linux-kernel - [PATCH] net: atm: Use IS_ENABLED in atm_dev

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Message-Id: <20190307165741.19870-1-natechancellor@gmail.com>
Date:   Thu,  7 Mar 2019 09:57:42 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] net: atm: Use IS_ENABLED in atm_dev_ioctl

When building with -Wsometimes-uninitialized, Clang warns:

net/atm/resources.c:256:6: warning: variable 'number' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
net/atm/resources.c:212:7: warning: variable 'iobuf_len' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]

Clang won't realize that compat is 0 when CONFIG_COMPAT is not set until
the constant folding stage, which happens after this semantic analysis.
Use IS_ENABLED instead so that the zero is present at the semantic
analysis stage, which eliminates this warning.

Link: https://github.com/ClangBuiltLinux/linux/issues/386
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---

I don't think this looks the greatest because of the IS_ENABLED + #ifdef
but the only other solution I could think of looks way uglier to me:

https://gist.github.com/74650e9139f704a5435f82fc80d59969

 net/atm/resources.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/atm/resources.c b/net/atm/resources.c
index bada395ecdb1..3e9f6391319e 100644
--- a/net/atm/resources.c
+++ b/net/atm/resources.c
@@ -203,13 +203,9 @@ int atm_dev_ioctl(unsigned int cmd, void __user *arg, int compat)
 	int __user *sioc_len;
 	int __user *iobuf_len;
 
-#ifndef CONFIG_COMPAT
-	compat = 0; /* Just so the compiler _knows_ */
-#endif
-
 	switch (cmd) {
 	case ATM_GETNAMES:
-		if (compat) {
+		if (IS_ENABLED(CONFIG_COMPAT) && compat) {
 #ifdef CONFIG_COMPAT
 			struct compat_atm_iobuf __user *ciobuf = arg;
 			compat_uptr_t cbuf;
@@ -253,7 +249,7 @@ int atm_dev_ioctl(unsigned int cmd, void __user *arg, int compat)
 		break;
 	}
 
-	if (compat) {
+	if (IS_ENABLED(CONFIG_COMPAT) && compat) {
 #ifdef CONFIG_COMPAT
 		struct compat_atmif_sioc __user *csioc = arg;
 		compat_uptr_t carg;
-- 
2.21.0