On Fri, Mar 29, 2024, at 11:02, Uwe Kleine-König wrote:
> The einj_driver driver is registered using platform_driver_probe(). In
> this case it cannot get unbound via sysfs and it's ok to put the remove
> callback into an exit section. To prevent the modpost warning about
> einj_driver referencing .exit.text, mark the driver struct with
> __refdata and explain the situation in a comment.
>
> This is an improvement over commit a24118a8a687 ("ACPI: APEI: EINJ: mark
> remove callback as non-__exit") which recently addressed the same issue,
> but picked a less optimal variant.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
I noticed another curiosity:
> static struct platform_device *einj_dev;
> -static struct platform_driver einj_driver = {
> - .remove_new = einj_remove,
> +/*
> + * einj_remove() lives in .exit.text. For drivers registered via
> + * platform_driver_probe() this is ok because they cannot get unbound at
> + * runtime. So mark the driver struct with __refdata to prevent modpost
> + * triggering a section mismatch warning.
> + */
> +static struct platform_driver einj_driver __refdata = {
> + .remove_new = __exit_p(einj_remove),
> .driver = {
> .name = "acpi-einj",
> },
I was wondering why this doesn't cause an "unused function"
warning for einj_remove(), given that __exit_p() turns the
reference into NULL.
As it turns out, the __exit annotation marks the function as
"__attribute__((used))", so it still gets put in the object
file but then dropped by the linker. The __used annotation
seems to predate the introduction of "__attribute__((unused))",
which would seem more appropriate here, which would allow
more dead-code elimination.
The patch below gets rid of the __used annotation completely,
which in turn uncovers some interesting bugs with __exit
functions in built-in code that are never called from
anywhere, like
drivers/video/fbdev/asiliantfb.c:627:20: error: 'asiliantfb_exit' defined but not used [-Werror=unused-function]
Arnd
diff --git a/include/linux/init.h b/include/linux/init.h
index 58cef4c2e59a..d0e6354f3050 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -82,7 +82,7 @@
#define __exitused __used
#endif
-#define __exit __section(".exit.text") __exitused __cold notrace
+#define __exit __section(".exit.text") __cold notrace
/* Used for MEMORY_HOTPLUG */
#define __meminit __section(".meminit.text") __cold notrace \
@@ -394,7 +394,7 @@ void __init parse_early_options(char *cmdline);
#ifdef MODULE
#define __exit_p(x) x
#else
-#define __exit_p(x) NULL
+#define __exit_p(x) (0 ? (x) : NULL)
#endif
#endif /* _LINUX_INIT_H */
