[PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

A code rework resulted in an uninitialized return code when COMPAT
mode is disabled:

io_uring/net.c:722:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
  722 |         if (io_is_compat(req->ctx)) {
      |             ^~~~~~~~~~~~~~~~~~~~~~
io_uring/net.c:736:15: note: uninitialized use occurs here
  736 |         if (unlikely(ret))
      |                      ^~~

Since io_is_compat() turns into a compile-time 'false', the #ifdef
here is completely unnecessary, and removing it avoids the warning.

Fixes: 685252678757 ("io_uring/net: unify *mshot_prep calls with compat")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 io_uring/net.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index bb454b9f6a4c..33e9be094131 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -224,7 +224,6 @@ static int io_net_import_vec(struct io_kiocb *req, struct io_async_msghdr *iomsg
 	return 0;
 }
 
-#ifdef CONFIG_COMPAT
 static int io_compat_msg_copy_hdr(struct io_kiocb *req,
 				  struct io_async_msghdr *iomsg,
 				  struct compat_msghdr *msg, int ddir,
@@ -263,7 +262,6 @@ static int io_compat_msg_copy_hdr(struct io_kiocb *req,
 	return io_net_import_vec(req, iomsg, (struct iovec __user *)uiov,
 				 msg->msg_iovlen, ddir);
 }
-#endif
 
 static int io_copy_msghdr_from_user(struct user_msghdr *msg,
 				    struct user_msghdr __user *umsg)
@@ -330,7 +328,6 @@ static int io_sendmsg_copy_hdr(struct io_kiocb *req,
 	iomsg->msg.msg_name = &iomsg->addr;
 	iomsg->msg.msg_iter.nr_segs = 0;
 
-#ifdef CONFIG_COMPAT
 	if (io_is_compat(req->ctx)) {
 		struct compat_msghdr cmsg;
 
@@ -339,7 +336,6 @@ static int io_sendmsg_copy_hdr(struct io_kiocb *req,
 		sr->msg_control = iomsg->msg.msg_control_user;
 		return ret;
 	}
-#endif
 
 	ret = io_msg_copy_hdr(req, iomsg, &msg, ITER_SOURCE, NULL);
 	/* save msg_control as sys_sendmsg() overwrites it */
@@ -720,7 +716,6 @@ static int io_recvmsg_copy_hdr(struct io_kiocb *req,
 	iomsg->msg.msg_iter.nr_segs = 0;
 
 	if (io_is_compat(req->ctx)) {
-#ifdef CONFIG_COMPAT
 		struct compat_msghdr cmsg;
 
 		ret = io_compat_msg_copy_hdr(req, iomsg, &cmsg, ITER_DEST,
@@ -728,7 +723,6 @@ static int io_recvmsg_copy_hdr(struct io_kiocb *req,
 		memset(&msg, 0, sizeof(msg));
 		msg.msg_namelen = cmsg.msg_namelen;
 		msg.msg_controllen = cmsg.msg_controllen;
-#endif
 	} else {
 		ret = io_msg_copy_hdr(req, iomsg, &msg, ITER_DEST, &iomsg->uaddr);
 	}
-- 
2.39.5

Re: [PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Pavel Begunkov]

On 2/27/25 13:20, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> A code rework resulted in an uninitialized return code when COMPAT
> mode is disabled:

As mentioned in the lkp report, it should be a false positive.

> 
> io_uring/net.c:722:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>    722 |         if (io_is_compat(req->ctx)) {
>        |             ^~~~~~~~~~~~~~~~~~~~~~
> io_uring/net.c:736:15: note: uninitialized use occurs here
>    736 |         if (unlikely(ret))
>        |                      ^~~
> 
> Since io_is_compat() turns into a compile-time 'false', the #ifdef
> here is completely unnecessary, and removing it avoids the warning.

I don't think __get_compat_msghdr() and other helpers are
compiled for !COMPAT. I'd just silence it like:

if (io_is_compat(req->ctx)) {
	ret = -EFAULT;
#ifdef CONFIG_COMPAT
	...
#endif CONFIG_COMPAT
}
	
Let's see if Jens wants to fix it up in the tree.

-- 
Pavel Begunkov

Re: [PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Arnd Bergmann]

On Thu, Feb 27, 2025, at 14:49, Pavel Begunkov wrote:
> On 2/27/25 13:20, Arnd Bergmann wrote:
>>        |                      ^~~
>> 
>> Since io_is_compat() turns into a compile-time 'false', the #ifdef
>> here is completely unnecessary, and removing it avoids the warning.
>
> I don't think __get_compat_msghdr() and other helpers are
> compiled for !COMPAT.

