLMSG_ALIGN.

I think I'll apply Kirill's original patch, it's good enough
and simpler.

Re: [PATCH] netlink: fix gcc -Wconversion compilation warning

[Eric W. Biederman]

David Miller <davem@davemloft.net> writes:

> From: ebiederm@xmission.com (Eric W. Biederman)
> Date: Mon, 13 Dec 2010 13:35:25 -0800
>
>> "Kirill A. Shutsemov" <kirill@shutemov.name> writes:
>> 
>>> From: Dmitry V. Levin <ldv@altlinux.org>
>>>
>>> $ cat << EOF | gcc -Wconversion -xc -S -o/dev/null -
>>> unsigned f(void) {return NLMSG_HDRLEN;}
>>> EOF
>>> <stdin>: In function 'f':
>>> <stdin>:3:26: warning: negative integer implicitly converted to unsigned type
>>>
>> This doesn't look like a bad fix, but I believe things will fail if
>> we give NLMSG_ALIGN an unsigned long like size_t.  Say like sizeof.
>
> What are you talking about? That's exactly his test case,
> look at what NLMSG_HDRLEN is defined to, it's exactly the
> case you're worried "will fail", it passes sizeof() to
> NLMSG_ALIGN.
>
> I think I'll apply Kirill's original patch, it's good enough
> and simpler.

Probably.  The case I was worried about was masks that become
0xffffffxx on 64bit instead of 0xffffffffffffxx.  Especially
when mixing those with ints.

It is possible to get some really weird things.

Eric