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Message-ID: <20251002233627.GA3978676@ax162>
Date: Thu, 2 Oct 2025 16:36:27 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Armin Wolf <W_Armin@....de>
Cc: kernel test robot <lkp@...el.com>, ilpo.jarvinen@...ux.intel.com,
hdegoede@...hat.com, chumuzero@...il.com, corbet@....net,
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llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
platform-driver-x86@...r.kernel.org, rdunlap@...radead.org,
alok.a.tiwari@...cle.com, linux-leds@...r.kernel.org,
lee@...nel.org, pobrn@...tonmail.com
Subject: Re: [PATCH v4 1/2] platform/x86: Add Uniwill laptop driver
Hi Armin,
On Thu, Oct 02, 2025 at 08:41:19PM +0200, Armin Wolf wrote:
> i think this is a problem inside the clang compiler. I did not encounter this warning when
> build for x86-64 using gcc.
Clang is actually saving you from yourself, it is a bug in GCC that it
does not warn for this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91951
> > vim +1243 drivers/platform/x86/uniwill/uniwill-acpi.c
> >
> > 1235
> > 1236 static int uniwill_notifier_call(struct notifier_block *nb, unsigned long action, void *dummy)
> > 1237 {
> > 1238 struct uniwill_data *data = container_of(nb, struct uniwill_data, nb);
> > 1239 struct uniwill_battery_entry *entry;
> > 1240
> > 1241 switch (action) {
> > 1242 case UNIWILL_OSD_BATTERY_ALERT:
> > > 1243 guard(mutex)(&data->battery_lock);
mutex_unlock() will be called on &data->battery_lock even when the
default case is taken, as demonstrated by the following test case.
> > 1244 list_for_each_entry(entry, &data->batteries, head) {
> > 1245 power_supply_changed(entry->battery);
> > 1246 }
> > 1247
> > 1248 return NOTIFY_OK;
> > 1249 default:
> > 1250 guard(mutex)(&data->input_lock);
> > 1251 sparse_keymap_report_event(data->input_device, action, 1, true);
> > 1252
> > 1253 return NOTIFY_OK;
> > 1254 }
> > 1255 }
> > 1256
> >
>
$ cat test.c
#include <stdio.h>
void cleanup_1(int *a) { printf("+ %s(%p)\n", __func__, a); }
void cleanup_2(int *a) { printf("+ %s(%p)\n", __func__, a); }
void cleanup_3(int *a) { printf("+ %s(%p)\n", __func__, a); }
void no_scopes(int a)
{
printf("%s(%d)\n", __func__, a);
switch (a) {
case 1:
int case_1 __attribute__((cleanup(cleanup_1)));
return;
case 2:
int case_2 __attribute__((cleanup(cleanup_2)));
return;
default:
int case_default __attribute__((cleanup(cleanup_3)));
return;
}
}
void with_scopes(int a)
{
printf("%s(%d)\n", __func__, a);
switch (a) {
case 1: {
int case_1 __attribute__((cleanup(cleanup_1)));
return;
}
case 2: {
int case_2 __attribute__((cleanup(cleanup_2)));
return;
}
default: {
int case_default __attribute__((cleanup(cleanup_3)));
return;
}
}
}
int main(void)
{
no_scopes(1); printf("\n");
no_scopes(2); printf("\n");
no_scopes(3); printf("\n");
with_scopes(1); printf("\n");
with_scopes(2); printf("\n");
with_scopes(3);
}
$ gcc -O2 test.c
$ ./a.out
no_scopes(1)
+ cleanup_1(0x7ffea3450c0c)
no_scopes(2)
+ cleanup_2(0x7ffea3450c10)
+ cleanup_1(0x7ffea3450c0c)
no_scopes(3)
+ cleanup_3(0x7ffea3450c14)
+ cleanup_2(0x7ffea3450c10)
+ cleanup_1(0x7ffea3450c0c)
with_scopes(1)
+ cleanup_1(0x7ffea3450c14)
with_scopes(2)
+ cleanup_2(0x7ffea3450c14)
with_scopes(3)
+ cleanup_3(0x7ffea3450c14)
$ clang -O2 test.c
test.c:12:9: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
12 | int case_1 __attribute__((cleanup(cleanup_1)));
| ^
test.c:15:9: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
15 | int case_2 __attribute__((cleanup(cleanup_2)));
| ^
test.c:18:9: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
18 | int case_default __attribute__((cleanup(cleanup_3)));
| ^
test.c:17:5: error: cannot jump from switch statement to this case label
17 | default:
| ^
test.c:15:13: note: jump bypasses initialization of variable with __attribute__((cleanup))
15 | int case_2 __attribute__((cleanup(cleanup_2)));
| ^
test.c:12:13: note: jump bypasses initialization of variable with __attribute__((cleanup))
12 | int case_1 __attribute__((cleanup(cleanup_1)));
| ^
test.c:14:5: error: cannot jump from switch statement to this case label
14 | case 2:
| ^
test.c:12:13: note: jump bypasses initialization of variable with __attribute__((cleanup))
12 | int case_1 __attribute__((cleanup(cleanup_1)));
| ^
3 warnings and 2 errors generated.
https://godbolt.org/z/1Tx7Gj1xf
I would add the scoping to the case labels or use scoped_guard() to
avoid this, which would also avoid the instances of -Wc23-extensions.
Cheers,
Nathan
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