They are not defined without CONFIG_COMPAT. My point in the
message is that io_is_compat() turning into a compile-time
'false' value means that they also don't get called, because
compilers are really good at this type of dead code elimination.

> I'd just silence it like:
>
> if (io_is_compat(req->ctx)) {
> 	ret = -EFAULT;
> #ifdef CONFIG_COMPAT
> 	...
> #endif CONFIG_COMPAT
> }

That seems even less readable. If you want to be explicit
about it, you could use

     if (IS_ENABLED(CONFIG_COMPAT) && io_is_compat(req->ctx)) {

to replace the #ifdef, but as I wrote in the patch
description, the compile-time check is really redundant
because io_is_compat() is meant to do exactly that.

       Arnd

Re: [PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Pavel Begunkov]

On 2/27/25 13:58, Arnd Bergmann wrote:
> On Thu, Feb 27, 2025, at 14:49, Pavel Begunkov wrote:
>> On 2/27/25 13:20, Arnd Bergmann wrote:
>>>         |                      ^~~
>>>
>>> Since io_is_compat() turns into a compile-time 'false', the #ifdef
>>> here is completely unnecessary, and removing it avoids the warning.
>>
>> I don't think __get_compat_msghdr() and other helpers are
>> compiled for !COMPAT.
> 
> They are not defined without CONFIG_COMPAT. My point in the
> message is that io_is_compat() turning into a compile-time
> 'false' value means that they also don't get called, because
> compilers are really good at this type of dead code elimination.
> 
>> I'd just silence it like:
>>
>> if (io_is_compat(req->ctx)) {
>> 	ret = -EFAULT;
>> #ifdef CONFIG_COMPAT
>> 	...
>> #endif CONFIG_COMPAT
>> }
> 
> That seems even less readable. If you want to be explicit
> about it, you could use
> 
>       if (IS_ENABLED(CONFIG_COMPAT) && io_is_compat(req->ctx)) {
> 
> to replace the #ifdef, but as I wrote in the patch
> description, the compile-time check is really redundant
> because io_is_compat() is meant to do exactly that.

I do like getting rid of #ifdef, just a bit surprised that we're
relying on dead code elimination, even though it's what any
reasonable compiler must do.

Btw, sth went wrong with the reply: (delivered after 24733 seconds)

-- 
Pavel Begunkov

Re: [PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Pavel Begunkov]

On 2/27/25 13:49, Pavel Begunkov wrote:
> On 2/27/25 13:20, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> A code rework resulted in an uninitialized return code when COMPAT
>> mode is disabled:
> 
> As mentioned in the lkp report, it should be a false positive.
> 
>>
>> io_uring/net.c:722:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>>    722 |         if (io_is_compat(req->ctx)) {
>>        |             ^~~~~~~~~~~~~~~~~~~~~~
>> io_uring/net.c:736:15: note: uninitialized use occurs here
>>    736 |         if (unlikely(ret))
>>        |                      ^~~
>>
>> Since io_is_compat() turns into a compile-time 'false', the #ifdef
>> here is completely unnecessary, and removing it avoids the warning.
> 
> I don't think __get_compat_msghdr() and other helpers are
> compiled for !COMPAT. I'd just silence it like:

I guess we're relying on dead code elimination to prevent
linking against them, if that's a normal practise and we
do mandate compilers to do that, then it looks fine to me

> 
> if (io_is_compat(req->ctx)) {
>      ret = -EFAULT;
> #ifdef CONFIG_COMPAT
>      ...
> #endif CONFIG_COMPAT
> }
> 
> Let's see if Jens wants to fix it up in the tree.
> 

-- 
Pavel Begunkov

Re: [PATCH] io_uring/net: fix build warning for !CONFIG_COMPAT

[Jens Axboe]

On Thu, 27 Feb 2025 14:20:09 +0100, Arnd Bergmann wrote:
> A code rework resulted in an uninitialized return code when COMPAT
> mode is disabled:
> 
> io_uring/net.c:722:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>   722 |         if (io_is_compat(req->ctx)) {
>       |             ^~~~~~~~~~~~~~~~~~~~~~
> io_uring/net.c:736:15: note: uninitialized use occurs here
>   736 |         if (unlikely(ret))
>       |                      ^~~
> 
> [...]

Applied, thanks!

[1/1] io_uring/net: fix build warning for !CONFIG_COMPAT
      commit: 4afc332bc86c34b74f1211650f748feb6942a9cc

Best regards,
-- 
Jens Axboe