linux-kernel - Re: [PATCH] kdev_t: Always inline major/minor helper functions

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Date:   Mon, 4 Jan 2021 13:28:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] kdev_t: Always inline major/minor helper functions

On Wed, Dec 23, 2020 at 09:30:48AM -0600, Josh Poimboeuf wrote:
> Silly GCC doesn't always inline these trivial functions.
> 
> Fixes the following warning:
> 
>   arch/x86/kernel/sys_ia32.o: warning: objtool: cp_stat64()+0xd8: call to new_encode_dev() with UACCESS enabled
> 
> Reported-by: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

The alternative is something like:

diff --git a/arch/x86/kernel/sys_ia32.c b/arch/x86/kernel/sys_ia32.c
index 6cf65397d225..6ca3da08dbcb 100644
--- a/arch/x86/kernel/sys_ia32.c
+++ b/arch/x86/kernel/sys_ia32.c
@@ -133,18 +133,23 @@ static int cp_stat64(struct stat64 __user *ubuf, struct kstat *stat)
 {
 	typeof(ubuf->st_uid) uid = 0;
 	typeof(ubuf->st_gid) gid = 0;
+	u64 dev, rdev;
+
 	SET_UID(uid, from_kuid_munged(current_user_ns(), stat->uid));
 	SET_GID(gid, from_kgid_munged(current_user_ns(), stat->gid));
+	dev = huge_encode_dev(stat->dev);
+	rdev = huge_encode_dev(stat->rdev);
+
 	if (!user_write_access_begin(ubuf, sizeof(struct stat64)))
 		return -EFAULT;
-	unsafe_put_user(huge_encode_dev(stat->dev), &ubuf->st_dev, Efault);
+	unsafe_put_user(dev, &ubuf->st_dev, Efault);
 	unsafe_put_user(stat->ino, &ubuf->__st_ino, Efault);
 	unsafe_put_user(stat->ino, &ubuf->st_ino, Efault);
 	unsafe_put_user(stat->mode, &ubuf->st_mode, Efault);
 	unsafe_put_user(stat->nlink, &ubuf->st_nlink, Efault);
 	unsafe_put_user(uid, &ubuf->st_uid, Efault);
 	unsafe_put_user(gid, &ubuf->st_gid, Efault);
-	unsafe_put_user(huge_encode_dev(stat->rdev), &ubuf->st_rdev, Efault);
+	unsafe_put_user(rdev, &ubuf->st_rdev, Efault);
 	unsafe_put_user(stat->size, &ubuf->st_size, Efault);
 	unsafe_put_user(stat->atime.tv_sec, &ubuf->st_atime, Efault);
 	unsafe_put_user(stat->atime.tv_nsec, &ubuf->st_atime_nsec, Efault);